Effect Of Transcranial Ultrasound Stimulation On Lfp-emg Coupling

Low-intensity transcranial pulsed ultrasound stimulation(TUS)is an emerging neuromodulation technique with advantages of non-invasion,good spatial resolution and deep penetration.These properties made it superior to other neuromodulatory modalities that based on the direct current,magnetism or optics,thus gained a lot of attention in the field of neuroscience and rehabilitation engineering recent years.TUS has began to be applied on many neurological disorders as a potential therapy,including stroke.Previous research has shown that TUS modulates neuronal activity in both vitro brain and vivo animal.Recently,TUS has also been demonstrated to be a safe and effective method for transient neuromodulation in human.However,the modulatory efficacy and mechanism of TUS on neuron circuits warrants further investigation,which causes limitations for its clinical application.Cortico-muscular coupling is an inherent phenomenon in motor neuron circuit,and is generally qualified by the calculating the coupling between LFP and EMG signals.It is necessary to investigate the effect of TUS on the coupling relationship between LFP and EMG,thereby revealing the TUS-induced changes of oscillatory activity between brain and muscle.Firstly,we introduced the background and meaning of this subject,and then reviewed the state of art of TUS,the significance of the coupling analysis between LFP and EMG as well as the limitations of the existing perspective for evaluating the effect of TUS.Given the deficiencies of existing research methods,this study aims to examine the effect of TUS on motor neuron circuits by analyzing the coupling relationship between LFP and EMG.We constructed the transcranial ultrasound stimulation system with synchronously LFP/EMG recording,and detailed the major devices as well as stimulation parameters.Secondly,two representative coupling analysis methods based on information theory,i.e.the mutual information(MI)and transfer entropy(TE),were introduced in the third chapter.Considering the accuracy of transfer entropy depending on the parameter selection,we presented to optimize relative parameters of transfer entropy by the hybrid particle swarm optimization(HPSO),and preliminarily verified the performance of HPSOusing a constructed numerical model.Thirdly,in order to further verify the proposed HPSO-TE,we built the neural mass model with various kinds of coupling relationship,by which the sensitiveness to coupling strength of HPSO-TE and the rebustness against noise and various delay of HPSO-TE were systematically assessed.The practicability of HPSO-TE for neural signals was also initially evaluated based on the EEG and EMG signals in human.Finally,in the ultrasound experiment,we delivered the TUS with different number of tone burst to mice motor cortex and concurrently recorded the LFP and EMG signals in mice motor cortex and tail muscle,respectively.After pre-processing,the LEP and EMG signals were analyzed by MI and HPSO-TE.The results showed that TUS could significantly improve the coupling strength between the motor cortex and terminal muscle.The coupling strength from LFP to EMG was prominently higher than the other direction,i.e.the EMG to LFP,and could be enhanced with the sonication duration.These results demonstrated that the efficacy of the MI and TE for examining the effects of TUS on motor neuron circuits,thus providing a new insight for the analyzing the neuromodulatory effects of TUS.