Do you see what I mean? Corticospinal excitability during observation of culture-specific gestures

Abstract

People all over the world use their hands to communicate expressively. Autonomous gestures, also known as emblems, are highly social in nature, and convey conventionalized meaning without accompanying speech. To study the neural bases of cross-cultural social communication, we used single pulse transcranial magnetic stimulation (TMS) to measure corticospinal excitability (CSE) during observation of culture-specific emblems. Foreign Nicaraguan and familiar American emblems as well as meaningless control gestures were performed by both a Euro-American and a Nicaraguan actor. Euro-American participants demonstrated higher CSE during observation of the American compared to the Nicaraguan actor. This motor resonance phenomenon may reflect ethnic and cultural ingroup familiarity effects. However, participants also demonstrated a nearly significant (p = 0.053) actor by emblem interaction whereby both Nicaraguan and American emblems performed by the American actor elicited similar CSE, whereas Nicaraguan emblems performed by the Nicaraguan actor yielded higher CSE than American emblems. The latter result cannot be interpreted simply as an effect of ethnic ingroup familiarity. Thus, a likely explanation of these findings is that motor resonance is modulated by interacting biological and cultural factors.

Figure 1. Examples of experimental stimuli.

A) Euro-American actor performs the classic American ‘hang loose’ gesture. B) Nicaraguan actor performs a typical Nicaraguan gesture ‘I swear (promise)’ and C) one of the control gestures modified from the ASL sign for ‘berries’. D) Euro-American actor in the ‘static’ condition.

Figure 2. Main effect of performer (F(1,7) = 6.85, p<0.05).

Percent change relative to the overall mean in motor evoked potential (MEP) responses recorded during observation of actions executed by the Euro-American actor versus Nicaraguan actor.

Gesture type x Performer interaction (F(3,5) = 5.24, p = 0.053).

Post-hoc paired t-tests on percent change relative to the overall mean in motor evoked potential (MEP) responses show no differences in CSE while observing emblems performed by the Euro-American actor. In contrast, the observation of Nicaraguan emblems yielded higher CSE than American emblems (P = 0.004) and control ASL signs (P = 0.028) when performed by the Nicaraguan actor.