Evidence of alterations in transcallosal motor inhibition as a possible long-term consequence of concussions in sports: A transcranial magnetic stimulation study

•TMS was used to test long-term effects of mild traumatic brain injury (mTBI) on corticospinal excitability and inter-hemispheric connectivity.•Corticospinal excitability measures and their hemispheric asymmetry were not different between mTBI and healthy controls.•The ipsilateral silent period, a measure of interhemispheric connectivity, was disrupted in mTBI compared to controls.

ObjectiveGrowing evidence suggests that long-term structural and physiological alterations are present in the brain of previously concussed athletes. In this study, we sought to further explore the long-term consequences of concussions with transcranial magnetic stimulation (TMS) by examining excitability changes both within and between hemispheres.MethodsParticipants (32 young adults with and without a history of concussions (HxC)) first underwent testing to assess cognitive and motor performance using standardized tests. Then, the following TMS measures were derived bilaterally: (1) resting motor threshold and motor evoked potentials (MEP), (2) afferent-induced modulation, (3) contralateral silent period (cSP) and MEP facilitation, and, (4) ipsilateral silent period (iSP).ResultsMultivariate analyses of performance data revealed no major group differences. For TMS data, no “hemisphere” effects were detected for all measures. Group differences were detected only for iSP derived measures owing to alterations in the onset latency and duration of transcallosal inhibition in the HxC group.ConclusionsWhile no major asymmetries were found between hemispheres, participants in the HxC group showed evidence of impaired transcallosal inhibition.SignificanceResults provide one of the first piece of evidence pointing to alterations in transcallosal inhibition as a potential neurophysiological marker of long-term consequences of concussions in sports.