Donders Institute for Brain, Cognition and Behaviour
Zoek in de site...

Thesis defense Matthias C. Meyer (Donder Series 175)

12 January 2015

Promotors: Prof.dr. D. Norris, Prof.dr. M. Barth

„Inbetween Modalitiers Combined EEG - (f)MRI“

Today, the noninvasive examination of brain functions at rest or while performing a task is the most common source of information in human neuroscience. However, the capabilities of existing methods to observe neuronal activity are rather limited and the basic mechanisms of how neuronal activity is reflected in the recorded data are not fully understood. This thesis investigates the relation between simultaneously acquired data of two different measurement techniques of neuronal activity namely electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). While EEG measures the electrical field on scalp level, which reflects the synchronized changes of the postsynaptic potential of neuronal populations, with high temporal resolution but low spatial accuracy of its sources, fMRI is capable of localizing differences in neuronal oxygen consumption and related blood flow and blood volume effects on the mm scale, but suffering a poor temporal resolution.

The combined measurement of EEG and fMRI therefore offers the potential to acquire information about neuronal processes with high spatial and temporal resolution. In practice however the combined recording has its own difficulties, since both methods interfere each other, making an extensive artifact correction crucial. Further, as stated above, the two modalities observe different processes related to neuronal activity, which raises questions of the relation of the two signals when analyzing the data.

Using combined EEG - fMRI, the presented studies in this thesis gave new insights in the relation between the electrophysiological signal and blood oxygen level dependent (BOLD) fluctuations of common neuronal activity. When investigating the two modalities using a resting state paradigm, we found complex and temporal unstable correlation between EEG frequency band power and BOLD RSNs time lines. In order to enable a more specific examination of the relation of the two modalities we developed a new Prior-based Realistic Integrative Source Model (PRISM) toolbox to separate the EEG signal according to fMRI derived sources, also accounting for anatomical factors. Using the PRISM toolbox we found strong evidence that anatomical differences between subjects explain part of the inter subject variance of VEPs and could further demonstrate a significant improvement in the correlation of the two modalities when compared to channel based analysis. Further, we found strong support for the hypothesis that the P1-N2 components of the VEP in a visual guided motor response paradigm are highly related to the BOLD activity in the primary visual cortex.