title: EEG oscillations: From correlation to causality.
abstract: Already in his first report on the discovery of the human EEG in 1929, Berger showed great interest in further elucidating the functional roles of the alpha and beta waves for normal mental activities. Meanwhile, most cognitive processes have been linked to at least one of the traditional frequency bands in the delta, theta, alpha, beta, and gamma range. Although the existing wealth of high-quality correlative EEG data led many researchers to the conviction that brain oscillations subserve various sensory and cognitive processes, a causal role can only be demonstrated by directly modulating such oscillatory signals. In this review, we highlight several methods to selectively modulate neuronal oscillations, including EEG-neurofeedback, rhythmic sensory stimulation, repetitive transcranial magnetic stimulation (rTMS), and transcranial alternating current stimulation (tACS). In particular, we discuss tACS as the most recent technique to directly modulate oscillatory brain activity. Such studies demonstrating the effectiveness of tACS comprise reports on purely behavioral or purely electrophysiological effects, on combination of behavioral effects with offline EEG measurements or on simultaneous (online) tACS-EEG recordings. Whereas most tACS studies are designed to modulate ongoing rhythmic brain activity at a specific frequency, recent evidence suggests that tACS may also modulate cross-frequency interactions. Taken together, the modulation of neuronal oscillations allows to demonstrate causal links between brain oscillations and cognitive processes and to obtain important insights into human brain function.
authors: Experimental Psychology Lab, Department of Psychology, Cluster of Excellence "Hearing4all", European Medical School, Carl von Ossietzky Universität, 26111 Oldenburg, Germany; Research Center Neurosensory Science, Carl von Ossietzky Universität, 26111 Oldenburg, Germany.
authors: Christoph S
authors: CS
authors: Herrmann
authors: Experimental Psychology Lab, Department of Psychology, Cluster of Excellence "Hearing4all", European Medical School, Carl von Ossietzky Universität, 26111 Oldenburg, Germany; Research Center Neurosensory Science, Carl von Ossietzky Universität, 26111 Oldenburg, Germany. Electronic address: daniel.strueber@uni-oldenburg.de.
authors: Daniel
authors: D
authors: Strüber
authors: Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors: Randolph F
authors: RF
authors: Helfrich
authors: Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors: Andreas K
authors: AK
authors: Engel
mesh_terms: D001683:Biological Clocks / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D058256:Brain Waves / Q000502:physiology*; D004569:Electroencephalography; D006801:Humans; D065908:Transcranial Direct Current Stimulation
keywords: Brain oscillations; EEG; Electroencephalography; Neuronal entrainment; Repetitive transcranial magnetic stimulation (rTMS); Transcranial alternating current stimulation (tACS)