Neuronal oscillations reveal the where and what of human working memory: an MEG source localization study

Supp, G. G., Engel, A. K., and Hipp, J. F.
Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf

Humans need to select and maintain visual information in a context-dependent, goal-directed manner. To investigate whether feature-specific working memory processes are associated with changes of oscillatory neural activity, we performed an MEG-study using a continuous shape- and motion-tracking paradigm. Participants were presented with a smoothly shaped blob that permanently changed its shape and position. During each interval, lasting for several seconds, subjects had to encode and, subsequently, to retain one of two visual features (either shape or motion) continuously. This design enabled us to analyze oscillatory responses by spectral analysis and source-localization using individual structural MRI. We observed an increase of oscillations in the gamma frequency, which was sustained for seconds and characterized the encoding as well as the retention of each visual feature. Both, encoding and retention involved common, highly equivalent gamma patterns, recruiting brain regions in a feature-specific manner (motion: FEF - bilaterally, IPS - left; shape: occipito-parietal areas). We found an increase of theta-power during both memory tasks, in the middle-temporal lobes (MTL) including both hippocampal formations. This suggests that working memory processes are reflected by a sustained gamma power increase in distinct, i.e. feature-specific local networks and, additionally, by an increase of theta-power in MTL brain structures.

Symposium 7: Novel Source Localisation Approaches in MEG-Data: Basic and Clinical Applications
11.06.2009, 14:30-15:45
Seminarraum 11