The relationship between the motor system activation during action observation and adaptation in the motor system following repeated action observation.

Repeated action observation has been shown to alter the cortical representation of the observed movement in the motor system. This change in cortical representation is thought to reflect a motor adaptation to observational training (observational training effect). One factor that may impact the observational training effect is the degree of motor system activation that occurs during the observation of the action (i.e., individual differences in the responsiveness of the motor system during action observation). The present study was conducted to test this hypothesis by assessing the relationship between the change in motor system activity during action observation and the change in cortical representation of action following repeated action observation. To this end, transcranial magnetic stimulation (TMS) was used to evoke contractions of thumb muscles in two different protocols: 1) during the observation of thumb movements to assess the responsiveness of each individual's corticospinal system during action observation; and, 2) after the observation of 1800 thumb movements to assess the amount of adaptation in the representation of the thumb following repeated action observation. The key finding was the significant positive relationship between the level of corticospinal system activation during action observation and the amount of change in the direction of TMS evoked thumb movements. These data support the hypothesized relationship between motor system activation during action observation and the motor systems adaptation following observational training. They are also consistent with the notion that a common neural mechanism underlies these effects.