Altered activation in sensorimotor network after applying rTMS over the primary motor cortex at different frequencies

Abstract

Introduction Repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) can modulate brain activity both in the stimulated site and remote brain areas of the sensorimotor network. However, the modulatory effects of rTMS at different frequencies remain unclear. Here, we employed finger‐tapping task‐based fMRI to investigate alterations in activation of the sensorimotor network after the application of rTMS over the left M1 at different frequencies. Materials and Methods Forty‐five right‐handed healthy participants were randomly divided into three groups by rTMS frequency (HF, high‐frequency, 3 Hz; LF, low‐frequency, 1 Hz; and SHAM) and underwent two task‐fMRI sessions (RH, finger‐tapping with right index finger; LH, finger‐tapping with left index finger) before and after applying rTMS over the left M1. We defined regions of interest (ROIs) in the sensorimotor network based on group‐level activation maps (pre‐rTMS) from RH and LH tasks and calculated the percentage signal change (PSC) for each ROI. We then assessed the differences of PSC within HF or LF groups and between groups. Results Application of rTMS at different frequencies resulted in a change in activation of several areas of the sensorimotor network. We observed the increased PSC in M1 after high‐frequency stimulation, while we detected the reduced PSC in the primary sensory cortex (S1), ventral premotor cortex (PMv), supplementary motor cortex (SMA), and putamen after low‐frequency stimulation. Moreover, the PSC in the SMA, dorsal premotor cortex (PMd), and putamen in the HF group was higher than in the LF group after stimulation. Conclusion Our findings suggested that activation alterations within sensorimotor network are dependent on the frequency of rTMS. Therefore, our findings contribute to understanding the effects of rTMS on brain activation in healthy individuals and ultimately may further help to suggest mechanisms of how rTMS could be employed as a therapeutic tool.

Low-Frequency Repetitive Transcranial Magnetic Stimulation Restores Dynamic Functional Connectivity in Subcortical Stroke

“…Studies on rs-fMRI have shown that functional connectivity (FC) and network indicators are disrupted during stroke ( 3 ). Moreover, low-frequency repetitive transcranial magnetic stimulation (LF-rTMS) combined with rehabilitation training can promote motor function recovery and cognitive enhancement and change the activation and FC of these networks ( 4 , 5 ). However, the methods used in previous studies ignored temporal changes in the fMRI signals; it is unclear whether FCs between brain networks change over time and how these changes are related to the LF-rTMS mechanism underlying the regulation of functional recovery in patients who have experienced a subcortical stroke.…”

“…As dFC analysis can extract more time-varying characteristics of information exchange between brain regions on a time scale and because these characteristics are significantly related to many physiological parameters ( 12 ), pathological features ( 13 ), and even intervention effects ( 14 ), dFC analysis seems to be particularly suitable for evaluating the complex and changeable characteristics of brain networks after stroke and exploring the neural mechanism of functional rehabilitation. Previous studies have shown that the proportion between integrated and segregated states was not balanced in patients who suffered from strokes ( 4 ) and that the temporal dynamics of FC were closely related to clinical severity ( 15 , 16 ). However, these studies focus mainly on patients with acute or chronic stroke; there are few reports on the dynamic relationship between brain networks in patients with a convalescence period of 1–3 months after stroke.…”

Repetitive transcranial magnetic stimulation modulates cortical–subcortical connectivity in sensorimotor network

“…The generated activation map of each participant was then projected to the anatomical image using brainsight software before rTMS intervention. Next, the most activated voxel in the left M1 was selected as the individual rTMS target for each participant (please see Wang, Li, et al, 2020, for more details); the locations of individual rTMS target were visualized in Figure 1b.…”

“…For instance, using task functional magnetic resonance imaging (fMRI) technique, the common mean to investigate the after‐effects of rTMS, Yoo et al (2008) found significant activation in the bilateral basal ganglia, left superior frontal gyrus, bilateral medial frontal cortex, right medial temporal lobe, right inferior parietal lobe and right cerebellar hemisphere after 10‐Hz rTMS applied over right M1 compared with sham stimulation. More recently, another task‐fMRI study revealed a reduced percentage signal change in the primary sensory cortex, ventral premotor cortex, supplementary motor cortex (SMA) and putamen (PUT) in left‐hand finger‐tapping task after 1‐Hz rTMS targeted on left M1 compared with the stage before rTMS intervention (Wang, Li, et al, 2020). Indeed, besides the modulatory effects on both stimulation and remote regions, previous studies have also provided evidence that rTMS can also lead to changes in connectivity within stimulated networks (Fox et al, 2012; Li et al, 2017; Riedel et al, 2019; Wang et al, 2014).…”

“…Previous studies have verified the effectiveness of rTMS targeted at M1 in the treatment for Parkinson's disease (Kim et al, 2015; Yokoe et al, 2018) or in the applications of promoting motor rehabilitation after stroke (Du et al, 2019; Kim et al, 2014; Wang, Zhang, et al, 2020). It is suggested that the after‐effects of rTMS were not only limited in the target region but also have influence on the remote regions (Di Lazzaro et al, 2011; Nathou et al, 2018; Wang, Li, et al, 2020; Yoo et al, 2008). For instance, using task functional magnetic resonance imaging (fMRI) technique, the common mean to investigate the after‐effects of rTMS, Yoo et al (2008) found significant activation in the bilateral basal ganglia, left superior frontal gyrus, bilateral medial frontal cortex, right medial temporal lobe, right inferior parietal lobe and right cerebellar hemisphere after 10‐Hz rTMS applied over right M1 compared with sham stimulation.…”