Examining the Role of the Motor System in Early Communicative Development

Action understanding is a proposed foundation for communicative development, such that infants can apply a similar process of interpreting the goal-structure of actions to the understanding of others’ gestures as well as spoken language. The mirror neuron system, as indexed by activation of the motor system during both performance and observation of actions, has been implicated as a neural correlate for action understanding, and may be recruited for understanding both gestures and speech. One’s experience with actions influences action understanding measured both behaviorally and neurally. This dissertation examines whether experience with gestures is related to recruitment of the mirror neuron system during observation of gestures in infancy, and whether individual differences in this activity might be related to or support communicative development. Mirror neuron system activity was measured in 10- to 12-month-old infants while they observed an experimenter producing gestures. Their experience with gestures was manipulated through a parent-directed intervention aimed at increasing parents’ use of pointing gestures with their child. Infant-parent dyads visited the lab twice. At the first visit, parent and infant pointing gesture production, infant vocabulary, and infant mirror neuron system activity were measured. Next, parents were randomly assigned to either receive the gesture intervention, or to a passive control group. One month after training, parent pointing, infant pointing and vocabulary, and infant mirror neuron system activity were reassessed. Infant vocabulary was measured a final time one month after the post-training follow-up. The findings suggest that the mirror neuron system plays a role in infants’ communicative development, and that experience with gestures can impact the mirror neuron system response when observing others’ gesture. Infants in the training group showed stronger mirror neuron system activity at follow-up compared to those in the control group. Increases in parents’ pointing production predicted increases in infants’ mirror neuron system activity, which in turn was related to increases in infants’ receptive vocabulary over the same time period. The implications of these findings are discussed