Sex differences in human virtual water maze performance: novel measures reveal the relative contribution of directional responding and spatial knowledge.

Sex differences in humans on virtual water maze navigation are well established when overall performance is measured, e.g., by the total time taken to find the hidden platform, total path length, or quadrant dwell time during probe trials. Currently, it is unknown whether males are better spatial learners than females, or if overall performance differences reflect other aspects of the task unrelated to spatial memory. Here, males and females were tested on a virtual analogue of the Morris water maze. We devised a novel method of analysis in which each trial was divided into an initial trajectory phase and search phase. We also implemented a new measure of spatial learning during early and late training, by including trials in which subjects were only required to indicate where they thought the hidden target zone was located. Consistent with previous reports, males outperformed females on overall measures of task performance. Males also performed significantly better on all initial trajectory phase variables. Interestingly, only small (non-significant) differences were observed during the search phase and when spatial learning was tested without the constraints of a typical water maze trial. Our results suggest that spatial knowledge regarding the location of the hidden target zone is not the main factor responsible for overall sex differences in virtual water maze performance. Instead, the largest sex differences were observed during the initial trajectory phase of the trial, which is thought to depend on effective processing of distal features of the environment.