Exploring the predictive power of iTBS induced prefrontal excitability using concurrent TBS/fNIRS

The effect of a single session intermittent theta-burst stimulation (iTBS) on dorsolateral prefrontal cortex (DLPFC) function remains uncertain. Additionally, the clinical relevance of predicting DLPFC function through iTBS-induced DLPFC excitability has not been investigated. To address these gaps, concurrent iTBS/functional near-infrared spectroscopy (fNIRS) was employed. Thirty healthy participants were recruited in this randomized, sham-controlled, crossover study. Working memory performance, a core function of the DLPFC, was assessed using 3-back task before and at five subsequent timepoints following iTBS. Prefrontal hemoglobin concentrations were measured concurrently by fNIRS throughout the whole procedure. No significant differences in post-stimulation 3-back task performance were observed between active and sham stimulation. Nevertheless, a significant decrease in iTBS-induced oxygen-hemoglobin (HbO) change was observed in the active group compared to the sham group. However, iTBS-induced HbO changes did not significantly predict working memory performance at any timepoint. These results reveal that a single iTBS session of the left DLPFC results in significant immediate cortical excitability changes. However, these changes do not translate into improved working memory compared to sham stimulation and iTBS-induced prefrontal excitability does not appear to predict subsequent working memory performance following a single session iTBS. Nevertheless, the potential predictive power of iTBS-induced prefrontal excitability in symptom changes of rTMS for depression is still worthy of an investigation given that such symptom changes are thought to result from rTMS effects. Further studies with larger sample sizes are needed to explore whether iTBS-induced excitability changes could serve as an imaging marker for clinical treatment response.