Formation of a Motor Memory by Action Observation

TLDR

Mirror neurons discharge during both action observation and execution, and the mirror neuron system—including primary motor cortex activity—has been proposed to underlie motor learning by forming motor memories. The study aimed to determine whether observing simple repetitive thumb movements can directly create a motor memory trace in human M1. Using transcranial magnetic stimulation, the authors demonstrated that observing another person perform thumb movements generates a kinematically specific memory trace in M1. Extended observation of thumb movements opposite to the habitual bias increased the probability, speed, and excitability balance of TMS‑evoked thumb movements toward the observed direction, supporting a role for the mirror neuron system in motor memory formation and learning.

Abstract

Mirror neurons discharge with both action observation and action execution. It has been proposed that the mirror neuron system is instrumental in motor learning. The human primary motor cortex (M1) displays mirror activity in response to movement observation, is capable of forming motor memories, and is involved in motor learning. However, it is not known whether movement observation can lead directly to the formation of motor memories in the M1, which is considered a likely physiological step in motor learning. Here, we used transcranial magnetic stimulation (TMS) to show that observation of another individual performing simple repetitive thumb movements gives rise to a kinematically specific memory trace of the observed motions in M1. An extended period of observation of thumb movements that were oriented oppositely to the previously determined habitual directional bias increased the probability of TMS-evoked thumb movements to fall within the observed direction. Furthermore, the acceleration of TMS-evoked thumb movements along the principal movement axis and the balance of excitability of muscle representations active in the observed movements were altered in favor of the observed movement direction. These findings support a role for the mirror neuron system in memory formation and possibly human motor learning.