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Abstract:
The STOP signal task has been successfully employed to
address inhibitory control in ADHD children (Logan et al, 1984;
Pliszka et al, 1997). This study aimed at addressing the
physiological basis of abnormal inhibitory control during the STOP
signal task. Ten ADHD children and ten controls served as subjects.
Stimuli were the letters A or B (GO, 150 msec, ISI 1.5 sec),
followed on 25% of the trials by the letter S (STOP, SOA 200-500
msec). Children responded to the A or B, but had to withdraw
responding upon seeing an S. 64-channel EEG was continuously
recorded, and ERPs were averaged off-line for Correct and Failed
Inhibitions and time-locked to the onset of the STOP signal. As in
the previous RT studies, the ADHD children performance showed a
flatter slope (Percent Failed Inhibition X SOA) than the control
group (t = 4.5, df = 18, p <
.01). There were three ERP findings in the ADHD group: A reduced
N200 to both Correct and Failed Inhibitions, particularly over
inferior frontal scalp (R>L; impaired gating of the Stop
signal); An absent negative Slow Wave to Correct Inhibitions
(600-900 ms, peaking over left mediofrontal scalp; impaired
processing of reward feedback?); A reduced positive complex to
Failed Inhibitions (peak=500 msec over medial parietal scalp;
impaired processing of punishment feedback?).
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