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BioMed Research International
Volume 2014, Article ID 936096, 8 pages
http://dx.doi.org/10.1155/2014/936096
Research Article

EEG Oscillatory Phase-Dependent Markers of Corticospinal Excitability in the Resting Brain

1Brain and Behaviour Research Group, School of Psychology, University of Surrey, Guildford, Surrey, GU2 7XH, UK
2Clinic for Neurology, Universitätsspital Zürich, Raemistr. 100, 8091 Zürich, Switzerland
3Brain Imaging and Neurostimulation Lab, Department of Neurology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany

Received 28 February 2014; Revised 12 May 2014; Accepted 14 May 2014; Published 11 June 2014

Academic Editor: Vincenzo Romei

Copyright © 2014 Barbara Berger et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Functional meaning of oscillatory brain activity in various frequency bands in the human electroencephalogram (EEG) is increasingly researched. While most research focuses on event-related changes of brain activity in response to external events there is also increasing interest in internal brain states influencing information processing. Several studies suggest amplitude changes of EEG oscillatory activity selectively influencing cortical excitability, and more recently it was shown that phase of EEG activity (instantaneous phase) conveys additional meaning. Here we review this field with many conflicting findings and further investigate whether corticospinal excitability in the resting brain is dependent on a specific spontaneously occurring brain state reflected by amplitude and instantaneous phase of EEG oscillations. We applied single pulse transcranial magnetic stimulation (TMS) over the left sensorimotor cortex, while simultaneously recording ongoing oscillatory activity with EEG. Results indicate that brain oscillations reflect rapid, spontaneous fluctuations of cortical excitability. Instantaneous phase but not amplitude of oscillations at various frequency bands at stimulation site at the time of TMS-pulse is indicative for brain states associated with different levels of excitability (defined by size of the elicited motor evoked potential). These results are further evidence that ongoing brain oscillations directly influence neural excitability which puts further emphasis on their role in orchestrating neuronal firing in the brain.