Transformation of ongoing EEG into source space

Person on the project: Astrid Knauth
In collaboration with Morten Stabenau and the Digital Signal Processing and System Theory Group of Prof. G. Schmidt from the Technical University of CAU Kiel.

The source localization of discrete EEG events such as spikes or evoked potentials is common practice (e.g. dipole analysis), and oscillatory EEG activity can be analyzed via beamforming. However, the transformation of the ongoing EEG into source space is an untackled quest. In our fMRI work, we analyzed voxel wise time courses and their interactions, and identified parameters of reduced conscious awareness. In order to apply most similar techniques, the goal of this project is to transfer ongoing EEG into source space such that we can perform analogous analyses to those already validated with fMRI (e.g. Tagliazucchi et al. "Large-scale brain functional modularity is reflected in slow electroencephalographic rhythms across the human non-rapid eye movement sleep cycle." Neuroimage 2013, and Tagliazucchi et al. "Breakdown of long-range temporal dependence in default mode and attention networks during deep sleep." PNAS 2013).

Sepctrum

Grand Average Map of 30 subjects (sensor space): Grand average spectrogram at electrode C3 from ten seconds before until 20 seconds after right hand tapping onset as detected by a surface EMG electrode over the right M. abductor pollicis brevis. Top panel: the grand average based on EMG-defined windows reveals a drop in broad band power (red arrow) including in the 8-12 Hz alpha band (below arrow: event-related desynchronization [ERD]). ERD preceding EMG changes might reflect motion preparation. Both is not apparent in the bottom panel: analogous display of a grand average based on windows defined randomly and irrespective of EMG activity (shuffled data).

spectral drop source space

Alpha band power in source space (right central region): 8-12 Hz band power [uV2] from ten seconds before until 20 seconds after right hand tapping onset. Projection into source space preserved the drop in power in the right central region during tapping of the left hand especially at the time of -2 to 4,5 sec (red arrow).

Arbeitsgruppen der Neurologie an der Christian-Albrechts-Universität zu Kiel

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