• Trevor A Seeger, Adam Kirton, Michael J Esser, Clare Gallagher, Jeff Dunn, Ephrem Zewdie, Omar Damji, Patrick Ciechanski, and Karen M Barlow.
• Cumming School of Medicine, University of Calgary, Calgary, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, Canada; Alberta Children's Hospital Research Institute, Alberta Children's Hospital, Calgary, Canada.
• Brain Stimul. 2017 Mar 1; 10 (2): 305-314.

IntroductionMild traumatic brain injury (mTBI) outcomes are variable, and 10-15% may suffer from prolonged symptoms beyond 3 months that impair the child's return to normal activities. Neurophysiological mechanisms of mTBI are incompletely understood, particularly in children, but alterations in cortical excitability have been proposed to underlie post-concussion syndrome. Improved understanding is required to advance interventions and improve outcomes.Objective/HypothesisTo determine if cortical excitability is altered in children with mTBI, and its association with clinical symptoms.MethodsThis was a cross-sectional controlled cohort study. School-aged children (8-18 years) with mTBI were compared to healthy controls. Cortical excitability was measured using multiple TMS paradigms in children with (symptomatic) and without (recovered) persistent symptoms one-month post-injury. Primary outcome was the cortical silent period (cSP), a potential neurophysiological biomarker of GABAergic inhibition. Secondary outcomes included additional TMS neurophysiology, safety and tolerability. Associations between neurophysiology parameters and clinical symptoms were evaluated.ResultsFifty-three children with mTBI (55% male; mean age 14.1 SD: 2.4 years; 35 symptomatic and 27 asymptomatic participants) and 28 controls (46% male; mean age 14.3 SD: 3.1 years) were enrolled. cSP duration was similar between groups (F (2, 73) = 0.55, p = 0.582). Log10 long interval intracortical inhibition (LICI) was reduced in symptomatic participants compared to healthy controls (F (2, 59) = 3.83, p = 0.027). Procedures were well tolerated with no serious adverse events.ConclusionsTMS measures of cortical excitability are altered at one month in children with mTBI. Long interval cortical inhibition is decreased in children who remain symptomatic at one month post-injury.Copyright © 2016 Elsevier Inc. All rights reserved.

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