Deficits in Attention and Movement Following the Removal of Postarcuate (Area 6) and Prearcuate (Area 8) Cortex in Macaque Monkeys

The effect of unilateral surgical ablations of the postarcuate cortex (area 6) has been studied in the macaque monkey (Macaca irus). Two series of neurological deficits were found: (1) a failure to grasp food with the mouth when presented contralaterally to the lesion and a reluctance to use the contralateral hand; (2) a severe hemi-inattention. This was present in both the somatosensory and visual modalities but, in the latter, was limited to the peripersonal space. Both motor and attentional deficits improved with time. However, when the symptomatology was stabilized, the animals tended to use the ipsilateral hand and, when presented with two stimuli, preferred that ipsilateral to the lesion. Control experiments in which area 8 (frontal eye fields) was ablated unilaterally showed a decrease of eye movements contralateral to the lesion and a neglect of the contralateral hemispace. No somatosensory deficits were found. The visual neglect was more prominent for 'far' space than for that near the animal. The role of area 6 in organizing motor acts and the strict relation between the type of motor deficit and the type of neglect are discussed.