Browsing by Author "Damji, Omar"

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    Cortical excitability after pediatric mild traumatic brain injury
    (Elsevier, 2016-11-19) Seeger, Trevor A.; Kirton, Adam; Esser, Michael J.; Gallagher, Clare; Dunn, Jeff F.; Zewdie, Ephrem Takele; Damji, Omar; Ciechanski, Patrick; Barlow, Karen M.
    Introduction: Mild traumatic brain injury (mTBI) outcomes are variable, and 10e15% 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/Hypothesis: To determine if cortical excitability is altered in children with mTBI, and its association with clinical symptoms. Methods: This was a cross-sectional controlled cohort study. School-aged children (8e18 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. Results: Fifty-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) ¼ 0.55, p ¼ 0.582). Log10 long interval intracortical inhibition (LICI) was reduced in symptomatic participants compared to healthy controls (F (2, 59) ¼ 3.83, p ¼ 0.027). Procedures were well tolerated with no serious adverse events. Conclusions: TMS 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.
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    Paired Afferent Stimulation in Children: Mechanisms of Developmental Plasticity
    (2013-10-02) Damji, Omar; Kirton, Adam
    Plasticity may be enhanced in the developing brain, but mechanisms are poorly understood. Transcranial magnetic stimulation (TMS) offers increasingly sophisticated means of assessing neurophysiology and mechanisms of neuroplasticity in vivo in adults. Paired associative stimulation (PAS) is an advanced modality that pairs sensory electrical peripheral nerve stimulation with TMS over the contralateral motor strip (M1). PAS induces rapidly evolving, long lasting, reversible and topographically specific increases in M1 excitability in adults consistent with NMDAR-dependent long-term potentiation (LTP). PAS has not been studied in the more plastic brains of children. Our aim was to determine the developmental profile of PAS neurophysiology in school-aged children, evaluating the putative correlation of PAS effect with age, and possible endogenous systems that may be modulators of PAS (i.e. Shot-Interval Intracortical Inhibition) and dictating plasticity. Twenty-eight children aged 6-18 years underwent PAS evaluations. Eighteen had significant PAS responses that were reproducible on repeat testing. Addition of inhibitory paired-pulse TMS appeared to block the PAS effect. The PAS effect did not correlate with age. PAS is safe and tolerable with effects comparable to adults. PAS may carry clinical and research utility in perinatal stroke and other pediatric brain injury populations.