Research On The Effect And Mechanism Of Low Intensity Ultrasound Stimulation On Neuromuscular System

As an emerging non-invasive neuromodulation technology,low intensity transcranial ultrasound stimulation(LITUS)has the characteristics of high spatial resolution,large stimulation depth and reversible effect,which has become a research hotspot in the field of neurorehabilitation engineering and can be used to treat and recover limb motor dysfunction.However,the essential role of LITUS in modulating the neuromuscular system and the underlying mechanism are not yet clear,and its application and evaluation in clinical treatment and rehabilitation still has certain limitations.Functional corticomuscular coupling(FCMC)can describe the functional connectivity and information interaction between the brain and muscles in the neuromuscular system at multiple levels,which is beneficial to understanding the deep mechanism of LITUS modulating the neuromuscular system and provides a new perspective for evaluating the effects of LITUS on the neuromuscular system.The purpose of this research is to study the neuromodulatory effects and mechanisms of LITUS on the neuromuscular system.From the two aspects of brain rhythm analysis and FCMC analysis,the effects of LITUS on the neural activities of motor cortex and the information interaction between motor cortex and peripheral muscles were studied.This research established a neural mass dynamic model based on bio-effects of ultrasound modulation,and deeply studied the partial frequency band characteristics of phase synchronization coupling of the neuromuscular system under LITUS,and expanded to analyze the partial frequency band characteristics of neuromuscular energy coupling and directional coupling under LITUS.The underlying mechanism of information interaction between the motor cortex and corresponding muscles provided a theoretical basis for the application of ultrasound neuromodulation to the rehabilitation of limb motor function.The work of this thesis mainly includes the following four parts:(1)Based on the physical and biological principles of LITUS,a synchronous LFP-EMG acquisition experimental platform for LITUS was designed and built.The mice were used to carry out the ultrasound modulation for tail motor cortex,to achieve precise positioning of ultrasound stimulation and synchronous acquisition of LFP and EMG signals,which provided data support for studying the neuromodulatory effects and mechanisms of LITUS on the neuromuscular system.(2)Regarding to the brain rhythm characteristics of the motor cortex under LITUS,based on the bio-effect of LITUS,a dynamic model of the brain rhythm in the motor cortex under LITUS was established in the scale of neural population.The passive membrane time constants were selected as the "bio-effect factor" connecting the ultrasound effect and neural activity to simulate the ultrasound evoked response(UER)under different ultrasound parameters.On this basis,the dynamic simulation of UER at different stimulation stages was realized through the strategy of ?segmentation simulation?.(3)Regarding to the phase synchronization characteristics of information transmission between the motor cortex and muscles under LITUS,this thesis proposed the time-frequency phase-locked value(TFPLV)method based on the phase-locked value(PLV)method.The partial frequency band characteristics of FCMC under different ultrasound parameters were studied from the perspective of LFP-EMG phase synchronization.This method completed the frequency domain decomposition of the LFP of the motor cortex and tail EMG signals using the narrowband filter.Then,the PLVs between narrowband LFP and EMG signals were calculated to achieve a quantitative description of neuromuscular phase synchronization at different frequencies under LITUS.By analyzing the partial frequency band characteristics of phase synchronization under different ultrasound parameters,the effect of ultrasound parameters on neuromuscular phase coupling was studied,which revealed that LITUS has the ability to modulate the information transmission in the neuromuscular system.(4)The coherence analysis methods were introduced to study the energy coupling and directional coupling characteristics between the motor cortex and muscle under LITUS.First,the inter-trial coherence(ITC)analysis method was used to study the event-related synchronization characteristics of LFP and EMG signals under LITUS.Then,based on the motor control theory of the neuromuscular system,the coherence analysis and directed coherence analysis methods were applied to study the neuromodulatory effect of LITUS on neuromuscular energy coupling and directional coupling characteristics,respectively.Finally,by analyzing the partial frequency band characteristics of coherence and directed coherence under different ultrasound parameters,the effects of ultrasound parameters on neuromuscular energy coupling and directional coupling were studied,which revealed the neural information causality between the motion control and sensory feedback in the neuromuscular system under LITUS.