Date of Award
2007
Degree Type
Thesis
Degree Name
Master of Science
Program
Neuroscience
Supervisor
Dr. Jody Culham
Abstract
Electrophysiological recordings in macaques and neuropsychological studies in humans have reliably shown that the parietal cortex encodes a unique representation of visual space within reach of the arm (peripersonal space). Here, I used functional magnetic resonance imaging (fMRI) to investigate whether human brain areas involved in reaching and grasping are more activated by objects that are within reach vs. beyond reach. In a slow event-related design, subjects were presented with graspable objects at different locations on a platform placed over each subject’s hips. In Experiment 1, objects were placed at three possible locations: adjacent to the hand, within reach at the furthest extent of the hand, and beyond reach. On some trials, subjects reached to touch or grasp objects at the reachable location; on other trials subjects simply passively viewed objects at one of the three locations. A reach-related area in the superior parieto-occipital cortex (SPOC) was more activated for targets within reach than beyond. In Experiment 2, I investigated whether the preferential response in SPOC to objects in near space occurred when visual confounds were controlled and whether it was modulated by giving subjects a tool to extend the effective range of the arm. On some trials, subjects performed grasping and reaching actions to a reachable object location using either the hand alone or a tool; on other trials, subjects passively viewed five other object locations, either within reach of the hand, within reach of the tool but not the hand, or far outside of reach for both the hand and tool. Object positions were chosen to control for possible visual confounds. In runs where the hand was used for actions, SPOC was significantly more active for passively viewed objects within reach than beyond reach. In runs where the tool was used for actions, SPOC activity remained highest when the object was placed iii within reach of the hand, as compared to the other four locations, which had comparable activation levels, suggesting that SPOC encodes only real distance relative to the arm and is not sensitive to the availability of a tool. Interestingly another brain region, the anterior intraparietal area (AIP), activated by grasping vs. reaching with the hand, was also activated by grasping vs. reaching with the tool. Taken together, these results suggest that SPOC, a reach-related brain region located at the parieto-occipital junction, is sensitive to visual space reachable by the arm and that AIP is involved for grasping with the hand or with a tool.
Recommended Citation
Gallivan, Jason P., "fMRI investigation of a preference for reachable objects within the superior parieto-occipital cortex (SPOC)" (2007). Digitized Theses. 5110.
https://ir.lib.uwo.ca/digitizedtheses/5110