title: Phase synchrony among neuronal oscillations in the human cortex.
abstract: Synchronization of neuronal activity, often associated with network oscillations, is thought to provide a means for integrating anatomically distributed processing in the brain. Neuronal processing, however, involves simultaneous oscillations in various frequency bands. The mechanisms involved in the integration of such spectrally distributed processing have remained enigmatic. We demonstrate, using magnetoencephalography, that robust cross-frequency phase synchrony is present in the human cortex among oscillations with frequencies from 3 to 80 Hz. Continuous mental arithmetic tasks demanding the retention and summation of items in the working memory enhanced the cross-frequency phase synchrony among alpha (approximately 10 Hz), beta (approximately 20 Hz), and gamma (approximately 30-40 Hz) oscillations. These tasks also enhanced the "classical" within-frequency synchrony in these frequency bands, but the spatial patterns of alpha, beta, and gamma synchronies were distinct and, furthermore, separate from the patterns of cross-frequency phase synchrony. Interestingly, an increase in task load resulted in an enhancement of phase synchrony that was most prominent between gamma- and alpha-band oscillations. These data indicate that cross-frequency phase synchrony is a salient characteristic of ongoing activity in the human cortex and that it is modulated by cognitive task demands. The enhancement of cross-frequency phase synchrony among functionally and spatially distinct networks during mental arithmetic tasks posits it as a candidate mechanism for the integration of spectrally distributed processing.
authors.affiliation: Department of Biological and Environmental Sciences, University of Helsinki, FIN-00014 Helsinki, Finland. matias.palva@helsinki.fi
authors.forename: J Matias
authors.initials: JM
authors.lastname: Palva
authors.forename: Satu
authors.initials: S
authors.lastname: Palva
authors.forename: Kai
authors.initials: K
authors.lastname: Kaila
mesh_terms: D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology* / Q000528:radiation effects; D003344:Cortical Synchronization / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D007839:Functional Laterality; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods; D008606:Mental Processes / Q000502:physiology*; D008959:Models, Neurological; D009483:Neuropsychological Tests; D011336:Probability