Neural correlates of visual working memory (WM) were examined using a task involving different delay conditions and requiring a constant monitoring of morphing figures. As stimuli we presented geometrical figures that could not easily be associated to common figures (such as triangles, stars). The preliminary analysis of the behavioural data of 11 healthy subjects showed a significant increase of reaction times and decreased performance accuracy with longer delay conditions. Lower performance accuracy was associated with less complex memorising strategies. In addition, the subjects performed a control task with lower cognitive demand, to examine the impact of cognitive load and attention on different neurophysiological parameters. In this condition subjects were instructed to search for a simple triangle amongst an ongoing stream of (morphing) common geometrical figures. The delay conditions in this task were adapted to the WM task with higher cognitive load. High density magnetoencephalographic recordings (148-channel whole-head neuromagnetometer, 4D) were obtained during each of the conditions described above. Source space analyses were performed on band-pass filtered data determined by event-related Fourier spectrum analyses and wavelet procedures. Different event-related time epochs were analysed by minimum-norm estimates and multiple dipole density procedures. Neuromagnetic generator activity was discussed due to the behavioural performance.
Research was supported by DFG (SFB517) and Center for Advanced Imaging – Bremen (CAI).