The central focus of my research is the dynamics of brain networks which I address at multiple spatial and temporal scales using neurophysiological approaches in humans and animals. My key goal is to relate local neural dynamics (particularly oscillations) and dynamic coupling across neural populations to sensorimotor and cognitive functions. To this end, I study the temporal dynamics of neural activity and neural interactions in the context of sensory processing, multisensory and sensorimotor integration, emotion, decision making, attention and consciousness.
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 recent work, supported by an ERC Advanced Grant, is 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 also study 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. These novel approaches are currently applied for the study of resting-state and task-related connectivity in healthy humans. Moreover, we employ these methods for the study of network alterations in patients with multiple sclerosis, schizophrenia and autism, as well as for studies on altered networks after early sensory deprivation.
Another aspect of critical interest is to work towards more causal evidence for a role of oscillations and neural coherence by interventions that allow frequency-specific entrainment of neural dynamics. In our human studies, we have therefore started to use transcranial alternating current stimulation (tACS). In a number of recent studies we have successfully combined tACS with concurrent EEG recordings, providing evidence that frequency-specific entrainment of oscillations can lead to specific perceptual effects.
My group is involved in cooperations with many partners at institutions in Germany and abroad, including:
- in-vivo neurophysiology groups (Wolf Singer, Frankfurt; Hagai Bergman, Jerusalem)
- EEG and MEG groups (Christoph Herrmann, Oldenburg; Brigitte Röder, Hamburg; Pascal Fries, Frankfurt; Mark Woolrich, Oxford)
- fMRI groups (Christian Büchel, UKE; Rainer Goebel, Maastricht; Maurizio Corbetta, St. Louis)
- neurology departments (Christian Gerloff, UKE; Peter Brown, Oxford)
- neurosurgery departments (Manfred Westphal, UKE)
- computational neuroscience groups (Peter König, Osnabrück; Claus Hilgetag, UKE)
- brain-computer interface groups (Bo Hong, Beijing)
- robotics groups (Jianwei Zhang, Hamburg; Danica Kragic, Stockholm; Paul Verschure, Barcelona)