Concurrent action observation modulates practice‐induced motor memory formation

Motor practice is associated with the formation of elementary motor memories. Here we tested in human subjects the hypothesis that observation of a motor training associated with physical practice will modulate the encoding process of a motor memory relative to physical practice alone. Voluntary thumb motions were practiced (i) alone in a direction opposite to the baseline direction of transcranial magnetic stimulation (TMS)‐evoked movements (physical practice, PP) and in combination with observation of synchronous movements that were either (ii) directionally congruent (same direction, PP + AOc) or (iii) non‐congruent (opposite direction, PP + AOnc) to the practiced ones. We evaluated the following measures of motor memory formation: percentage of TMS‐evoked thumb movements falling in the direction of practiced motions, acceleration of TMS‐evoked movements along the principal movement axis and corticomuscular excitability of training muscles as indexed by motor‐evoked potential amplitudes. Both PP and PP + AOc, but not PP + AOnc, significantly increased the percentage of TMS‐evoked movements falling in the practiced direction, changed the compound acceleration vector into the trained direction and enhanced the motor‐evoked potential amplitudes in the training agonist muscle. The percentage of TMS‐evoked movements falling in the practiced direction increased significantly more after PP + AOc than after PP. Across all measures of motor memory formation, PP + AOc was most efficacious, followed by PP and PP + AOnc. Action observation modulates practice effects on formation of a motor memory. Strengthening of the process of motor memory encoding depends on the directional congruency of the observed model.