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Updated: Jun 14, 2026

Corticospinal Excitability Modulation During Action Observation
Published on: December 31, 2013
Observing how others lift light or heavy objects: which visual cues mediate the encoding of muscular force in the
Kaat Alaerts1, Stephan P Swinnen, Nicole Wenderoth
1Motor Control Laboratory, Research Center of Movement Control and Neuroplasticity, Department of Biomedical Kinesiology, Group Biomedical Sciences, Katholieke Universiteit Leuven, Tervuursevest 101, B-3001 Heverlee, Belgium. Kaat.Alaerts@faber.kuleuven.be
Abstract:
Observers are able to judge quite accurately the weights lifted by others. Only recently, neuroscience has focused on the role of the motor system to accomplish this task. In this respect, a previous transcranial magnetic stimulation (TMS) study showed that the muscular force requirements of an observed action are encoded by the primary motor cortex (M1). Overall, three distinct visual sources may provide information on the applied force of an observed lifting action, namely, (i) the perceived kinematics, (ii) the hand contraction state and finally (iii) intrinsic object properties. The principal aim of the present study was to disentangle these three visual sources and to explore their importance in mediating the encoding of muscular force requirements in the observer's motor system. A series of experiments are reported in which TMS was used to measure 'force-related' responses from the hand representation in left M1 while subjects observed distinct action-stimuli. Overall, results indicated that observation-induced activity in M1 reflects the level of observed force when kinematic cues of the lift (exp. 1) or cues on the hand contraction state (exp. 2) are available. Moreover, when kinematic cues and intrinsic object properties provide distinct information on the force requirements of an observed lifting action, results from experiment 3 indicated a strong preference for the use of kinematic features in mapping the force requirements of the observed action. In general, these findings support the hypothesis that the primary motor cortex contributes to action observation by mapping the muscle-related features of observed actions.
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