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.
Highlights
Transcranial magnetic stimulation (TMS) is a focal and noninvasive technique that utilizes short, rapidly changing magnetic field pulses to induce electrical currents in underlying cortical tissue (Hallett, 2007; Fox et al, 2012)
The application of repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1), one of the vital brain areas responsible for motor control and execution, has been proven effective in several studies which explored its usage for promoting motor rehabilitation after stroke (Corti et al, 2012) or Parkinson’s disease (Lomarev et al, 2006; González-García et al, 2011). rTMS over M1 has induced brain activity changes in the stimulated area (Bestmann et al, 2003, 2004) and influenced regions belonging to the sensorimotor network (SMN) which was spatially beyond the stimulated site (Bestmann et al, 2003, 2004; Yoo et al, 2008; Salinas et al, 2011, 2013, 2016)
We employed resting-state fMRI to investigate the topological alterations in functional SMN after application of different frequencies of rTMS over M1
Summary
Transcranial magnetic stimulation (TMS) is a focal and noninvasive technique that utilizes short, rapidly changing magnetic field pulses to induce electrical currents in underlying cortical tissue (Hallett, 2007; Fox et al, 2012). Bestmann et al (2004) measured MRI signal changes during high-frequency rTMS (3.125 Hz) over the left primary sensorimotor cortex (M1/S1) with supra- and subthreshold intensity. They found high-frequency rTMS at different intensities activated a similar pattern of primary motor and sensorimotor regions such as supplementary motor area (SMA), premotor cortex, cingulate motor cortex and thalamus though subthreshold stimulation was with reduced effects. In addition to the stimulated M1 area, the significant increased CBF were found in regions within SMN (SMA and premotor cortex) for all high-frequency rTMS (Salinas et al, 2013).
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