Effects Of Noninvasive Deep Brain Stimulation On Neuromuscular Function And Its Neural Mechanism

Purposes: Previous studies showed that anodal transcranial direct current stimulation on the M1 can increase the excitability of the M1,promote neuromuscular function,and enhance the sports/exercise performance.However,the current transcranial direct current stimulation montages cannot achieve deeper and focal stimulation.In order to improve the effect of t ES,Grossman and his colleagues proposed the concept of temporal interference stimulation(TI)in 2017,which can achieve focused deeply brain stimulation.In addition,the mechanism of transcranial electrical stimulation on the central and peripheral nerves in improve sports/exercise performance is still unclear.Therefore,the purpose of this study is to took the first dorsal interosseous muscle in primary motor cortex region as target area,using TI stimulation,combined with kinetics,neuro-electrophysiology and neuroimaging research methods,to observe the effect of TI on the first dorsal interosseous muscle neuromuscular function in maximum voluntary and motor control.,and further explore the neural mechanism of TI effects on neuromuscular function.According to the purpose of the research,this study is divided into two specific studies.Study 1: To explore the effects of TI on the muscle strength and neuromuscular recruitment capacity in maximal voluntary contraction,and motor control;Study 2: To explore the effect of TI on resting state neural spontaneous activity and neural functional connectivity.Methods: Participants: this study recruited 40 healthy subjects(18-35 years old),including 31 males and 9 females.The subjects were all right-handed and had no neurological diseases.Study 1: 38 subjects actually completed test.Each subject randomly accepted three interventions of HD-tDCS,TI or sham stimulation for 20 minutes,with an interval of more than 48 hours between each intervention.Before and after the intervention,the first interosseous dorsal muscle performed 20 s maximum isometric voluntary contraction(MVC)and 40% MVC isometric contraction trapezoidal force.At the same time,the force(peak muscle strength,maximum force power and muscle strength decrease rate)and high-precision electromyography data(peak electromyography amplitude,mean electromyography amplitude,peak electromyography frequency,mean electromyography frequency and number of recruited motor units)were collected.One-way analysis of variance were used to statistically analyzed by SPSS25.0 software,and the significance threshold was set at P<0.05.Study 2,40 participants completed test.Each participant randomly accepted HD-tDCS,TI or sham stimulation for 20 minutes,with an interval of more than 48 hours between each intervention.Before stimulation,during stimulation and after stimulation,each participant accepted the resting state functional image scan for 8minutes,20 minutes,and 8 minutes,and finally accepted the structure image scan for 6minutes.The original data is preprocessed by Dpabi5.0 software for slice timing,head movement correction,registration and standardization to MNI space,and calculates the amplitude of low frequency fluctuation(ALFF)and homogeneity(ReHo).The raw data is preprocessed by SPM12 software for slice timing,head movement correction,registration and standardization to MNI space,and calculated the seed point(the first interosseous dorsal muscle area of the primary motor cortex)and the functional connectivity(FC)of the whole brain.All values are statistically calculated by the second-order linear model of SPM12 software,the voxel threshold is set at: P<0.001,and the threshold of cluster threshold is set to: P<0.05.Results: Study 1: Compared with sham stimulation,the number of recruited motor units increased significantly after TI stimulation.Study 2: Autonomous neuronal activity(1)After stimulation,compare to Sham stimulation,HD-tDCS significantly increased ALFF in the left hemisphere: medial superior frontal gyrus;right:supplementary motor area,medial superior frontal gyrus,superior frontal gyrus,middle frontal gyrus.(2)During stimulation,compare to Sham stimulation,HD-tDCS(HD-tDCS-Sham(stim))significantly increased ReHo in the left hemisphere: the middle frontal gyrus,the superior frontal gyrus.(3)During stimulation,compare to TI,HD-tDCS(HD-tDCS-TI(stim))significantly increased ReHo in the left hemisphere:the middle frontal gyrus,the superior frontal gyrus,supplementary motor area.(4)In TI,compare to baseline,during stimulation(Stim-Pre(TI))significantly increased ReHo in the left hemisphere: paracentral lobule,precentral gyrus,postcentral gyrus,supplementary motor area,precuneus lobe;in the right hemisphere: paracentral lobule,precentral gyrus,postcentral gyrus,supplementary motor area.Whole brain functional connectivity.(1)During stimulation,compare to Sham stimulation,HD-tDCS(HD-tDCS-Sham(stim))significantly increased FC in the left hemisphere: inferior occipital gyrus,superior occipital gyrus,superior parietal gyrus;in the right hemisphere: fusiform gyrus,inferior occipital gyrus,lingual gyrus.(2)During stimulation,compare to TI,HD-tDCS(HD-tDCS-TI(stim))significantly increased FC in the left hemisphere: superior occipital gyrus,inferior occipital gyrus,lingual gyrus,Cuneus,fusiform gyrus,cerebellum;in the right hemisphere: superior parietal lobe,inferior parietal lobe.(3)In TI,compare to baseline,during stimulation(Stim-Pre(TI))significantly increased FC in the left hemisphere: superior parietal lobe,postcentral gyrus,precentral gyrus,supplementary motor area,superior frontal gyrus,middle frontal gyrus.(4)In HD-tDCS,compare to baseline,during stimulation(Stim-Pre(HD-tDCS))significantly increased FC in the left hemisphere: paracentral lobule,precentral gyrus,supplementary motor area,superior frontal gyrus,middle frontal gyrus,medial superior frontal gyrus;in the right hemisphere: supplementary motor area,medial superior frontal gyrus.(5)In HD-tDCS.compare to baseline,after stimulation(Post-Pre(HD-tDCS))significantly increased FC in the left hemisphere:middle frontal gyrus.Conclusion:(1)TI may enhance the ability of nerves recruit motor units by enhancing the Beta-band oscillations in the brain.The failure of TI and HD-tDCS to induce other changes in muscle strength and electromyographic characteristics may be caused by the sense of unknown indicators and the presynaptic effect of transcranial electrical stimulation.(2)There is a difference time effect between TI and HD-tDCS.TI has only online effect,while HD-tDCS has both online effect and after-effect.(3)The mechanism of TI and HD-tDCS is different.TI may enhance the functional connectivity in sensory motor network and ReHo in the corresponding cortex of sensory motor network,modulate the brain oscillation,then improve motor performance.HD-tDCS may increase the excitability of the motor cortex and improve motor performance by enhancing the neurons activity in the secondary motor cortex and the functional connectivity between the primary motor cortex and the secondary motor cortex.(4)The differences neuron activation pattern between online effect and after-effect in HD-tDCS.Online HD-tDCS electric field may induce a ReHo increase in the autonomous activity of neurons in the secondary motor cortex and frontal cortex on both sides.The after-effect of HD-tDCS may increases blood perfusion and improves the level of autonomous activity of neurons in the secondary motor cortex and frontal cortex on bilateral hemisphere.