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Abstract

Mirror neurons (MNs), as originally described in the macaque monkey, respond to object-
directed movements (ODMs) both when the action is executed and when the same action is observed. These neurons have been suggested to be the supporting neural mechanism for action recognition and understanding. However, there is a current debate about the localization of MNs in humans. Functional magnetic resonance imaging studies using adaptation paradigms (fMRI-A) for the identification of MNs provide mixed results. Studies supporting the existence of MNs restricted thei analysis to a-priori candidate regions, whereas studies that failed to find evidence used non-object-directed movements (NDMs) as stimuli. In the present fMRI-A experiment we tackled these limitations by using ODMs and
performing a whole-brain analysis. Participants observed and executed simple grasping movements differing only in their object-directness (grasping a button vs. grasping beside it). We reasoned that MN areas should be (1) more activated by DMs than by NDMs and (2) exhibit cross-modal adaptation. The analysis revealed four significant clusters in the right anterior intraparietal sulcus (aIPS), right primary somatosensory cortex (S1), left premotor
cortex (PM) and right cerebellum that showed these characteristics. While the aIPS and the PM have been reported before as a possible region for MNs, the S1 and the cerebellum have not been yet associated directly with MNs. We discuss the potential role of these regions in a human MN system. In the second experiment we addressed the question of whether the cross-modal adaptation as measured with fMRI has a behavioral correlate. Measuring the
recognition speed of ODMs versus NDMs, depending on the previously executed movement type, revealed no significant differences.