Bidirectional effects on interhemispheric resting‐state functional connectivity induced by excitatory and inhibitory repetitive transcranial magnetic stimulation

Abstract

Several recent studies using functional magnetic resonance imaging (fMRI) have shown that repetitive transcranial magnetic stimulation (rTMS) affects not only brain activity in stimulated regions but also resting-state functional connectivity (RSFC) between the stimulated region and other remote regions. However, these studies have only demonstrated an effect of either excitatory or inhibitory rTMS on RSFC, and have not clearly shown the bidirectional effects of both types of rTMS. Here, we addressed this issue by performing excitatory and inhibitory quadripulse TMS (QPS), which is considered to exert relatively large and long-lasting effects on cortical excitability. We found that excitatory rTMS (QPS with interstimulus intervals of 5 ms) decreased interhemispheric RSFC between bilateral primary motor cortices, whereas inhibitory rTMS (QPS with interstimulus intervals of 50 ms) increased interhemispheric RSFC. The magnitude of these effects on RSFC was significantly correlated with that of rTMS-induced effects on motor evoked potential from the corresponding muscle. The bidirectional effects of QPS were also observed in the stimulation over prefrontal and parietal association areas. These findings provide evidence for the robust bidirectional effects of excitatory and inhibitory rTMSs on RSFC, and raise a possibility that QPS can be a powerful tool to modulate RSFC.

Imaging human brain networks to improve the clinical efficacy of non-invasive brain stimulation

“…2A). This idea is supported by earlier work that showed that excitatory rTMS over the primary motor cortex (an output region with a relatively low connectivity density) induces measurable BOLD changes, but these changes are generally restricted to the sensorimotor network (Bestmann et al, 2004;Cardenas-Morales et al, 2011; but see Watanabe et al, 2014).…”

Inter-individual variability in cortical excitability and motor network connectivity following multiple blocks of rTMS

“…This finding implies that a linear relationship between MEP and rsFC is rather found at the global level considering average changes in motor system connectivity. Interestingly, Watanabe et al (2014) reported a relationship between the effects of quadripulse TMS (QPS) on MEPs and rsFC. The magnitude of changes between the stimulated and the contralateral M1 was significantly correlated with the magnitude of changes in MEPs.…”

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…Only one study has used TMS to investigate the relationship between polarity (high/low frequency) and FC changes in the motor network [40]. The study targeted the left M1 and reported reduced FC following excitatory TMS, while inhibitory TMS increased FC.…”