EEG COHERENCE OR EEG CORRELATION

In view of the widespread use of electroencephalographic correlation ( r) and coherence (Coh) analyses in studying brain functional relations hips, it seems important to illustrate results yielded by both methods . Although they are considered as equivalent, they show important diff erences. Results obtained from r and Coh were compared using: (a) 2 Hz sinusoidal signals, where phase and amplitude were artificially manip ulated and, (b) Coh and r spectra obtained: between each pair of deriv ations (C3, C4, F3, F4, T3 and T4) from wakefulness, stage 2, stage 4 and paradoxical sleep (n = 8). The following results were obtained: si gnificant Pearson product-moment coefficients were obtained between r and Coh spectra in the range of 0.86 to 0.96 for interhemispheric and 0.60 to 0.90, for intrahemispheric pairs; as a result of principal com ponent analyses, the same three frequency bands were formed for r and Coh spectra with the exception of one single bin; similar results for r and Coh were obtained by two-way ANOVAs (physiological stages by der ivations). In conclusion, as expected, a high degree of comparability between r and Coh was observed under normal physiological conditions a nd with the use of good quality recordings.