Bridging the gap to clinical use: A systematic review on TMS–EEG test-retest reliability

Background: Transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) can provide insight on cortical excitability and brain circuits. TMS-evoked potentials (TEPs) are phase-locked waveforms reflecting neural activity, with potential applications in psychiatry and neurology. However, the reliability of TEPs remains underexplored, hindering clinical standardization. This systematic review evaluates TEP reliability, focusing on commonly used measures and assessments. Methods: A systematic review was conducted on PubMed for studies from 2002 to October 10, 2024, using keywords combining TMS, EEG, and reliability terms. Systematic reviews and non-English articles were excluded. Results: Eighteen studies met inclusion criteria, mostly assessing young, healthy populations. Late TEP components demonstrated high relative reliability, while early components exhibited lower reliability and variability across sessions. Analytical methods like the intraclass and concordance correlation coefficients, and Pearson's correlations consistently favored late TEPs. Discussion: Late TEPs exhibit higher reliability, while early components require further research. TMS artifacts complicate interpretation, in both late and early responses. Formal reliability assessments, standardized protocols, and diverse populations are essential for advancing TEP reliability for clinical application. Conclusions: A more comprehensive reliability assessments is needed before the implementation of clinical applications.