The influence of sensory potentials on transcranial magnetic stimulation - Electroencephalography recordings.

Objective: It remains unclear to what extent Transcranial Magnetic Stimulation-evoked potentials (TEPs) reflect sensory (auditory and somatosensory) potentials as opposed to cortical excitability. The present study aimed to determine; a) the extent to which sensory potentials contaminate TEPs using a spatially-matched sham condition, and b) whether sensory potentials reflect auditory or somatosensory potentials alone, or a combination of the two.
Methods: Twenty healthy participants received active or sham stimulation, with the latter consisting a sham coil click combined with scalp electrical stimulation. Two additional conditions i) electrical stimulation and ii) auditory stimulation alone, were included in a subset of 13 participants.
Results: Signals from active and sham stimulation were correlated in spatial and temporal domains > 55 ms post-stimulation. Relative to auditory or electrical stimulation alone, sham stimulation resulted in a) larger potentials, b) stronger correlations with active stimulation and c) a signal that was not a linear sum of electrical and auditory stimulation alone.
Conclusions: Sensory potentials can confound interpretations of TEPs at timepoints > 55 ms post-stimulation. Furthermore, TEP contamination cannot be explained by auditory or somatosensory potentials alone, but instead reflects a non-linear interaction between both.
Significance: Future studies may benefit from controlling for sensory contamination using spatially-matched sham conditions, and which consist of combined auditory and somatosensory stimulation.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2022 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)