title: Global Neuromagnetic Cortical Fields Have Non-Zero Velocity.
abstract: Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent activity occurred in the delta, theta, alpha and beta bands of the signal in the form of large-scale waves, which propagated with a variety of velocities. Their mean speed at each frequency band was proportional to temporal frequency, giving a range of 0.06 to 4.0 m/s, from delta to beta. The wave peaks moved over the entire measurement array, during both ongoing activity and task-relevant intervals; direction of motion was more predictable during the latter. A large proportion of the cortical signal, measurable at the scalp, exists as large-scale coherent motion. We argue that the distribution of observable phase velocities in MEG is dominated by spatial filtering considerations in combination with group velocity of cortical activity. Traveling waves may index processes involved in global coordination of cortical activity.
authors.affiliation: Brain and Cognition Research Unit, KU Leuven - University of Leuven, Leuven, Belgium.
authors.forename: David M
authors.initials: DM
authors.lastname: Alexander
authors.affiliation: Brain and Cognition Research Unit, KU Leuven - University of Leuven, Leuven, Belgium.
authors.forename: Andrey R
authors.initials: AR
authors.lastname: Nikolaev
authors.affiliation: RIKEN Brain Science Institute, Wako-shi, Japan.
authors.forename: Peter
authors.initials: P
authors.lastname: Jurica
authors.affiliation: Department of Psychiatry, Psychotherapy and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Zvyagintsev
authors.affiliation: Department of Psychiatry, Psychotherapy and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Mathiak
authors.affiliation: Brain and Cognition Research Unit, KU Leuven - University of Leuven, Leuven, Belgium.|Kaiserslautern University of Technology, Kaiserslautern, Germany.
authors.forename: Cees
authors.initials: C
authors.lastname: van Leeuwen
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D060526:Magnetic Fields; D008297:Male; D008959:Models, Neurological; D013997:Time Factors; D055815:Young Adult