Attention deficits in children with low performance IQ: arguments for right hemisphere dysfunction

The attentional component of cognitive functioning in children might be viewed from several interrelated angles that nearly all point to right hemisphere (RH) neural circuits, subserving nonverbal attention. Neuropsychological aspects indicative of RH brain dysfunction are one aspect, studied here. Among children with learning disabilities (LD) we distinguish between LD with emphasis on nonverbal cognitive deficits and LD with verbal dysfunction. We approached this dichotomy by studying the extremes of these two LD categories (89 ss) with respect to attention deficit disorder with (ADHD) or without hyperactivity (ADD). We examined 44 children with at least average verbal IQ (VIQ > or = 95) and lower performance IQ (PIQ at least 25 points lower than VIQ), i.e. the nonverbal group, and 45 children with at least average performance IQ (PIQ > or = 95) and lower verbal IQ (VIQ at least 25 points lower than PIQ). The percentage of AD(H)D among the nonverbal LD group was more than twice as high as among the verbal LD group. Although a convincing right hemisphere (RH) syndrome could not be shown on a neurological basis in most subjects of the non-verbal LD group, a large body of evidence points on the one hand to RH dysfunction associated with nonverbal LD and on the other hand to an association between RH dysfunction and ADD. However, on clinical grounds, discussed here, we consider ADD and low visuospatial cognition, being the most important component of low PIQ, as dissociated functions, largely subserved by the RH.