Objectives: Although ADHD and ASD seem very distinct, they have been shown to share some similarities in their symptoms. The aim of this study involved comparing the ERP profiles of ADHD, ASD, and typical control subjects in a shape recognition task in order to investigate effectiveness of differentiation of target and non-target stimuli. Our hypothesis was that children with ADHD and ASD will show less pronounced differences in ERP response to target and non-target stimuli as compared to typical children. We expected to find other ERP manifestations of attention regulation and other executive function differences between ASD and ADHD.
Methods: Participants with ASD (N=16) and ADHD (N=16) were referred by the Department of Pediatrics. Typical children (N=16) were recruited through advertisements in the local media and schools. There was no significant difference in age (mean 13.6 years, SD=2.5), gender, or IQ between the three groups. EEG was collected using 128 channel EGI EEG system. The task involves the recognition of a specific illusory shape, in this case a square or triangle, created by three or four inducer disks. Subjects were instructed to press button only in response to an illusory square figure.
Results: There were no between group differences in reaction time (RT) to target stimuli, but both ASD and ADHD committed more errors, specifically the ASD group had statistically higher commission error rate than controls. Post-error RT in this group was exhibited in a post-error speeding rather than corrective RT slowing typical for the controls. The ASD group also demonstrated an attenuated error-related negativity (ERN) as compared to ADHD and controls. The fronto-central P200, N200, and P300 were enhanced and less differentiated in response to target and non-target figures in the ASD group. The same ERP components were featured by more prolonged latencies in the ADHD group as compared to both ASD and typical controls.
Conclusions: Our results show significant differences both in behavioral and electrocortical responses between ASD, ADHD, and typical controls during performance on illusory figure test. The findings are interpreted according to the “minicolumnar” hypothesis proposing existence of neuropathological differences in ASD and ADHD, in particular minicolumnar number/width morphometry spectrum differences. In autism, a model of local hyperconnectivity and long-range hypoconnectivity explains many of the behavioral and cognitive deficits present in the condition, while the inverse arrangement of local hypoconnectivity and long-range hyperconnectivity in ADHD explains some deficits typical for this disorder (Williams & Casanova, Med Hypotheses, 2010, 74:59) Current ERP study supports the proposed suggestion that some between group differences could be manifested in the frontal ERP indices of executive functions during performance on illusory figure categorization task.
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