The Alteration Of Degree Centrality Of The Motor Cortex Of Suprahyoid Muscles With Theta-burst Stimulation In Healthy Subjects

Background Dysphagia seriously affects rehabilitation and the quality of life in patients,resulting in aspiration pneumonia,dehydration,malnutrition and other serious complications.At present,the clinical treatment of swallowing disorder mainly focus on the biomechanics of rehabilitation and prevention of complications of peripheral swallowing organs.However,there still has no enough evidence to verify the effectiveness of conventional treatment for dysphagia in the recent meta-analysis.How to promote the functional recovery of the damaged central nervous network is urgent for the treatment of dysphagia.Repetitive transcranial magnetic stimulation(r TMS),a noninvasive and safe bioelectricity stimulation technology,has been confirmed to be a promising in the rehabilitation of dysphagia.Furthermore,as a newly developed r TMS,theta burst stimulate(TBS)TBS can produce more powerful cortical excitability by using shorter stimulating time and smaller stimulus intensity compared with the traditional r TMS.There are two patterns ofTBS,named as continuousTBS(cTBS)and intermittentTBS(iTBS)which display inhibition and excitement effect on neuronal excitability respectively.However,the underlying neural mechanism ofTBS has not yet fully understood.Resting-state functional MRI(Rs-f MRI)can show the alteration in the brain network,therefore,it could be used as a novel approach to explore the physiological and pathological mechanism ofTBS treatment in swallowing.Objective To explore the alteration of degree centrality(DC)following different patterns ofTBS over the motor cortex of suprahyoid muscles in healthy subjects,and to reveal the underlying mechanism ofTBS on brain networks of swallowing for providing theoretical basis forTBS in treatment of dysphagia.Materials and methods This study was approved by the local ethics committee of Guangzhou first people's hospital and informed consent of all subjects was obtained.Sixty right-handed healthy volunteers(23.45±2.73 years,range 20-33,30 males)were recruited through advertising.All subjects were randomly distributed into three groups(i.e.cTBS group,iTBS group and combined cTBS/iTBS group)which completed threeTBS protocols respectively.A stereotaxic neuronavigation system facilitated accurate TMS positioning,and the TMS coil was applied on the cortex of suprahyoid muscles in all subjects.The stimulus protocols were as follows: for Group 1,cTBS was positioned on the left motor cortex of the suprahyoid muscles;in Group 2,iTBS was placed on the same position as that in Group 1;and in Group 3,iTBS was performed on the contralateral homologous area immediately after cTBS on the left suprahyoid muscles motor cortex.The data of Resting-state functional magnetic resonance imaging(Rs-f MRI)of the subjects was acquired from a Siemens Verio 3.0 T MR 2 hours before and 30 minutes afterTBS stimulation respectively.The DC values with threshold of 0.25 were measured and compared between pre-TBS and post-TBS stimulation within groups.Moreover,different threshold values(0.2,0.3)were calculated to verify the reliability of the DC values.Results1.In the cTBS group,decreased DC values were displayed in the left paracentral gyrus, right thalamus and right angular gyrus(P < 0.05),increased DC values were observed in the left middle frontal gyrus and left inferior frontal gyrus(P < 0.05).2.In the iTBS group,decreased DCs were found in the vermis of cerebellum,left lentiform nucleus,left middle frontal gyrus,right insular and right thalamus(P <0.05).In addition,increased DCs were seen in the right lingual gyrus,right dorsolateral superior frontal gyrus,bilateral superior temporal gyrus and bilateral pre/post central gyrus(P < 0.05).3.In the cTBS/iTBS group,decreased DC values were seen in the posterior cingulate cortex and the left angular gyrus(P < 0.05);and increased DCs were observed in the left fusiform gyrus,right precuneus and right supramarginal gyrus(P < 0.05).Conclusion1.cTBS mainly results in decreasing DC in the left supplementary motor cortex,and sensory network,and increasing DC in ipsilateral attention network.2.iTBS can increase DC in bilateral primary sensorimotor network and contralateral attention network,and decrease DC in multiple bilateral subcortical areas related to swallowing network.3.The after effect of iTBS followed cTBS may counteract by each other,and the iTBS can reverse the partial after effect of inhibition of cortical excitability induced by cTBS.4.Rs-f MRI can provide novel evidence for underlying mechanism ofTBS on swallowing brain network.