Cross-validating the iTBS-induced Hemodynamic Response From fNIRS and fMRI: a Concurrent iTBS-fMRI-fNIRS Study

Intermittent theta-burst stimulation (iTBS) targeting the left dorsolateral prefrontal cortex (DLPFC) is well established in treating patients with major depressive disorder (MDD). However, the iTBS-induced hemodynamic response during or immediately after a full session of stimulation has not been fully investigated. Although several concurrent iTBS/functional Near Infrared Spectroscopy (fNIRS) and iTBS/functional magnetic resonance imaging (fMRI) studies have investigated the hemodynamic response during or immediately after left DLPFC iTBS, they revealed inconsistent findings in the stimulated DLPFC. Given that the variability in iTBS-induced hemodynamic response in the stimulated DLPFC could be modulated by various inter- and intra-individual factors, cross-validating the findings from both techniques (fNIRS and fMRI) in the same group of participants under the same conditions through a simultaneous fMRI/fNIRS setting enables a straightforward comparison and interpretation of results from each technique. However, to our knowledge, cross-validation of iTBS-related fNIRS and simultaneous fMRI data has not been conducted yet, even the implementation of a simultaneous iTBS/fMRI/fNIRS setup is technically feasible with the mutually compatible equipment. Therefore, the current study has two primary objectives: Firstly, to establish a novel and practical methodological pipeline for simultaneously conducting iTBS/fMRI/fNIRS. Secondly, to cross-validate the hemodynamic responses during and immediately after iTBS, respectively monitored by fNIRS and fMRI.