POSTERIOR NEOCORTICAL SYSTEMS SUBSERVING AWARENESS AND NEGLECT - NEGLECT ASSOCIATED WITH SUPERIOR TEMPORAL SULCUS BUT NOT AREA-7 LESIONS

Objective: In humans and monkeys, the intraparietal sulcus separates t he superior parietal lobule from the inferior parietal lobule (IPL). W hereas in humans Brodmann's area 7 is above this sulcus, in monkeys it is below and therefore part of the IPL. In humans, the IPL consists o f Brodmann's areas 39 and 40. Some investigators contend that the monk ey homologue of the human IPL (areas 39 and 40) is the monkey's IPL (a rea 7). Others contend that it is, at least in part, in the monkey's s uperior temporal sulcus (STS). In humans, IPL lesions induce neglect. Although IPL lesions in monkeys also have been reported to induce negl ect, the STS was involved in these lesions. We sought to learn which o f these two areas, when ablated, produces neglect. Design: Study of fi ve adult stump-tailed macaque monkeys by making five isolated STS and six IPL lesions. Results: Inferior parietal lobule lesions were associ ated with misreaching but not with unilateral neglect. Neglect was obs erved in association with five of the six STS lesions. Conclusions: Wi th regard to neglect, STS may be the monkey homologue of the human IPL . Animals with STS lesions and humans with IPL lesions may manifest un ilateral neglect because these areas are necessary for normal awarenes s of external stimuli. This awareness may result from the integration of the areas important in stimulus localization (the ''where is it?'' system) and stimulus identification (the ''what is it?'' system), as w ell as the areas important in defining the biologic importance of stim uli, such as the frontal lobes and limbic areas.