Visual, somatosensory, and bimodal activities in the macaque parietal area PEc.

Caudal area PE (PEc) of the macaque posterior parietal cortex has been shown to be a crucial node in visuomotor coordination during reaching. The present study was aimed at studying visual and somatosensory organization of this cortical area. Visual stimulations activated 53% of PEc neurons. The overwhelming majority (89%) of these visual cells were best activated by a dark stimulus on a lighter background. Somatosensory stimulations activated 56% of PEc neurons: most were joint neurons (73%); a minority (24%) showed tactile receptive fields, most of them located on the arms. Area PEc has not a clear retinotopy or somatotopy. Among the cells tested for both somatosensory and visual sensitivity, 22% were bimodal, 25% unimodal somatosensory, 34% unimodal visual, and 19% were insensitive to either stimulation. No clear clustering of the different classes of sensory neurons was observed. Visual and somatosensory receptive fields of bimodal cells were not in register. The damage in the human brain of the likely homologous of macaque PEc produces deficits in locomotion and in whole-body interaction with the visual environment. Present data show that macaque PEc has sensory properties and a functional organization in line with the view of an involvement of this area in those processes.