@article{FellnerVolbergWimberetal., author = {Fellner, Marie-Christin and Volberg, Gregor and Wimber, Maria and Goldhacker, Markus and Greenlee, Mark W. and Hanslmayr, Simon}, title = {Spatial mnemonic encoding: Theta power decreases and medial temporal lobe BOLD increases co-occur during the usage of the method of loci}, series = {eNeuro}, volume = {3}, journal = {eNeuro}, number = {6}, publisher = {Society for Neuroscience}, address = {Washington, DC}, issn = {2373-2822}, doi = {10.1523/ENEURO.0184-16.2016}, pages = {1 -- 16}, abstract = {The method of loci is one, if not the most, efficient mnemonic encoding strategy. This spatial mnemonic combines the core cognitive processes commonly linked to medial temporal lobe (MTL) activity: spatial and associative memory processes. During such processes, fMRI studies consistently demonstrate MTL activity, while electrophysiological studies have emphasized the important role of theta oscillations (3-8 Hz) in the MTL. However, it is still unknown whether increases or decreases in theta power co-occur with increased BOLD signal in the MTL during memory encoding. To investigate this question, we recorded EEG and fMRI separately, while human participants used the spatial method of loci or the pegword method, a similarly associative but nonspatial mnemonic. The more effective spatial mnemonic induced a pronounced theta power decrease source localized to the left MTL compared with the nonspatial associative mnemonic strategy. This effect was mirrored by BOLD signal increases in the MTL. Successful encoding, irrespective of the strategy used, elicited decreases in left temporal theta power and increases in MTL BOLD activity. This pattern of results suggests a negative relationship between theta power and BOLD signal changes in the MTL during memory encoding and spatial processing. The findings extend the well known negative relation of alpha/beta oscillations and BOLD signals in the cortex to theta oscillations in the MTL.}, language = {en} } @article{GoldhackerFellnerVolbergetal., author = {Goldhacker, Markus and Fellner, Marie-Christin and Volberg, G. and Mullinger, K. J. and Greenlee, Mark W. and Hanslmayr, Simon}, title = {Spurious correlations in simultaneous EEG-fMRI driven by in-scanner movement}, series = {NeuroImage}, volume = {133}, journal = {NeuroImage}, number = {June}, publisher = {Elsevier}, doi = {10.1016/j.neuroimage.2016.03.031}, pages = {354 -- 366}, abstract = {Simultaneous EEG-fMRI provides an increasingly attractive research tool to investigate cognitive processes with high temporal and spatial resolution. However, artifacts in EEG data introduced by the MR scanner still remain a major obstacle. This study, employing commonly used artifact correction steps, shows that head motion, one overlooked major source of artifacts in EEG-fMRI data, can cause plausible EEG effects and EEG-BOLD correlations. Specifically, low-frequency EEG (< 20 Hz) is strongly correlated with in-scanner movement. Accordingly, minor head motion (< 0.2 mm) induces spurious effects in a twofold manner: Small differences in task-correlated motion elicit spurious low-frequency effects, and, as motion concurrently influences fMRI data, EEG-BOLD correlations closely match motion-fMRI correlations. We demonstrate these effects in a memory encoding experiment showing that obtained theta power (~ 3-7 Hz) effects and channel-level theta-BOLD correlations reflect motion in the scanner. These findings highlight an important caveat that needs to be addressed by future EEG-fMRI studies.}, language = {en} }