Abnormal early stages of task stimulus processing in children with attention-deficit hyperactivity disorder - evidence from event-related gamma oscillations

Objectives: Attention-related differences in early stages of stimulus proce ssing were assessed in healthy controls and children with attention-deficit hyperactivity disorder (ADHD) by analyzing phase-locked gamma band (31-63 Hz) responses to auditory stimuli in a selective-attention task. Methods: A total of 28 children aged 9-12 years (ADHD and matched healthy c ontrols) pressed a button in response to each target stimulus presented at the attended side (right or left). Auditory gamma band responses (GBRs) wit hin 0-120 ms were analyzed at 8 electrodes with wavelet transform. Effects of attended channel, stimulus type. and group were evaluated for GBR power and phase-locking. Results: For both groups. GBRs had a frontal-central distribution, were sig nificantly larger and more strongly phase-locked to target than to non-targ et stimuli. and did not differentiate the attended from the unattended chan nel. ADHD children produced larger and more strongly phase-locked GBRs than controls only to right-side stimuli, irrespective of whether these were th e attended or the ignored stimuli. Conclusions: The association between auditory GBR and motor task stimulus i n children suggests that phase-locked gamma oscillations may reflect proces ses of sensory-motor integration. ADHD-related deviations of GBRs indicate that early mechanisms of auditory stimulus processing are altered in ADHD. presumably as a result of impaired motor inhibition. (C) 2001 Elsevier Scie nce Ireland Ltd. All rights reserved.