Brain functional connectivity analysis using single trial EEG for understanding individual mechanisms

In this paper, a method has been developed to track brain functional connectivity (FC) by using cross correlation method. The EEG data was acquired from twenty subjects using oddball paradigm to examine the connectivity across brain lobes for different oddball cases. Pairwise zero lag correlation coefficient of 10-20 electrodes was computed for each segment for 20 samples and the connectivity matrices were formed. For higher strength connectivity, the matrices were thresholded. The connection between the electrodes that have correlation value higher than the specified threshold value at zero lag is plotted. We have done single trial EEG analysis for subjects for different oddball cases (Target with Response-TR, Target with no Response-TNR, No Target no Response-NTNR). Single trial analysis helps to analyse individual mechanisms, behavioral information and a systematic mapping between brain activity and stimulus information space. For target with response, high connectivity was observed for all cases in general for all segments compared with other cases. TNR has less connectivity than TR cases for all segments. High connectivity was observed only in the first segment for NTNR case. For 10-20 electrodes FC can be observed for Fz, F3, F4, C3 or C4 electrodes. C3 or C4 electrodes locations are responsible for motor planning or sensorimotor integrations in the last segment when subject responds to the target or nontarget stimuli. Hence using this method, it is possible to identify the individual differences between different oddball cases within and across subjects using single trial EEG as a function of time.