UCLA

Humans have an automatic tendency to imitate, as illustrated by unconscious mimicry during social interactions and behavioral interference effects in the laboratory. Automatic imitation is thought to arise from activation of the imitative motor representation during action observation, which is likely mediated by the overlapping representation of observed and executed actions in the mirror neuron system. In contrast to mechanisms of automatic imitation, models attempting to explain how automatic imitative tendencies are brought under intentional control are incomplete. In this dissertation, I use functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) to measure and disrupt neural activity during imitation interference tasks to expand current models of imitation control. In particular, I focus on dissociating imitation control from control over a related prepotent response tendency--spatial compatibility--to determine (1) whether control mechanisms involved in overcoming automatic response tendencies evoked by action observation utilize a dedicated mechanism and (2) whether imitation control involves modulation of the mirror neuron system. In addition, I explore the hypothesis that imitative control mechanisms may differ depending on whether control is exerted in reaction to a stimulus (after the automatic response tendency has been evoked) or in advance of a stimulus (reducing the degree of automatic response activation in the first place).

Results indicate that neural systems involved in reactive control of imitation are dissociable from those involved in controlling spatially compatible response tendencies. I propose a model of reactive imitation control involving interactions between prefrontal control regions and the mirror neuron system. In contrast to reactive control, I found no evidence of a dissociable preparatory imitation control mechanism in an fMRI study. However, TMS results suggest that preparatory control of imitation involves suppression of MNS activity, which can be reconciled with neuroimaging results through a general control that reduces the influence of visual input on the motor system. Thus, regardless of the timing, imitation control seems to involve modulation of MNS activity through interactions between general cognitive control systems and the more specific imitation circuits.