Special Speaker: Hideo Sakata
Sunday December 19, 14:00
15:00
Linkage of Spatial Perception to Action and Memory
in the Parietal Cortex
Hideo Sakata
(
Department of Physiology, School of Medicine, Nihon University, Japan)
The parietal cortex of human brain is known to be related to spatial perception, and spatial memory. The initial idea came from neurological studies of the parietal lobe lesions describing the symptoms of visuospatial agnosia, and disturbance of topogtraphical memory. Recent studies of functional brain imaging support this idea. The parietal cortex is also known to be related to the visual control of hand movements and actions as suggested by the symptomes of optic ataxia and apraxia. Neurophysiological studies of the parietal cortex with microelectrode recordings of the neuronal activity in alert behaving monkeys have revealed various functions related to these symptomes. As a result various functional subdivisions are identified in the parietal cortex. We are particularly interested in the visual functions of the parietal cortex.
The most prominent visual area in the parietal cortex is area MST (V5A) in the funds of caudal superior temporal sulcus (STS) and adjacent posterior parietal (PP) area. Here we found the depth-movement-sensitive neurons and the rotation sensitive neurons that were closely related to the perception of object motion. In dorsal MST, Duffy and Wurtz (1991) found neurons sensitive to optical flow that were closely related to the perception of self motion. Among these motion sensitive neurons we found a few neurons that was activated after the stimulus disappeared as if they represent the position of an object behind the body. In a recent experiment of hand manipulation related neurons in an area of anterior part of the lateral bank of the intraparietal sulcus (area AIP), we found neurons representing object-centered position of the target, including those which preferred the button switch behind or inside a box. In the same area we recorded visual-dominant neurons that showed sustained response to a particular object among six geometrical solids during delay period of a memory-guided hand manipulation task. These evidences support the idea that the parietal cortex represent the space around us including positions beyond the visual field. Short-term memory is implicated in this peripersonal space.
More recently, we found an area of higher order processing of stereopsis in the caudal part of the lateral bank of intraparietal sulcus (area CIP) adjacent to area V3A which contains many neurons sensitive to binocular disparity. We found axis-orientation-selective (AOS) neurons and surface-orientations-selective (SOS) neurons as well as those which were selective for 3D shape of objects. Many SOS neurons responded to slanted surface in the random dot stereogram suggesting to compute surface orientation from disparity gradient. About one fourth of SOS neurons showed sustained activity during delay period of the delayed matching to sample task. Some of the AOS neurons also sustained its activity for a couple of seconds after the cessation of the stimulus. These evidences support the view that the parietal visual neurons link the visual perception to memory.