Temporal correlations versus noise in the correlation matrix formalism: Anexample of the brain auditory response

We adopt the concept of the correlation matrix to study correlations among sequences of time-extended events occurring repeatedly at consecutive time intervals. As an application we analyze the magnetoencephalography recordin gs obtained From the human auditory cortex in the epoch mode during the del ivery of sound stimuli to the left or right car. We look into statistical p roperties and the eigenvalue spectrum of the correlation matrix C calculate d for signals corresponding to different trials and originating from the sa me or opposite hemispheres. The spectrum of C largely agrees with the unive rsal properties of the Gaussian orthogonal ensemble of random matrices, wit h deviations characterized by eigenvectors with high eigenvalues. The prope rties of these eigenvectors and eigenvalues provide an elegant and powerful way of quantifying the degree of the underlying collectivity during well-d efined latency intervals with respect to stimulus onset. We also extend thi s analysis to study the time-lagged interhemispheric correlations, as a com putationally less demanding alternative to other methods such as mutual inf ormation.