Visual, Somatosensory, and Bimodal Activities in the Macaque Parietal Area PEc

Abstract

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.

Mapping multisensory parietal face and body areas in humans

“…In this study, we found that the posterior parts of the parietal leg and toe areas overlap or adjoin retinotopic areas activated by looming stimuli predominantly in the lower visual field. We suggest that they could be human homologs of a multisensory area in the caudal part of the superior parietal lobule (area PEc) of macaque monkeys (21,22), and that they are important for visually guided locomotion. One limitation of the present study is that looming stimuli were presented near the face but not close to the lower body.…”

“…Hindlimb representations in the medial PPC have been suggested by recent studies on nonhuman primates (15,18,21,22). In this study, we found parietal leg and toe areas at the superior and medial end of the postcentral sulcus, a superior parietal region that is posterior to S-I in the postcentral gyrus driven by passive stimulation on the foot (49, 50), anterior to a posterior parietal area activated by self-generated foot movements with visual feedback (51), and consistent with a superior parietal area activated during the planning of foot movements (25).…”

“…Based on the locations of movements evoked, action zones are approximately organized into overlapping areas of upper, middle, and lower spaces near the body. Other studies using tactile stimulation or retrograde neuronal tracing on nonhuman primates have also suggested that topographic organizations of multiple body parts exist in the PPC, and some subdivisions also receive visual input (19)(20)(21)(22). A few human neuroimaging studies have shown evidence of distinct body-part representations in the superior parietal lobule (23)(24)(25).…”

Is the Medial Posterior Parietal Area V6A a Single Functional Area?

“…Bimodal responses in single V6A cells were assessed by testing a cell with both somatosensory and visual stimulations. To avoid biases, the two types of stimulation were performed across cells in a randomized order (Breveglieri et al, 2008).…”

Limb-Specific Representation for Reaching in the Posterior Parietal Cortex

“…For example, neurons in caudal Brodmann area 5 (PEc) (Pandya and Seltzer, 1982) located in the posterior part of the superior parietal lobule show a strong contralateral-limb bias after somatosensory stimulation to the limbs (Breveglieri et al, 2006). A subgroup of these PEc neurons respond to both visual and somatosensory stimuli (Breveglieri et al, 2008). Many neurons in MIP that respond to somatosensory stimulation also show a contralateral-limb bias in visually guided reaching (Colby and Duhamel, 1991).…”