Limbic and prefrontal contributions to somesthetic learning in monkeys.

Monkeys with forebrain commissurotomies and either lateral temporal, medial temporal, dorsal prefrontal, or ventral prefrontal removals from the right hemisphere were compared with control animals in learning tactual discriminations and reversal with the left hand. The lateral temporal removal yielded no effect, confirming the modality-specific roles of this sector in audition (superior temporal gyrus) and vision (inferior temporal gyrus). The dorsal prefrontal removed yielded a deficit in discrimination learning, possibly as a result of the contralateral sensory neglect or the spatial disorder produced by this lesion. Each of the two remaining lesions, medial temporal and ventral prefrontal, yielded deficits in both discrimination learning and reversal; and the effects of combined removal of these two limbic sectors appeared to be additive. Taken together with earlier findings in vision and audition, the results indicate that the two limbic sectors contribute to learning in all sensory modalities, and that they do so through cortico-cortical interaction with the sensory systems.