Test-Retest Reliability of Short-Interval Intracortical Inhibition Assessed by Threshold-Tracking and Automated Conventional Techniques

• Published in: eNeuro Vol. 8; no. 5; p. ENEURO.0103-21.2021
• Main Authors: Nielsen, Christina S.-Z., Samusyte, Gintaute, Pugdahl, Kirsten, Blicher, Jakob U., Fuglsang-Frederiksen, Anders, Cengiz, Bülent, Tankisi, Hatice
• Format: Journal Article
• Language: English
• Published: United States Society for Neuroscience 01.09.2021
• Subjects: Electromyography; Evoked Potentials, Motor; Humans; Methods/New Tools; Motor Cortex; Neural Inhibition; Reproducibility of Results; automated conventional TMS; threshold-tracking TMS; test-retest reliability; transcranial magnetic stimulation; short-interval intracortical inhibition
• ISSN: 2373-2822; 2373-2822
• DOI: 10.1523/ENEURO.0103-21.2021

Two novel short-interval intracortical inhibition (SICI) protocols, assessing SICI across a range of interstimulus intervals (ISIs) using either parallel threshold-tracking transcranial magnetic stimulation (TT-TMS) or automated conventional TMS (cTMS), were recently introduced. However, the test-retest reliability of these protocols has not been investigated, which is important if they are to be introduced in the clinic. SICI was recorded in 18 healthy subjects using TT-TMS (T-SICI) and cTMS (A-SICI). All subjects were examined at four identical sessions, i.e., morning and afternoon sessions on 2 d, 5–7 d apart. Both SICI protocols were performed twice at each session by the same observer. In one of the sessions, another observer performed additional examinations. Neither intraobserver nor interobserver measures of SICI differed significantly between examinations, except for T-SICI at ISI 3 ms ( p  = 0.00035) and A-SICI at ISI 2.5 ms ( p  = 0.0103). Intraday reliability was poor-to-good for A-SICI and moderate-to-good for T-SICI. Interday and interobserver reliabilities of T-SICI and A-SICI were moderate-to-good. Although between-subject variation constituted most of the total variation, SICI repeatability in an individual subject was poor. The two SICI protocols showed no considerable systematic bias across sessions and had a comparable test-retest reliability profile. Findings from the present study suggest that both SICI protocols may be reliably and reproducibly employed in research studies, but should be used with caution for individual decision-making in clinical settings. Studies exploring reliability in patient cohorts are warranted to investigate the clinical utility of these two SICI protocols.