Modulation of cortical excitability during action observation: a transcranial magnetic stimulation study

Paired-pulse transcranial magnetic stimulation (TMS) was used to examine ch anges in cortical excitability during action observation. We stimulated the left primary motor cortex (MI) of eight healthy volunteers during rest, ob servation of handwriting and observation of arm movements. Motor evoked pot entials (MEP) were recorded from the first dorsal intereosseous (FDI) and b iceps (BIC) muscles. Our results showed that action observation induced a f acilitation of the MEP amplitude evoked by the single test stimulus and red uced intracortical inhibition and facilitation at 3 ms and 12 ms interstimu lus intervals (ISIs), respectively, during paired-pulse stimulation. These changes were specific for the muscle involved in the observed action. Our s tudy presents further evidence that motor excitability is significantly mod ified when the subject observes an action performed by another individual. NeuroReport 11:2289-2292 (C) 2000 Lippincott Williams & Wilkins.