Changes in Cortical Plasticity in Relation to a History of Concussion during Adolescence.

Sean K. Meehan,Jasmine L. Mirdamadi,Steven P. Broglio,Douglas N. Martini

doi:10.3389/fnhum.2017.00005

Sean K. Meehan, Jasmine L. Mirdamadi + Show 2 more

Open Access

https://doi.org/10.3389/fnhum.2017.00005

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Abstract

Adolescence and early adulthood is a critical period for neurophysiological development potentially characterized by an increased susceptibility to the long-term effects of traumatic brain injury. The current study investigated differences in motor cortical physiology and neuroplastic potential across a cohort of young adults with adolescent concussion history and those without. Transcranial magnetic stimulation (TMS) was used to assess motor evoked potential (MEP) amplitude, short-interval cortical inhibition (SICI) and intracortical facilitation (ICF) before and after intermittent theta burst stimulation (iTBS). Pre-iTBS, MEP amplitude, but not SICI or ICF, was greater in the concussion history group. Post-iTBS, the expected increase in MEP amplitude and ICF was tempered in the concussion history group. Change in SICI was variable within the concussion history group. Post hoc assessment revealed that SICI was significantly lower in individuals whose concussion was not diagnosed at the time of injury compared to both those without a concussion history or whose concussion was medically diagnosed. Concussive impacts during adolescence appear to result in a persistent reduction of the ability to modulate facilitatory motor networks. Failure to report/identify concussive impacts close to injury during adolescence also appears to produce persistent change in inhibitory networks. These findings highlight the potential long-term impact of adolescent concussion upon motor cortical physiology.

Highlights

Mild traumatic brain injury or concussion, has traditionally been associated with transient declines in cognitive and motor function
The purpose of the current study was to investigate the persistent changes in motor cortical plasticity in asymptomatic young adults who last suffered a concussion during adolescence
Post hoc effect size calculations comparing the magnitude of the effects in the Diagnosed and Concussion-Like cohorts revealed consistently small effects across each cohort for reaction time (Diagnosed, Cohen’s d = 0.04; Concussion-Like, Cohen’s d = −0.19) and accuracy (Diagnosed, Cohen’s d = 0.04; Concussion-Like, Cohen’s d = 0.04)

Summary

Introduction

Mild traumatic brain injury or concussion, has traditionally been associated with transient declines in cognitive and motor function. In most cases neuropsychological functioning resolves to pre-injury benchmarks within 7–10 days of the injury (McCrory et al, 2013) This timeline parallels the acute neurometabolic events triggered by the concussive impact (Giza and Hovda, 2014) propagating the belief that concussive effects are functional in nature and brief. Increased fractional anisotropy and reduced mean diffusivity across the whole brain in adolescents 2 months post-injury highlights persistent decreases in white matter integrity despite no significant difference in clinical testing (Virji-Babul et al, 2013). More worrisome, decreased fractional anisotropy and increased mean diffusivity in the corpus callosum, right inferior and bilateral superior longitudinal fasciculus in older retired collegiate athletes correlate with the extent of cognitive decline (Tremblay et al, 2014b)

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