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Humboldt-Universitaet zu Berlin - Collaborative Research Center for Theoretical Biology

Non-invasive 'single-trial' analysis of interactions between somatosensory evoked potentials (SEP) and macroscopic EEG-rhythms in humans

Brains must be able to process environmental stimuli in a "single-trial" mode. Accordingly, human cortical neurophysiology should be approached using "single-trial" analysis as well. While EEG and MEG can serve as non-invasive measurement tools with adequate temporal resolution (milliseconds), a reliable extraction of single-trial stimulus processing is currently not available: only after averaging over a series of repeated stimuli somatosensory evoked potentials (SEPs) can be obtained at a signal-to-noise ratio (SNR) low enough for a stable source reconstruction, i.e., the assignment of SEP-components to neural generators in different brain areas. Sub-projects B1-B3 develop concepts for stimulus processing based on invasive microscopic measurements, with a special focus on the interactions between stimulus responses of single cells and the ongoing activity of locally surrounding cell populations. In a complementary way, project B4 will scrutinize such concepts with respect to their applicability and limitations for non-invasive recordings. To this end, SEP after median nerve stimulation will be interpreted in relation to the local EEG background activity, serving as a macroscopic marker for interactions between activated neural subpopulations at the primary somatosensory cortex S-I and regional (mu-/beta-) oscillatory EEG background activities. From the perspective of signal processing, algorithms for the extraction of spatial activation patterns of corticals as well as subcortical sources will be developed further, including blind, i.e., data-driven approaches such as independent component analysis (ICA). Based on EEG time series derived from such extracted cortical sources, possible non-linear interactions between the ongoing background activity and the "single trial" source responses will be explored.

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