Functional brain mapping of monkey tool use.

When using a tool, we can perceive a psychological association between the tool and the body parts-the tool is incorporated into our "body-image." During tool use, visual response properties of bimodal (tactile and visual) neurons in the intraparietal area of the monkey's cerebral cortex were modified to include the hand-held tool. Visual properties of the monkey intraparietal neurons may represent the body-image in the brain. We explored tool use-induced activation within the intraparietal area and elsewhere in alert monkey brain using positron emission tomography (PET). Tool use-related activities compared with the control condition (simple-stick manipulation) revealed a significant increase in cerebral blood flow in the corresponding intraparietal region, basal ganglia, presupplementary motor area, premotor cortex, and cerebellum. These tool use-specific areas may participate in maintaining and updating the body-image for the precise guidance of a hand-held rake onto a distant reward.