RT Journal Article SR Electronic T1 Formation of a Motor Memory by Action Observation JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 9339 OP 9346 DO 10.1523/JNEUROSCI.2282-05.2005 VO 25 IS 41 A1 Stefan, Katja A1 Cohen, Leonardo G. A1 Duque, Julie A1 Mazzocchio, Riccardo A1 Celnik, Pablo A1 Sawaki, Lumy A1 Ungerleider, Leslie A1 Classen, Joseph YR 2005 UL http://www.jneurosci.org/content/25/41/9339.abstract AB 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.