Clinical Neurophysiology - Articles in Press

The organization of physiological brain networks - Corrected Proof

C.J. Stam, E.C.W. van Straaten — 2012-02-22

Highlights: ► The brain can be represented as a complex network with functionally connected units at several levels that changes in neurological and psychiatric disease. ► Existing clinical neurophysiology techniques and network models to explain network properties are reviewed. ► In addition to the already established network models, we suggest a heuristic model including hierarchical modularity.Abstract: One of the central questions in neuroscience is how communication in the brain is organized under normal conditions and how this architecture breaks down in neurological disease. It has become clear that simple activation studies are no longer sufficient. There is an urgent need to understand the brain as a complex structural and functional network. Interest in brain network studies has increased strongly with the advent of modern network theory and increasingly powerful investigative techniques such as “high-density EEG”, MEG, functional and structural MRI. Modern network studies of the brain have demonstrated that healthy brains self-organize towards so-called “small-world networks” characterized by a combination of dense local connectivity and critical long-distance connections. In addition, normal brain networks display hierarchical modularity, and a connectivity backbone that consists of interconnected hub nodes. This complex architecture is believed to arise under genetic control and to underlie cognition and intelligence. Optimal brain network organization becomes disrupted in neurological disease in characteristic ways. This review gives an overview of modern network theory and its applications to healthy brain function and neurological disease, in particular using techniques from clinical neurophysiology, such as EEG and MEG.

Single-trial analysis of auditory evoked potentials improves separation of normal and schizophrenia subjects - Corrected Proof

Darshan Iyer, Nash N. Boutros, George Zouridakis — 2012-02-22

Highlights: ► Used independent component analysis to estimate the P50 and N100 components on single-trial auditory evoked responses. ► Normal controls responded earlier, their individual responses had significantly higher amplitude and considerably less latency variability compared to schizophrenia patients. ► The latency and amplitude of the P50 and N100 estimated from single trials could classify subjects with 100% accuracy, whereas the same measures computed from average responses provided a maximum of 76% correct classification.Abstract: Objective: In this study, we employed iterative independent component analysis of single-trial auditory evoked responses to identify features of the P50 and N100 components that provide maximum separation between normal controls and schizophrenia subjects and compared the results against classical ensemble averaging.Method: We analyzed data from 13 schizophrenia and 20 normal control subjects. Responses were obtained in a paired-stimulus paradigm, in which an auditory stimulus S1 is followed by an identical S2. The amplitude and latency of the P50 and N100 components in response to the S1 and S2 stimuli were measured in each single trial and used as features to classify the responses into two groups. Several methods were used for classification, while their performance was quantified in a 10-fold stratified cross-validation approach.Results: We found that normal controls tended to respond earlier and their individual responses had significantly higher amplitude (p<0.01) and significantly less latency variability (p<0.01) compared to schizophrenia patients. The S1 latency was the most significant discriminatory feature (p<0.01) followed by S2 latency (p<0.01). The S2 amplitude, though relatively larger in normal subjects (p<0.05), was the least discriminatory feature. Classification based on single-trial analysis yielded 100% accuracy, while the classical ensemble averaging yielded only a maximum of 76% accuracy.Conclusions: Our results demonstrate that single-trial analysis can accurately separate schizophrenia patients from normal controls and suggest that inter-trial variability plays a significant role in information processing in the human brain.Significance: The proposed technique may have a significant impact as a clinical tool in the quest for identifying physiological markers of schizophrenia.

Developmental profiles of infant EEG: Overlap with transient cortical circuits - Corrected Proof

2012-02-20

Abstract: Objective: To quantify spectral power in frequency specific bands and commonly observed types of bursting activities in the EEG during early human development.Methods: An extensive archive of EEG data from human infants from 35 to 52weeks postmenstrual age obtained in a prior multi-center study was analyzed using power spectrum analyses and a high frequency burst detection algorithm.Results: Low frequency power increased with age; however, high frequency power decreased from 35 to 45weeks. This unexpected decrease was largely attributable to a rapid decline in the number of high frequency bursts.Conclusions: The decline in high frequency bursting activity overlaps with a developmental shift in GABA’s actions on neurons from depolarizing to hyperpolarizing and the dissolution of the gap junction circuitry of the cortical subplate.Significance: We postulate that quantitative characterization of features of the EEG unique to early development provide indices for tracking changes in specific neurophysiologic mechanisms that are critical for normal development of brain function.

A practical guide to diagnostic transcranial magnetic stimulation: Report of an IFCN committee - Corrected Proof

2012-02-20

Highlights: ► This guideline paper provides an up-date on the clinical use of transcranial magnetic stimulation (TMS). ► The clinically relevant technical and physiological principles of TMS are outlined. ► A detailed description how to examine corticomotor conduction to the hand, leg, trunk and facial muscles is presented.Abstract: Transcranial magnetic stimulation (TMS) is an established neurophysiological tool to examine the integrity of the fast-conducting corticomotor pathways in a wide range of diseases associated with motor dysfunction. This includes but is not limited to patients with multiple sclerosis, amyotrophic lateral sclerosis, stroke, movement disorders, disorders affecting the spinal cord, facial and other cranial nerves. These guidelines cover practical aspects of TMS in a clinical setting. We first discuss the technical and physiological aspects of TMS that are relevant for the diagnostic use of TMS. We then lay out the general principles that apply to a standardized clinical examination of the fast-conducting corticomotor pathways with single-pulse TMS. This is followed by a detailed description of how to examine corticomotor conduction to the hand, leg, trunk and facial muscles in patients. Additional sections cover safety issues, the triple stimulation technique, and neuropediatric aspects of TMS.

Abnormal spinal cord pain processing in Huntington’s disease. The role of the diffuse noxious inhibitory control - Corrected Proof

2012-02-20

Highlights: ► Huntington’s disease patients showed abnormalities in the temporal processing of the nociceptive stimuli at spinal level. ► In Huntington’s disease patients the supraspinal control of pain expressed by diffuse noxious inhibitory control seems to work normally. ► Our data support the hypothesis that the striatum is involved in pain matrix and that its atrophy could interfere with pain processing.Abstract: Objectives: Our study is aimed to evaluate the spinal cord pain processing in Huntington’s disease (HD) by testing both the temporal summation threshold (TST) of the nociceptive withdrawal reflex (NWR) and the functional activity of the diffuse noxious inhibitory control (DNIC) as form of supraspinal control of pain.Methods: We enrolled 19 HD patients and 17 healthy controls. We measured threshold (Th), Area, TST and related psychophysical pain sensations of the NWR, at baseline and during and after activation of the DNIC by means of cold pressor test (CPT) as heterotopic noxious conditioning stimulation.Results: In HD patients we found a significantly higher Th and TST as well as a lower Area when compared to controls. During the CPT, a significant inhibition of reflex and psychophysical pain responses were found in both HD patients and controls when compared to baseline, without differences between the groups in CPT results.Conclusions: Our study demonstrated an abnormal spinal cord pain processing in HD patients. Abnormalities in pain processing are not apparently linked to a dysfunctional DNIC inhibitory projection system in HD patients.Significance: Our findings support the hypothesis that the striatum could play a role in pain modulation and that its atrophy could affect pain processing without change the DNIC efficiency.

Cue-induced beta rebound during withholding of overt and covert foot movement - Corrected Proof

2012-02-20

Abstract: Objective: Beta rebound is the term for bursts of EEG activity in the beta band observable after movement or somatosensory stimulation. It is assumed to reflect an active inhibition process. Our aim was to investigate the differences in the beta rebound between movement termination and withholding of movement, and the withholding of overt and covert movement.Methods: Twenty healthy persons completed Go/NoGo experiments with real and imaginary foot movements (dorsiflexion of both feet). Only participants that presented a beta rebound were considered. Event-related (de)synchronization provided the time course of the beta rebound from a participant specific frequency band. Statistical analyses revealed the significant differences between pairs of conditions: motor execution Go vs. motor execution NoGo, and motor execution NoGo vs. motor imagery NoGo.Results: The beta rebound is stronger and lasts longer after termination of movement than during withholding of a motor response (9 participants). Withholding of overt movement generates a stronger, longer, and more widespread beta rebound than the withholding of imaginary movement (7 participants). The beta rebound is more common after termination (16/16) and withholding of real movement (12/16) than during withholding of imaginary movements (7/16).Conclusions: These phenomena share a common origin and a common frequency band. Their functional meaning is assumed to be the same, although there are differences in time span and intensity of the beta ERS.Significance: First direct comparison of the beta rebound between motor execution and motor withholding, as well as withholding of overt and covert foot movement. A beta rebound also occurs during withholding of a motor task, and it is more common and strong for overt movement than for covert movement.

Smoothing of electromyographic signals can influence the number of extracted muscle synergies - Corrected Proof

François Hug, Nicolas A. Turpin, Sylvain Dorel, Arnaud Guével — 2012-02-20

Low-dimensional modules formed by muscles activated in synchrony, named muscle synergies, have been proposed as building blocks that simplify the construction of motor behaviors (). Each muscle synergy is presumed to be modulated by a single neural command signal. Consequently, it provides an attractive simplifying strategy for the control of complex movements because it reduces the number of output patterns that the nervous system has to specify. Muscle synergy analysis has clinical relevance because it may offer the clinician a better view of the neural structure underlying motor behaviors and how they change in motor deficits and rehabilitation (; or for review see ). In this way, demonstrated that extraction of muscle synergies is a better technique than Fugl-Meyer Assessment to assess post-stroke motor impairment. Another study showed that fewer muscle synergies are needed to account for muscle activity during walking in post-stroke subjects compared to healthy subjects (2.7±0.8 vs. 3.5±0.7), suggesting a lower complexity in motor control (). reported age-related modifications of muscle synergies during locomotion that could be interpreted as age-related changes of both nervous system and motor control strategies during locomotion.

Fibrillation potentials of denervated rat skeletal muscle are associated with expression of cardiac-type voltage-gated sodium channel isoform Nav1.5 - Corrected Proof

Kenji Sekiguchi, Fumio Kanda, Shigeru Mitsui, Nobuo Kohara, Kazuo Chihara — 2012-02-15

Highlights: ► Novel expression of cardiac type sodium channel Nav1.5 participates in the generation of fibrillation potentials in denervated rat skeletal muscle. ► Nav1.5 block by lidocaine suppressed fibrillation potentials without changing the amplitude of compound muscle action potential (CMAP) in innervated muscle. ► Changes after denervation that occur in ion channels including Nav1.5 contribute to fibrillation potentials.Abstract: Objective: The molecular mechanisms underlying fibrillation potentials are still unclear. We hypothesised that expression of the cardiac-type voltage-gated sodium channel isoform Nav1.5 in denervated rat skeletal muscle is associated with the generation of such potentials.Methods: Muscle samples were extracted and analysed biologically from surgically denervated rat extensor digitorum longus muscle after concentric needle electromyographic recording at various time points after denervation (4h to 6days).Results: Both nav1.5 messenger RNA (mRNA) signal on northern blotting and Nav1.5 protein expression on immunohistochemistry appeared on the second day after denervation, exactly when fibrillation potentials appeared. Administration of lidocaine, which has much stronger affinity for sodium channels in cardiac muscle than for those in skeletal muscle, dramatically decreased fibrillation potentials, but had no effect on contralateral compound muscle action potentials.Conclusions: Expression of Nav1.5 participates in the generation of fibrillation potentials in denervated rat skeletal muscle.Significance: We proposed an altered expression of voltage-gated sodium channel isoforms as a novel mechanism to explain the occurrence of fibrillation potentials following skeletal muscle denervation.

Anisotropy and spatial tactile acuity on human lips - Corrected Proof

Gabrielle Todd — 2012-02-15

Highlights: ► Spatial tactile acuity is greater on the upper lip than on the lower lip in humans. ► A property of spatial tactile acuity known as anisotropy (or directional dependence) is absent on human lips. ► The lack of anisotropy on human lips is surprising given that anisotropy is present on the finger and that mechanoreceptor afferents that supply human lips exhibit similar characteristics to those of the hand.Abstract: Objective: To investigate tactile anisotropy on human lips.Methods: Spatial tactile acuity was assessed with a three-alternative, forced-choice grating orientation task. Circular probes with horizontal (parallel to lip), vertical (perpendicular to lip), or oblique (45° right of vertical) grooves and ridges of equal width were applied (n=60) to the midline of each lip. Participants (n=13) were asked to state the grating orientation whilst blindfolded. The percentage of correct responses was plotted as a function of the log gap width. Data were fitted with a four-parameter sigmoid function. Response bias was assessed (n=13) with application of a smooth polished Perspex probe. 65.5%, 71.5%, and 63.0% correct was adopted as the threshold estimate for the vertical, horizontal, and oblique orientations based on the measured response bias.Results: Across orientations, the threshold on the upper lip (1.5±0.9mm) was significantly greater than on the lower lip (1.0±0.7mm; P=0.006). However, there was no significant main effect of orientation or orientation-by-lip interaction on threshold.Conclusion: Tactile anisotropy is absent on human lips.Significance: The lack of anisotropy is surprising given that anisotropy is present on fingers and that afferent input and sensory processing for human lips and fingers share similarities.

Cortical activation to voluntary movement in amyotrophic lateral sclerosis is related to corticospinal damage: Electrophysiological evidence - Corrected Proof

2012-02-13

Highlights: ► Movement-related cortical overactivation in ALS as revealed by analysis of sensorimotor EEG rhythms occurs in the post-movement phase and not in the pre-movement phase. ► The amount of movement-related cortical overactivation in ALS, measured with analysis of sensorimotor EEG rhythms, is proportional to the amount of corticospinal damage evident at MRI and TMS measures. ► Motor cortical overactivation in ALS patients may be related to reduced cortical inhibition or idling rather than to generalized hyperexcitability.Abstract: Objectives: The time course of mu and beta sensorimotor rhythms, with event-related desynchronisation (ERD) to preparation and execution of voluntary movement followed by synchronisation (ERS) after movement, is considered to indicate cortical activation and idling, respectively. We investigated ERD and ERS in amyotrophic lateral sclerosis (ALS) patients and the relationship with anatomical and neurophysiological measures of corticospinal tract damage.Methods: Pre-movement mu and beta ERD, and post-movement beta ERS were analysed in 16 ALS patients and 15 healthy controls performing self-paced brisk right thumb extensions. Apparent diffusion coefficient (ADC) of corticospinal tract was measured with magnetic resonance imaging (MRI). Motor-evoked potentials (MEPs) to the right abductor pollicis brevis were obtained using transcranial magnetic stimulation (TMS).Results: Movement-related electromyographic activity was similar in the two groups. Post-movement ERS was significantly reduced in ALS group and negatively correlated with the amount of corticospinal damage as from MRI and TMS measures. ERD did not significantly differ between groups.Conclusions: Alterations of cortical activity in ALS patients were limited to the post-movement phase, as indicated by reduced ERS, and could be linked to reduced cortical inhibition rather than to generalised hyperexcitability.Significance: The correlation between ERS and corticospinal damage severity might be interpreted as a functional compensation or dysfunction of inhibitory systems paralleling corticospinal damage.

Evidence for a dual versus single origin of the MMNs evoked by cued versus cueless deviants - Corrected Proof

I. Hoonhorst, P. Deltenre, E. Markessis, G. Collet, X. Pablos Martin, C. Colin — 2012-02-10

Highlights: ► The mismatch negativity (MMN) evoked by cued deviants containing a frequency sweep within a tone is much larger than the one evoked by cueless deviants. ► A cued–cueless asymmetry between behavioural discrimination and neurophysiological data was demonstrated. ► The respective contributions of the memory-based and adaptation/fresh-afferent models of MMN generation are discussed on the basis of the present results.Abstract: Objective: This study was designed to separately test the effect of the cued/cueless nature of deviant stimuli and that of temporal distance between sound and deviance onsets on the mismatch negativity (MMN) as well as to look for discrepancies between behavioural discrimination performances and MMN amplitude when deviants are cueless.Methods: Ten healthy adults passively listened to stimuli that were contrasted by the presence or absence of a frequency sweep starting early or late within the sound. Discrimination performances were collected after the electrophysiological sessions.Results: MMNs were much larger for cued than for cueless deviants. The temporal distance between sound and deviance onsets affected MMNs evoked by both cued and cueless deviants, even to the point of abolishing the MMN when cueless deviance occurred late in the stimulus. Behavioural data were at ceiling levels for all conditions, contrasting with the absence of MMN evoked by cueless deviants with late onset.Conclusions: Two mechanisms contribute to the MMN evoked by cued deviants: the memory comparison process and the adaptation/fresh-afferent one. Within the temporal window of integration, the delay at which each component disappears is different.Significance: Comparing waveforms evoked by cued versus cueless deviants provides a fairly simple way of isolating the MMN memory-based component.

Reconstruction of quasi-radial dipolar activity using three-component magnetic field measurements - Corrected Proof

2012-02-10

Highlights: ► Novel vector-biomagnetometers enable reconstruction of quasi-radial brain activity. ► We demonstrate this reconstruction of radial brain activity for Brodmann area 1 in the somatosensory system. ► Vector-biomagnetometers provide greater insight into brain activity than does standard magnetoencephalography.Abstract: Objective: While standard magnetoencephalographic systems record only one component of the biomagnetic field, novel vector-biomagnetometers enable measurement of all three components of the field at each sensing point. Because information content in standard one-component magnetoencephalography (MEG) is often not adequate to reconstruct quasi-radial dipolar activity, we tested the hypothesis that quasi-radial activity can be estimated using three-component MEG.Methods: We stimulated the right median nerve in 11 healthy volunteers and recorded the somatosensory evoked fields over the contralateral hemisphere using a novel vector-biomagnetometer system comprised of SQUID-based magnetometer triplets. Source reconstruction for the early cortical components N20m and P25m was subsequently performed.Results: Both tangential and quasi-radial dipolar activity could be reconstructed in 10 of the 11 participants. Dipole locations were found in the vicinity of the central sulcus, and dipole orientations were predominantly tangential for N20m and quasi-radial for P25m. The mean location difference between the tangential and quasi-radial dipoles was 11.9mm and the mean orientation difference was 97.5°.Conclusions: Quasi-radial dipolar activity can be reconstructed from three-component magnetoencephalographic measurements.Significance: Three-component MEG provides higher information content than does standard MEG.

Radial and tangential components of dipolar sources and their magnetic fields - Corrected Proof

Jan C. de Munck, Andreas Daffertshofer — 2012-02-10

Since the advent of magneto-encephalography (MEG) some confusion exists regarding the visibility of tangential and radial components of dipolar sources as the latter is typically considered inaccessible for MEG. A similar confusion pertains when comparing MEG with EEG as it is sometimes claimed that volume currents would only affect EEG but not MEG. A key-factor underlying this confusion is the use of spherically symmetric volume conductors, wherein the human head is described as a set of concentric spherical shells with distinct conductivities. The spherical symmetry allows for a unique definition of “radial” and “tangential” components: radial refers to the direction pointing toward the centre of the sphere and tangential is any direction perpendicular to radial. For spherically symmetric head models the three components of the magnetic field outside the conductor that are caused by a dipolar source located within one of the shells can be computed by mere algebra. The derivations by revealed that all magnetic field components indeed vanish if the dipole has radial orientation. Here it is important to note that the fact of a vanishing -field is fully independent of the geometry and orientation of a sensor measuring it. Furthermore, for a tangential dipole the magnetic field appears to be independent of the conductivities of the spherical shells. The radial magnetic field caused by such dipole results in the same expression as that for a dipole in an infinite non-conducting medium, implying that MEG would be insensitive to volume currents, as opposed to EEG. If the MEG sensor is not precisely radial, however, this simplification becomes invalid and volume currents maintain their pivotal role in the physics of MEG because they are in fact responsible for the disappearance of all the magnetic fields components for radial dipoles. In it has been suggested that the concept of symmetry provides a more fruitful basis than that of volume currents for understanding the absence of magnetic fields and its independence of conductivities for certain source and conductor geometries.

Widening the horizon of neonatal neurophysiology - Corrected Proof

Jasenka Sarajlija, Pietro Avanzini, Gaetano Cantalupo, Carlo Alberto Tassinari — 2012-02-10

“Only children know what they are looking for.”(The Little Prince, A. de St. Exupéry) Neonatal neurology constitutes a field of increasing interest from both clinical and research perspectives. Progress in care has lowered gestational age of preterm newborns admitted in NICUs and led to an increase of the number of survivors. Due to this, a strong interest has arisen in issues involving maturational and pathological processes (). On the other hand, parallel technical improvements in both hardware and software tools have shifted further the frontiers of the research in neurophysiology.

Motor unit number index (MUNIX) versus motor unit number estimation (MUNE): A direct comparison in a longitudinal study of ALS patients - Corrected Proof

2012-02-10

Highlights: ► This study shows that the motor unit number index (MUNIX) and high-density motor unit number estimation (MUNE) outcomes measured on the thenar muscle are significantly correlated in ALS patients. ► After 8months follow-up, MUNIX and high-density MUNE values in ALS patients showed significantly more decline compared to CMAP, ALS functional rating scale and MRC-scale. ► There was no significant difference in relative decline between MUNIX and high-density MUNE values, showing their equivalent potential in detecting motor neuron loss.Abstract: Objective: To evaluate how the motor unit number index (MUNIX) is related to high-density motor unit number estimation (HD-MUNE) in healthy controls and patients with amyotrophic lateral sclerosis (ALS).Methods: Both MUNIX and HD-MUNE were performed on the thenar muscles in 18 ALS patients and 24 healthy controls. Patients were measured at baseline, within 2weeks, and after 4 and 8months. Clinical evaluation included Medical Research Council (MRC) scale and the ALS functional rating scale (ALSFRS).Results: There was a significant positive correlation between MUNE and MUNIX values in ALS patients (r=0.49 at baseline; r=0.56 at 4months; r=0.56 at 8months, all p<0.05), but not in healthy controls. After 8months, both MUNE and MUNIX values of the ALS patients decreased significantly more compared to MRC scale, ALS functional rating scale (ALSFRS) and compound muscle action potential (CMAP) (p<0.05). There was no significant difference in relative decline of MUNIX and HD-MUNE values.Conclusions: In ALS patients, MUNIX and HD-MUNE are significantly correlated. MUNIX has an almost equivalent potential in detecting motor neuron loss compared to HD-MUNE.Significance: MUNIX could serve as a reliable and sensitive marker for monitoring disease progression in ALS.

Statistical evaluation of recurrence quantification analysis applied on single trial evoked potential studies - Corrected Proof

2012-02-10

Highlights: ► Recurrence quantification analysis (RQA) allows quantifying signal characteristics of single trial ERPs measured with and without noise induced by parallel MRI. ► RQA power to discriminate responses to different tone types in an oddball experiment was not significantly superior to a linear amplitude analysis. ► However, RQA has the potential to provide additional trial-by-trial information compared to classical amplitude based analysis.Abstract: Objective: We evaluated the potential of recurrence quantification analysis (RQA) to improve the analysis of trial-by-trial-variability in event-related potentials (ERPs) experiments.Methods: We use an acoustic oddball paradigm to compare the efficiency of RQA with a linear amplitude based analysis of single trial ERPs with regard to the power to distinguish responses to different tone types. We further probed the robustness of both analyses towards structured noise induced by parallel magnetic resonance imaging (MRI).Results: RQA provided robust discrimination of responses to different tone types, even when EEG data were contaminated by structured noise. Yet, its power to discriminate responses to different tone types was not significantly superior to a linear amplitude analysis. RQA measures were only moderately correlated with EEG amplitudes, suggesting that RQA may extract additional information from single trial responses not detected by amplitude evaluation.Conclusions: RQA allows quantifying signal characteristics of single trial ERPs measured with and without noise induced by parallel MRI. RQA power to discriminate responses to different tone types was similar to linear amplitude based analysis.Significance: RQA has the potential to detect differences of signal features in response to a standard oddball paradigm and provide additional trial-by-trial information compared to classical amplitude based analysis.

Coactivation of ankle muscles during stance phase of gait in patients with lower limb hypertonia after acquired brain injury - Corrected Proof

John W. Chow, Stuart A. Yablon, Dobrivoje S. Stokic — 2012-02-10

Highlights: ► After stroke or traumatic brain injury, the magnitude of coactivation between tibialis anterior (TA) and medial gastrocnemius (MG) muscles is increased in the more-affected limb during initial and late double support. ► The duration of TA–MG coactivation is prolonged in the less-affected limb also during initial and late double support. ► The correlation between coactivation and stretch velocity-dependent increase in MG activity in TBI patients suggests central contribution to MG output during its lengthening in stance phase of gait.Abstract: Objective: Examine (1) coactivation between tibialis anterior (TA) and medial gastrocnemius (MG) muscles during stance phase of gait in patients with moderate-to-severe resting hypertonia after stroke or traumatic brain injury (TBI) and (2) the relationship between coactivation and stretch velocity-dependent increase in MG activity.Methods: Gait and surface EMG were recorded from patients with stroke or TBI (11 each) and corresponding healthy controls (n=11) to determine the magnitude and duration of TA–MG coactivation. The frequency and gain of positive (>0) and significant positive (p<0.05) EMG–lengthening velocity (EMG–LV) slope in MG were related to coactivation parameters.Results: The magnitude of coactivation was increased on the more-affected (MA) side, whereas the duration was prolonged on the less-affected (LA) side of both stroke and TBI patients. The difference reached significance during the initial and late double support. The magnitude of coactivation positively correlated with the gain of significant positive EMG–LV slope in TBI patients.Conclusions: Increased coactivation between TA and MG during initial and late double support is a unique feature of gait in stroke and TBI patients with muscle hypertonia.Significance: Increased coactivation may represent an adaptation to compensate for impaired stability during step transition after stroke and TBI.

Increased phase synchronization during continuous face integration measured simultaneously with EEG and fMRI - Corrected Proof

Mara Kottlow, Kay Jann, Thomas Dierks, Thomas Koenig — 2012-02-06

Highlights: ► Using a visual binding task as example, this study presents a method to measure the amount of EEG gamma zero-lag phase synchronization and to locate its underlying regions with fMRI. ► We found an increased amount of gamma zero-lag phase synchronization during FACE compared to NOFACE with positive BOLD correlates in the left and right middle fusiform gyrus and the left precuneus. ► We thus suggest that the difference in gamma band phase between remote regions of the human visual system shifts toward zero during visual binding and can be measured with simultaneously acquired EEG/fMRI.Abstract: Objective: Gamma zero-lag phase synchronization has been measured in the animal brain during visual binding. Human scalp EEG studies used a phase locking factor (trial-to-trial phase-shift consistency) or gamma amplitude to measure binding but did not analyze common-phase signals so far. This study introduces a method to identify networks oscillating with near zero-lag phase synchronization in human subjects.Methods: We presented unpredictably moving face parts (NOFACE) which – during some periods – produced a complete schematic face (FACE). The amount of zero-lag phase synchronization was measured using global field synchronization (GFS). GFS provides global information on the amount of instantaneous coincidences in specific frequencies throughout the brain.Results: Gamma GFS was increased during the FACE condition. To localize the underlying areas, we correlated gamma GFS with simultaneously recorded BOLD responses. Positive correlates comprised the bilateral middle fusiform gyrus and the left precuneus.Conclusions: These areas may form a network of areas transiently synchronized during face integration, including face-specific as well as binding-specific regions and regions for visual processing in general.Significance: Thus, the amount of zero-lag phase synchronization between remote regions of the human visual system can be measured with simultaneously acquired EEG/fMRI.

sLORETA-qm for interictal MEG epileptic spike analysis: Comparison of location and quantity with equivalent dipole estimation - Corrected Proof

2012-02-02

Abstract: Objective: To determine whether quantitative modification of a standardised low-resolution brain electromagnetic tomography (sLORETA-qm) could be used as a reliable tool for quantitative analysis of magnetoencephalography (MEG) for analysis of the interictal epileptic spike. To verify the performance of sLORETA-qm, magnetic source location and quantity were compared with the equivalent current dipole (ECD) method.Methods: A total of 50 sources from 10 patients with epilepsy were obtained. Analyses were performed after the MEG data were 3–70Hz band-pass filtered. Time points for analysis were selected referring to waveform patterns and the isofield contour map. With the same spherical model, source estimation was conducted with two methods of analysis: ECD and sLORETA-qm. Distance from the centre of the spherical model and intensities were compared between the methods.Results: There were no significant differences between the methods in the distance from the spherical model (paired t-test, p=0.8761). Source intensities between the methods were strongly correlated (Spearman’s Rho=0.9803, p<0.001).Conclusions: sLORETA-qm was closely correlated with ECD concerning point source location and quantity in analysis of the interictal epileptic spike.Significance: sLORETA-qm is a reliable quantifiable method without arbitrariness for analysis of the interictal epileptic spike.

Automatic detection and analysis of the EEG sharp wave–slow wave patterns evoked by fluorinated inhalation anesthetics - Corrected Proof

2012-02-02

Highlights: ► Epileptiform patterns that possess both “sharp wave” and “slow wave” components (SWSW patterns) appear during volatile anesthesia in anesthetic concentration- and anesthetic type-dependent way. ► The novelty of the proposed method of automatic detection of epileptiform patterns during anesthesia consists in the analysis of morphology of individual SWSW patterns and not, as it was the case so far, on the quantification of 5s EEG segments containing monophasic activity and/or spikes. ► The on-line analysis of SWSW patterns’ rate and morphology offered by the proposed method is important in view of possible side effects of volatile anesthetics.Abstract: Objective: The aim of this study was to develop a method for the automatic detection of sharp wave–slow wave (SWSW) patterns evoked in EEG by volatile anesthetics and to identify the patterns’ characteristics.Methods: The proposed method consisted in the k-NN classification with a reference set obtained using expert knowledge, the morphology of the EEG patterns and the condition for their synchronization. The decision rules were constructed and evaluated using 24h EEG records in ten patients.Results: The sensitivity, specificity and selectivity of the method were 0.88±0.10, 0.81±0.13 and 0.42±0.16, respectively. SWSW patterns’ recruitment was strictly dependent on anesthetic concentration. SWSW patterns evoked by different types of anesthetics expressed different characteristics.Conclusions: Synchronization criterion and adequately selected morphological features of “slow wave” were sufficient to achieve the high sensitivity and specificity of the method.Significance: The monitoring of SWSW patterns is important in view of possible side effects of volatile anesthetics. The analysis of SWSW patterns’ recruitment and morphology could be helpful in the diagnosis of the anesthesia effects on the CNS.

Conductive neuromagnetic fields in the lumbar spinal canal - Corrected Proof

2012-01-30

Highlights: ► We used a superconducting quantum interference device fluxmeter developed for use with the spine to measure propagating neuromagnetic fields at the surface of the lower back after stimulation of tibial nerves at the ankle. ► We simultaneously measured cauda equina action potentials with an epidural catheter-type electrode to validate the accuracy of the neuromagnetic field measurements. ► This method provides a noninvasive functional examination tool for lumbar spine disease.Abstract: Objective: To measure neuromagnetic evoked fields in the lumbar spinal canal.Methods: Using a newly developed superconducting quantum interference device (SQUID) fluxmeter, neuromagnetic fields of 5 healthy male volunteers were measured at the surface of the lower back after stimulation of the tibial nerves at the ankles. For validation, we inserted a catheter-type electrode percutaneously in the lumbar epidural space in 2 of the subjects and measured cauda equina action potentials after tibial nerve stimulation.Results: Neuromagnetic fields propagating from the intervertebral foramina into the spinal canal were measured, and the latencies of the magnetic fields corresponded largely with those of the cauda equina action potentials.Conclusions: We successfully measured ascending neuromagnetic fields originating at the nerve root and the cauda equina with high spatial resolution. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for the identification of the disordered site in spinal nerves.Significance: We successfully measured neuromagnetic fields in the lumbar spinal canal, which have previously been difficult to verify. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for identifying disorders of spinal nerves.

Lateralized movement-related potential amplitudes differentiate between schizophrenia/schizoaffective disorder and major depression - Corrected Proof

2012-01-30

Highlights: ► Lateralized movement-related potentials were reduced in subjects with schizophrenia/schizoaffective disorder compared to subjects with a major depressive episode. ► The time interval around movement execution was affected. ► Deficits in lateralized primary motor cortex activation during the command to muscle contraction may distinguish schizophrenia/schizoaffective disorder from non-psychotic forms major depression.Abstract: Objective: To examine whether deficits in focal lateralized motor system activation would differentiate between subjects with schizophrenia/schizoaffective disorder and subjects with a major depressive episode. Reductions of Bereitschaftspotential amplitude have been described for both diagnostic groups.Methods: We analyzed multi-channel lateralized movement-related potentials (LMRP) during choice reaction movements in 16 schizophrenic/schizoaffective patients in partial remission with predominant negative symptoms, 18 patients with a non-psychotic major depression and two healthy control groups age-matched to the respective patient groups (20/23 subjects).Results: A significant reduction of lateralized potentials over the (pre-)motor areas immediately preceding and around movement execution was found only in subjects with schizophrenia/schizoaffective disorder but not with a major depressive episode. Reduced LMRP amplitudes correlated with negative symptoms (SANS score). Other movement stages (preceding response-locked ‘contingent negative variation’ during response selection and post-movement evaluation during motor postimperative negative variation) were not affected in the same way.Conclusions: Deficits in focal motor cortex activation during movement execution may reflect rather schizophrenia-specific deficits in fronto-striatal circuits. A general lack of drive and depressed mood did not alter the degree of lateralization of motor activation during movement execution.Significance: Lateralization of movement-related potentials could differentiate psychotic from non-psychotic disorders on the group level.

Bidirectional modulation of sensory cortical excitability by quadripulse transcranial magnetic stimulation (QPS) in humans - Corrected Proof

2012-01-27

Highlights: ► The newly designed quadripulse transcranial magnetic stimulation (QPS) was applied to the study of long-lasting sensory cortical excitability changes in humans. ► Sensory cortical excitability was modulated by QPS over the primary motor cortex or dorsal premotor cortex, but not by QPS over the primary sensory cortex itself. ► QPS might be a useful method in studies of heterotopic long-term potentiation/depression (LTP/LTD)-like effects in humans.Abstract: Objective: Quadripulse transcranial magnetic stimulation (QPS) is a newly designed patterned repetitive transcranial magnetic stimulation (TMS). Previous studies of QPS showed bidirectional effects on the primary motor cortex (M1), which depended on its inter-stimulus interval (ISI): motor evoked potentials (MEPs) were potentiated at short ISIs and depressed at long ISIs (homotopic effects). These physiological characters were compatible with synaptic plasticity. In this research, we studied effects of QPS on the primary sensory cortex (S1).Methods: One burst consisted of four monophasic TMS pulses at an intensity of 90% active motor threshold. The ISI of four pulses was set at 5ms (QPS-5) or at 50ms (QPS-50). Same bursts were given every 5s for 30min. QPS-5 and QPS-50 were performed over three areas (M1, S1 and dorsal premotor cortex (dPMC)). One sham stimulation session was also performed. Excitability changes of S1 were evaluated by timeline of somatosensory evoked potentials (SEPs).Results: QPS-5 over M1 or dPMC enhanced the P25–N33 component of SEP, and QPS-50 over M1 depressed it. By contrast, QPSs over S1 had no effects on SEPs.Conclusions: QPSs over motor cortices modulated the S1 cortical excitability (heterotopic effects). Mutual connections between dPMC or M1 and S1 might be responsible for these modulations.Significance: QPSs induced heterotopic LTP or LTD-like cortical excitability changes.

The utility of amplitude-integrated EEG and NIRS measurements as indices of hypoxic ischaemia in the newborn pig - Corrected Proof

Dandan Zhang, Xinlin Hou, Yunfeng Liu, Congle Zhou, Yuejia Luo, Haiyan Ding — 2012-01-25

Highlights: ► Early detection and stratification of hypoxic-ischaemia (HI) injury in neonates are crucial for reducing the risk of disability or death. ► Near-infrared spectroscopy (NIRS) was highly sensitive to HI but demonstrated a low correlation with the HI severity; amplitude-integrated electroencephalogram (aEEG) correlated well with HI severity but was insensitive to mild insult. ► aEEG and NIRS have additive and complementary roles in early HI assessment.Abstract: Objective: The early detection and stratification of potential hypoxic ischaemia (HI) injury in neonates are crucial for reducing the risk of neural disability. This study investigates early changes in brain function caused by acute HI of varying severities in the neonatal pig.Methods: Two non-invasive techniques, amplitude-integrated electroencephalogram (aEEG) and near-infrared spectroscopy (NIRS), were used to monitor electrocortical and cerebral haemodynamic function, respectively. The fraction of inspired oxygen (FiO2) was varied to produce different HI severities. The sensitivity and HI correlation of these methods were systematically analysed to assess their abilities to both detect injury early and assess HI severity accurately.Results: The tissue oxygen index measured via NIRS detected acute changes in cerebral oxygenation and was highly sensitive to HI (sensitivity=0.97), whereas aEEG was comparatively insensitive to HI. On the other hand, aEEG measurements correlated well with FiO2 during the entire HI event as well as the 3-h recovery period (R=0.43–0.61). NIRS measurements did not correlate well with FiO2.Conclusions: Parameters measured via aEEG and NIRS displayed different time profiles during and following the HI event.Significance: These results highlight the potential advantage of using aEEG and NIRS in conjunction to monitor neonatal brain function, and provide an objective and rigorous method for the characterisation of cerebral function both during and following HI insults.

Upper-extremity H-reflex measurement post-stroke: Reliability and inter-limb differences - Corrected Proof

2012-01-25

Highlights: ► Flexor carpi radialis (FCR) H-reflexes can be reliably evoked in non-disabled participants and in both paretic and non-paretic arms of participants post-stroke. ► FCR H-reflexes (recruitment slope, amplitude, and threshold) are a sensitive measure of changes in spinal excitability post-stroke. ► FCR H-reflex recruitment slope and amplitude were significantly greater in the paretic arm compared to the non-paretic arm post-stroke.Abstract: Objective: To establish test–retest reliability of flexor carpi radialis (FCR) H-reflexes in non-disabled and stroke participants. We also investigated inter-limb differences and effects of chronicity post-stroke compared to non-disabled group and age-related effects in the non-disabled group.Methods: Sixteen chronic stroke and twenty-two non-disabled participants were recruited. Bilateral FCR H-reflexes were tested on two separate days by stimulating the median nerve and recording surface electromyography responses. FCR recruitment curves were plotted for H-reflex (H) and motor (M) waves and normalized as a percentage of maximal M-wave (ordinate) and motor threshold (abscissa).Statistics: Intraclass correlation coefficients [two-way mixed model-ICC (1, 2)], one-way ANOVA, Bland–Altman plots, standard error of measurement (SEM), and smallest real difference (SRD).Results: ICCs ranged from 0.55 to 0.95 (stroke) and 0.69–0.88 (non-disabled). SEM% (% of the mean) ranged from 9% to 24% (stroke) and 18–38% (non-disabled); SRD% ranged from 18% to 66% (stroke) and 6% to 50% (non-disabled). H-reflex amplitude and slope were greater in the paretic vs. non-paretic arm post-stroke (p=0.07 and 0.01, respectively) and the paretic arm vs. non-disabled participants (p=0.007 and 0.002, respectively). Stroke participants with longer chronicity (mean 9.4years) revealed a significantly greater Hslp/Mslp on the paretic side compared to shorter chronicity (2.5years; p=0.05). Mean Hslp/Mslp was significantly greater in the young (mean 29years) compared to the older group (62years; p=0.045).Conclusions: These results establish reliability of FCR H-reflexes in stroke and non-disabled participants. SEM and SRD measurements can be used to interpret recovery patterns and longitudinal effects of therapeutic interventions.Significance: FCR H-reflex amplitude and slope can be reliably measured and used to investigate neurophysiological mechanisms of motor recovery post-stroke.

Somatosensory evoked potentials are of additional prognostic value in certain patterns of brain injury in term birth asphyxia - Corrected Proof

2012-01-20

Highlights: ► SEPs can be of additional prognostic value to EEG and MRI in term asphyxiated newborns. ► Unilaterally abnormal SEP in combination with unilateral injury in the posterior frontal cortex due to asymmetrical watershed injury in perinatal asphyxia predicts the development of hemiparesis. ► SEPs seem to be more accurate in predicting motor than cognitive outcome.Abstract: Objective: (a) To relate MRI patterns of brain injury to somatosensory evoked potentials (SEPs), and (b) to determine the prognostic value of SEPs in addition to continuous EEG monitoring (cEEG) and cerebral imaging, in term asphyxiated newborns.Methods: Fifty one consecutive neonates were studied. Survivors were followed for at least 2years. cEEG, started within 24h, was done for ⩾24h and scored. SEPs and MRIs were performed in the first week. Brain injury patterns were classified.Results: Bilaterally abnormal SEPs had a sensitivity of 90% (28/31) and specificity of 85% (17/20) in predicting a poor outcome, defined as death or severe handicap. SEPs were of particular value in predicting outcome in isolated symmetrical white matter injury and predicting the development of hemiparesis in isolated asymmetrical watershed injury. Binary logistic regression analysis revealed a significant relation to outcome separately for cEEG, deep grey matter injury on MRI and SEPs. SEPs provided additional value when added to cEEG and MRI in the model (p=0.034).Conclusions: SEPs are of additional prognostic value after term birth asphyxia.Significance: In certain patterns of postasphyxial neonatal brain injury like asymmetrical watershed lesions and symmetrical white matter injury, EPs are complementary to information obtained from cEEG and MRI for prognostication.

Selective autonomic failure: Ross syndrome - Corrected Proof

Vaughan G. Macefield — 2012-01-20

Nature has given neurology quite a few gems of disordered neural function that highlight, on the one hand, how extensive the influence of a particular neuronal control system is and, on the other, how limited the effects of disturbances in one system can be. Many of nature’s models are common, while others are rare. Given its pervasive influence on diverse aspects of physiology and homeostatic regulation, the autonomic nervous system features in many neurological disorders, including one of the most common – idiopathic hyperhidrosis, in which sudomotor outflow is affected without any disturbance to the other components of the sympathetic or parasympathetic nervous systems. Less common neurological conditions include pure autonomic failure, in which all branches of the autonomic nervous system are ultimately affected: because muscle (and splanchnic) vasoconstrictor drive is interrupted patients suffer from severe orthostatic hypotension and, because sudomotor drive is interrupted, anhidrosis also features. There are a few rare conditions that also feature anhidrosis. One such condition is congenital insensitivity to pain with anhidrosis – one of the hereditary sensory and autonomic neuropathies (HSAN type IV). This is due to a genetic mutation that results in a selective loss of unmyelinated afferent axons, resulting in a loss of nociception, and a loss of efferent axons to the skin (); because these individuals cannot sweat thermoregulation is greatly compromised, resulting in dangerous febrile episodes that can lead to death in infancy. An even rarer condition affecting the autonomic nervous system is Ross syndrome, which features anhidrosis as well as a tonic (Adie’s) pupil and loss of deep tendon reflexes (). In this issue of Clinical Neurophysiology, Vincenzo Donadio and colleagues, from the Istituto delle Scienze Neurologiche di Bologna, Italy, have attempted to characterize the underlying neurological disturbances in sympathetic outflow (). had previously shown, using punch biopsy of the skin, that cholinergic sudomotor fibres are absent in patients with Ross syndrome. However, whether this deficiency in sympathetic innervation of the skin extends to the innervation of the blood vessels in the skin was, until now, largely unknown. Using invasive microelectrode recordings (microneurography) from the common peroneal nerve in awake patients, the authors have now shown that spontaneous and evoked skin sympathetic nerve activity (SSNA) is absent on Ross syndrome, as are sudomotor and cutaneous vasoconstrictor responses. However, spontaneous muscle sympathetic nerve activity (MSNA) was preserved in these patients, which fits the clinical picture of there being little disturbance to blood pressure regulation in this condition. So, while pure autonomic failure affects both SSNA and MSNA (), microneurography has revealed that Ross syndrome affects SSNA but not MSNA. In another rare condition associated with anhidrosis – idiopathic pure sudomotor failure – microneurography revealed that SSNA is intact; evidently the failure occurs at the cholinergic synapse with the sweat glands in this condition (). Of course, given the involvement of sympathetic and parasympathetic innervation of the pupil, the autonomic signs of Ross syndrome are not limited to the skin, but at least the current study has provided further differentiation in the expression of autonomic disturbances across neurological conditions.

Introducing a novel approach of network oriented analysis of ERPs, demonstrated on adult attention deficit hyperactivity disorder - Corrected Proof

2012-01-19

Highlights: ► Introducing a novel network-oriented analysis method of event related potential (ERP) activities and evaluating its value in the identification and severity-grading of adult ADHD patients. ► The analysis yielded high specificity and sensitivity and individual scores correlated well with behavioral assessments, suggesting that the proposed approach may have merit as an objective electrophysiological marker and individual subject severity grader in adult ADHD patients. ► This novel approach may provide both diagnostic and drug development tools for use in diverse neurological disorders.Abstract: Objective: Introducing a network-oriented analysis method (brain network activation [BNA]) of event related potential (ERP) activities and evaluating its value in the identification and severity-grading of adult ADHD patients.Methods: Spatio-temporal interrelations and synchronicity of multi-sited ERP activity peaks were extracted in a group of 13 ADHD patients and 13 control subjects for the No-go stimulus in a Go/No-go task. Participants were scored by cross-validation against the most discriminative ensuing group patterns and scores were correlated to neuropsychological evaluation scores.Results: A distinct frontal–central–parietal pattern in the delta frequency range, dominant at the P3 latency, was unraveled in controls, while central activity in the theta and alpha frequency ranges predominated in the ADHD pattern, involving early ERP components (P1–N1–P2–N2). Cross-validation based on this analysis yielded 92% specificity and 84% sensitivity and individual scores correlated well with behavioral assessments.Conclusions: These results suggest that the ADHD group was more characterized by the process of exerting attention in the early monitoring stages of the No-go signal while the controls were more characterized by the process of inhibiting the response to that signal.Significance: The BNA method may provide both diagnostic and drug development tools for use in diverse neurological disorders.

Comparison of a row-column speller vs. a novel lateral single-character speller: Assessment of BCI for severe motor disabled patients - Corrected Proof

Gabriel Pires, Urbano Nunes, Miguel Castelo-Branco — 2012-01-16

Highlights: ► We propose a novel P300-based lateral single-character (LSC) speller, that explores layout, event strategy, and hemispheric asymmetries in visual perception to improve the performance of brain–computer interfaces. ► The online performance of the LSC paradigm is compared to that of the standard row-column (RC) paradigm. ► The paradigms are tested by individuals with neuromuscular disorders (amyotrophic lateral sclerosis, cerebral palsy, Duchenne muscular dystrophy, and spinal cord injury).Abstract: Objective: Non-invasive brain–computer interface (BCI) based on electroencephalography (EEG) offers a new communication channel for people suffering from severe motor disorders. This paper presents a novel P300-based speller called lateral single-character (LSC). The LSC performance is compared to that of the standard row-column (RC) speller.Methods: We developed LSC, a single-character paradigm comprising all letters of the alphabet following an event strategy that significantly reduces the time for symbol selection, and explores the intrinsic hemispheric asymmetries in visual perception to improve the performance of the BCI. RC and LSC paradigms were tested by 10 able-bodied participants, seven participants with amyotrophic lateral sclerosis (ALS), five participants with cerebral palsy (CP), one participant with Duchenne muscular dystrophy (DMD), and one participant with spinal cord injury (SCI).Results: The averaged results, taking into account all participants who were able to control the BCI online, were significantly higher for LSC, 26.11bit/min and 89.90% accuracy, than for RC, 21.91bit/min and 88.36% accuracy. The two paradigms produced different waveforms and the signal-to-noise ratio was significantly higher for LSC. Finally, the novel LSC also showed new discriminative features.Conclusions: The results suggest that LSC is an effective alternative to RC, and that LSC still has a margin for potential improvement in bit rate and accuracy.Significance: The high bit rates and accuracy of LSC are a step forward for the effective use of BCI in clinical applications.

Online use of error-related potentials in healthy users and people with severe motor impairment increases performance of a P300-BCI - Corrected Proof

2012-01-16

Highlight: ► Error-related potential detected during operation of a P3 speller brain–computer interface. ► Bit rate estimated to improve by 0.44bit/trial in a group of six ALS patients. ► Online implementation achieved bit rate improvement of 0.52bit/trial for healthy and motor impaired users.Abstract: Objective: To investigate whether error-related potentials can be used to increase information transfer rate of a P3 brain–computer interface (BCI) in healthy and motor-impaired individuals.Methods: Extraction and classification of the error-related potential was performed offline on data recorded from six amyotrophic lateral sclerosis (ALS) patients. An online study with 17 healthy and six motor impaired participants followed, using a modified P3 speller to provide explicit feedback of spelled letters. On recognition of error-related potentials, the interface informed users that the incorrect letter was automatically deleted.Results: The offline cross-validation estimate of P3 speller data of six ALS patients increased bit rate by 0.44bit/trial. During online copy spelling, the participants increased their bit rate by 0.52bit/trial with the error correction system (ECS). Some participants performed free spelling and were able to increase their bit rate. Finally, we demonstrated that healthy participants could increase their bit rate by using a classifier pre-trained on other users’ data.Conclusions: Error-related potentials as a secondary source of information can be used to increase overall bit rate in a P3 BCI.Significance: The method should be made available to any patient using the P3 BCI for communication.

Muscle ultrasonography: A diagnostic tool for amyotrophic lateral sclerosis - Corrected Proof

2012-01-16

Highlights: ► Muscle ultrasound can differentiate between amyotrophic lateral sclerosis and mimics with high sensitivity and specificity. ► Ultrasound is a sensitive tool to screen for regional lower motor neuron involvement. ► Ultrasound might reduce the number of muscles that require needle examination in the search for LMN involvement.Abstract: Objective: In a prospective study we tested whether muscle ultrasonography can differentiate between amyotrophic lateral sclerosis (ALS) and mimics. Furthermore, we assessed the ability of ultrasonography to identify subclinical lower motor neuron involvement.Methods: In 59 patients, suspected for adult onset motor neuron disease, ultrasound scans were made of 12 different muscle groups. Echo intensity was determined and each muscle was screened for fasciculations. Ultrasonography was considered diagnostic for ALS when echo intensity was 1.5 SD above normal in at least two muscles and fasciculations were present in at least four muscles.Results: Ultrasonography differentiated between ALS and mimics with 96% sensitivity and 84% specificity. In the 27 ALS patients, ultrasonography detected 15 regions with lower motor neuron involvement that were negative using either clinical examination or needle EMG.Conclusions: Muscle ultrasound can differentiate between amyotrophic lateral sclerosis and mimics with high sensitivity and specificity, and is a sensitive tool to screen for regional lower motor neuron involvement.Significance: Muscle ultrasonography is a promising tool in the diagnostic work up of ALS.

The bilateral movement condition facilitates maximal but not submaximal paretic-limb grip force in people with post-stroke hemiparesis - Corrected Proof

Stacey L. DeJong, Catherine E. Lang — 2012-01-16

Highlights: ► Although healthy individuals produce less force during bilateral muscle contractions compared to unilateral contractions, emerging evidence suggests that the paretic limb post-stroke may benefit from bilateral movement. ► The bilateral condition increased maximal grip force on the paretic side in the majority of people with post-stroke hemiparesis, but decreased maximal grip forces on the non-paretic side and on both sides of healthy controls. ► In a submaximal bilateral grip task, as might be expected during daily activities, there was no enhancement of paretic-limb performance.Abstract: Objectives: Although healthy individuals have less force production capacity during bilateral muscle contractions compared to unilateral efforts, emerging evidence suggests that certain aspects of paretic upper limb task performance after stroke may be enhanced by moving bilaterally instead of unilaterally. We investigated whether the bilateral movement condition affects grip force differently on the paretic side of people with post-stroke hemiparesis, compared to their non-paretic side and both sides of healthy young adults.Methods: Within a single session, we compared: (1) maximal grip force during unilateral vs. bilateral contractions on each side, and (2) force contributed by each side during a 30% submaximal bilateral contraction.Results: Healthy controls produced less grip force in the bilateral condition, regardless of side (−2.4% difference), and similar findings were observed on the non-paretic side of people with hemiparesis (−4.5% difference). On the paretic side, however, maximal grip force was increased by the bilateral condition in most participants (+11.3% difference, on average). During submaximal bilateral contractions in each group, the two sides each contributed the same percentage of unilateral maximal force.Conclusions: The bilateral condition facilitates paretic limb grip force at maximal, but not submaximal levels.Significance: In some people with post-stroke hemiparesis, the paretic limb may benefit from bilateral training with high force requirements.

Muscle and skin sympathetic activities in Ross syndrome - Corrected Proof

2012-01-13

Highlights: ► Microneurographic study of sympathetic activity from affected skin confirmed the selective involvement of skin sympathetic activity (SSNA) with spared muscle sympathetic activity (MSNA) in Ross syndrome (RS). ► Microneurographic findings represented the neurophysiological hallmark of the disease and together with clinical and skin biopsy findings may contribute to RS diagnosis. ► We disclosed normal MSNA and cardiovascular reflexes suggesting that autonomic damage in RS does not involve cardiovascular activity.Abstract: Objectives: Ross syndrome (RS) is a rare degenerative disorder characterized by tonic pupil, areflexia and anhydrosis. The underlying lesion affects postganglionic skin sympathetic nerve fibers whereas the postganglionic muscle sympathetic branch is thought to be spared. Microneurography explores both skin and muscle peripheral sympathetic branches and it does not usually detect peripheral sympathetic outflow in either branch in chronic autonomic failure syndromes. The aim of this study was to record sympathetic activity by microneurography for the first time in RS patients to confirm the selective involvement of skin sympathetic nerve activity (SSNA) with spared muscle sympathetic nerve activity (MSNA).Methods: We studied seven patients (49±14years, four males) with a typical clinical picture and skin biopsy findings. Patients underwent cardiovascular reflexes and microneurography from the peroneal nerve (anhydrotic skin) to record MSNA, SSNA and the corresponding organ effector responses (skin sympathetic response-SSR and skin vasomotor response-SVR) in the same innervation field. The absence of sympathetic bursts was established after exploring at least three different corresponding nerve fascicles. Twenty age-matched healthy subjects served as controls.Results: RS patients complained of diffuse anhydrosis and they showed tonic pupil and areflexia. Cardiovascular reflexes were normal. All patients displayed absent SSNA, SSR and SVR whereas MSNA was always recorded showing normal characteristics.Conclusion: Microneurographic study of sympathetic activity from affected skin confirmed the selective involvement of skin sympathetic activity with spared muscle sympathetic activity and it may represent the neurophysiological hallmark of the disease.Significance: Microneurography together with clinical and skin biopsy findings may contribute to RS diagnosis. Our data also suggest that autonomic damage in RS does not involve cardiovascular activity.

Muscle artifacts in multichannel EEG: Characteristics and reduction - Corrected Proof

Junshui Ma, Peining Tao, Sevinç Bayram, Vladimir Svetnik — 2012-01-12

Highlights: ► This study expands our knowledge of muscle activities in EEG from muscle-controlled experiments to general clinical trials by studying the temporal, spectral, and spatial signal characteristics of unintentional muscle activities. ► The proposed high-throughput muscle artifact reduction method provides an urgently needed solution with validated performance for processing large volumes of clinical EEG. ► The muscle activity topography generated by the proposed method can be used as a biofeedback tool to reveal the unintentionally stressful spots on a person’s head.Abstract: Objective: To study the characteristics of unintentional muscle activities in clinical EEG, and to develop a high-throughput method to reduce them for better revealing drug or biological effects on EEG.Methods: Two clinical EEG datasets are involved. Pure muscle signals are extracted from EEG using Independent Component Analysis (ICA) for studying their characteristics. A high-throughput method called ICA-SR is introduced based on a new feature named Spectral Ratio (SR).Results: The spectral and temporal characteristics of the muscle artifacts are illustrated using representative muscle signals. The spatial characteristics are presented at both the group- and the subject-level, and are consistent under three different electrode reference methodologies. Objectively compared with an existing method, ICA-SR is shown to reduce more artifacts, while introduce less distortion to EEG. Its effectiveness is further demonstrated in real clinical EEG with the help of a CO2-inhalation EEG recording session.Conclusion: The characteristics of unintentional muscle activities align with the reported characteristics of controlled muscle activities. Artifact spatial characteristics can be EEG equipment dependent. The ICA-SR method can effectively and efficiently process clinical EEG.Significance: Armed with advanced signal processing algorithms, this study expands our knowledge of muscle activities in EEG from muscle-controlled experiments to general clinical trials. The ICA-SR method provides an urgently needed solution with validated performance for efficiently processing large volumes of clinical EEG.

Pattern-specific changes and discordant prognostic values of individual leg-muscle motor evoked potentials during spinal surgery - Corrected Proof

2012-01-09

Highlights: ► Muscle motor evoked potentials (mMEPs) were generated at a high rate in the abductor hallucis (AH) and had high positive predictive values for sustained postoperative motor deficits. ► However, mMEPs in the tibialis anterior were more sensitive in detecting perioperative neural damage and in predicting sustained postoperative motor deficits than mMEPs in the AH. ► The interpretations of intra-operative mMEPs should be individualised according to the type of muscles recorded, and a tailored approach using multi-muscle recordings may contribute to better outcomes for spinal surgery.Abstract: Objective: The aim of the study is to evaluate the efficacy of muscle motor evoked potentials (mMEPs) in individual leg muscles for spinal surgery monitoring.Methods: Data were obtained from 209 patients who underwent spine surgery with intra-operative mMEP monitoring in the tibialis anterior (TA) and abductor hallucis (AH) muscles. The mMEP generation, pattern-specific mMEP loss and recovery, and the accuracy of individual mMEP changes in predicting postoperative motor deficit were assessed.Results: Generation rate of mMEPs was higher in the AH than in the TA (p<0.001). The mMEP in the TA was more sensitive in detecting mMEP loss than in the AH (p<0.001); however, mMEP in the AH was more sensitive in detecting mMEP recovery (p<0.001). The mMEPs in the TA had high sensitivity in predicting sustained postoperative motor deficits. By contrast, mMEPs in the AH showed a high positive predictive value.Conclusions: Although mMEPs were generated at a high rate in the AH, mMEP in the TA can play an important complementary role in intra-operative mMEP monitoring, because mMEP in the TA can be more sensitive to potential neural damage.Significance: Using a combination of muscles with individual sensitivities and clinical significances will improve intra-operative mMEP monitoring strategies.

Sleep cyclic alternating pattern analysis in infants with apparent life-threatening events: A daytime polysomnographic study - Corrected Proof

2012-01-09

Highlights: ► Sleep arousal level is increased in infants with apparent life threatening events. ► NREM sleep instability studied by means of cyclic alternating pattern analysis is increased in infants with apparent life threatening events. ► Sleep maturation is not complete in infants with apparent life threatening events.Abstract: Objective: Non-REM sleep is characterized by a physiologic oscillating pattern that exhibits different levels of arousal, coded as cyclic alternating pattern. The aim of this study was to analyze the development of cyclic alternating pattern parameters in a group of infants with apparent life-threatening events.Methods: A total of 26 infants with apparent life-threatening events (14 females, mean age 3.4months, 2.37 S.D., age range 0.5–9months) were studied while they slept in the morning between feedings, by means of a 3-h video-electroencephalographic–polygraphic recording. Sleep was visually scored using standard criteria. The control group was composed of 36 healthy infants (16 females, mean age 3.2months, 2.17 S.D., age range 0.5–9months).Results: Children with apparent life-threatening events showed an increased frequency of periodic breathing, gastroesofageal reflux and of other risk conditions. They presented also an increased obstructive apnoea/hypopnea index. A full NREM sleep development was found in a significantly smaller percentage of patients, and they showed a significant reduction of the percentage of REM sleep, of cyclic alternating pattern A1 subtypes, an increased percentage of A2 and A3 subtypes and increased index of A2, A3 subtypes and arousal, compared to normal controls. Cyclic alternating pattern rate showed a significant positive correlation with age, only in controls.Conclusions: Our results show a higher level of arousal and an increased non-REM sleep discontinuity in babies with apparent life-threatening events, compared to controls.Significance: The enhanced mechanism of arousal might counteract life-threatening events and represent an important neurophysiologic distinction from future victims of sudden infant death syndrome who also experience similar events.

Reply to “Unmasking of presynaptic cutaneous HFOs burst by DBS lead recordings” - Corrected Proof

Isamu Ozaki, Isao Hashimoto — 2012-01-09

Our point was to emphasize that high frequency oscillations (HFOs) following natural mechanical stimulation of a finger or electrical stimulation of pure cutaneous digital nerves had not been reported as yet (). Now, we congratulate that they have succeeded in recording HFOs around N20 peak from the cortical surface after pure cutaneous nerve stimulation, similar to mixed nerve stimulation.

Electromyography and muscle ultrasound in ALS diagnosis, complementary or competitive? - Corrected Proof

Reinhard Dengler — 2012-01-09

The gold standard of ALS diagnosis are the revised El Escorial Criteria (). Although the El Escorial Criteria are mainly based on clinical demonstration of upper and lower motor neuron signs they appreciate the diagnostic role of electromyography (EMG) in the search for lower motor neuron involvement. Muscle ultrasound is not recommended. The El Escorial Criteria are very specific, but fairly rigid and insensitive and, therefore, of only limited value in routine patient care. For this reason, the electrodiagnostic Awaji Criteria have recently been proposed () which have since been shown to increase the diagnostic sensitivity of the El Escorial Criteria without decreasing their specificity (). The essential step forward made by the Awaji Criteria was the acceptance of fasciculation potentials as signs of active denervation equivalent to fibrillation potentials and positive sharp waves in the clinical context of motor neuron disease. This “upgrading” of fasciculations is novel and important as the El Escorial Criteria require the demonstration of both signs of active and of chronic denervation in the same muscle for the diagnosis of ALS.

Semiautomatic quantification of spiking in patients with continuous spikes and waves in sleep: Sensitivity to settings and correspondence to visual assessment - Corrected Proof

M.E. Peltola, K. Palmu, E. Liukkonen, E. Gaily, S. Vanhatalo — 2012-01-06

Highlights: ► An objective paradigm for quantification of continuous spikes and waves in sleep (CSWS) is needed for both scientific and clinical use. ► Semiautomatic quantification of spike index (SI) with appropriate parameter settings is a robust and a promising tool. ► SI of the first hour of sleep is representative of the whole night SI.Abstract: Objective: To define the optimal analysis protocol for semiautomatic quantification of spike index (SI) in continuous spikes and waves in sleep (CSWS).Methods: Ten overnight EEGs (nine patients) with abundant spiking were used to quantify SI with a previously published semiautomatic quantification based on spike detection with BESA software. We studied (i) dependency of SI on maximal interspike interval (maxISI) defining the continuous discharge, (ii) sensitivity of SI to variations in the spike search protocol, and (iii) stability of SI over time. Finally, the semiautomatic method was compared with the quantification based on visual scoring by two neurophysiologists.Results: MaxISI of 3s appeared to yield the best combination of sensitivity and stability in SI quantification. The SI of the first hour of sleep did not differ significantly from the SI of the whole night. Mean error of the semiautomatic method compared to visual scoring was only seven percentage units.Conclusions: Semiautomatic quantification of SI functions well with maxISI of 3s, and the first hour of sleep represents the whole night SI with a clinically relevant accuracy.Significance: This method opens a possibility for objective quantification of near-continuous epileptiform spiking during sleep, and it supports the use of shorter epochs for quantitative assessment of CSWS.

Unmasking of presynaptic cutaneous HFOs burst by DBS lead recordings - Corrected Proof

Angelo Insola, Luca Padua, Paolo Mazzone, Domenico Restuccia — 2012-01-06

We have carefully read the article: exploring the physiology and function of high-frequency oscillations (HFOs) from the somatosensory cortex, by . Although we find this paper very interesting, we disagree with the method described to obtain HFOs due to pure cutaneous stimulation and we disagree with the conclusions on the consecutive presynaptic cortical burst reported as undetectable. In fact the index finger stimulation through a pair of ring electrodes attached at the proximal and distal interphalangeal joint elicited action potentials coming from both cutaneous and the Golgi tendon organs afferent fibers; accordingly, the HFOs are not of a pure cutaneous origin. In a previous report () we have described the detailed technique for selective electrical stimulation of muscle as well as cutaneous afferents able to evoke modality-specific responses in somatosensory evoked potentials (SEPs) recorded on the scalp of humans. To obtain pure cutaneous responses we have recorded SEPs after stimulation of the distal phalanx of the thumb, which selectively involve only cutaneous afferent. Our results are substantially in agreement with those of Ozaki and Hashimoto in which cutaneous inputs elicit larger cortical low frequency potentials compared to proprioceptive inputs (see Fig. 6 and Table 1 of ). Therefore we support the assertion that electrical median nerve stimulation at the wrist evokes sensory responses at the subcortical or primary somatosensory cortex that are attributed mainly to volleys of cutaneous afferents rather than those of muscle spindle afferents or tendon organ afferents.

Quantitative assessment of nerve echogenicity: Comparison of methods for evaluating nerve echogenicity in ulnar neuropathy at the elbow - Corrected Proof

J. Boom, L.H. Visser — 2012-01-04

Abstract: Objective: The objective is to evaluate different methods to assess nerve echogenicity in a quantitative way by comparing a group of patients with ulnar neuropathy at the elbow (UNE) and a healthy control group, subsequently selecting the best tests for quantitative assessment of nerve echogenicity.Methods: We included 56 patients with UNE and 37 healthy controls. High-resolution ultrasonography images of the ulnar nerve at the level of the medial epicondyle were saved in JPEG, TIFF or DICOM format, with a 19pixels/mm resolution. Hypoechoic fraction was calculated by using 1 manual and 16 automatic thresholding methods.Results: A significant difference in mean hypoechoic fraction between patients and controls was found using the following automatic thresholding methods: MaxEntropy 82% versus 74% (p<0.001), RenyiEntropy 80% versus 69% (p<0.001), Shanbhag 76% versus 68% (p=0.002), Triangle 45% versus 58% (p=0.036) and Yen 79% versus 67% (p<0.001). Of these five tests a significant correlation between hypoechoic fraction and the cross-sectional area was found for: MaxEntropy 0.542 (p<0.001), RenyiEntropy 0.558 (p<0.001), Shanbhag 0.219 (p=0.035) and Yen 0.513 (p<0.001). The manual thresholding method did not detect a significant difference in hypoechoic fraction between patients and controls, and inter-rater agreement in hypoechoic fraction for manual thresholding was poor.Conclusion: Quantitative nerve echogenicity assessment can be successfully used to distinguish between a group of patients with UNE and a healthy control group, preferably by using the MaxEntropy, RenyiEntropy or Yen methods.Significance: Automatic thresholding techniques using the MaxEntropy, RenyiEntropy or Yen methods are the best quantitative tests, and these quantitative measures can probably be used in further studies evaluating echogenicity in mono- and polyneuropathies.

Emotional anticipation rather than processing is altered in patients with vasovagal syncope - Corrected Proof

2012-01-04

Highlights: ► Syncopal patients show reduced cortical negativity in anticipation of unpleasant pictures. ► Syncopal patients and healthy individuals show similar electrocortical responses to arousing stimuli. ► Syncopal patients possibly engage in cognitive distraction to down-regulate emotional anticipation.Abstract: Objective: To investigate whether the electrocortical activity underlying the anticipation and processing of emotional stimuli is enhanced in individuals with recurrent episodes of vasovagal syncope (VVS).Methods: Fifteen fainters and 15 age-matched healthy controls were presented a S1–S2 task, where the content of high-arousal pleasant and unpleasant, and neutral pictures (S2) was forecasted by word cues (S1). Stimulus Preceding Negativity (SPN) amplitude during the S1–S2 interval was computed as a measure of affective anticipation. The event-related potentials (ERPs) to S1 and S2 were measured to assess the processing of emotional warning stimuli and pictures.Results: Relative to controls, fainters showed smaller P300 to warning cues anticipating emotional (and, particularly, unpleasant) pictures, and smaller SPN during anticipation of unpleasant pictures. No differences between groups were found with regard to ERP amplitudes during picture processing.Conclusions: These results suggest that the anticipation, rather than the processing, of aversive stimuli is altered in syncopal patients.Significance: The reduced cortical anticipation in fainters might reflect the use of non-adaptive emotion regulation strategies for reducing the impact of upcoming highly arousing (and, particularly, of unpleasant) events.

Cross-frequency decomposition: A novel technique for studying interactions between neuronal oscillations with different frequencies - Corrected Proof

Vadim V. Nikulin, Guido Nolte, Gabriel Curio — 2012-01-04

Highlights: ► We present a novel cross-frequency decomposition (CFD) technique. ► CFD recovers oscillatory components phase-coupled at different frequencies. ► CFD recovered complex relationships between EEG alpha and beta oscillations in the human brain.Abstract: Objective: We present a novel method for the extraction of neuronal components showing cross-frequency phase synchronization.Methods: In general the method can be applied for the detection of phase interactions between components with frequencies f1 and f2, where f2rf1 and r is some integer. We refer to the method as cross-frequency decomposition (CFD), which consists of the following steps: (a) extraction of f1-oscillations with the spatio-spectral decomposition algorithm (SSD); (b) frequency modification of the f1-oscillations obtained with SSD; and (c) finding f2-oscillations synchronous with f1-oscillations using least-squares estimation.Results: Our simulations showed that CFD was capable of recovering interacting components even when the signal-to-noise ratio was as low as 0.01. An application of CFD to the real EEG data demonstrated that cross-frequency phase synchronization between alpha and beta oscillations can originate from the same or remote neuronal populations.Conclusions: CFD allows a compact representation of the sets of interacting components. The application of CFD to EEG data allows differentiating cross-frequency synchronization arising due to genuine neurophysiological interactions from interactions occurring due to quasi-sinusoidal waveform of neuronal oscillations.Significance: CFD is a method capable of extracting cross-frequency coupled neuronal oscillations even in the presence of strong noise.

Bilateral N20 absence in post-anoxic coma: Do you pay attention? - Corrected Proof

2012-01-03

In this issue of Clinical Neurophysiology, Van Putten presents an interesting simple biophysical model to explain the lack of correlation between EEG rhythms and the preservation of the N20 component of the somatosensory evoked potential (SSEP) in comatose patients after cardiac arrest. The author argues that EEG and SSEPs may reveal two distinctive functions of cortical neurons: input processing, supported by thalamocortical input, launching intracellular currents that trigger generation of cortical SSEP components, and output signals, processed by the synaptic mechanisms involved in EEG generation, where this latter process is seemingly more sensitive to hypoxia ().

Origin of the low-level EMG during the silent period following transcranial magnetic stimulation - Corrected Proof

2012-01-03

Abstract: Objective: The cortical silent period refers to a period of near silence in the electromyogram (EMG) after transcranial magnetic stimulation (TMS) of the motor cortex during contraction. However, low-level EMG of unknown origin is often present. We hypothesised that it arises through spinal reflexes. Sudden lengthening of the muscle as force drops during the silent period could excite muscle spindles and facilitate motoneurones.Methods: Subjects (n=8) performed maximal isometric, shortening and lengthening contractions of the elbow flexors during which TMS (90–100% output) was delivered over the motor cortex. The rate of flexion during shortening contractions reduced muscle lengthening caused by muscle relaxation. Surface EMG was recorded from biceps brachii and brachioradialis, and the low-level EMG during silent periods produced by TMS was measured.Results: Low-level EMG activity was reduced on average by 68% in biceps and 63% in brachioradialis in the shortening contraction compared to all other contraction conditions (p<0.001). Levels of pre-stimulus EMG were similar between conditions.Conclusions: Muscle lengthening contributes to low-level EMG activity in the silent period, through spinal reflex facilitation by muscle spindle afferents.Significance: The silent period depth is not only dependent on cortical output but also reflex effects evoked by muscle lengthening.

Chronic trauma-induced neck pain impairs the neural control of the deep semispinalis cervicis muscle - Corrected Proof

Jochen Schomacher, Dario Farina, René Lindstroem, Deborah Falla — 2011-12-29

Highlights: ► This study is the first to present neurophysiological data from the deep semispinalis cervicis muscle in patients with chronic neck pain. ► Patients with neck pain showed reduced and less defined activity of the semispinalis cervicis muscle during a multidirectional isometric task. ► This finding might be relevant for the maintenance or recurrence of neck pain.Abstract: Objective: The deep cervical extensors show structural changes in patients with neck pain however their activation has never been investigated in patients. This study is the first to present neurophysiological data from the deep semispinalis cervicis muscle in patients.Methods: Ten women with chronic neck pain and 10 healthy controls participated. Activity of the semispinalis cervicis was measured as subjects performed isometric contractions at 15 and 30N force with continuous change in force direction in the range 0–360°. Tuning curves of the EMG amplitude (average rectified value, ARV) were computed and the mean point of the ARV curves defined a directional vector, which determined the directional specificity of the muscle activity.Results: Patients displayed reduced directional specificity of the semispinalis cervicis (P<0.05). Furthermore, the EMG amplitude during the circular contraction was lower for the patients (86.3±38.0 and 104.4±47.0μV for 15 and 30N, respectively) compared to controls (226.4±128.5 and 315.8±205.5μV; P<0.05).Conclusions: The activity of the semispinalis cervicis muscle is reduced and less defined in patients with neck pain confirming a disturbance in the neural control of this muscle.Significance: This finding suggests that exercises that target the deep semispinalis cervicis muscle may be relevant to include in the management of patients with neck pain.

Differences in excitability between median and superficial radial sensory axons - Corrected Proof

2011-12-28

Highlights: ► This study compared excitability properties of human median and radial sensory axons (e.g., innervating the hairy and the non-hairy skin of the hand). ► The results suggest that membrane potential is more negative in median axons than in radial axons, possibly due to greater activity of electrogenic Na+–K+ pump activity in median axons. ► Biophysical properties are not identical in different human sensory axons, and therefore their responses to disease may differ.Abstract: Objective: The aim of this study was to investigate differences in excitability properties of human median and superficial radial sensory axons (e.g., axons innervating the glabrous and hairy skin in the hand). Previous studies have shown that excitability properties differ between motor and sensory axons, and even among sensory axons between median and sural sensory axons.Methods: In 21 healthy subjects, threshold tracking was used to examine excitability indices such as strength–duration time constant, threshold electrotonus, supernormality, and threshold change at the 0.2ms inter-stimulus interval in latent addition. In addition, threshold changes induced by ischemia for 10min were compared between median and superficial radial sensory axons.Results: Compared with radial sensory axons, median axons showed shorter strength–duration time constant, greater threshold changes in threshold electrotonus (fanning-out), greater supernormality, and smaller threshold changes in latent addition. Threshold changes in both during and after ischemia were greater for median axons.Conclusions: These findings suggest that membrane potential in human median sensory axons is more negative than in superficial radial axons, possibly due to greater activity of electrogenic Na+/K+ pump. These results may reflect adaptation to impulses load carried by median axons that would be far greater with a higher frequency.Significance: Biophysical properties are not identical in different human sensory axons, and therefore their responses to disease may differ.

Impact of aging on visual reweighting during locomotion - Corrected Proof

Jessica Berard, Joyce Fung, Anouk Lamontagne — 2011-12-28

Highlights: ► Young adults can reweight sensory information while walking and are less reliant on visual cues with increased walking speed. ► Older adults have difficulty ignoring irrelevant visual cues when walking and are less adept at sensory re-weighting. ► Age-related changes in sensory-motor control may related to mobility challenges in older adults.Abstract: Objectives: The purpose of this study was to investigate the ability of young and old subjects to reweight visual cues while walking at normal and fast speeds.Methods: Ten young (23.49±4.72) and ten older adults (age 76.22±3.11) were asked to physically walk straight while viewing a virtual scene in a head-mounted display (HMD) unit under three conditions: no visual perturbation, blank (no visual input), and visual perturbation. Subjects performed the tasks walking at two speeds: preferred self-pace and fast. Variables calculated included trajectory, heading angle, and body segment orientations.Results: In the perturbation condition, the older adults walked with higher segmentation and more deviations of the body’s centre of mass. Only the young subjects were affected by the walking speed, with an improved performance when walking fast.Conclusions: Old age affects the ability to re-weight visual information and make postural or locomotor adjustments in real time. The lower errors of the young adults in the fast conditions suggest decreased cortical control of locomotion with increasing speeds.Significance: Visual information presented in real time can impact on balance and mobility in older adults, and thus should be given serious consideration for the purpose of evaluation and intervention.

The auditory P200 is both increased and reduced in schizophrenia? A meta-analytic dissociation of the effect for standard and target stimuli in the oddball task - Corrected Proof

2011-12-26

Highlights: ► Conflicting reports of P200 abnormalities in schizophrenia have been meta-analyzed. ► P200 in schizophrenia is smaller for standard tones, and larger for target tones. ► This stimulus effect partially accounts for the conflicting findings.Abstract: Objective: Conflicting reports of P200 amplitude and latency in schizophrenia have suggested that this component is increased, reduced or does not differ from healthy subjects. A systematic review and meta-analysis were undertaken to accurately describe P200 deficits in auditory oddball tasks in schizophrenia.Methods: A systematic search identified 20 studies which were meta-analyzed. Effect size (ES) estimates were obtained: P200 amplitude and latency for target and standard tones at midline electrodes.Results: The ES obtained for amplitude (Cz) for standard and target stimuli indicate significant effects in opposite directions: standard stimuli elicit smaller P200 in patients (d=−0.36; 95% CI [−0.26, −0.08]); target stimuli elicit larger P200 in patients (d=0.48; 95% CI [0.16, 0.82]). A similar effect occurs for latency at Cz, which is shorter for standards (d=−0.32; 95% CI [−0.54, −0.10]) and longer for targets (d=0.42; 95% CI [0.23, 0.62]). Meta-regression analyses revealed that samples with more males show larger ES for amplitude of target stimuli, while the amount of medication was negatively associated with the ES for the latency of standards.Conclusions: The results obtained suggest that claims of reduced or augmented P200 in schizophrenia based on the sole examination of standard or target stimuli fail to consider the stimulus effect.Significance: Quantification of effects for standard and target stimuli is a required first step to understand the nature of P200 deficits in schizophrenia.

Eliminating muscle artifacts from EEG recordings: A necessary imperative - Corrected Proof

Ramon Edmundo D. Bautista — 2011-12-26

The proper identification of muscle artifacts continues to be an issue affecting the interpretation of electroencephalograms (EEG). As housestaff, we were asked to train our eyes to “read through” artifacts, and overcome the temptation to adjust the filter settings in order to “clean” the recording. We were given general guidelines that distinguished muscle artifacts from cerebral activity. For example, muscle artifacts typically occurred at frequencies that were above what could be reasonably obtained by electrocerebral activity. These waveforms had higher amplitudes that could not be accounted for by the resonant frequencies of EEG recording. Artifacts could also be minimized by asking the patient to relax.