Research On Central Proprioceptive Response Induced By NMES-evoked Finger Muscle Contraction

Proprioception plays a key role to human hand to perform flexible and precise movements.Lack of proprioception is an important problem significantly affecting the reconstruction of motor function in hand,which has become a main reason for rejecting the use of myoelectric hand prosthesis.Therefore,providing effective artificial proprioceptive feedback has become one of the hot topics in hand prosthetic control.Muscle spindle is the main sensory receptor of limb movement.Muscle contraction evoked by neuromuscular electrical stimulation(NMES)above the motor threshold can activate muscle spindle to generate proprioceptive afferent volley,ascending to the central nervous system(CNS)to activate the excitatory activity of sensorimotor cortex,and then evoke the corresponding limb sensations.However,it is not clear how CNS responses to NMES-evoked muscle contractions and its proprioceptive information above motor threshold.Meanwhile,hand amputation will cause the changes of functional reorganization of the motor ouput and sensory input pathways and central nerval function of the residual limb.How the loss of proprioceptive information of the distal joint caused by hand amputation affects the central response pattern to NMES-evoked muscle contraction at the residual limb is also unclear.In order to explore the modulation role of NMES above motor threshold evoking muscle contraction in fore limb on central proprioceptive response pattern.Supported by the National Natural Science Foundation of China(NSFC31771069)and China Scholarship Council(201906050128),this thesis performed the following research work:(1)The differences of muscle contractions evoked by four NMES patterns in controlling the same joint movements were evaluated using event-related desynchronization(ERD)in the Beta band of the sensorimotor cortex.The results showed that compared to conventional pulses(CP),modulated pulses(MP),especially MP with long pulse width,induces significantly stronger Beta ERD in sensorimotor cortex(),indicating coding NMES pulses can modulate central kinesthetic response.Moreover,a new quantitative index for Beta oscillation activities was firstly proposed in this thesis revealed that the reason MP could promote central kinesthetic response is increasing the central recruitment contribution to evoked muscle contraction,that is,activated muscle spindle afferent fibers to generate more sensory volleys,and thus enhancing Beta activities in the sensorimotor cortex.These results indicate that the coding pattern of the stimulation pulses is expected to improve the regulation of NMES above motor threshold on muscle contraction on the residual limb muscles,and then to induce a more natural proprioception.(2)The model of acute hand loss was established successfully,and Beta ERD and adaptive directed transfer function(ADTF)were used to explore the local and global responses of Beta oscillations in the sensorimotor cortex induced by NMES-evoked finger movements and muscle contractions using EEG signals.The results showed that after INB,Beta ERD of contralateral sensorimotor cortex and network properties induced by NMES-evoked muscle contraction were significantly weaker than those before INB,but the change trend was similar to that induced by NMES-evoked finger movements before INB,and their similarity coefficients were 0.6531 ± 0.21(clustering coefficient)and 0.8447 ± 0.06(global efficiency),respectively.What’s more,NMES-evoked finger movements resulted in significantly stronger Beta ERD and network connections in the contralateral sensorimotor cortex.After hand loss,the ipsilateral sensorimotor cortex showed significantly stronger Beta ERD and network connections during NMES-evoked muscle contraction,that is,this is the compensatory dynamic response pattern of Beta oscillations in ipsilateral sensorimotor cortex.It will contribute to the transformation of central response from ipsilateral central nervous function compensation to normal contralateral central nervous feedback response through the mudulation of NMES above the motor threshold on the muscles of the residual limb.(3)The dynamic changes of human hand movements reflect the time variability of muscle contraction.In this thesis,NMES with different stimulation durations was designed to evoke muscle contraction of finger extensor,recorded and analyzed NMES-evoked muscle contraction,finger movement(Before INB)and EEG signals in sensorimotor cortex.EEG source analysis and granger causality network were used to study the neural responses in sensorimotor cortex induced by NMES-evoked finger movements and muscle contractions from local source activities and global networks respectively.The results showed that the angular acceleration of NMES-evoked finger movements at different periods was linearly correlated with the characteristic time and corresponding characteristic values of Beta ERD in source activities of the contralateral sensorimotor cortex,and the correlation levels were in the descending order of contralateral somatosensory cortex(BA3a L),contralateral motor cortex(BA4p L)and contralateral premotor cortex(BA6L).The clustering coefficient and global efficiency of sensory-motor cortex source network were negatively and positively correlated with the angular acceleration respectively.This provides an objective criteria to desgin the duration of electrical stimulation pulses more reasonably when NMES evoke hand proprioception.Further source network analysis showed that the contralateral sensorimotor cortex source network during NMES-evoked finger movements presented a down-top feedback mode.What’s more,after hand joint were blocked,NMES-evoked muscle contractions induced Beta ERD response patterns and network properties similar to those before INB.Ipsilateral Beta ERD in sensorimotor cortex and network connections was significantly enhanced,further indicating that ipsilateral sensorimotor cortex synergistically compensated for the proprioceptive response during NMES-evoked muscle contraction.In conclusion,the value of this thesis lies in using INB technology for the first time,to explore the proprioceptive neural response regulated by NMES-evoked muscle contraction and clarify its intrinsic neurophysiological mechanism,combined with multilevel EEG analysis method.It provides a new method and electrophysiological reference for the improvement and evaluation of the central motor perception ability of hand amputees and the research on the proprioceptive feedback for EMG-controlled hand prosthesis.