40Hz

My early work as a postdoc in the group of Wolf Singer at the MPI for Brain Research (Frankfurt) aimed at testing the hypothesis that correlated firing of neurons may provide a solution to the problem of integrating distributed information in the brain. Using the visual system as a model, we obtained substantial evidence supporting this „temporal binding model“. My colleagues and I observed synchronized firing of neurons within visual cortical regions, between cortical areas and even between the two cerebral hemispheres. Furthermore, we were able to demonstrate that neural synchrony in visual cortex depends on whether the cells are actually responding to the same object. In particular, we studied the properties and stimulus-dependence of neuronal gamma-band oscillations, which reflect the coherent activity of local neuronal groups and are frequently associated with the occurrence of synchrony between spatially separate cortical sites.

In 1996, I received a fellowship of the DFG Heisenberg Program, which enabled me to establish an independent research group at the MPI for Brain Research. In the following years, the work of my group made key contributions to demonstrating a functional role for oscillatory neural activity and to establishing a relation of neural synchrony to perceptual and sensorimotor integration. In addition, we provided the first evidence for a specific relation between neural synchrony and visual awareness. This work has gained impact in the debate about neural correlates of consciousness, which I explored as a Daimler-Benz Fellow at the Institute for Advanced Study Berlin during the winter term 1997-1998.

Between 2000 and 2002, I joined the Institute for Medicine at the Research Center Jülich to set up a newly established „Cellular Neurobiology Group“. The facilities at Jülich opened up the possibility to broaden the scope of my research, now including EEG- and fMRI-studies and intraoperative microelectrode studies in humans in addition to the recordings in animals. A key topic that we started to address in these studies was the top-down modulation of oscillatory neural dynamics.

In 2002, I accepted an offer for the chair of neurophysiology at the University Medical Center Hamburg-Eppendorf (UKE). Within a few years, I established a new research program in systems and cognitive neurosciences at the Dept. of Neurophysiology and Pathophysiology. This included the implementation of a BMBF-funded whole-head MEG facility, as well as of labs for EEG recordings, animal studies, and for intraoperative microelectrode studies in patients. This broad spectrum of approaches is also reflected in a highly interdisciplinary composition of my institute that accommodates scientists with backgrounds in psychology, biology, medicine, physics, computer science and engineering.

Using EEG and MEG in combination with advanced source modeling techniques, we have been able to provide novel evidence for an importance of neuronal oscillations and neural synchrony for perceptual and cognitive processes. The role of oscillatory activity in perception was addressed in source-level studies on visual, auditory and pain systems. An important focus of my work in the past ten years, which has been supported by an ERC Advanced Grant, has been on studying neural dynamics in multisensory processing. Looking at the interaction of visual, auditory and tactile systems, we have been able to obtain novel evidence for a role of oscillations and neural coherence for crossmodal integration of information. Our studies on multisensory processing in the human brain are complemented by studies in animals, allowing a more detailed analysis of dynamic interactions at the level of small populations or single-cell activity. In a number of human studies we have addressed the modulation of sensory processing by factors like emotion and attention. Furthermore, we have been able to show that coherent oscillations are relevant for decision-making and for the emergence of conscious states in the human brain. Conceptually, this has led us to the hypothesis that there may be generic „spectral fingerprints“ of specific cortical computations.

Another major focus of my work is on sensorimotor interactions, both in cortical and cortico-subcortical networks. We have addressed this issue in EEG and MEG studies both in healthy human participants and in patients with movement disorders, providing evidence for a role of oscillatory activity in sensorimotor remapping and in predictive timing functions. Furthermore, we employ intraoperative recordings during surgery for deep brain stimulation to study altered neuronal dynamics and coupling in patients with Parkinson’s disease or dystonia. Complementing the research in patients, we have also studied cortex-basal ganglia interactions and their pathological alteration in rodent models.

Furthermore, my group has pioneered novel methods and concepts for the electrophysiological analysis of functional connectivity. These developments are motivated by our interest in data-driven approaches for connectivity analysis, as well as by the need to obtain results that are robust against artefacts resulting, e.g., from volume conduction that strongly confound connectivity measured by EEG or MEG. Using these novel approaches we have characterized functional networks defined by envelope coupling in the healthy brain. Moreover, we have investigated ongoing and task-related connectivity in diseased brains, leading to novel findings on functional connectivity in patients with Parkinson’s disease, multiple sclerosis, schizophrenia and autism-spectrum disorder, as well as in participants with altered networks after early sensory deprivation. These novel methodologies and the resulting observations have led to the proposal of different types of intrinsic coupling modes (ICMs), which interact across multiple spatiotemporal scales. 

Another aspect of critical interest is to work towards more causal evidence for a role of oscillations and neural coherence by interventions that allow specific entrainment of neural dynamics. In our human studies, we therefore use transcranial alternating current stimulation (tACS). In a number of recent studies we have also made substantial contributions to validation of tACS as a tool for network modulation. Recently, we have been able to provide critical evidence for the efficacy of tACS in frequency- and phase-specific modulation of oscillations and functional coupling. Furthermore, we use optogenetic approaches for modulation of network dynamics in animal models. 

Beyond our main focus on coupling and network dynamics, we have pursued application-oriented approaches in the development of novel types of non-invasive brain-computer-interfaces. Furthermore, we have made major contributions to research in action-oriented cognition and, more recently, to action-oriented concepts of social cognition, which we study under the aspect of sensorimotor coupling between interacting subjects, extending our concepts on coupling modes to the interpersonal case.