Progress in Motor Control by Michael J. Richardson Michael A. Riley & Kevin Shockley

Author:Michael J. Richardson, Michael A. Riley & Kevin Shockley
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

The Parieto-Frontal Mirror Neuron Circuit

One of the main issues about mirror neuron properties still under dispute concerns the source of visual information to the mirror system. It has been reported that neurons recorded in the anterior region of the superior temporal sulcus (STSa) discharge during the observation of biological movements such as walking, head rotation, forelimb movements (Perrett et al. 1989; Barraclough et al. 2006). A small percentage of these neurons also discharged during the observation of hand goal-directed movements. STSa region cannot be strictly considered as a part of the mirror neuron system because its neurons do not exhibitmotor-related discharge, but it is likely the source of visual information for this system. However, this STS region is not directly linked to premotor cortex, thus an intermediate node is required. As a matter of fact, mirror neurons having properties similar to that described in F5 have been recently described in the inferior parietal lobule (IPL) (Fogassi et al. 2005; Rozzi et al. 2008), more precisely in the cytoarchitectonic area PFG (Pandya and Seltzer 1982; Gregoriou et al. 2006). Thus, inferior parietal cortex can be considered as the first node of the mirror neuron system receiving visual information on biological stimuli.

Although the main findings of the presence of the mirror neuron mechanism has been provided by electrophysiological studies performed on specific cortical areas of the monkey, a complete picture of the areas involved in the action observation circuit can be better obtained from neuroimaging studies. Recently, two fMRI studies in the monkey provided evidence for the involvement of the parieto-frontal circuit in action observation. Both studies were performed in awake monkeys trained to fixate, while movies showing actions were presented to them. The first fMRI investigation (Nelissen et al. 2005) provided a functional parcellation of F5. In fact, the authors identified three different sectors of this area that were differently activated depending on whether the observed video represented a person grasping an object (acting person), or only a hand grasping objects (hand action). The results show that the convexity of F5 (F5c), where mirror neurons have been recorded, was more activated during the observation of the full view of a person executing a grasping act. The other two subdivisions, F5a and F5p, corresponding to the anterior and posterior sector of the arcuate sulcus, respectively, were more activated during the observation of a grasping hand, thus appearing to code actions in a less context-dependent way.

The second fMRI experiment (Nelissen et al. 2011), conducted using the same visual stimuli as the previous one, gave two main results. The first was that, in analogy with the findings of the previous study, the area PFG was more active during observation of the whole person grasping an object, while area AIP preferred the view of the hand grasping. The second is that during the observation of grasping motor acts different areas of STS, both in its upper and lower banks, became active. Hodological studies showed that those areas are anatomically connected with different areas of IPL (Rozzi et al.

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