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Short-interval intracortical inhibition: Comparison between conventional and threshold-tracking techniques

Samusyte, G; Bostock, H; Rothwell, J; Koltzenburg, M; (2018) Short-interval intracortical inhibition: Comparison between conventional and threshold-tracking techniques. Brain Stimulation , 11 (4) pp. 806-817. 10.1016/j.brs.2018.03.002. Green open access

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Abstract

BACKGROUND: Short-interval intracortical inhibition (SICI) is conventionally measured as the relative amplitude reduction of motor evoked potentials (MEPs) by subthreshold conditioning stimuli. In threshold-tracking SICI (T-SICI), stimulus intensity is instead adjusted repeatedly to maintain a constant MEP and inhibition is measured as the relative threshold increase. T-SICI is emerging as a useful diagnostic test, but its relationship to conventional amplitude SICI (A-SICI) is unclear. OBJECTIVE: To compare T-SICI and its reliability with conventional A-SICI measurements. METHODS: In twelve healthy volunteers (6 men, median age 30 years), conventional and T-SICI were recorded at conditioning stimuli (CS) of 50-80% resting motor threshold (RMT) and interstimulus interval of 2.5 ms. Measurements were repeated on the same day and at least a week later by a single operator. RESULTS: Across the CS range, mean group T-SICI showed a strong linear relationship to the mean group values measured by conventional technique (y = 29.7-0.3x, R2 = 0.99), but there was considerable interindividual variability. At CS 60-80% RMT, T-SICI had excellent intraday (intraclass correlation coefficient, ICC, 0.81-0.92) and adequate-to-excellent interday (ICC 0.61-0.88) reproducibility. Conventional SICI took longer to complete (median of 5.8 vs 3.8 min, p < 0.001) and tended to have poorer reproducibility (ICC 0.17-0.42 intraday, 0.37-0.51 interday). With T-SICI, smaller sample sizes were calculated for equally powered interventional studies. CONCLUSION: The close relationship between conventional and T-SICI suggests that both techniques reflect similar cortical inhibitory mechanisms. Threshold-tracking measurements of SICI may be able to improve reproducibility, to shorten acquisition time and to reduce sample sizes for interventional studies compared with the conventional technique.

Type: Article
Title: Short-interval intracortical inhibition: Comparison between conventional and threshold-tracking techniques
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.brs.2018.03.002
Publisher version: https://doi.org/10.1016/j.brs.2018.03.002
Language: English
Additional information: Copyright © 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Keywords: Threshold-tracking TMS, Short-interval intracortical inhibition, Reliability, Intraclass correlation coefficient, Coefficient of repeatability
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Clinical and Movement Neurosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Department of Neuromuscular Diseases
URI: http://discovery.ucl.ac.uk/id/eprint/10046683
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