The Effect of Transcranial Magnetic Stimulation (TMS) on Neural Plasticity in Young Adults with a Concussion History

During the acute recovery phase of concussion injury and mild TBI, injured individuals commonly demonstrate increased symptom reports (eg headache, dizziness, nausea, etc), impaired motor control (eg gait and balance), and slowed cognitive functioning. In the majority of instances, concussed individuals return to a pre-injury level of clinical functioning within 10 days of injury. Our research laboratory however, has demonstrated that subtle differences in balance, gait, brain electrophysiology and upper extremity visuomotor control remain undetectable by standard clinical tests and persist for years after injury. These subtle differences documented in young adults (18-29 years) may be the beginnings of chronic traumatic encephalopathy (CTE) reported in older adults with a concussion history. As such, we are proposing the application of repetitive transcranial magnetic stimulation (TMS) as a novel marker of persistent injury and potential intervention to decrease subtle declines in cerebral functioning.

With growing attention being placed on concussive injuries and growing evidence demonstrating the persistent effects of injury on motor control, this investigation is the first to demonstrate the potential to reverse those changes. Overall, the current results demonstrate that sports-related concussions early in life can have persistent effects upon sensorimotor performance. These deficits may be attributable to greater cortical excitability in primary motor cortex that likely reflects loss of differentiation of muscle representations. Further, changes in the ability to scale local intracortical networks activity may contributed to the abnormal increase in baseline cortical excitability. This is a worrying trend, as the inability to scale intracortical network activity could lead to greater increases in cortical excitability over time. Although the effect sizes in our current population are small to medium, further work in older adults with and without a history of concussion is needed to determine whether these differences become greater with age. In particular, the differences in the ability to scale intracortical network activity could lead to accelerated changes in individuals with a history of concussion as they age.