Early non‐specific modulation of corticospinal excitability during action observation

Abstract

Activity of the primary motor cortex (M1) during action observation is thought to reflect motor resonance. Here, we conducted three studies using transcranial magnetic stimulation (TMS)-induced motor-evoked potentials (MEPs) of the first dorsal interosseus muscle (FDI) during action observation to determine: (i) the time course of M1 corticospinal excitability during the observation of a simple finger movement; (ii) the specificity of M1 modulation in terms of type of movement and muscle; and (iii) the relationship between M1 activity and measures of empathy and autistic traits. In a first study, we administered single-pulse TMS at 30-ms intervals during the observation of simple finger movements. Results showed enhanced corticospinal excitability occurring between 60 and 90 ms after movement onset. In a second experiment, TMS-induced MEPs were recorded from the FDI and abductor digiti minimi muscles while pulses were delivered 90 ms after movement onset during observation of simple finger movement and dot movement. Increased corticospinal excitability was restricted to finger movement and was present in both muscles. Finally, in an exploratory experiment, single-pulse TMS was administered at 30, 90 and 150 ms after movement onset, and participants were asked to complete the Empathy Quotient (EQ) and the Autism Spectrum Quotient (AQ). Correlational analysis revealed a significant link between motor facilitation at 90 ms and the EQ and AQ scores. These results suggest that corticospinal excitability modulation seen at M1 during action observation is the result of a rapid and crude automatic process, which may be related to social functioning.

Direct mapping rather than motor prediction subserves modulation of corticospinal excitability during observation of actions in real time

“…The narrow time window examined in our study established that motor facilitation in the UA took place sometime between 40 and 80 ms after hand closure, which is in line with previous work (Lepage et al 2010;Nishitani and Hari 2000). Given that at least 40 ms are required to process basic aspects of visual stimuli such as orientation (Bacon-Macé et al 2005;Berens et al 2012), it is unlikely that the observer may have both detected the hand closure and loaded a different motor plan that better matched the observed kinematics within a 40-ms window.…”

Social Interaction Enhances Motor Resonance for Observed Human Actions

“…The optimal location was marked on a Lycra swim cap worn by participants, and a mechanical arm was used to hold the coil in a fixed position. Once the optimal location for MEPs was identified, stimulator output was lowered at 2% intervals until the minimum intensity capable of eliciting MEPs of ϳ1 mV peak-topeak amplitude on 50% of TMS pulses had been identified (Lepage et al, 2010;Obhi et al, 2011). Stimulator output was held constant at this intensity for the rest of the experiment (i.e., baseline and action observation blocks), ranging from 55% to 83% (mean, 64%) in the present sample.…”

Corticospinal Excitability Modulation During Action Observation

“…Compute ratio values using the participant's individual baseline value (MEP ratio = MEP obtained /MEP baseline ) 39 .…”