Scopolamine disrupts hippocampal activity during allocentric spatial memory in humans: an fMRI study using a virtual reality analogue of the Morris Water Maze

The role of the septohippocampal cholinergic system in memory disorders is well established. The effects of cholinergic challenge in animals have been extensively studied using the Morris Water Maze (MWM) which engages allocentric spatial memory. The present study investigated the effect of the centrally active muscarinic antagonist scopolamine on allocentric spatial memory in humans using a virtual reality analogue of the MWM task, the Arena task. Twenty right-handed healthy male adults with a mean age of 28 years (range 23-35 years) were studied using functional MRI in a randomized double-blind cross-over design with scopolamine bromide (0.4 mg i.m.) or placebo (saline) administered 70-90 min before the beginning of the functional scan. Scopolamine induced a significant reduction in the activation of the hippocampus/parahippocampal gyrus compared with placebo. Furthermore, there was dissociation between hippocampus-based and striatal-based memory systems, which were significantly more activated in the placebo and scopolamine conditions, respectively. The activation of the striatal system under scopolamine challenge was accompanied by the activation of the amygdala. In conclusion, the study extends the well-documented finding in animals of the attenuating effect of scopolamine on hippocampal activity during allocentric spatial memory to humans. Furthermore, the results call for further investigation of the dissociation between the hippocampal and neostriatal memory systems during allocentric spatial processing under cholinergic blockade in humans.