title: Non-Sinusoidal Activity Can Produce Cross-Frequency Coupling in Cortical Signals in the Absence of Functional Interaction between Neural Sources.
abstract: The analysis of cross-frequency coupling (CFC) has become popular in studies involving intracranial and scalp EEG recordings in humans. It has been argued that some cases where CFC is mathematically present may not reflect an interaction of two distinct yet functionally coupled neural sources with different frequencies. Here we provide two empirical examples from intracranial recordings where CFC can be shown to be driven by the shape of a periodic waveform rather than by a functional interaction between distinct sources. Using simulations, we also present a generalized and realistic scenario where such coupling may arise. This scenario, which we term waveform-dependent CFC, arises when sharp waveforms (e.g., cortical potentials) occur throughout parts of the data, in particular if they occur rhythmically. Since the waveforms contain both low- and high-frequency components, these components can be inherently phase-aligned as long as the waveforms are spaced with appropriate intervals. We submit that such behavior of the data, which seems to be present in various cortical signals, cannot be interpreted as reflecting functional modulation between distinct neural sources without additional evidence. In addition, we show that even low amplitude periodic potentials that cannot be readily observed or controlled for, are sufficient for significant CFC to occur.
authors.affiliation: Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Edden M
authors.identifier: http://orcid.org/0000-0001-6704-0013
authors.initials: EM
authors.lastname: Gerber
authors.affiliation: Helen Wills Neuroscience Institute, University of California, Berkeley, California.
authors.forename: Boaz
authors.initials: B
authors.lastname: Sadeh
authors.affiliation: Helen Wills Neuroscience Institute, University of California, Berkeley, California.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ward
authors.affiliation: Helen Wills Neuroscience Institute, University of California, Berkeley, California.|Department of Psychology, University of California, Berkeley, California.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Knight
authors.affiliation: Department of Psychology, and Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Leon Y
authors.initials: LY
authors.lastname: Deouell
mesh_terms: D001921:Brain / Q000502:physiology*; D058256:Brain Waves; D003198:Computer Simulation; D004569:Electroencephalography; D055724:Electrophysiological Phenomena; D006801:Humans; D008959:Models, Neurological; D015233:Models, Statistical; D012815:Signal Processing, Computer-Assisted