FRONTAL-LOBE NEGLECT IN MONKEYS

Using a crossed-response task, monkeys with neglect induced by frontal lesions appear to have motor rather than sensory neglect. However, th e crossed-response task may not reveal sensory neglect (inattention) i f no perceptual discrimination is required. We therefore trained two m onkeys in a perceptually complex crossed-response task. Following unil ateral frontal (arcuate gyrus) ablation, we found no contralateral per ceptual disorders or sensory neglect in either monkey but did find a f ailure to respond with the contralateral arm (motor neglect) in both m onkeys. We also found that the monkeys made more incorrect responses w ith the arm ipsilateral to the lesion than they did with the contralat eral arm. The errors made by the ipsilateral arm could be a compensato ry strategy or a disinhibition phenomenon. Because these incorrect res ponses were not rewarded and became more frequent as motor neglect imp roved, the incorrect responses of the ipsilateral arm are not a compen satory strategy, but rather a defect we term ''disinhibition hyperkine sia'' or ''allokinesia.''