Connections of the Parietal Cortex

Abstract

Recently, many functional areas have been identified in the parietal cortex of the brain in monkeys, and owing to this, cytoarchitectonic subdivision has been elaborated in the monkey parietal cortex. This review deals with sulcal patterns of the parietal lobe in human and monkey brains, and corticocortical connections of both neurophysiologically defined regions and cytoarchitectonic areas of the parietal cortex in monkeys. The author proposes that the transverse occipital sulcus is a boundary between the parietal and occipital cortices in the human brain. A brain map of the monkey is presented. The parietal cortical areas are subdivided into somatosensory, eye movement related, hand or upper limb movement related, vestibular, and auditory areas, according to neurophysiologically defined functions of individual cortical areas. The somatosensory system contains areas 3a, 3b, 1, 2, 5, 7b, and SII: S1 projects to motor and premotor areas and somatosensory association areas project to premotor areas, the prefrontal, temporal, and limbic cortices, and the hippocampus. The eye movement system is composed of areas 7a, LIP, and PIP: It receives input from visual and temporal cortices and sends output to premotor areas, the prefrontal cortex, and the hippocampus. Hand movements are mediated in areas AIP, VIP, CIP, MIP, PEc, and V6A: These areas receive afferents from somatosensory areas, visual and temporal cortices and send efferents to the ventral premotor area. The vestibular functions are executed by coordination of areas 3aNV, 3aHV, 2NV, Ri, and VPS: These areas reciprocate with the cingulate cortex and insula and project to the ventral premotor area, SWA, and frontal eye field. The auditory system involves areas VIP and LIP: It receives afferents from the superior temporal sulcal cortex and sends efferents to the premotor area, frontal eye field, and prefrontal cortex.