Abstract
PurposeThe utility of transcranial magnetic stimulation (TMS) has been growing rapidly in both neurocognitive studies and clinical applications in decades. However, it remains unclear how the responses of the stimulated site and the site-related functional network to the external TMS manipulation dynamically change over time.MethodsA multi-session combining TMS-fMRI experiment was conducted to explore the spatiotemporal effects of TMS within the fronto-limbic network. Ten healthy volunteers were modulated by intermittent theta-burst stimulation (iTBS) at a precise site within the left dorsolateral prefrontal cortex (DLPFC, MNI coordinate [-44 36 20]), navigated by individual structural MRI image. Three-session resting-state fMRI images were acquired before iTBS (TP1), immediately after iTBS (TP2), and 15 min after iTBS (TP3) for each participant. Seventy-four regions of interests (ROIs) within the fronto-limbic network were chosen including the bilateral superior frontal gyrus (SFG), middle frontal gyrus (MidFG), inferior frontal gyrus (IFG), orbital gyrus (OrG), cingulate gyrus (CG), and subcortical nuclei (hippocampus and amygdala). Regional fractional amplitude of low-frequency fluctuation (fALFF) and ROI-to-ROI functional connectivity (FC) were compared among TP1, TP2, and TP3.ResultsThe immediate iTBS effect was observed at the stimulated site. FC between the left dorsolateral SFG and left dorsal IFG and between the left rostral IFG and right MidFG increased at TP2 as compared to at TP1 (all FDR-p < 0.05), while FC within the left OrG decreased. The relatively long-term iTBS effect transmitted with decreased FC between the left IFG and right amygdala, increased FC between the left MidFG and left OrG, and decreased FC between bilateral IFG and OrG at TP3 than at TP1 (all FDR-p < 0.05). Meanwhile, mean fALFF values over the left SFG, MidFG, ventral CG, and IFG were significantly increased at TP3 as compared to those at TP2 (all p < 0.05 with Bonferroni correction).ConclusionBy combining TMS and fMRI, it becomes possible to track the spatiotemporal dynamics of TMS after-effects within the fronto-limbic network. Our findings suggested that the iTBS effect dynamically changed over time from the local neural activation at the stimulated site to its connected remote regions within the fronto-limbic network.
Highlights
Transcranial magnetic stimulation (TMS) provides a noninvasive way to explore the brain function in both basic neuroscience and clinical applications (Lefaucheur et al, 2014)
Written informed consent was obtained from each participant
The immediate intermittent theta burst stimulation (iTBS) effect was observed within the left frontal areas and between the bilateral frontal areas
Summary
Transcranial magnetic stimulation (TMS) provides a noninvasive way to explore the brain function in both basic neuroscience and clinical applications (Lefaucheur et al, 2014). TMS pulses induce current within the cortex underneath the site of stimulation, leading to local neural activation (Allen et al, 2007) as well as consequent alterations within a distributed network (Chen et al, 2013). After one-session TMS modulation, i.e., intermittent theta burst stimulation (iTBS), the after-effects can be beyond the duration of stimulation and may last about 30 min (Huang et al, 2005). The TMS after-effects should be temporally and spatially dynamic over the local region and within the whole-brain network (Ruff et al, 2009; Hawco et al, 2017, 2018). There is few evidence of the duration of TMS after-effects over the primary motor cortex in humans. To further clarify the TMS aftereffects beyond the motor cortex, other neuroimaging techniques are required to measure the TMS induced neural activity
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