Chapter 18 Event-related oscillations reflect functional asymmetry in children with attention deficit/hyperactivity disorder Juliana Yordanova a,* , Vasil Kolev a , and Aribert Rothenberger b a Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 23, 1113 Sofia, Bulgaria b Child and Adolescent Psychiatry, University of Go ¨ ttingen, D-37075 Go ¨ ttingen, Germany ABSTRACT Previous studies have found that event-related theta and gamma oscillations elicited in an auditory selective attention task are deviant in children with attention deficit/hyperactivity disorder (ADHD). It has been suggested that these deviations are associated with defi- cient motor inhibition in ADHD, which may lead to increased excitability of not only the motor generation networks but also the networks involved in sensory and cognitive processing of the stimulus requiring motor response. Within this suggestion, the present study used the same experimental database to compare the motor cortical activation of healthy controls and children with ADHD during the performance of the auditory selective attention task. Electroencephalography mu (8–12 Hz) activity at C3 and C4 electrodes was used as a measure of motor cortical activation. Mu power was analyzed for four stimulus conditions of the task (attended target, unattended target, attended nontarget, and unattended nontarget). It was found that motor cortical activation as reflected by mu power suppression was not overall greater in ADHD than healthy children. However, stimuli that possessed only partial target features and did not require motor responding (unattended target and attended nontarget) produced a significant reduction of mu activity in ADHD patients. These results suggest that motor cortical excitability is not generally increased in ADHD children. Rather, the co-existence of conflict features in complex stimuli induces task-irrelevant motor activation in these children. The deficient inhibition of motor cortical networks contralateral to the response may therefore be responsible for the func- tional asymmetry in stimulus processing in ADHD. KEYWORDS Attention deficit/hyperactivity disorder; Selective attention; Event-related oscillation; Motor activation; Functional asymmetry 18.1. The concept of event-related oscillations Neuroelectric oscillations provide important tools to study brain functions. In addition to spontane- ous electroencephalographic (EEG) activity, event-related oscillations (EROs) have been introduced to explore the neurophysiologic mech- anisms of information processing (Bas ¸ar, 1980, 1998). There are several conceptual and methodo- logical advantages of EEG oscillations that help reveal new specific aspects of neural dynamics (e.g., Yordanova et al., 2009). First, within the con- cept of neuroelectric oscillations, signals from uni- tary frequency-specific systems produce both the * Correspondence to: Dr. Juliana Yordanova, Ph.D., Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 23, 1113 Sofia, Bulgaria. Tel./fax: þ 359-2-979-37-49; E-mail: jyord@bio.bas.bg 289 Application of Brain Oscillations in Neuropsychiatric Diseases (Supplements to Clinical Neurophysiology, Vol. 62) Editors: E. Bas ¸ar, C. Bas ¸ar-Erog ˘lu, A. O ¨ zerdem, P.M. Rossini, G.G. Yener # 2013 Elsevier B.V. All rights reserved