Theoretical and experimental study of P300 ERP in the context of Brain-computer interfaces. Part I: Study and analysis of functional connectivity methods.

Abstract

The analysis of connectivity in brain networks has been widely researched and it has been shown that certain cognitive processes require the integration of distributed brain areas. Functional connectivity attempts to statistically quantify the interdependencies between these brain areas. For this study, an analysis of functional connectivity in an ERP context, more specifically on the P300 component using the Granger Causality metric was proposed. To this end, an analysis method is proposed which consists in quantifying the causality in the P300 signal and the non-P300 signal using the MVCG toolbox to determine if there are differences between the two results obtained. In this respect, a dataset from a Brain-Computer Interface (BCI) based on P300 is analyzed. Causality is determined in overlapping windows calculated from the signals under three aspects: i) Using standard electrodes, ii) Using electrodes selected by Bayesian Linear Discriminant Analysis and exhaustive search by forward selection (BLDA-FS), and iii) Using electrodes selected by the coefficient of determination (r2). Based on this analysis, it is shown that the Granger Causality metric is valid to show the existence of a significant connectivity difference between the P300 signal and the non-P300 signal. This measure shows higher connectivity values for the P300 signal and lower connectivity values for the non-P300 signal. Among the three approaches considered, the standard electrodes and the electrodes selected with BLDA-FS were found to be more discriminative in showing differences between P300 and nonP300 connectivity. Furthermore, through this study, it was possible to differentiate the level of functional connectivity between subjects with cognitive disabilities and nondisabled subjects, observing that the measured functional connectivity was higher in subjects without an underlying cognitive pathology. Studying functional connectivity with Granger Causality may help to incorporate this information as new features that allow better detection of the P300 signal and consequently improve the performance of P300-based BCIs.