Functional connections among cortical regions: topography of EEG coherence.

The covariance among EEG signals can be examined with coherence analysis. Evidence that the right hemisphere has a more diffuse receptotopic organization than the left, together with evidence that it may have a higher proportion of white to gray matter, suggests a high degree of functional connectedness among right hemisphere regions. To determine whether this is reflected in greater EEG coherence among right than left hemisphere locations, we constructed a matrix of cross-spectra among all unique pairs of EEG channels in an 8-channel montage, then statistically de-structured this matrix to examine multiple coherences and both inter- and intra-hemispheric partial multiple coherences. Analyses on data from the resting EEGs of 14 right-handed men examined weekly for several months showed higher coherences for right hemisphere locations. For the inter-hemispheric partial multiple coherences the frontal lobe values were also higher on the right, but the occipital inter-hemispheric coherences were higher on the left. These asymmetries have interesting parallels with anatomical asymmetries of the human cortex and may have functional implications.