Cortico-cortical associations and EEG coherence: a two-compartmental model.

EEG coherence was computed from 19 scalp locations from 189 children ranging in age from 5 to 16 years. Tests of spatial homogeneity of EEG coherence were conducted by comparing EEG coherence as a function of different interelectrode distances in the anterior-to-posterior versus posterior-to-anterior directions. Highly significant inhomogeneities were observed since greater coherence was present in the anterior-to-posterior direction than in the posterior-to-anterior directions. Greater coherence was also present in frontal derivations than in posterior derivations and from the right hemisphere in comparison to the left hemisphere. These data indicate that at least two separate sources of EEG coherence were present (1) coherence produced through the action of short length axonal connections, and (2) coherence produced through the action of long distance connections. Measures of phase delays as a function of interelectrode distance supported the development of a 'two-compartmental' model of EEG coherence in which different features of coherence are produced by different length fiber systems. Based on this model a number of hypotheses were developed to explain differences in connectivity between left and right hemispheres and frontal versus occipital cortex.