Study On SSVEP Response Mechanism Based On EEG And FMRI And Regulation Mechanism Of TACS On SSVEP

When the brain is subjected to external visual stimulation of a constant frequency,the neural network that is consistent with the stimulation frequency or harmonic frequency will resonate,resulting in significant changes in the electrical activity of the brain,thus generating Steady-state visual evoked potential(SSVEP).Because of its high signal-to-noise ratio,it has become the most typical experimental paradigm of Brain Computer Interface(BCI).On the other hand,this kind of exogenous brain electricity can be induced as a mediator to study the effect of brain stimulated signal modulation.Transcranial alternating current stimulation(tACS)is a promising non-invasive brain conditioning technique that can directly affect neural activity and induce brain state changes.In this paper,SSVEP and tACS were combined.First,EEG and magnetic resonance signals were collected to explore the correlation between SSVEP response and brain functional network,and then phase specific modulation of SSVEP was studied based on tACS.Specifically include the following three points:(1)In the study of exploring SSVEP response based on EEG,the differences in the response of the large brain under different stimulation frequencies in alpha band were observed.The results showed that the fundamental frequency doubling response of alpha band stimulation was superior in frequency doubling below 10 Hz,while the fundamental frequency above 10 Hz was superior.This may have something to do with the brain’s endogenous oscillating state;Inter-Trial Coherence(ITC),as an index of brain response stability,has a positive effect on SSVEP classification Accuracy and information transfer rate(ITR),and shows a faster response phase-lock rate with increasing frequency of stimulation.(2)In the study of the association between SSVEP and brain functional network based on magnetic resonance,the combined analysis of EEG magnetic resonance data showed that the difference of SSVEP fundamental frequency and frequency multiplier response was reflected in VN1 and VN2 networks;The ITC index of SSVEP response is related to the coordination of multiple networks in the brain,that is,the ITC of SSVEP response produced when the brain is stimulated by a fixed frequency flash is positively correlated with the primary visual cortex,and negatively correlated with the left frontoparietal network and the post-default mode network.(3)Based on the phase specific modulation effect of transcranial alternating current stimulation on steady-state visual induction,the results show that SSVEP can be specifically modulated by tACS after different phase conditions of tACS stimulation.The phase of the stimulus with the best modulation effect(the photostimulus-electrical phase difference)is related to the photostimulus-SSVEP phase difference of the subject,and the phase difference of the best effect is different between different participants.In general,this paper collaboratively studies the response mechanism of SSVEP,a classical EEG paradigm,by combining EEG magnetic resonance data,and adopts multiphase intermittent tACS regulation scheme,and finally finds that tACS can phase specific modulate SSVEP.