Acute stress switches spatial navigation strategy from egocentric to allocentric in a virtual Morris water maze.

Stress and stress hormones are known to influence the function of the hippocampus, a brain structure critical for cognitive-map-based, allocentric spatial navigation. The caudate nucleus, a brain structure critical for stimulus-response-based, egocentric navigation, is not as sensitive to stress. Evidence for this comes from rodent studies, which show that acute stress or stress hormones impair allocentric, but not egocentric navigation. However, there have been few studies investigating the effect of acute stress on human spatial navigation, and the results of these have been equivocal. To date, no study has investigated whether acute stress can shift human navigational strategy selection between allocentric and egocentric navigation. The present study investigated this question by exposing participants to an acute psychological stressor (the Paced Auditory Serial Addition Task, PASAT), before testing navigational strategy selection in the Dual-Strategy Maze, a modified virtual Morris water maze. In the Dual-Strategy maze, participants can chose to navigate using a constellation of extra-maze cues (allocentrically) or using a single cue proximal to the goal platform (egocentrically). Surprisingly, PASAT stress biased participants to solve the maze allocentrically significantly more, rather than less, often. These findings have implications for understanding the effects of acute stress on cognitive function in general, and the function of the hippocampus in particular.

Direct measurement of spontaneous strategy selection in a virtual Morris water maze shows females choose an allocentric strategy at least as often as males do.

Considerable evidence indicates that males navigate large-scale space better than females, and some have previously attributed this difference to a greater ability of males to select or use an allocentric (cognitive mapping) navigational strategy. We directly tested this proposal by having males and females navigate in an "ambiguous" virtual Morris water maze environment that permitted participants to choose and use either an allocentric or an egocentric strategy. A novel probe trial at the end of training revealed which strategy each participant had been using and showed that the strategy selected by the greatest number of males and females was allocentric, and that this bias was even greater for females. Traditional measures of navigational performance (distance, latency, probe dwell time) indicated that overall, males were more efficient than females. However, this gender difference was not related to strategy choice: males were better than females regardless of strategy, though the difference was significant only in those navigating allocentrically. These data indicate that while males may navigate allocentrically more efficiently than females, this does not account for the male advantage in navigation. The data also indicate that under specific circumstances, females may also prefer and use an allocentric strategy to navigate. These findings have implications for theories regarding the differential use of the hippocampus by men and women.

Simple gaze analysis and special design of a virtual Morris water maze provides a new method for differentiating egocentric and allocentric navigational strategy choice.

We present a novel method of combining eye tracking with specially designed virtual environments to provide objective evidence of navigational strategy selection. A simple, inexpensive video camera with an easily built infrared LED array is used to capture eye movements at 60Hz. Simple algorithms analyze gaze position at the start of each virtual maze trial to identify stimuli used for navigational orientation. To validate the methodology, human participants were tested in two virtual environments which differed with respect to features usable for navigation and which forced participants to use one or another of two well-known navigational strategies. Because the environmental features for the two kinds of navigation were clustered in different regions of the environment (and the video display), a simple analysis of gaze-position during the first (i.e., orienting) second of each trial revealed which features were being attended to, and therefore, which navigational strategy was about to be employed on the upcoming trial.