Study On Cortical Response Associated With Balance Perturbation Under The Upper Limb Assisted Standing And Normal Standing Conditions

The human balance ability is of importance to maintain stable walking,standing,and various complex movements in life.In activities of daily living,people are experiencing different balance perturbations at any time,which are great challenges for human to keep balance.The perturbations may result in human’s falling and injuries.As the author aware,there is no complete explanation for human brain’s response mechanism of balance perturbation.In order to explore the brain’s response for the balance perturbation,two experiments was designed to explore the cortical response evoked by the perturbation.In the first experiment,the experimental platform was designed to make the upper limb support force change rapidly to simulate the balance perturbation of the upper limb under upper limb assisted standing condition for rehabilitation scene of patients with balanced dysfunction.Twenty healthy subjects were recruited in this study whilst the Electroencephalogra signals(EEG),functionalnear-infrared spectroscopy signals(f NIRS),two sides of supporting force and surface electromyogram(s EMG)of smaller forearm extensors on both sides were recorded simultaneously.In the second experiment,the experimental platform was set up to apply random directional balance perturbation(front,back,left,right)with expected or unexpected conditions while the subject was in the natural standing state for the normal physiological state human.Fifteen healthy subjects participated in this study where the EEG signals and bilateral foot plantar pressures of the subjects were recorded synchronously.This paper analyzed the event-related perturbation(ERP)of EEG under different balance perturbations.Following balance perturbation onset upper limb under upper limb assisted standing condition,N1 potentials were observed with a peak latency of62.3±5.5 ms and the peak activity was located at FCz electrode with a peak amplitude of 15.6±6.1 μV,and the blood oxygen concentration in the head region of the brain was significantly reduced.The application of the balance perturbations in the natural standing state induced a P1 potential with a small amplitude,and then N1 potentials were observed with a peak latency of 193.2±14.3 ms and the peak activity was located at FCz electrode with a peak amplitude of 7.4±3.5 μV.The results showed that both balance perturbations induced N1 potential,and EEG traceability results showed that N1 potential may be related to BA38 brain region.A significant negative potential was observed 950 ms before the expected equilibrium disturbance was applied.Finally,the author did a preliminary study on the recognition of human non-equilibrium state by the ERP feature,using two different algorithms: one is based on CSP and SVM recognition algorithm,and the other is based on XDAWN and LDA recognition algorithm.The results showed that the XDAWN and LDA algorithm obtained a higher accuracy.The accuracy of non-equilibrium recognition under the balance perturbation of the upper limb assisted standing position reached up to 97.3%,and the maximum recognition rate of non-equilibrium state caused by the equilibrium disturbance under the normal standing position was 95%.In general,the thesis explored the cortical response of perturbation of balance under the upper limb assisted standing and the normal standing.The feasibility of identifying the non-equilibrium state of the human body based on the EEG response characteristics was verified in the two experiements.The experimental results provide a new theoretical and experimental basis for the development of rehabilitation techniques based on Brain-computer interface(BCI).