The key theme of my research is the large-scale dynamics of cortical and subcortical networks, which we address by combining electrophysiological and neuroimaging methods. My specific focus lies on the study of functional and effective connectivity in brain networks. We try to demonstrate and understand the possible functional role of dynamic large-scale coupling for perception, cognition and action. To this end, we also aim at testing hypotheses on causal mechanisms by modulation of networks and connectivity. Furthermore, we have a strong interest in the pathophysiological relevance of neural synchrony and changes of large-scale coupling in brain disorders.
Using EEG and MEG, we investigate the relation between functional connectivity and perceptual, sensorimotor, attentional and working memory processes in the human brain. Furthermore, we investigate the relation between neural synchrony and changes in level and contents of consciousness. An important methodological focus is the improvement of data-driven methods for the analysis of functional coupling. A major focus of our research, currently funded by the ERC Advanced Grant Multisense – "The merging of the senses: understanding multisensory experience“, addresses the mechanisms of multisensory interactions in the human brain. This work is also part of the newly established SFB TRR 169 „Cross-modal learning“, where we address the role of oscillatory activity for multisensory predictive processing using a combination of MEG measurements and computational modelling. Furthermore, we have recently begun to extend our coupling analyses to two-brain interactions. In the EU-funded project „socSMCs – Socializing sensorimotor contingencies“ we study the grounding of social cognition in interpersonal sensorimotor coordination. We aim for quantifying social interaction by applying coupling measures and information-theoretic measures to hyperscanning EEG and motion tracking data in joint action paradigms.
Neural Coupling Modes
One of the key goals of our studies on brain networks is to test the functional relevance of different types of coupling reflecting dynamic coordination at different spatial and temporal scales. Our hypothesis is that two distinct types of intrinsically generated coupling can be distinguished which may reflect to operation of different coupling mechanisms. One type arises from phase coupling of band-limited oscillatory signals, whereas the other results from coupled aperiodic fluctuations of signal envelopes. We are now systematically investigating, in various datasets, the spatial and temporal features of these two coupling modes and potential differences in their association with sensory and cognitive processing. These analyses also aim at deriving spectral fingerprints of connectivity in different subnetworks of the brain. Another important aspect is to go beyond temporally averaged connectivity measures and to characterize the temporal variability of connectivity within and across subnetworks. A related aspect is the study of bottom-up vs. top-down modes of coupling and the testing of frequency-specific communication channels for predictive top-down processing.
As a large number of neurological and psychiatric disorders involve malfunctions in brain networks, we have a strong interest in translational application of our network research. In cooperation with the UKE departments of neurosurgery and neurology, intraoperative microelectrode recordings are performed in the basal ganglia and thalamic nuclei. The recordings are carried out in patients with Parkinson’s disease, dystonia or essential tremor to improve the depth localization of the target sites for deep brain stimulation. Data collected during these measurements are used to test hypotheses on the pathophysiological role of neural synchronization phenomena in these disorders. At the same time, this setting provides us with the highly interesting opportunity to study correlates of cognitive processing at the level of single cells or small populations in the human brain. In addition to the work on movement disorders, we investigate alterations of network dynamics in patients with multiple sclerosis. As part of a BMBF-funded project we have acquired a multimodal dataset comprising clinical, neuropsychological, structural and functional MRI data as well as MEG data from a cohort of multiple sclerosis patients. For this cohort, analyses are in progress on cross-sectional and longitudinal changes of functional connectivity and their relation to cognitive decline and structural connectivity changes. In cooperation with the UKE department of psychiatry, we analyse alterations of connectivity in patients with schizophrenia as well as in patients with high-functioning autism. In both patient groups, we have been able to demonstrate changes in phase or envelope coupling that correlate with clinical symptom scores.
In order to corroborate the functional relevance of oscillatory signals and dynamic connectivity, interventions are required that allow to manipulate these phenomena in a specific manner and to test the effects on task- or stimulus-related processing. In humans, transcranial alternating current stimulation (tACS) seems particularly promising because it opens up the possibility of entraining ongoing activity in a frequency-specific way. In several recent studies, we have combined tACS with EEG to monitor neural entrainment during the stimulation. An important step has been to improve the spatial specificity of tACS by stimulating through appropriately placed EEG electrodes, as shown by modeling of the electric field distribution in source space. A particular focus in our studies is on modulation of long-range connectivity by tACS which we have recently successfully demonstrated.
We conduct experiments in both anesthetized and behaving animals to test the functional relevance of neural synchronization for sensory processing in the visual, tactile and auditory modality, as well as for cross-modal interactions. Complementing the intraoperative recordings in patients, we also study neural dynamics in cortex and basal ganglia in mouse lines with mutations related to Parkinson‘s disease. In awake animals, we perform multi-site recordings with chronically implanted electrodes to allow the direct monitoring of neural interactions during spontaneous behaviours and during task performance. An important aim of our animal studies is the investigation of spectral and spatial features of different modes of large-scale coupling. Furthermore, we aim at characterizing, by analysis of directed coupling, bottom-up vs top-down information flow across cortical areas.
As part of several EU-funded projects, my group has contributed to implementing robot systems that combine visual, tactile and auditory information processing to achieve orienting behavior, object recognition, navigation, and memory formation. These projects have combined a synthetic biorobotics approach with neurophysiological studies and computational modeling that allows to identify relevant information processing principles. In the context of the EU-funded project eSMCs – „Extending sensorimotor contingencies to cognition“, we have continued this research to study how cognitive processing can potentially be grounded in sensorimotor interactions. Currently, we apply neurophysiological insights to improve human-robot interaction in the EU project socSMCS - „Socializing sensorimotor contingencies“. The key hypothesis is that enhancing interpersonal entrainment at the level of basic sensorimotor interactions could help to augment human-robot cooperation. Moreover, we address the issue of neural dynamics in the context of non-invasive brain-computer-interfaces.
Complementing the physiological lines of my research, I am deeply interested in the conceptual and philosophical implications of neurobiological results and in the fundamental discussion of the contributions that empirical neuroscience can make to theories of perception, cognition and action. A major focus of my work is to trace implications of network-based approaches for understanding the mechanisms of consciousness and subjective experience. Moreover, I am interested in links between neural dynamics and enactive views of cognition, aiming to explore the possibilites of grounding of cognition in sensorimotor and interpersonal coupling. Furthermore, I am interested in interdisciplinary approaches in network science pursuing the question whether semantic, social or economic networks can be modelled using similar approaches as those used for modelling brain networks.
Our research topics are addressed using a set of complementary approaches in humans and animal models.
- For studies on the human brain, we have established two labs for high-density (128 channel) EEG recordings and a BCI lab with a 2x64 channel EEG system.
- The institute accomodates a MEG lab with a 275-channel CTF whole-head system.
- MRI studies are carried out in cooperation with the Dept. of Systems Neuroscience and the Dept. of Neuroradiology at the UKE.
- We are running several laboratories equipped for in-vivo multielectrode studies in anesthetized and behaving animals.
- We perform intraoperative microelectrode recordings in patients with neurological disorders; these studies are carried out in cooperation with the Depts. of Neurosurgery and Neurology at the UKE.