NEUROELECTRIC MAPPING REVEALS PRECURSOR OF STOP FAILURES IN CHILDREN WITH ATTENTION DEFICITS

Children with attention deficit disorders (ADD) may have specific prob lems with response inhibition in the STOP task. This task requires tha t subjects stop responses to a primary task if a second signal follows . However, it is unclear whether these problems reflect an impairment of the stopping process per se, whether they are related to reduced fr ontal lobe activation and whether they are confined to severe and perv asive forms of ADD. In Il ADD and nine control children, 32 channel ev ent-related EEG potentials (ERPs) were recorded in a STOP and a delaye d GO task. Mapping revealed that both tasks evoked a similar sequence of neuroelectric microstates, i.e. of time segments with stable map to pography. Adaptive segmentation identified the transition between thes e microstates. Reliable group differences were found in several micros tates and in both tasks despite matched performance. In the GO task, A DD children had topographically altered P2/N2 microstates and attenuat ed P300-type microstates. In the STOP task, a topographically altered N1 microstate which coincided with the onset of the stop signal preced ed the stop failures of ADD children. The timing of this microstate is too early to reflect deficits in actual stop signal processing and in stead suggests altered initial orienting of attention to the primary s ignal in ADD children. Imaging with low resolution tomography (LORETA) during this microstate to stop failures indicated mainly posterior ac tivation for both groups and increased rather than reduced frontal act ivation in ADD children. For a later microstate (P550), LORETA indicat ed strong frontal activation after successful stopping, but no group d ifferences. The results suggest that information processing of ADD chi ldren deviates during activation of posterior mechanisms which may be related to the orienting of attention and which precedes and partly de termines inhibitory control problems in ADD. (C) 1998 Elsevier Science B.V. All rights reserved.