Corticospinal excitability is specifically modulated by the social dimension of observed actions

Abstract

A large body of research reports that perceiving body movements of other people activates motor representations in the observer's brain. This automatic resonance mechanism appears to be imitative in nature. However, action observation does not inevitably lead to symmetrical motor facilitation: mirroring the observed movement might be disadvantageous for successfully performing joint actions. In two experiments, we used transcranial magnetic stimulation (TMS) to investigate whether the excitability of the corticospinal system was selectively modulated by the social dimension of an observed action. We recorded motor-evoked potentials (MEPs) from right-hand muscles during the observation of an action sequence which, depending on context, might or might not elicit a complementary response. The results demonstrate a differential motor facilitation depending on action context. Specifically, when the context called for a complementary action, the excitability pattern reflected the under-threshold activation of a complementary action, whereas when the context did not imply acting in a complementary manner, the observer's corticospinal activity reflected symmetrical motor resonance. We contend that the mechanisms underlying action observation are flexible and respond to contextual factors that guide the social interaction between individuals beyond emulation.

The multiform motor cortical output: Kinematic, predictive and response coding

“…A finding in accordance with behavioral (Bertenthal, Longo, & Kosobud, 2006;Liepelt et al, 2010) and neurophysiological (Press, Bird, Walsh, & Heyes, 2008) studies showing motor facilitation effects for transitive as well as intransitive actions . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 15 Moreover, the present findings extends previous evidence on response preparation in hand muscles (Newman-Norlund, Noordzij, Meulenbroek, & Bekkering, 2007;Ocampo & Kritikos, 2010;Sartori, Cavallo, Bucchioni, & Castiello, 2011b, 2012bSartori, Betti, & Castiello, 2013a, 2013bSartori et al, 2013c) showing a modulation of CS excitability also when the observed action calls for a gesture involving different body parts with respect to the observed ones. In the present study, observers' upper limb muscles were activated while observing a soccer player kicking a ball straight in their direction.…”

Corticospinal Excitability Modulation During Action Observation

“…During the experiments carried out, modulation of corticospinal excitability was a reliable, indirect measure of the capacity to activate appropriate motor programs in an interactive context. Previous studies utilizing the TMS/MEP technique have shown that corticospinal activation resulting from action observation does not invariably possess an imitative bias but, depending on contextual factors, can also prime motor activation for complementary actions 29,30 . Single-pulse TMS studies have demonstrated that observing a two-step action sequence in which a complementary request is embedded prompts a switch from emulation to responsiveness in the participants' corticospinal activity.…”

“…In this respect, some researchers showed that the automatic effects of mirroring can be abolished following incompatible training: mirror and counter-mirror responses seem to follow the same timecourse 27,28 . Interestingly, in contrast to previous studies, MEPs induced by spTMS were recently used to assess spontaneous corticospinal activation while video-clips evoking emulative or nonidentical complementary gestures were being simply observed 29,30 . Results showed a natural switch from an emulative to a context-related action in corticospinal activity.…”

Human Motor Plasticity Induced by Mirror Visual Feedback

“…The primate MNS is a frontoparietal motor network of bimodal visuomotor mirror neurons that discharge when they perform a particular action and when observing a similar action performed by another (Rizzolatti and Craighero, 2004). The human M1 has MNS-like properties, because its facilitation during action observation is effector-specific , lateralized (AzizZadeh et al, 2002), and significantly greater in a first-person perspective than a third-person perspective (Fadiga et al, 2005;Sartori et al, 2011). In one fMRI study (Matthys et al, 2009), the superior temporal gyrus was activated during MVF intervention, suggesting a link between MVF and MNS.…”