Fig. 1.

Experimental setup. (A) Constant infusion of FDG started at time 0 and continued for 60 min. The FDG uptake was modeled using the GLM with separate regressors for the manipulation (difficult) and maintenance (easy) WM tasks in the shape of ramp functions that increase by one during the respective 6-min task blocks (i.e., after the two manipulation blocks that regressor has ramped up to 12). Structural images were collected during the first 18 min, and fMRI-BOLD data were collected between 18 and 60 min. To provide suitable contrast for both fPET and BOLD, an embedded block design is used (45), in which each “slow” 6 min task block has six “fast” 1-min blocks embedded within, each involving a 45-s task and 15-s rest. (B) Mean uptake of FDG averaged across subjects over the first 24-min task-free period. (C) The manipulation and maintenance WM tasks.