Neural mechanisms of visual guidance of hand action in the parietal cortex of the monkey.

We studied the functional properties of the hand manipulation task-related neurons (N = 136) in the posterior bank of the intraparietal sulcus (IPS) using four kinds of objects for manipulation. We performed cluster analysis by comparing the profiles of activity of these neurons across objects during manipulation in the light, and classified them into nine groups, four highly selective, four moderately selective, and one nonselective group. Activity profiles of these neurons across objects were analyzed in four task conditions: object manipulation and object fixation both in the light and in the dark. Cells were classified as "motor-dominant," "visual-dominant," and "visual and motor" neurons, and the latter two were further subdivided into object type and non-object type. Most of the highly selective neurons (35 of 136) preferred the same object for manipulation in the dark as in the light. The object type "visual and motor" neurons preferred the same object for manipulation and fixation, suggesting that these neurons play an important role in matching the pattern of hand movement to the visuo-spatial characteristics of the object to be manipulated. A large majority of highly selective hand manipulation neurons were localized in the rostral part of the posterior bank of IPS, which we designated as the anterior intraparietal (AIP) area. We propose a conceptual model of the system for visual guidance of hand action including parietal hand manipulation neurons.