Dr Til Ole Bergmann | On the function of neuronal oscillations: insights from transcranial brain stimulation and electrophysiology

Neuronal oscillations are a ubiquitous feature of brain activity, observed across species, neuronal structures, and behavioral states. They are believed to rhythmically organize neural activity across multiple temporal and spatial scales and thereby orchestrate local information processing as well as communication between brain structures. The hierarchical nesting of specific oscillatory frequencies in large-scale neuronal networks may therefore provide the basic computational principles mediating a plethora of cognitive functions. Consequently, aberrant oscillatory activity is frequently associated with neuropsychiatric and neurological conditions. Electrophysiological recording methods, such as electro- and magnetoencephalography (EEG/MEG), serve well to non-invasively study neuronal oscillations in humans with excellent temporal and good spatial resolution. However, the information obtained with these techniques remains correlative, while direct manipulation of neural activity is needed to reveal the actual relevance and causal contribution of neuronal oscillations for cognition. Transcranial magnetic stimulation (TMS) and transcranial current stimulation (TCS) can be combined with EEG and MEG, either concurrently (online) or consecutively (offline), to non-invasively manipulate and measure neuronal oscillations in the human brain. Online approaches, assessing the immediate neural response to stimulation, can be used to (i) quantify neuronal network properties such as excitation, inhibition, or connectivity in a phase and amplitude specific manner, (ii) interfere with ongoing spontaneous or task-related oscillatory activity, or (iii) modulate the level and timing of neuronal oscillations. In contrast, offline approaches can be utilized to either (iv) inhibit or (v) facilitate local neuronal excitability via the induction of synaptic plasticity, assessing its subsequent effects on neuronal oscillations. I will illustrate these different approaches by examples of my own work on sleep-dependent memory consolidation and visuospatial attention. I will also introduce the novel approach of open- and closed-loop brain state-dependent brain stimulation, which allows to trigger TMS/TCS in realtime by the expression of specific oscillatory brain states of interest and thereby provides a unique opportunity to causally interact with ongoing oscillatory activity to study its role in information processing and synaptic plasticity.