Ablations of areas 3a and 3b of monkey somatosensory cortex abolish cutaneous responsivity in area 1.

Cortex traditionally referred to as S-I in monkeys is a composite of 4 separate and complete representations of the contralateral body surface, one in each of the 4 cytoarchitectonic fields, areas 3a, 3b, 1 and 2. We investigated the significance of interconnections between these architectonic areas by assessing the immediate effects of ablations of parts of areas 3a and 3b on the responsivity of neurons in area 1. Ablations of specific parts of the hand representations in areas 3a and 3b immediately deactivated the corresponding part of the hand representation in area 1. We conclude that the processing of somesthetic inputs across anterior parietal cortex is predominantly hierarchical.