Investigating The Effects Of Different Frequencies Of Repetitive Transcranial Magnetic Stimulation On Sensorimotor Network

Repetitive transcranial magnetic stimulation(r TMS)is a painless and noninvasive brain stimulation tool,which could either increase or decrease the brain activity.r TMS have been increasingly employed both in clinical practice and in research for the treatment of patients with motor dysfunctions.Application of r TMS over the primary motor cortex(M1)could modulate the activity not only in the stimulated site but also in remote brain regions of the sensorimotor network.However,the modulatory effect of r TMS at different frequencies remains unclear.Here,we employed task and restingstate functional magnetic resonance imaging(f MRI)to investigate alterations in activation and functional connectivity(FC)of the sensorimotor network after the application of r TMS over the left M1 at different frequencies.45 right-handed healthy participants were randomly divided into three groups by r TMS frequency(HF,high-frequency,3 Hz;LF,low-frequency,1 Hz;and SHAM)and underwent two task-f MRI sessions(RH,finger tapping with right index finger;LH,finger tapping with left index finger)and one resting-state f MRI session before and after applying r TMS over the left M1.In study 1,we employed finger-tapping task-f MRI to investigate the alterations in activation of the sensorimotor network after the application of r TMS over left M1.We defined regions of interest(ROIs)in the sensorimotor network based on group level activation maps(pre-r TMS)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.We found several regions of sensorimotor network,such as M1,primary sensory cortex(S1),premotor cortex(PMC),supplementary motor cortex(SMA)and subcortical area — putamen,showed significant changed activation in LH or RH tasks after the application of r TMS at different frequencies.In study 2,we applied resting-state f MRI to investigate the alterations in FC between each pair of regions of the sensorimotor network after the application of r TMS over left M1.We found distinct effects on FC caused by different frequencies of r TMS: low-frequency stimulation resulted in the increased FC,while high-frequency stimulation decreased the FC.In addition,we found that the low-frequency stimulation could induce significant changed FC of the subcortical areas,especially putamen and basal ganglia thalamo-cortical circuit,when compared with high-frequency stimulation.In sum,we employed task and resting-state f MRI to investigate the alteration in activation and FC of the sensorimotor network after application of r TMS over M1 at different frequencies.Our findings suggested that changed activation and FC of the sensorimotor network are dependent on the frequency of r TMS: high-frequency stimulation resulted in increased activation and FC of the sensorimotor network,while low-frequency stimulation decreased the activation and FC.Therefore,our findings contribute to understanding the effects of r TMS on brain activation and FC in healthy individuals,and ultimately may further help to suggest mechanisms of how r TMS could be employed as a therapeutic tool for the treatment of patients with motor dysfunctions,such as stroke or Parkinson’s disease.