INHIBITORY DYSFUNCTION IN HYPERACTIVE BOYS

Recent evidence suggests that the main deficit in childhood hyperactiv ity is in frontal lobe-mediated self-regulative functions such as inhi bitory control. Hyperactives have consistently been shown to perform p oorly on the stop task, which is a laboratory measurement of inhibitor y control. This study was aimed at extending knowledge about inhibitor y processes involved in the hyperactive's performance on this task. Fo r this purpose, the performance of 11 pervasive hyperactives was compa red to the performance of normal children on two stop tasks which diff ered from each other in the contingency of timing of the stop signal. In Stop1 stop signals were internally related, i.e. presented at time intervals after onset of the response stimulus, whereas in Stop2 stop signals were externally related, i.e. presented at time intervals rela ted to the subject's own go-process. Both tasks were modifications of the classical stop task in modality of the stop signal-visual instead of auditory-and in event rate, which was half-shortened. The aim of th is study was: (a) to replicate the findings of deficient inhibitory fu nctions in hyperactive children in the stop task in spite of modificat ions in modality and event rate; and (b) to elucidate (dis)similaritie s of stopping processes or of group differences in these stopping proc esses triggered by stop delays related either to external or to intern al processes. Hyperactive children were less efficient than controls i n inhibiting their motor response in both versions of the stop task, i ndependent of whether the stop signals were externally or internally r elated. Furthermore, the go-process of the hyperactives was more varia ble and erratic in both tasks. Thus, the results strengthen the effect iveness of stop tasks in distinguishing hyperactive from normal childr en. (C) 1998 Elsevier Science B.V. All rights reserved.