Invited reviewA review of electrophysiology in attention-deficit/hyperactivity disorder: I. Qualitative and quantitative electroencephalography
Introduction
This paper reviews the field of electroencephalography (EEG) in attention-deficit/hyperactivity disorder (AD/HD). Here, and in the companion paper reviewing the field of event-related potentials (ERPs) in AD/HD (Barry et al., 2003), we examine current knowledge of the electrophysiology of AD/HD. We first provide a brief overview of the syndrome, and outline the shifting perspectives which have both reflected and informed research in the field, up to and including the present international differences in diagnostic systems. These shifting perspectives impose a particular burden when considering data in this field, as differences in diagnostic criteria, and the consequent grouping of children into categories with different symptom clusters, can be expected to contribute substantially to different research outcomes, making the sifting of meaningful data difficult. In this regard, we report data using the diagnostic categories of the particular piece of research under discussion, but attempt to separate out the systematic effects relatable to symptom clusters in the modern diagnostic categories. It should be noted that even simple aspects of the disorder, such as its prevalence rate, are further impacted upon by issues of different types of AD/HD, as well as comorbidity, age and gender differences, and these variables serve to further cloud our understanding of the electrophysiology of AD/HD.
Section snippets
The syndrome of attention-deficit/hyperactivity disorder
AD/HD refers to a variable cluster of hyperactivity, impulsivity, and inattention symptoms, the occurrence of which substantially affects normal cognitive and behavioural functioning of the individual. Children and adolescents with AD/HD are at risk for later delinquency problems (e.g. Satterfield et al., 1982, Weiss and Trokenberg-Hechtman, 1986), and some symptoms may persist through the lifespan. Over the last 30 years, substantial changes have occurred in the conceptualization of AD/HD, and
Electroencephalographic studies in AD/HD
EEG provides information about the electrical activity of the brain, but due to the intervening media, the scalp-recorded signal provides a diffuse picture of that underlying activity. Nevertheless, that record can provide valuable information on the brain, with high temporal (but poor spatial) resolution. From our perspective, the EEG is a useful source of information on the background state of the brain, indexing the substrate of cognition and behaviour. Basic research has demonstrated
EEG-based models of AD/HD
While reasonably consistent EEG results have been found across a number of studies, the interpretation of what these results represent remains contentious within the literature. Two main models of AD/HD have been proposed, based on EEG studies.
Future directions
In the context of the studies reviewed above, we briefly sketch future directions for research and development in the applications of EEG in the AD/HD field.
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