Long-term and cumulative effects of sports concussion on motor cortex inhibition

OBJECTIVE: Using transcranial magnetic stimulation paradigms, this study investigated motor cortex integrity as a function of an athlete's prior history of concussions. PATIENTS AND METHODS: Motor cortex excitatory and inhibitory mechanisms were studied in athletes using four different transcranial magnetic stimulation protocols, namely 1) resting motor threshold, 2) intracortical inhibition and intracortical facilitation in a paired-pulse paradigm, 3) excitability of the corticospinal system using an input-output curve, and 4) intracortical inhibition in a cortical silent-period paradigm. Motor-evoked potentials were recorded from the first dorsal interosseous muscle of the right hand. RESULTS: Cortical silent-period duration in athletes who have experienced multiple concussions was prolonged when compared to that of normal control participants. Linear regression suggested that concussion severity was the main factor explaining motor cortex dysfunction. Moreover, when we retested the athletes, the cortical silent period was more prolonged in those who sustained another concussion after baseline testing had occurred. CONCLUSION: Findings from this study indicate that sports-related concussions result in long-term motor system dysfunctions that seem to be attributable to subclinical intracortical inhibitory system abnormalities. This study also shows that sustaining subsequent concussions exacerbates this deficit, and thus provides additional support for the contention that the adverse effects of sports-related concussions on intracortical inhibitory systems are cumulative.