Repeated Concussions Impair Behavioral and Neurophysiological Changes in the Motor Learning System.

Background. Concussions affect nearly 3 million people a year and are the leading cause of traumatic brain injury-related emergency department visits among youth. Evidence shows neuromotor regions are sensitive to concussive events and that motor symptoms may be the earliest clinical manifestations of neurodegenerative traumatic brain injuries. However, little is known about the effects repeated concussions play on motor learning. Namely, how does concussion acuity (time since injury) affect different behavioral and neurophysiological components of motor learning? Methods. Using a 3-pronged approach, we assessed (1) behavioral measures of motor learning, (2) neurophysiological measures underlying retention of motor learning known as occlusion, and (3) quantitative survey data capturing affective symptoms of each participant. Collegiate student athletes were stratified across 3 groups depending on their concussion history: (1) NonCon, no history of concussion; (2) Chronic, chronic-state of concussion (>1 year postinjury), or (3) Acute, acute state of concussion (<2 weeks postinjury). Results. We found that athletes in both the acute and chronic state of injury following a concussion had impaired retention and aberrant occlusion in motor skill learning as compared with athletes with no history of concussion. Moreover, higher numbers of previous concussions (regardless of the time since injury) correlated with more severe behavioral and neurophysiological motor impairments by specifically hindering neurophysiological mechanisms of learning to affect behavior. Conclusions. These results indicate the presence of motor learning impairment that is evident within 2 weeks postinjury. Our findings have significant implications for the prognosis of concussion and emphasize the need for prevention, but can also direct more relevant rehabilitation treatment targets.