Study On The Neural Mechanism Of RTMS Based On Brain Perfusion Imaging

Backgrounds: Brain neural activity can cause changes in cerebral blood flow(CBF).Repetitive transcranial magnetic stimulation(r TMS)is a non-invasive neuromodulational tool that directly affects the brain's neural activity.Previous studies have shown that the application of r TMS to the dorsolateral prefrontal cortex(DLPFC)in the left side of the brain can alleviate or improve a variety of mental or neuropsychological disorders,but the underlying neural mechanisms is still unclear.The purpose of this study was to observe and analyze the effects of r TMS on brain neural activity using functional magnetic resonance imaging(f MRI),especially cerebral blood flow(CBF)imaging.Unlike previous studies,we studied the effects of r TMS with different stimulation frequencies(20Hz and c TBS)on brain function.Methods: This study consists of two parts,the study of the effect of a 20 Hz r TMS on CBF(experiment1);and the effect of c TBS r TMS on CBF(experiment2).Thirty-eight healthy young adults participated in experiment1 and were randomly divided into two groups: 20 Hz r TMS group(n = 20,mean age: 22.20 years,10 females/10 males)and SHAM group(n = 18,mean age: 23.40 years,12 females/6 males).Thirty-five healthy young adults participated in experiment2,including the c TBS r TMS group(n = 17,mean age: 22.50 years,8 females/9 males)and SHAM group.The information in the SHAM group was the same as in the experiment1.Each subject received two sessions of Magnetic Resonance Imaging scans(pre-r TMS and post-r TMS)which were performed on two separate days with 48 hours.In the present study,CBF changes before and after 20 Hz r TMS group,c TBS r TMS group and SHAM group were assessed with paired-sample t-tests.Two-sample t-tests were performed to assess r TMS(20Hz and c TBS)vs SHAM induced changes to the CBF.Results: Experiment1 found that 20 Hz DLPFC r TMS induced relative CBF(r CBF)redistribution in the default mode network,including increased r CBF in left medial temporal cortex(MTC)/hippocampus,but reduced r CBF in precuneus and right cerebellum.Meanwhile,SHAM stimulation didn't produce any r CBF changes.After controlling SHAM effects,only the r CBF increase in MTC/hippocampus remained.In the experiment2(c TBS group),significant CBF increase was found on left parahippocampal,left hippocampus,left amygdala,left inferior temporal cortex,left inferior parietal cortex and left precuneus after c TBS r TMS.SHAM stimulation didn't produce any significant CBF changes.A two-sample t-test was performed between the c TBS r TMS and SHAM groups,the results did not reveal any significant difference in CBF between the two groups.Conclusion: Our data show that both excitatory and inhibitory TMS can cause an increase in CBF.Although we did not find significant changes in CBF at the stimulation target,these preliminary findings may suggest that redistribution of CBF in the brain may be a potential neural mechanism of the r TMS effect.