Jaw-movement-related Mirror Neuron System in Humans

Objectives: A group of neurons in the monkey premotor cortex discharge when the monkey is performing a given action as well as when it is observing the experimenter performing a similar action (mirror neuron system; MNS). Neuromagnetic studies have shown that the primary motor cortex is included in the human MNS. The present study was aimed to determine spatial and temporal activation patterns of the human MNS in association with jaw movements. Methods: Neuromagnetic activities of the cerebral cortex in 6 healthy adults were recorded using a 306-channel whole-head neuromagnetometer. The subjects were asked to carefully observe, on videotape, symmetrical jaw opening movements performed by another individual. Neuromagnetic responses were examined using time-varying multi-dipole analysis to estimate current dipoles which were superimposed in the individual MRI to determine the source locations. Results: The magnetic signals were averaged at the onset of jaw-opening movements. During observation of the movements, prominent magnetic fields were detected on the occipital region and the lateral parieto-frontal region bilaterally with four peak signal components. Their peak latencies were 130, 220, 340 and 440 ms. In the multi-dipole analysis, four main source areas with left hemisphere dominance were sequentially activated during observation of the movements: 1) occipito-temporal area near inferior temporal sulcus (MT/V5), 2) inferior parietal cortex (IPC), 3) inferior part of precentral gyrus (maxillofacial area of primary motor cortex; M1mx), and 4) primary visual cortex (V1). Conclusions: These results indicated that both the M1mx and IPC were activated during observation of jaw movements and involved in jaw-movement related-MNS which play important roles in orofacial motor recognition in human. (Supported by Grants (HRC 3A04, 12 and 13) for High-Tech Research Center Projects from the MEXT in Japan) yshibuka@tdc.ac.jp