The Mirror Neuron System in the Monkey and its Role in Action Understanding

Massachusetts General Hospital, Boston MA

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Abstract

Abstract The discovery of a special class of visual-motor neurons in the premotor cortex of the macaque1,2 discharging both during action execution and action observation, has had an enormous impact in cognitive neuroscience and led to a boom in brain imaging research, as well as highly speculative claims about its cognitive implications in humans. While originally it was proposed that these neurons are involved in action understanding in the macaque6,12, several suggestions have been made that the human mirror system is involved not only in action understanding11, but also in imitation learning3, understanding of intentions5, theory of mind and empathy7. Currently, there appears to be a discrepancy between a well defined monkey mirror system consisting of two areas (premotor area F5 and parietal area PFG) and a diffuse, extended human mirror system network, consisting of extrastriate, parietal and frontal brain regions. Here we propose to investigate the mirror neuron system in the awake macaque using high-field (3T and 7T) fMRI, as a perfect tool to bridge the gap between monkey electrophysiology and human imaging data8. While many cortical areas in the brain respond to a mere action observation, as we showed previously8, a brain region can only be considered to be part of the `mirror' system, if it also responds during actual action execution. Therefore, using fMRI, we will localize the whole macaque mirror system while the monkeys are either executing grasping movements or passively observing grasping movements. Furthermore, to assess the role of the mirror system in actual action understanding, we will train monkeys on an action categorization task and scan brain activity, while the monkey actively decides whether or not a particular action belongs to a certain class of actions. Additional experiments will include pharmacological reversible lesions of possible candidate `action understanding' mirror regions to investigate its behavioral and functional consequences throughout the brain. As it has been suggested that the human mirror system may be crucial during language development10 and that its dysfunction might lay at the basis of autism4,9 a full understanding of the complete extent of the mirror system in the monkey may lead to a better understanding of language development and the causes of autism. The proposed research could also lead to a development of an animal model for autism in which pharmacological and behavioral therapies can be tested.