Clinical Neurophysiology

2010-03-01

Editorial Board

2010-03-01

Two Scientific Awards in Clinical Neurophysiology

2010-03-01

TMS–EEG: A technique that has come of age?

Paul B. Fitzgerald — 2010-03-01

Transcranial magnetic stimulation (TMS) is now a tool that is widely used in clinical and cognitive neuroscience to understand mechanisms underlying both normal and abnormal brain activity. Despite its broad use, we still lack a complete understanding of the immediate effects of TMS on the cortex. The tools that have been used to study this – predominately combining TMS with functional imaging – do not have the temporal sensitivity to allow an investigation into the immediate effects of TMS on the brain as blood flow responses usually take some seconds following changes in neuronal activity. For this reason, researchers have been interested for a long time in the possibility of combining TMS with EEG recordings (). Developing the capacity to do this will not only allow more detailed exploration of the effects of TMS on the brain but will also facilitate the development of this as a potentially useful tool for investigating cortical excitability and cortical connectivity. Prior to the development of TMS–EEG methods, this has not been possible outside of the motor cortex, where the response to stimulation is readily measurable in regards to peripheral motor evoked responses. Combining TMS and EEG would also allow for the study of the effects of sub motor threshold stimulation in motor cortex and other brain regions.

Measuring cortical activity – We will only detect what we are looking for

Julia Jacobs — 2010-03-01

In this issue of Clinical Neurophysiology, Fukuda and colleagues investigate the timeline of EEG oscillation changes following somatosensory stimulation of the median nerve (). Their result seems straightforward; gamma augmentation is the first cortical response of the somatosensory cortex and precedes any changes in the alpha and beta bands. The largest gamma augmentation was noted around 25ms after the stimulation; it was followed by augmentation of beta activity at 42ms and alpha activity at 97ms. Beta attenuation was only seen at 146ms and alpha attenuation at 221ms after the stimulus. The authors use ECOG–EEG signals animated as a temporal sequence overlaid on the MRI to evaluate the timeline, in which oscillations at different frequencies reflect cortical activation. A video of this observer-friendly visual approach, which gives an overview over the time sequence of oscillations can be found in the supplementary material.

Degeneration/re-organization coupling in retinitis pigmentosa

Silvia Bisti — 2010-03-01

The extensive and often conflicting array of hypotheses concerning neuronal representation of objects (sensory, motor or “internally generated” ideas or concepts), reflects an important topic in physiology. At each and every level of observation, physiologists report an ever-increasing range of reaction time scales that are involved in the generation of action potentials and their transformation to post-synaptic signals. Recently, provided evidence “in vitro” for the existence of neuronal stations through which activity is required to pass in order to propagate further into the network. The authors found it convenient to think about these sequences of neuronal stations in terms of chain-like effective structures; thus, even in the face of activity-dependent changes in synaptic efficacies or membrane excitability, activity has nowhere else to go but through ordered stations, reassuring that the rank remains stable. Network architecture, in that sense, serves to protect the representation of stimuli. While activity-dependence of neuronal reactions is a valuable driving force for exploration in a variety of adaptation and learning processes (where representations are modified), it must be balanced mechanisms that allow for stabilization and hence exploitation of existing representations. Since many combinations of latencies to first spikes may realize any given representation by recruitment order, existing representations are invariant to the exploration process, as long as the latter does not degrade the order of neuronal recruitment. Effectively, a separation is formed between the level of absolute time delays, where exploration for new representations occurs, and the level of recruitment order where representations are stable enough to adaptively interact with the environment. But what if one of the stations undergoes major changes including a re-wiring?

Do we need to consider non-linear information flow in corticomuscular interaction?

Andreas A. Ioannides, Georgios D. Mitsis — 2010-03-01

The cortex is a mosaic of patches, each with its own cytoarchitectonic and receptor signatures (). These patches and the sub-cortical areas and nuclei are expected to contribute differentially to specific functions, and evidence for this is already accumulating (). It is however obvious that the operations within each patch cannot depend only on the internal organization. The connectivity between these patches must also play a role. No matter how many complex and refined operations take place within an area, they cannot be performed without input from other areas and the output of these “computations” must be communicated to other areas. These considerations lead naturally to a description of the brain in terms of a network. At the most basic level the description can be thought of as a graph with cytoarchitectonic areas defining the nodes and the white matter pathways connecting these areas describing the edges between them ().

Prognostic value of standard EEG in traumatic and non-traumatic disorders of consciousness following coma

2010-03-01

Abstract: Objective: To investigate the prognostic value of standard electroencephalogram (EEG) in predicting the improvement of the level of consciousness in patients suffering from severe disturbances of consciousness following coma caused by acute brain injuries.Methods: A standard EEG was recorded at admission in our rehabilitation department in a total of 46 patients with impaired consciousness states following coma (22 patients with traumatic brain injuries, 24 patients with non-traumatic brain injuries). We quantified the EEG abnormalities using the scale of and correlated them with the basal level of cognitive functioning (LCF) scale score and with its variation after three months.Results: EEG scores correlated with LCF scores at admission (p<0.01) and with LCF scores’ variation after three months (p<0.01) in patients with traumatic brain injury; EEG scores correlated only with LCF scores variation after three months (p<0.01) in patients with non-traumatic brain injury.Conclusions: Standard EEG, analysed using the Synek scale, has a good prognostic value in both groups of patients with disorders of consciousness.Significance: This work may have implications for clinical care, rehabilitative programs and medical–legal decisions in patients with impaired consciousness states following coma due to acute brain injuries.

Independent component approach to the analysis of EEG recordings at early stages of depressive disorders

Vera A. Grin-Yatsenko, Ineke Baas, Valery A. Ponomarev, Juri D. Kropotov — 2010-03-01

Abstract: Objective: A modern approach for blind source separation of electrical activity represented by Independent Components Analysis (ICA) was used for QEEG analysis in depression.Methods: The spectral characteristics of the resting EEG in 111 adults in the early stages of depression and 526 non-depressed subjects were compared between groups of patients and healthy controls using a combination of ICA and sLORETA methods.Results: Comparison of the power of independent components in depressed patients and healthy controls have revealed significant differences between groups for three frequency bands: theta (4–7.5Hz), alpha (7.5–14Hz), and beta (14–20Hz) both in Eyes closed and Eyes open conditions. An increase in slow (theta and alpha) activity in depressed patients at parietal and occipital sites may reflect a decreased cortical activation in these brain regions, and a diffuse enhancement of beta power may correlate with anxiety symptoms playing an important role on the onset of depressive disorder.Conclusions: ICA approach used in the present study allowed us to localize the EEG spectra differences between the two groups.Significance: A relatively rare approach which uses the ICA spectra for comparison of the quantitative parameters of EEG in different groups of patients/subjects allows to improve an accuracy of measurement.

Seizure lateralization in scalp EEG using Hjorth parameters

T. Cecchin, R. Ranta, L. Koessler, O. Caspary, H. Vespignani, L. Maillard — 2010-03-01

Abstract: Objective: This paper describes and assesses a new semi-automatic method for temporal lobe seizures lateralization using raw scalp EEG signals.Methods: We used the first two Hjorth parameters to estimate quadratic mean and dominant frequency of signals. Their mean values were computed on each side of the brain and segmented taking into account the seizure onset time identified by the electroencephalographist, to keep only the initial part of the seizure, before a possible spreading to the contralateral side. The means of segmented variables were used to characterize the seizure by a point in a (frequency, amplitude) plane. Six criteria were proposed for the partitioning of this plane for lateralization.Results: The procedure was applied to 45 patients (85 seizures). The two best criteria yielded, for the first one, a correct lateralization for 96% of seizures and, for the other, a lateralization rate of 87% without incorrect lateralization.Conclusions: The method produced satisfactory results, easy to interpret. The setting of procedure parameters was simple and the approach was robust to artifacts. It could constitute a help for neurophysiologists during visual inspection.Significance: The difference of quadratic mean and dominant frequency on each side of the brain allows lateralizing the seizure onset.

Pitfalls of high-pass filtering for detecting epileptic oscillations: A technical note on “false” ripples

C.G. Bénar, L. Chauvière, F. Bartolomei, F. Wendling — 2010-03-01

Abstract: Objectives: To analyze interictal High frequency oscillations (HFOs) as observed in the medial temporal lobe of epileptic patients and animals (ripples, 80–200Hz and fast ripples, 250–600Hz). To show that the identification of interictal HFOs raises some methodological issues, as the filtering of sharp transients (e.g., epileptic spikes or artefacts) or signals with harmonics can result in “false” ripples. To illustrate and quantify the occurrence of false ripples on filtered EEG traces.Methods: We have performed high-pass filtering on both simulated and real data. We have also used two alternate methods: time-frequency analysis and matching pursuit.Results: Two types of events were shown to produce oscillations after filtering that could be confounded with actual oscillatory activity: sharp transients and harmonics of non-sinusoidal signals.Conclusions: High-pass filtering of EEG traces for detection of oscillatory activity should be performed with great care. Filtered traces should be compared to original traces for verification of presence of transients. Additional techniques such as time-frequency transforms or sparse decompositions are highly beneficial.Significance: Our study draws the attention on an issue of great importance in the marking of HFOs on EEG traces. We illustrate complementary methods that can help both researchers and clinicians.

Background intracranial EEG spectral changes with anti-epileptic drug taper

2010-03-01

Abstract: Objective: Previous studies have revealed a surprising decrease in spike counts and Teager energy between on- and off-AEDs states during intracranial EEG (icEEG) monitoring. Here, we expand the measures evaluated to icEEG power and frequency band power.Methods: Two icEEG epochs, on- and off-AEDs, each 1h in duration, were studied for each of 21 unselected adult patients. Spike counts, Teager energy and total power were evaluated for each electrode contact. Power was also evaluated for delta (0–4Hz), theta (4–8Hz), alpha (8–13Hz), beta (13–25Hz), gamma (25–55Hz) and high (65–128Hz) frequency bands.Results: A decrease in power accompanies AED taper and the previously reported decrease in spike counts and Teager energy. The decrease in power was underpinned by a spatially widespread and broadband decrease in power in delta through gamma frequency bands with maximum decrease in the lowest frequency bands. An increase in high-frequency power was observed in some patients.Conclusions: There is a decrease in spike counts, Teager energy and power from on- to off-AEDs state during intracranial monitoring. The decrease in power is spatially widespread and broadband including power in the delta through gamma frequency bands.Significance: The decrease in cortical activity with AED taper suggests that seizure generation during intracranial monitoring may not be mediated solely by poorly regulated cortical excitation.

Photosensitive epilepsy: Spectral and coherence analyses of EEG using 14Hz intermittent photic stimulation

2010-03-01

Abstract: Objective: To evaluate the EEG recorded in photosensitive idiopathic generalised epilepsy (IGE) patients at rest and during 14Hz IPS, frequency capable of inducing photoparoxysmal responses (PPRs).Methods: Power spectrum density and coherence profiles were estimated using a block autoregressive parametric model (AR) in 28 patients and 22 controls.Results: At rest, the intra- and inter-hemispheric coherence spectra showed a significantly larger number of coherence peaks in the gamma band in patients with respect to controls. During intermittent photic stimulation (IPS), coherent gamma activity is mainly presented as IPS frequency harmonics; moreover, the patients’ mean coherence values significantly increased. In six patients re-evaluated with IPS after putting on glasses with Z1 blue lens (which counteracts PPR) the spectral and coherence profiles tended to return to the resting ones.Conclusions: Patients are endowed with inherited EEG hyper-synchrony as shown by the large number of coherence peaks detectable under resting conditions, whereas IPS enhances intra- and inter-hemispheric mean coherence values in the gamma band. The persistence of alpha activity peaks during IPS in most controls but not in patients suggests that the alpha generating network plays a significant role in counteracting PPR.Significance: Both gamma and alpha EEG generators are involved in the PPR generation and in the widespread synchronisation characterising the IGE-associated photosensitivity.

Interictal MEG/MSI in intractable mesial temporal lobe epilepsy: Spike yield and characterization

Kitti Kaiboriboon, Srikantan Nagarajan, Mary Mantle, Heidi E. Kirsch — 2010-03-01

Abstract: Objective: To evaluate the ability of MEG to detect medial temporal spikes in patients with known medial temporal lobe epilepsy (MTLE) and to use magnetic source imaging (MSI) with equivalent current dipoles to examine localization and orientation of spikes and their relation to surgical outcome.Methods: We prospectively obtained MSI on a total of 25 patients previously diagnosed with intractable MTLE. MEG was recorded with a 275 channel whole-head system with simultaneous 21-channel scalp EEG during inpatient admission one day prior to surgical resection. The patients’ surgical outcomes were classified based on one-year follow-up after surgery.Results: Nineteen of the 22 patients (86.4%) had interictal spikes during the EEG and MEG recordings. Thirteen of 19 patients (68.4%) demonstrated unilateral temporal dipoles ipsilateral to the site of surgery. Among these patients, five (38.5%) patients had horizontal dipoles, one (7.7%) patient had vertical dipoles, and seven (53.8%) patients had both horizontal and vertical dipoles. Sixty percent of patients with non-localizing ictal scalp EEG had well-localized spikes on MSI ipsilateral to the side of surgery and 66.7% of patients with non-localizing MRI had well-localized spikes on MSI ipsilateral to the side of surgery. Concordance between MSI localization and the side of lobectomy was not associated with a likelihood of an excellent postsurgical outcome.Conclusions: MSI can detect medial temporal spikes. It may provide important localizing information in patients with MTLE, especially when MRI and/or ictal scalp EEG are not localizing.Significance: This study demonstrates that MSI has a good ability to detect interictal spikes from mesial temporal structures.

Differences in TMS-evoked responses between schizophrenia patients and healthy controls can be observed without a dedicated EEG system

2010-03-01

Abstract: Objective: The combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) has been hampered by the large artifact that the TMS generates in the EEG. Using TMS with EEG necessitates a sophisticated artifact-resistant EEG system that can acquire reliable signals in the crucial several tens of milliseconds immediately following the TMS pulse. Here, we demonstrate the use of a novel artifact removal algorithm together with a 24-bit EEG system to achieve similar recordings as those obtained with the dedicated TMS-compatible EEG system.Methods: This setup was used to compare TMS-evoked responses between a group of healthy controls and a group of patients with schizophrenia, a condition in which effective neural connectivity is thought to be compromised.Results: We observe differences in TMS-evoked responses between the two groups, similar to those recently reported in a study that used a dedicated TMS-compatible EEG system.Conclusions: The standard 24-bit EEG system combined with an artifact removal algorithm produces results similar to the dedicated TMS-compatible system.Significance: This paves the way for more researchers and clinicians to use TMS-evoked responses for research and diagnosis of a wide spectrum of disorders.

Measurement of brain function in pre-school children using a custom sized whole-head MEG sensor array

Blake W. Johnson, Stephen Crain, Rosalind Thornton, Graciela Tesan, Melanie Reid — 2010-03-01

Abstract: Objective: Conventional whole-head MEG systems have fixed sensor arrays designed to accommodate most adult heads. However arrays optimised for adult brain measurements are suboptimal for research with the significantly smaller heads of young children. We wished to measure brain activity in children using a novel whole-head MEG system custom sized to fit the heads of pre-school-aged children.Methods: Auditory evoked fields were measured from seven 4-year-old children in a 64-channel KIT whole-head gradiometer MEG system.Results: The fit of heads in the MEG helmet dewars, defined as the mean of sensor-to-head centre distances, were substantially better for children in the child helmet dewar than in the adult helmet dewar, and were similar to head fits obtained for adults in a conventional adult MEG system. Auditory evoked fields were successfully measured from all seven children and dipole source locations were computed.Conclusions: These results demonstrate the feasibility of routinely measuring neuromagnetic brain function in healthy, awake pre-school-aged children.Significance: The advent of child-sized whole-head MEG systems opens new opportunities for the study of cognitive brain development in young children.

Induced theta oscillations as biomarkers for alcoholism

Colin Andrew, George Fein — 2010-03-01

Abstract: Objective: Studies have suggested that non-phase-locked event-related oscillations (ERO) in target stimulus processing might provide biomarkers of alcoholism. This study investigates the discriminatory power of non-phase-locked oscillations in a group of long-term abstinent alcoholics (LTAAs) and non-alcoholic controls (NACs).Methods: EEGs were recorded from 48 LTAAs and 48 age and gender comparable NACs during rest with eyes open (EO) and during the performance of a three-condition visual target detection task. The data were analyzed to extract resting power, ERP amplitude and non-phase-locked ERO power measures. Data were analyzed using MANCOVA to determine the discriminatory power of induced θ ERO vs. resting θ power vs. P300 ERP measures in differentiating the LTAA and NAC groups.Results: Both groups showed significantly more θ power in the pre-stimulus reference period of the task vs. the resting EO condition. The resting θ power did not discriminate the groups, while the LTAAs showed significantly less pre-stimulus θ power vs. the NACs. The LTAAs showed a significantly larger θ event-related synchronization (ERS) to the target stimulus vs. the NACs, even after accounting for pre-stimulus θ power levels. ERS to non-target stimuli showed smaller induced oscillations vs. target stimuli with no group differences. Alcohol use variables, a family history of alcohol problems, and the duration of alcohol abstinence were not associated with any θ power measures.Conclusions: While reference θ power in the task and induced θ oscillations to target stimuli both discriminate LTAAs and NACs, induced θ oscillations better discriminate the groups. Induced θ power measures are also more powerful and independent group discriminators than the P3b amplitude.Significance: Induced frontal θ oscillations promise to provide biomarkers of alcoholism that complement the well-established P300 ERP discriminators.

The effects of aging on evoked otoacoustic emissions and efferent suppression of transient evoked otoacoustic emissions

2010-03-01

Abstract: Objective: There is still controversy regarding the effects of aging on evoked otoacoustic emissions (EOAEs), as well as on the efferent system measured by contralateral acoustic stimulation of EOAEs. The purpose of this study was to investigate the deterioration in EOAEs and efferent suppression (ES) in a representative sample statistically controlling for the differences in hearing thresholds.Methods: Seventy-one ears (20–79years) were included in the study, 47 of which had normal hearing thresholds, and 24 ears had a sensorineural high-frequency hearing loss caused by presbycusis. The effects of aging on transient evoked (TEOAEs) and distortion product OAEs (DPOAEs), and on ES were evaluated using multiple regression and correlation coefficients.Results: EOAEs and ES were more strongly correlated with age, than with pure-tone thresholds (PTTs). Moreover, the increase in the amount of variance explained by the regression model using both predictors was larger for PTTs as compared to the variable age.Conclusions: The deterioration of EOAEs and ES with advancing age is caused mainly by pure age-effects, and additionally by the reduction in hearing thresholds.Significance: The relative contribution of age and hearing thresholds on EOAEs, as well as on ES is important for their interpretation in clinical settings.

Somatosensory-related gamma-, beta- and alpha-augmentation precedes alpha- and beta-attenuation in humans

Miho Fukuda, Csaba Juhász, Karsten Hoechstetter, Sandeep Sood, Eishi Asano — 2010-03-01

Abstract: Objective: Several human studies have demonstrated that the amplitudes of cortical oscillations are altered by various sensorimotor and cognitive tasks. Event-related augmentation of gamma oscillations and attenuation of alpha and beta oscillations have been often used as surrogate markers of cortical activation elicited by tasks especially in presurgical identification of eloquent cortices. In the present study, we addressed a question whether somatosensory-related gamma augmentation ‘precedes’ or ‘co-occurs with’ somatosensory-related attenuation of alpha–beta oscillations.Methods: We studied 10 patients who underwent intracranial electrocorticography for epilepsy surgery, and determined the temporal and spatial characteristics of median-nerve somatosensory-related amplitude changes at gamma- (30–100Hz), beta- (14–28Hz) and alpha-band (8–12Hz) oscillations.Results: We found that somatosensory-related gamma augmentation involving the post- and pre-central gyri evolved into beta and alpha augmentation, which was subsequently followed by beta and alpha attenuation involving the post- and pre-central gyri.Conclusions: These observations support the hypothesis that somatosensory-related gamma augmentation but not alpha–beta attenuation represents the initial cortical processing for external somatosensory stimuli. Somatosensory-related alpha–beta attenuation appears to represent a temporally distinct stage of somatosensory processing.Significance: The present study has increased our understanding of event-related gamma augmentation and alpha–beta attenuation seen on electrocorticography.

Phosphene thresholds evoked with single and double TMS pulses

Thomas Kammer, Lisa W. Baumann — 2010-03-01

Abstract: Objective: To evaluate the quantitative advantage of double pulses vs. single pulses in TMS phosphenes evoked from the occipital cortex.Methods: In 10 healthy subjects single pulse thresholds were compared with thresholds from double pulses of equal strength at a stimulus onset asynchrony (SOA) of 2, 5, 10, and 20ms, both with biphasic and monophasic pulse forms. In a second experiment fusion time, i.e. the double pulse SOA where the percept passes from one into two phosphenes was determined.Results: Thresholds obtained with double pulses did not depend on SOA. They were lowered to about 90% of single pulse thresholds. Biphasic pulses yielded lower thresholds (89%) than monophasic pulses. Fusion time was about 45ms but highly varied inter-individually and did not depend on stimulation intensity.Conclusions: Although double pulses are more efficient compared to single pulses the advantage is rather small. Previous recommendations to apply double pulses in phosphene studies cannot be confirmed, at least for SOAs up to 20ms. The independence of fusion time to stimulus intensity indicates a non-linear relation between network activity and the percept of phosphene persistence.Significance: Phosphene threshold studies do not gain advantages by the application of double pulses.

Impact of regional retinal responses on cortical visually evoked responses: Multifocal ERGs and VEPs in the retinitis pigmentosa model

2010-03-01

Abstract: Objective: To determine the impact of the regional retinal responses on cortical visually evoked responses, by evaluating the relationship between multifocal ERG (mfERG) and multifocal VEP (mfVEP), in the retinitis pigmentosa (RP) model.Methods: MfERGs and mfVEPs were recorded from 20 typical RP patients. Response amplitude density (RAD, nV/deg2) and implicit time (ms) of the mfERG 1st order binary kernel (N1-P1) and mfVEP 2nd order binary kernel (P1) components were measured. Ring analysis, matched for mfERG and mfVEP stimuli, was performed between fovea and mid-periphery (0–2.5, 2.5–5, 5–10, 10–15 and 15–20deg).Results: At central and pericentral retinal regions (four eccentricities between 0 and 15deg), mfERG N1 RADs were positively correlated (r⩾0.68, p<0.01) with corresponding mfVEP P1 RADs. Similarly, mfERG P1 implicit times were positively correlated (r⩾0.65, p<0.01) with corresponding mfVEP N1 implicit times.Conclusions: There are quantitative correlations between mfERG and mfVEP components in RP.Significance: The data suggest that regional responses of the photoreceptors and off-bipolar cells, the main generators of mfERG N1, have a major impact on the corresponding cortical activity.

P1 and P2 components of human visual evoked potentials are modulated by depth perception of 3-dimensional images

2010-03-01

Abstract: Objective: To determine the cerebral activity correlated with depth perception of 3-dimensional (3D) images, by recording of human visual evoked potentials (VEPs).Methods: Two figures consisting of smaller and larger squares were presented alternately. VEPs were recorded in two conditions. In condition I, we used two figures which yielded flat 2-dimensional images. In condition II, we used two figures which yielded 3D images, which were concave and convex, respectively.Results: P1, P2, and N1/P2 amplitude were significantly greater in condition II than in condition I. The P1/N1 amplitude tended to be greater in condition II than in condition I. P1 and N1 were predominantly distributed over the right temporo-parieto-occipital regions. P2 and N2 were distributed over bilateral parieto-occipital regions.Conclusions: The difference in P1 amplitude between two conditions can be explained by the difference between conditions, one of which yielded depth perception while the other did not, since previous studies showed that P1 and N1 are modulated by perception of images in depth. The role of P2 and the mechanism responsible for the increase in P2 amplitude during condition II remain unknown.Significance: We recorded VEPs and identified electrophysiological correlates of depth perception with 3D images produced by concave/convex figures.

Linear and nonlinear information flow based on time-delayed mutual information method and its application to corticomuscular interaction

Seung-Hyun Jin, Peter Lin, Mark Hallett — 2010-03-01

Abstract: Objective: To propose a model-free method to show linear and nonlinear information flow based on time-delayed mutual information (TDMI) by employing uni- and bi-variate surrogate tests and to investigate whether there are contributions of the nonlinear information flow in corticomuscular (CM) interaction.Methods: Using simulated data, we tested whether our method would successfully detect the direction of information flow and identify a relationship between two simulated time series. As an experimental data application, we applied this method to investigate CM interaction during a right wrist extension task.Results: Results of simulation tests show that we can correctly detect the direction of information flow and the relationship between two time series without a prior knowledge of the dynamics of their generating systems. As experimental results, we found both linear and nonlinear information flow from contralateral sensorimotor cortex to muscle.Conclusions: Our method is a viable model-free measure of temporally varying causal interactions that is capable of distinguishing linear and nonlinear information flow. With respect to experimental application, there are both linear and nonlinear information flows in CM interaction from contralateral sensorimotor cortex to muscle, which may reflect the motor command from brain to muscle.Significance: This is the first study to show separate linear and nonlinear information flow in CM interaction.

Intermanual transfer of sensorimotor memory for grip force when lifting objects: The role of wrist angulation

Djamel Bensmail, Anna-Sophia Sarfeld, Gereon R. Fink, Dennis A. Nowak — 2010-03-01

Abstract: Objective: To investigate the mechanisms underlying the intermanual transfer of sensorimotor memory when lifting an object.Methods: Twenty healthy subjects grasped and lifted an object with constant mechanical properties with the right hand (RH) first and then with the left hand (LH). Ten of the subjects lifted the object with the RH in a regular wrist angulation (WA), followed by lifts with the LH in a regular WA. The remaining 10 subjects lifted the object with the RH in a hyper-flexed WA, followed by lifts with the LH in a regular WA.Results: Subjects generated greater peak grip force (GF) rates, grip and lift forces when lifting the object with the wrist in a regular WA compared to lifts with the wrist in hyper-flexion. Importantly, subjects transferred the predictive scaling of GF from the RH to the LH, regardless of the WA.Conclusions: Biomechanical properties of the object do not seem to be used by the CNS as a first line information to evaluate GF when handling an object or transferring information about the grasp to the opposite hemisphere.Significance: The predictive scaling of GF rather reflects an internal sense of effort than an internal representation of the mechanical object properties.

Inhibition of the anterior intraparietal area and the dorsal premotor cortex interfere with arbitrary visuo-motor mapping

2010-03-01

Abstract: Objective: The contribution of the human anterior intraparietal area and the dorsal premotor cortex to arbitrary visuo-motor mapping during grasping were tested.Methods: Trained right-handed subjects reached for and pincer-grasped a cube with the right hand in the absence of visual feedback after the cube location had been displayed for 200ms. During the reaching movements, the colour of the cube changed and visual feedback about the change of colour was provided for 100ms at 500ms after movement onset (at the time of peak grasp aperture). Depending on colour, subjects were instructed to either pincer-grasp the cube in a horizontal or vertical grasp position with the latter necessitating wrist rotation (experiment 1) or to pincer-grasp and transport the cube to either a left or right target position (experiment 2). Within two consecutive 200ms time windows (TMS 1 and 2) starting 500ms and 700ms after movement onset, respectively, double pulses of supra-threshold transcranial magnetic stimulation (inter-stimulus interval: 100ms) were delivered over (i) the left primary motor cortex (90° vertically angulated coil position, control stimulation), (ii) the left dorsal premotor cortex or (ii) the left anterior intraparietal area.Results: Compared to control stimulation, stimulation of the anterior intraparietal area, but not of the dorsal premotor cortex, at TMS 1 delayed the times to wrist rotation (experiment 1) and hand transport (experiment 2). Compared to control stimulation, stimulation of the dorsal premotor cortex, but not of the anterior intraparietal area, at TMS 2 delayed both wrist rotation (experiment 1) and hand transport (experiment 2).Conclusions: We contend that the anterior intraparietal area and the dorsal premotor cortex are both involved albeit at different phases during the mapping of arbitrary visual cues with goal directed grasp and transport movements.Significance: These data add to the current understanding of how human cortical areas work in concert during manual activities.

Changes in subthalamic activity during movement observation in Parkinson’s disease: Is the mirror system mirrored in the basal ganglia?

2010-03-01

Abstract: Objective: The observation of a voluntary movement executed by another person is associated with an alpha and beta EEG desynchronization over the motor cortex, thought to reflect activity from the human “mirror neuron” system. The aim of our work was to study the changes in local field potentials (LFP) recorded from the subthalamic nucleus (STN) and their relationship with cortical activity, during movement observation.Methods: Bilateral EEG and STN LFP recordings were acquired in 18 patients with Parkinson’s disease, through surgically implanted electrodes for deep brain stimulation. Oscillatory changes during movement execution and movement observation were compared with two different control conditions (simple stimulus and rotating stimulus observation), in “off” and “on” motor states. Time–frequency transforms and event-related coherence were used for the analysis.Results: Movement observation was accompanied by bilateral beta reduction in subthalamic power and cortico-STN coherence, which was smaller than the decrease observed during movement execution, but significant when compared with the two control conditions.Conclusions: Movement observation is accompanied by changes in the beta oscillatory activity of the STN, similar to those observed in the EEG.Significance: These changes suggest that the basal ganglia might be engaged by the activity of the human mirror system.

Breaks during 5Hz rTMS are essential for facilitatory after effects

H. Rothkegel, M. Sommer, W. Paulus — 2010-03-01

Abstract: Objective: Stimulation frequency has been considered the most important factor in conventional repetitive transcranial magnetic stimulation (rTMS) for determining the direction of after effects on corticospinal excitability. Here, we examined the functional relevance of breaks during high-frequency subthreshold rTMS for the induction of facilitatory after effects.Methods: The after effects on corticospinal excitability of a standard 5Hz rTMS protocol in a block design were compared to a continuous rTMS protocol using the same number of pulses. In addition the effect of current direction both for rTMS and single pulse TMS was included in the study design.Results: While 5Hz rTMS in a standard block design induces facilitatory after effects on corticospinal excitability, the continuous protocol does not induce facilitation but rather inhibition. In our study only rTMS using an initially posterior–anterior current direction in the brain leads to significant neuroplastic effects at all.Conclusions: Breaks during conventional high-frequency rTMS are a crucial factor determining the direction of induced neuroplastic changes.Significance: These results contribute to the understanding of rTMS-induced neuroplasticity and are important for the design of rTMS protocols both for experimental and clinical studies.

Low back pain associates with altered activity of the cerebral cortex prior to arm movements that require postural adjustment

Jesse V. Jacobs, Sharon M. Henry, Keith J. Nagle — 2010-03-01

Abstract: Objective: To determine whether low back pain (LBP) associates with altered postural stabilization and concomitant changes in cerebrocortical motor physiology.Methods: Ten participants with LBP and 10 participants without LBP performed self-initiated, voluntary arm raises. Electromyographic onset latencies of the bilateral internal oblique and erector spinae muscles were analyzed relative to that of the deltoid muscle as measures of anticipatory postural adjustments (APAs). Amplitudes of alpha event-related desynchronization (ERD) and of Bereitschaftspotentials (BP) were calculated from scalp electroencephalography as measures of cerebrocortical motor physiology.Results: The APA was first evident in the trunk muscles contralateral to the arm raise for both groups. Significant alpha ERD was evident bilaterally at the central and parietal electrodes for participants with LBP but only at the electrodes contralateral and midline to the arm raise for those without LBP. The BP amplitudes negatively correlated with APA onset latencies for participants with (but not for those without) LBP.Conclusions: Cerebrocortical activity becomes altered prior to arm movements requiring APAs for individuals with chronic LBP.Significance: These results support a theoretical model that altered central motor neurophysiology associates with LBP, thereby implying that rehabilitation strategies should address these neuromotor impairments.

Reduced motor cortex plasticity following inhibitory rTMS in older adults

Gabrielle Todd, Thomas E. Kimber, Michael C. Ridding, John G. Semmler — 2010-03-01

Abstract: Objective: Ageing is accompanied by diminished practice-dependent plasticity. We investigated the effect of age on another plasticity inducing paradigm, repetitive transcranial magnetic stimulation (rTMS).Methods: Healthy young (n=15; 25±4years) and old (n=15; 67±5years) adults participated in two experiments. Motor evoked potentials (MEPs) were measured in the target muscle (first dorsal interosseus, FDI) and a remote muscle (abductor digiti minimi) during a set of single stimuli. Subjects then received real or sham inhibitory rTMS (intermittent subthreshold trains of 6Hz stimulation for 10min). MEPs were measured for 30min after rTMS.Results: In young adults, MEPs in the target FDI muscle were ∼15% smaller in the real rTMS experiment than in the sham rTMS experiment (P<0.026). In old adults, FDI MEP size did not differ between experiments.Conclusions: Advancing age is associated with reduced efficacy of inhibitory rTMS.Significance: This work has important implications for the potential therapeutic use of rTMS in stroke and neurological disease.

Behavioural exposure and sleep do not modify corticospinal and intracortical excitability in the human motor system

Sebastian H. Doeltgen, Michael C. Ridding — 2010-03-01

Abstract: Objective: Behavioural exposure and sleep may bidirectionally modify the excitability of cortical networks including those in the motor cortex. Here we tested whether the excitability of intracortical inhibitory and excitatory networks within the primary motor cortex exhibited changes suggestive of a time of day influence.Methods: Short-interval intracortical inhibition (SICI) and facilitation (ICF), and input–output curves (IO curves) were investigated using transcranial magnetic stimulation (TMS). Recordings were made from the resting right first dorsal interosseous (FDI) muscle in 10 healthy subjects on three occasions: 9A.M. and 4P.M. of the same day, and 9A.M. of the following day.Results: There was no significant change in any of the measures across the three assessments.Conclusions: These findings provide evidence that time of day does not significantly influence corticospinal and intracortical excitability in the primary motor cortex.Significance: These results provide no support for the hypothesis that synapses within the motor cortex undergo potentiation due to daytime use and behavioural experiences. Additionally, these findings provide evidence that measurement of motor cortical excitability is not systematically biased by time-of-day dependent variability and thus does not pose a confound in studies assessing corticospinal excitability longitudinally.

Effect of Globus Pallidus internus stimulation on gait in multifocal dystonia: A case study

2010-03-01

Dystonia is a movement disorder characterized by sustained, repetitive muscle contractions of opposing muscles accompanied by twisting and abnormal posture. Recently, deep brain stimulation (DBS) of the Globus Pallidus internus (GPi) has been shown to be an effective treatment in reducing symptoms of primary dystonia () in children and adults () as well as in generalized, focal or segmental dystonia ().

Theta rhythm heterogeneity in humans

Jonghan Shin — 2010-03-01

Rhythmic oscillatory activity within the theta frequency band (4–8Hz in humans; 4–12Hz in rodents) has long attracted attention, as it has been implicated in diverse brain functions. After Klimesch and colleagues reported experimental evidence showing that episodic memory processes are associated with activity within the theta band (), the existence of an association between theta rhythm and episodic memory in humans () and rodents () has become widely accepted. Episodic memory impairment is one of the most prevalent cognitive impairments in patients with Alzheimer’s disease (AD) (), and a subtle decline in episodic memory often occurs prior to the emergence of the full dementia syndrome in nondemented older adults who develop Alzheimer’s disease (). This pattern of episodic memory impairment is consistent with anomalies in theta rhythm, which are more prevalent in patients with AD than in normal elderly subjects (). However, reports on the relationship between theta rhythm and memory function in humans are inconsistent. Some reports indicate that there is a negative correlation between theta rhythm amplitude and memory performance (), whereas others indicate that there is a positive correlation between theta rhythm amplitude and memory performance (). In particular, the theta rhythm during rest with closed eyes, the resting theta rhythm, is negatively correlated with memory performance, whereas the theta rhythm during the performance of cognitive tasks, the induced theta rhythm, is positively correlated with memory performance. Amnestic mild cognitive impairment (aMCI) is primarily characterized by substantial episodic memory deficits in the absence of dementia (). Patients with AD have difficulty in understanding the cognitive tasks necessary to generate an induced theta rhythm, whereas subjects with aMCI are able to perform such cognitive tasks. Therefore, both resting and induced theta rhythms are observed in subjects with aMCI. Recently published results showed that compared with normal control subjects, subjects with aMCI had an increased resting theta rhythm (), but a decreased induced theta rhythm (). How can these conflicting results in human theta rhythms be explained? Does this mean that there are multiple theta rhythms in humans? If so, studies on theta rhythm heterogeneity in rodents () may help to resolve the controversy surrounding human theta rhythms.

Clinical Neurophysiology

Contents

Editorial Board

Two Scientific Awards in Clinical Neurophysiology

TMS–EEG: A technique that has come of age?

Measuring cortical activity – We will only detect what we are looking for

Degeneration/re-organization coupling in retinitis pigmentosa

Do we need to consider non-linear information flow in corticomuscular interaction?

Prognostic value of standard EEG in traumatic and non-traumatic disorders of consciousness following coma

Independent component approach to the analysis of EEG recordings at early stages of depressive disorders

Seizure lateralization in scalp EEG using Hjorth parameters

Pitfalls of high-pass filtering for detecting epileptic oscillations: A technical note on “false” ripples

Background intracranial EEG spectral changes with anti-epileptic drug taper

Photosensitive epilepsy: Spectral and coherence analyses of EEG using 14Hz intermittent photic stimulation

Interictal MEG/MSI in intractable mesial temporal lobe epilepsy: Spike yield and characterization

Differences in TMS-evoked responses between schizophrenia patients and healthy controls can be observed without a dedicated EEG system

Measurement of brain function in pre-school children using a custom sized whole-head MEG sensor array

Induced theta oscillations as biomarkers for alcoholism

The effects of aging on evoked otoacoustic emissions and efferent suppression of transient evoked otoacoustic emissions

Somatosensory-related gamma-, beta- and alpha-augmentation precedes alpha- and beta-attenuation in humans

Phosphene thresholds evoked with single and double TMS pulses

Impact of regional retinal responses on cortical visually evoked responses: Multifocal ERGs and VEPs in the retinitis pigmentosa model

P1 and P2 components of human visual evoked potentials are modulated by depth perception of 3-dimensional images

Linear and nonlinear information flow based on time-delayed mutual information method and its application to corticomuscular interaction

Intermanual transfer of sensorimotor memory for grip force when lifting objects: The role of wrist angulation

Inhibition of the anterior intraparietal area and the dorsal premotor cortex interfere with arbitrary visuo-motor mapping

Changes in subthalamic activity during movement observation in Parkinson’s disease: Is the mirror system mirrored in the basal ganglia?

Breaks during 5Hz rTMS are essential for facilitatory after effects

Low back pain associates with altered activity of the cerebral cortex prior to arm movements that require postural adjustment

Reduced motor cortex plasticity following inhibitory rTMS in older adults

Behavioural exposure and sleep do not modify corticospinal and intracortical excitability in the human motor system

Effect of Globus Pallidus internus stimulation on gait in multifocal dystonia: A case study

Theta rhythm heterogeneity in humans