@article {NielsenENEURO.0103-21.2021, author = {Christina S. Nielsen and Gintaute Samusyte and Kirsten Pugdahl and Jakob U. Blicher and Anders Fuglsang-Frederiksen and B{\"u}lent Cengiz and Hatice Tankisi}, title = {Test-retest reliability of short-interval intracortical inhibition assessed by threshold-tracking and automated conventional techniques}, elocation-id = {ENEURO.0103-21.2021}, year = {2021}, doi = {10.1523/ENEURO.0103-21.2021}, publisher = {Society for Neuroscience}, abstract = {Two novel short-interval intracortical inhibition (SICI) protocols, assessing SICI across a range of interstimulus intervals (ISI) 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 two days, five to seven days 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 intra- nor inter-observer measures of SICI differed significantly between examinations, except for T-SICI at ISI 3ms (P=0.00035) and A-SICI at ISI 2.5ms (P=0.0103). Intra-day reliability was poor-to-good for A-SICI and moderate-to-good for T-SICI. Inter-day and inter-observer 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.Significance statementThreshold-tracking short-interval intracortical inhibition (T-SICI) measured with threshold-tracking transcranial magnetic stimulation (TT-TMS) was introduced two decades ago (Fisher et al., 2002). Earlier studies have shown that T-SICI may be used for diagnosing ALS (Vucic and Kiernan, 2006, 2008). However, limitations of the existing serial T-SICI protocol was recently reported and two novel SICI protocols, with potential experimental and clinical utility, were introduced (Samusyte et al., 2018; Tankisi et al., 2021a). These studies were conducted on healthy subjects. The test-retest reliability of the aforementioned protocols was investigated over four identical sessions on two days, five to seven days apart. These results suggest that the two SICI protocols may be reliably and reproducibly employed in research studies with healthy subjects.}, URL = {https://www.eneuro.org/content/early/2021/09/23/ENEURO.0103-21.2021}, eprint = {https://www.eneuro.org/content/early/2021/09/23/ENEURO.0103-21.2021.full.pdf}, journal = {eNeuro} }