The Neurophysiological Responses of Concussive Impacts: A Systematic Review and Meta-Analysis of Transcranial Magnetic Stimulation Studies

• Published in: Frontiers in human neuroscience Vol. 14; p. 306
• Main Authors: Scott, Emily, Kidgell, Dawson J., Frazer, Ashlyn K., Pearce, Alan J.
• Format: Journal Article
• Language: English
• Published: Lausanne Frontiers Research Foundation 27.08.2020; Frontiers Media S.A
• Subjects: Brain research; Central nervous system; Concussion; Electroencephalography; evoked potentials; Excitability; Human Neuroscience; Latency; Magnetic fields; Medical Subject Headings-MeSH; Meta-analysis; motor; Motor evoked potentials; Pathophysiology; Physiology; Reviews; Systematic review; Transcranial magnetic stimulation; Trauma; Traumatic brain injury
• ISSN: 1662-5161; 1662-5161
• DOI: 10.3389/fnhum.2020.00306

Aim: This systematic review and meta-analysis investigated neurophysiological responses using transcranial magnetic stimulation (TMS) following a concussion or sub-concussion. Methods: A systematic searching of relevant databases for peer-reviewed literature quantifying motor evoked potentials from TMS between 1999 and 2019. A meta-analysis quantified pooled data for measures including: motor threshold, motor latency, motor evoked potential amplitude; and inhibitory measures: cortical silent period duration, short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) ratios. Results: Fifteen articles met the inclusion criteria. Studies were arbitrarily classified into the groups, based on time post concussion: ‘acute’ (subjects 0-3 months post injury, n=8) and ‘post acute’ (3 months – 2 years post concussion, n=7). A TMS quality of studies checklist rated studies from moderate to high in methodological quality, however the risk of bias analysis found the included studies were categorised as high risk of bias, particularly for a lack of allocation concealment and blinding of participants in the methodologies. Meta-analysis showed no differences in excitability measures, apart from a decreased motor threshold that was observed in the concussed group (SMD -0.28, 95% CI -0.51, -0.04; P = 0.02) for the post acute time frame. Conversely, all inhibitory measures showed differences between groups. Cortical silent period duration was found to be significantly increased in the acute (SMD 1.19, 95% CI 0.58, 1.81; P < 0.001) and post acute (SMD 0.55, 95% CI 0.12, 0.98; P = 0.01) time frames. SICI (SMD -1.15, 95% CI -1.95, -0.34; P = 0.005) and LICI (SMD -1.95, 95% CI -3.04, -0.85; P = 0.005) ratios were reduced, inferring increased inhibition, for the post acute time frame. Conclusion: This systematic review and meta-analysis demonstrates that inhibitory pathways are affected in the acute period post concussion. However, persistent alterations in cortical excitability remain with increased intracortical inhibition. While TMS should be considered as a reliable technique to measure the functional integrity of the central nervous system, the high risk of bias and heterogeneity in data suggests that future studies should aim to incorporate standardised methodological techniques, particularly with threshold determination and stimulus intervals for paired-pulse measures.