Mechanistic Studies Of Steady-state Visual Induced Response Based On Brain Network Reconfiguration

Because of high signal-to-noise ratio and strong robustness,steady-state visual evoked potentials(SSVEP)have been widely used in studies of cognitive neuroscience and neural engineering.Although recent studies have indicated that the response of SSVEP is associated with multiple brain regions,the underlying generation mechanisms of steady-state visual induced response are still not fully understood.In this thesis,we applied the brain network reconfiguration analysis method to investigate the response mechanism of SSVEP under both the fundamental frequency and the second harmonics.Our main results are summarized as follows:1.We studied the effects of the network reconfiguration from the resting-state network to the stimulus-evoked network on the response of the SSVEP under the fundamental frequency and the second harmonic,respectively.During the network reconfiguration from the resting-state network to the stimulus-evoked network,most of the connections are increased in the brain network.Furthermore,we observed that the connections showed significant correlations with SNRs mainly existed between the parietal–occipital and frontal regions.By performing the Pearson’s correlation analysis between SNR and the three network reconfiguration metrics indexes,we found that SNR is significantly positively correlated with both network distance and mean connection alteration.This indicates that brain networks topology are changed through network reconfiguration and the connections between brain regions become stronger.Besides,the SNR also shows significant positive correlation with the clustering coefficient,global efficiency and local efficiency,but exhibits significant negative correlation with the feature path length,implying increased information transmission efficiency in the brain.Compared with the resting-state network,the stimulus-evoked network generates more efficient topological structure through network reconfiguration,thus resulting in a relatively larger SSVEP response.2.In the same periodic flash stimulation experiment,the SSVEP responses of different subjects showed tremendous differences at the 7.5 Hz,12 Hz and 15 Hz stimulation frequencies.The network distances between the resting-state network and the stimulus-evoked network varied greatly among the 21 subjects,indicating that the change of network topology are different among subjects.The differences in the mean connection alteration showed that the closeness of connections among different regions in the brain varied differently during the network reconfiguration.The alterations in the four topological properties between the two types of networks reflect the change level of the local and global information transfer efficiency.Accordingly,we postulate that different subjects have different levels of brain network reconfiguration capability even driven by the same external-driven stimulus.Theoretically,the differences in the capability of network reconfiguration from the resting-state to the stimulus-evoked state lead to a large difference in the response amplitude of the SSVEP among different subjects.In conclusion,our above results show that the steady-state visual evoked response is the consequence of contact and cooperation among multiple brain regions.Network reconfiguration is a key factor affecting the strength of SSVEP response.The main way of this impact produced is that the new network topology changed greatly in both global and local efficiency after the network reconfiguration.The higher the information transfer efficiency of the new network topology generated by the network reorganization,the stronger and faster the contact between the brain regions will be,and then promote the generation of SSVEP response.