The representation of tool use in the monkey cerebral cortex. An fMRI study

The representation of tool use in the monkey cerebral cortex. An fMRI study. Though other species of primates also use tools, humans appear unique in their capacity to understand the causal relationship between tools and the result of their use. The present fMRI experiments are part of a comparative study, parallel experiments were carried out in humans. We scanned naive monkeys, and two monkeys trained to use tools, while they observed hand actions and actions performed using simple tools. In monkeys, the observation of an action, regardless of how performed, activated occipitotemporal, intraparietal, and ventral premotor cortex, bilaterally. In humans, the observation of actions done with simple tools yielded an additional, specific activation of a rostral sector of the left inferior parietal lobule (IPL). This latter site it was not observed in monkey IPL for any of the tool videos presented, even after monkeys had become proficient in using a rake or pliers through extensive training. In conclusion, while the observation of a grasping hand activated similar regions in humans and monkeys, an additional specific sector of IPL devoted to tool use has evolved in Homo sapiens, although tool-specific neurons might reside in the monkey grasping regions. These results shed new light on the changes of the hominid brain during evolution.