Spectral dissociation of lateralized brain rhythms.

Using high resolution spectral methods to uncover neuromarkers of social, cognitive and behavioral function, we have found that hemi-lateralized pairs of oscillations such as left and right occipital alpha or left and right rolandic mu dissociate spectrally. That is, they show a shifted frequency distribution, with one member of the pair peaking at a slightly lower frequency than the other. Resorting to the analysis of EEG spatio-spectral patterns, we provide examples of dissociations in the 10Hz frequency band. Occasionally, hemi-lateralized pairs blend into medial aggregates, probably when functional interactions lead to strongly coherent dynamics through frequency-locking or metastability. Our observations support the hypothesis that homologous pairs of neuromarkers have characteristically distinct intrinsic frequencies and coordinate their oscillations into synchronous ensembles only transiently. This property could play a role in the balance of integration and segregation in the brain: spectral separation of the oscillations from homologous cortical areas allows them to function independently under certain circumstances, all the while preserving a potential for stronger interactions supported by structural and functional symmetries. Spectral dissociation (and its methodological corollary: spectral analysis with high frequency resolution) may be harnessed to better track the individual power of each member of a hemi-lateralized pair and their respective time-course, leading to enhanced internal validity and reproducibility of research on neural oscillations. Resulting insights may shed light on the functional interaction between homologous cortices in studies of attention (alpha), e.g. during perceptual and social interaction tasks, and in studies of somatomotor processing (mu), e.g. in bimanual coordination and neuroprosthetics.