Functional properties of the left parietal tool use region

In the present fMRI study we investigated the responses of the anterior supramarginal gyrus (aSMG) to the observation of tool and hand actions. Three experiments were carried out. In the first, we studied the specificity of the aSMG region for tool action observation, relative to the observation of hand action, and compared it with that of neighboring parietal regions. This experiment showed that there is a clear difference between aSMG and other posterior parietal regions, i.e. the putative homologue of anterior intraparietal (phAIP) area, and the dorsal intraparietal anterior (DIPSA) area. These regions are also activated by tool action observation, but in a way not significantly different from that due to hand action observation. The second experiment revealed that aSMG is equally activated by observing a tool action and a hand action carried out without the typical finger movements, but in a rigid way, imitating a tool. This indicates that aSMG uses, as visual cues, specific tool-related kinematics parameters. The third experiment showed that aSMG is strongly influenced by a concomitant attention-demanding acuity task. Taken together, the three experiments clearly show that human anterior IPL includes a specific, high-level aSMG region devoted to tool-action observation, distinct from the biological hand-action observation circuit.