Abstract
Humans are faster to perform a given action following observation of that same action. Converging evidence suggests that the human mirror neuron system (MNS) plays an important role in this phenomenon. However, the specificity of the neural mechanisms governing this effect remain controversial. Specialist theories of imitation suggest that biological cues are maximally capable of eliciting imitative facilitation. Generalist models, on the other hand, posit a broader role for the MNS in linking visual stimuli with appropriate responses. In the present study, we investigated the validity of these two theoretical approaches by disrupting the left and right inferior frontal gyrus (IFG) during the preparation of congruent (imitative) and incongruent (complementary) actions cued by either biological (hand) or non-biological (static dot) stimuli. Delivery of TMS over IFG abolished imitative response facilitation. Critically, this effect was identical whether actions were cued by biological or non-biological stimuli. This finding argues against theories of imitation in which biological stimuli are treated preferentially and stresses the notion of the IFG as a vital center of general perception–action coupling in the human brain.
Highlights
A well-studied phenomenon in the motor literature is that humans are faster to execute a movement after observing another actor make the same movement even in cases where the observed action is irrelevant to the task (Brass et al, 2000, 2001; Sturmer et al, 2000; Craighero et al, 2002)
In the following we focus mainly the reaction time (RT) results and do not discuss movement time (MT) results in greater detail due to our predictions being on the level of response times and the fact that we found no significant interaction effects in the MT results
SUMMARY In the present experiment we investigated the validity of two general classes of theories, specialist and generalist, capable of explaining imitative facilitation using a grasping paradigm in which participants produced congruent or incongruent actions in response to biological or non-biological cues
Summary
A well-studied phenomenon in the motor literature is that humans are faster to execute a movement after observing another actor make the same movement even in cases where the observed action is irrelevant to the task (Brass et al, 2000, 2001; Sturmer et al, 2000; Craighero et al, 2002). In the typical experiment of this variety, participants observe a simple finger/hand movement being made by an actor and respond by either generating the same (congruent) or a different (incongruent) action. Despite numerous studies on the topic, the exact neural mechanisms underlying imitative facilitation still remain unclear (Brass et al, 2005; Makuuchi, 2005; Hurley, 2008). There is some controversy about the exact functional role of the IFG in translating perception into subsequent actions (Jacob and Jeannerod, 2005; Makuuchi, 2005; Hamilton and Grafton, 2008), as well as possible functional differences between its left, right, dorsal and ventral subdivisions
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