Cortical Excitability During Passive Action Observation in Hospitalized Adults With Subacute Moderate to Severe Traumatic Brain Injury: A Preliminary TMS Study.

Studies indicate that motor functions in patients with traumatic brain injury (TBI) can be improved with action observation. It has been hypothesized that this clinical practice relies on modulation of motor cortical excitability elicited by passive action observation in patients with TBI, a phenomenon shown thus far only in normal controls. The purpose of this work was to test this hypothesis and characterize the modulation of motor cortex excitability during passive action observation in patients with subacute moderate to severe TBI. We measured motor evoked potentials induced by single-pulse transcranial magnetic stimulation to the left primary motor cortex and recorded from the contralateral first dorsal interosseus while 20 participants observed videos of static and moving right index finger. Results were compared with those of 20 age-and gender-matched healthy controls. As expected, greater excitability was elicited during moving than static stimuli in healthy subjects. However, this was not observed in patients with TBI. Modulation of motor excitability during action observation is impaired in patients with TBI depending on motor dysfunction, lesion site, and number of days postinjury. These preliminary results suggest a strategy to identify patients in whom action observation might be a valuable neurorehabilitative strategy.