The role of inferior parietal cortex and the frontal eye-fields in visuospatial discriminations in the macaque monkey.

Macaque monkeys with bilateral lesions of either the frontal eye-fields (Area 8) or the inferior parietal lobule (Area 7a or PG) were compared with unoperated controls on their ability to perform a series of 8 pre-operatively learnt visual discriminations. Simple non-spatial discriminations were not affected, but the frontal group was affected when the stimuli in a shape discrimination varied in position from trial to trial and the parietal group was impaired on the judgement of centre. Both groups were impaired on a spatial landmark test which used luminous stimuli presented in the dark, in positions that varied randomly with respect to the monkey so that only allocentric cues were available. Postoperative trial-by-trial error analysis on the landmark test showed that, whereas spatial discriminability was a factor in determining the performance of the experimental groups, degree of cue-response separation and response perseveration were not. A comparison of the performance of the two groups on all 8 tests suggests that although both are impaired on spatial discriminations, the frontal eye-fields are concerned with spatially organising responses to explore the environment, while the inferior parietal lobule is concerned more directly with the processing of spatial information and the perception of spatial relationships.