Development of the Mu Rhythm: Understanding Function Through Translational Research

Abstract

The incidental discovery of mirror neurons (MN) has renewed interest in motor theories of development and has sparked considerable debate as to the existence and potential function of mirror neurons in humans. The use of invasive single-cell recordings, however, has precluded identification of single MNs in humans or developmental populations of non-human primates. Non-invasive techniques, such as the modulation of the mu rhythm in the electroencephalogram (EEG) of young infants and children, have demonstrated the existence of an action observation/execution matching system in humans. Moreover, the mu rhythm has become an effective tool for addressing questions of MN system ontogeny in other species. The aim of this project is to address two questions that have thus far remained untested. The goal of study one is to address the question of whether or not we can identify activation of the human action observation/execution system under conditions in which the participants cannot see themselves executing a grasping action. Evidence from study one further validates our EEG measures as representing activation of the putative human MN system. The goal of study two is to examine the origins of MNs in 3-day-old mother- and nursery-reared infant rhesus macaques and the extent to which differential experience may contribute to the MN system during episodes of neonatal imitation. The results of study one demonstrated activation of the putative human MN system to actions completed in the absence of visual feedback in both human adults and infants. The magnitude of mu rhythm activity in infants was significantly less than in the adults suggesting a role of experience in the formation of the putative human MN system. The results from study two further emphasized the role of early experience showing significantly greater modulation of the mu rhythm in the mother-reared compared to the nursery-reared infants to the observation of socio-affiliative facial gestures. The evidence of studies one and two are discussed within a developmental framework of ongoing behavioral development and highlight the role experience plays, not in the foundation of, but rather the elaboration of the MN system.