Spatial neuronal synchronization and the waveform of oscillations: Implications for EEG and MEG

• Published in: PLoS computational biology Vol. 15; no. 5; p. e1007055
• Main Authors: Schaworonkow, Natalie, Nikulin, Vadim V
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.05.2019; Public Library of Science (PLoS)
• Subjects: Adult; Aged; Amplitudes; Biology and Life Sciences; Brain; Brain - physiology; Brain Mapping - statistics & numerical data; Brain research; Brain Waves - physiology; Computational Biology; Computer Simulation; Constituents; EEG; Electrodes; Electroencephalography; Electroencephalography - statistics & numerical data; Electroencephalography Phase Synchronization; Engineering and Technology; Female; Harmonics; Humans; Magnetoencephalography; Magnetoencephalography - statistics & numerical data; Male; Medicine and Health Sciences; Methods; Middle Aged; Models, Neurological; Morphology; Neural oscillations; Neurology; Neurons; Neurons - physiology; Neurophysiology; Neurosciences; Observations; Oscillations; Physiological aspects; Research and Analysis Methods; Rhythms; Signal processing; Signal Processing, Computer-Assisted; Signal-To-Noise Ratio; Simulation; Synchronism; Synchronization; Young Adult; Germany
• ISSN: 1553-7358; 1553-734X; 1553-7358
• DOI: 10.1371/journal.pcbi.1007055

Neuronal oscillations are ubiquitous in the human brain and are implicated in virtually all brain functions. Although they can be described by a prominent peak in the power spectrum, their waveform is not necessarily sinusoidal and shows rather complex morphology. Both frequency and temporal descriptions of such non-sinusoidal neuronal oscillations can be utilized. However, in non-invasive EEG/MEG recordings the waveform of oscillations often takes a sinusoidal shape which in turn leads to a rather oversimplified view on oscillatory processes. In this study, we show in simulations how spatial synchronization can mask non-sinusoidal features of the underlying rhythmic neuronal processes. Consequently, the degree of non-sinusoidality can serve as a measure of spatial synchronization. To confirm this empirically, we show that a mixture of EEG components is indeed associated with more sinusoidal oscillations compared to the waveform of oscillations in each constituent component. Using simulations, we also show that the spatial mixing of the non-sinusoidal neuronal signals strongly affects the amplitude ratio of the spectral harmonics constituting the waveform. Finally, our simulations show how spatial mixing can affect the strength and even the direction of the amplitude coupling between constituent neuronal harmonics at different frequencies. Validating these simulations, we also demonstrate these effects in real EEG recordings. Our findings have far reaching implications for the neurophysiological interpretation of spectral profiles, cross-frequency interactions, as well as for the unequivocal determination of oscillatory phase.