Altered Topological Organization in the Sensorimotor Network After Application of Different Frequency rTMS

Abstract

The application of repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) could influence the intrinsic brain activity in the sensorimotor network (SMN). However, how rTMS modulates the topological organization of the SMN remains unclear. In this study, we employed resting-state fMRI to investigate the topological alterations in the functional SMN after application of different frequency rTMS over the left M1. To accomplish this, we collected MRI data from 45 healthy participants who were randomly divided into three groups based on rTMS frequency (HF, high-frequency 3 Hz; LF, low-frequency 1 Hz; and SHAM). Individual large-scale functional SMN was constructed by correlating the mean time series among 29 regions of interest (ROI) in the SMN and was fed into graph-based network analyses at multiple levels of global organization and nodal centrality. Our results showed that compared with the network metrics before rTMS stimulation, the left paracentral lobule (PCL) exhibited reduced nodal degree and betweenness centrality in the LF group after rTMS, while the right supplementary motor area (SMA) exhibited reduced nodal betweenness centrality in the HF group after rTMS. Moreover, rTMS-related alterations in nodal metrics might have been attributable to the changes in connectivity patterns and local activity of the affected nodes. These findings reflected the potential of using rTMS over M1 as an effective intervention to promote motor function rehabilitation.

Keywords: graph theory; primary motor cortex (M1); rTMS (repetitive transcranial magnetic stimulation); resting-state functional MRI; sensorimotor network (SMN).

FIGURE 1

The distribution of 29 ROIs in the sensorimotor network (Power et al., 2011) was visualized in surface space using the BrainNet Viewer (Xia et al., 2013).

FIGURE 2

Mean normalized local efficiency (A) and mean normalized global efficiency (B) of the sensorimotor network before and after rTMS. ${\tilde{E}}_{loc}$, normalized local efficiency; ${\tilde{E}}_{glob}$, normalized global efficiency.

FIGURE 3

Significant differences in nodal betweenness centrality (A) and nodal degree centrality (B) before and after rTMS. Error bars indicate standard errors. lPCL, left paracentral lobule; rSMA, right supplementary motor area; LF, low-frequency group; HF, high-frequency group.

FIGURE 4

Significant differences in the functional connectivity (FC) patterns in the left PCL and right SMA in the functional sensorimotor network before and after rTMS. (A) Nodes with significantly changed FC were visualized in surface space; (B) FC between the left PCL and left M1 in the LF group and FC between the right SMA and right precentral gyrus in the HF group. Error bars indicate standard errors. lPCL, left paracentral lobule; lM1, left primary motor cortex; rSMA, right supplementary motor area; rPreCG, right precentral gyrus; LF, low-frequency group; HF, high-frequency group.

FIGURE 5

Correlation between the differences in ALFF and the differences in degree centrality in the left PCL before and after rTMS in the LF group. lPCL, left paracentral lobule; LF, low-frequency group.