The Effrets Of Transcranial Direct Current Stimulation On Steady State Visual Evoked Potional

Steady-state visual evoked potential brain-computer interface(SSVEP-BCI)with short training time,high signal-to-noise ratio(SNR),and high information transfer rate(ITR)and other advantages are widely used.But "SSVEP deficit",visual stimulation-induced fatigue and less frequency of induction have limited the study of SSVEP-BCI.Transcranial direct current stimulation(t DCS)provides the possibility of improving the performance of SSVEP-BCI due to its ability to non-invasively regulate cortical excitability.In this study,single t DCS and repetitive t DCS were applied to SSVEP-BCI.The EEG data of of resting state experiment,off-line experiment of task state and on-line experiment of task state were analyzed by frequency domain analysis and brain functional connectivity analysis.The effects of t DCS on spontaneous EEG and SSVEP were studied.In this study,firstly,the,sham stimulation and anodal t DCS(2 m A,21 min)were applied to the occipital area of the subjects for investigating effects of t DCS on resting state EEG.The 5 min EEG data before stimulation,after sham stimulation,and after anodal t DCS were collected.The spectral analysis,the functional connectivity,the brain network and the corresponding statistical analysis were used for three groups of data.It was concluded that the anodal t DCS significantly improved the alpha amplitude of the parietal occipital region and the coherence and phase synchronization of the various brain regions in the alpha band.And it improved the the small-world characteristic of brain network.Secondly,the offline experiment and online experiment was carried out for obtaining the effect of single t DCS on SSVEP.In the offline experiment,EEG data in the parietal and occipital regions of three groups with SSVEP visual stimulation tasks were collected before stimulation,after sham stimulation and after anodal t DCS.The visual stimulation task of online experiment with the feedback link collected the EEG data in the parietal and occipital regions before and after anodal t DCS.Amplitudes and signal-to-noise rate of data acquired in online experiment were computed.The results of offline experiments show that t DCS has no significant effects on amplitudes and signal-to-noise rates.The results of online experiment show that t DCS significantly improves the recognition accuracy of the subjects who are unable to adapt to SSVEP-BCI system,but it had no significant effects on amplitudes and signal-to-noise rates.Finally,the effect of repetitive t DCS was researched by subjects receiving five consecutive days of sham stimulation and anodal t DCS(one week between two stimulations).Data of resting and task state before and after sham stimulation and anodal t DCS were collected,including states of both opening eyes(two minutes)and closing eyes(two minutes),and two groups of offline task state data(six minutes per group).The analysis of resting data shows that t DCS enhanced the beta activity of opening eyes,gamma activity of opening eyes and alpha activity of closing eyes in the right parietal lobe,and weakened the alpha activity of closing eyes in the middle parietal lobe.The analysis of task state data shows that repetitive t DCS significantly enchanced the average signal-to-noise ratio of the parieto-occipital lobe at 10.75 Hz and 11 Hz.TDCS can enhance alpha activity and improve the SNR of SSVEP,which is of great significance for the research and application of t DCS and SSVEP-BCI.