Our group is interested in the general mechanisms by which neuronal oscillations contribute to the organization of information flow and the gating of synaptic plasticity in the human brain. We study the role of specific oscillations for a variety of cognitive functions, such as attention and memory, and during different brain states, such as wakefulness and the various stages of sleep.
To do so, we not only combine multimodal non-invasive neuroimaging and electrophysiological techniques to characterize the oscillatory networks associated with certain neuronal processes and cognitive functions. We also use non-invasive brain stimulation techniques to directly interact with these oscillations to investigate their neurophysiological underpinnings and to manipulate them experimentally in order to unravel their causal contribution.
Attention and the gating of information flow
Alpha oscillations (8-14 Hz), are hypothesized mediate attention through the active gating of information flow in the brain by means of ‘pulsed inhibition’, i.e., the rhythmic suppression of task-irrelevant neuronal representations and the prioritization of task-relevant ones. Beside the basic neuronal mechanisms underlying the cyclic modulation of cortical excitability, we are also investigating how primary sensory alpha oscillations (visual alpha as well as sensorimotor mu-alpha) are top-down controlled (e.g., by the frontal eye fields) during voluntary shifts of attention and whether they can be entrained and modulated transcranially by means of magnetic and electrical stimulation.
Oscillations for memory consolidation during sleep
We are principally interested in the oscillations and their cross-frequency as well as inter-regional coupling subserving the encoding, consolidation/reorganization, and retrieval of (emotional) memories. These include the classical theta rhythm (4-8 Hz) during encoding and retrieval in wakefulness, as well as several sleep-specific oscillations that mediate systems memory consolidation during sleep, such the neocortical slow oscillation (< 1 Hz), thalamo-cortical sleep spindles (10-16 Hz), and hippocampal ripples (> 80 Hz) during NREM sleep, and theta (4-8 Hz) and beta (~20 Hz) oscillations during REM sleep. We are thus investigating the oscillatory mechanisms mediating the induction, consolidation, and homeostatic regulation of cortical plasticity, as well as the underpinnings of the hippocampo-neocortical dialogue.
At the German Resilience Center (DRZ), we are currently starting a new research line aiming to identify those neural networks and oscillations that mediate and regulate in particular the encoding, consolidation/reorganization, and retrieval of emotional memories, as we believe successful emotional memory updating (EMU) to be a key factor for the resilience against stress-related disorders resulting from negative life events. Sleep not only plays a fundamental role in the regulation of emotional reactivity but also for the (re-)integration of (re-)evaluated emotional memories and therefore deserves consideration in the context of resilience.
An important methodological aim of our research is to improve the combination of brain stimulation and neuroimaging both consecutively (offline) and concurrently (online), such as simultaneous TMS-EEG, TMS-fMRI, and TCS-MEG. For example, we study factors confounding the assessment of TMS-evoked EEG potentials (TEPs) and use functional/structural connectivity-informed concurrent TMS-fMRI for the transsynaptic stimulation of deeper brain structures via connected superficial cortical entry sites and proof of target engagement. Another goal is to develop and refine novel interventional approaches including brain state-dependent brain stimulation, such as EEG-triggered TMS to target specific oscillatory brain states (e.g., amplitude levels and phase angles of ongoing neuronal oscillations). Eventually, we develop open-source software solutions to support more precise and reproducible brain stimulation research and fully automated stimulation procedures.