1. A vanishing sex difference Effects of environmental contingencies in a virtual Morris water task on male and female spatial navigation Mühl, Griego, Kabisch, Kolomiyets, Kunkemöller, James, Neubauer, Liu, Schumann, Nagel & Kreitz Introduction Sex differences in spatial navigation A standard measure for spatial navigation in rodents are mazes, like the Morris water maze, the Hebb-Williams maze or corridor mazes. Virtual reality offers the possibility to investigate human spatial navigation behaviour under similar conditions with a high degree of control. Astur et al. (1998) showed in various experiments a reliable sex difference in the virtual Morris water task. The participants showed continual increase of their performance to locate a hidden platform, that is the swim latency decreased. Men were faster in finding the hidden platform, showed smaller heading errors, and a better spatial strategy (search in the right quadrant) in the probe trials compared to women. The sex difference was not the result of motivational, motor or sensory differences regarding the computer program, rather it could traced back to navigational ability. A study applying the virtual MWT paradigm showed differential cue use for women and men (Sandstrom et al., 1998). Women rely on the use of distal cues, e.g. objects in the background. Men make use of distal cues and geometric cues, e.g. the ground plan. A fMRI study (Grön et al., 2000) revealed significantly different activations between women and men while performing a complex, three-dimensional, virtual-reality maze. Both, men and women, showed, besides others, strong activations in the hippocampus proper, the parahippocampal gyrus and parietal regions. Compatible with the differential cue use mentioned above woman showed stronger activations in a right parietal area and a right prefrontal area, whereas men exhibited stronger activation in the left hippocampus. In our experiment we wanted to investigate the influence interleaved non- stationary platform trials have on sex differences. Subjects had to perform an Morris water task with interleaved non-stationary platform blocks after each stationary platform block. While the platform location did not change over the stationary platform blocks, it was randomly assigned to a different location for each non-stationary platform block. Stationary and non-stationary blocks differed in the distal cue design. Abstract In tasks of spatial navigation males in general show a superior performance compared to females, independent of the species studied. A study using a virtual version of the Morris water task (MWT) to investigate human navigational behaviour found a reliable sex difference (Astur et al., 1998). To investigate this difference further we used the virtual MWT similar in design to that used by Astur et al., but interleaved the stationary platform blocks with non-stationary platform blocks. The general sex difference was replicated and there was a stronger effect of the interleaved non-stationary blocks on male navigation. Materials and Method Results & Conclusion References Astur, R.S., Ortiz, M.L., & Sutherland, R.J. (1998). A characterization of performance by men and women in a virtual Morris water task: a large and reliable sex difference. Behavioral Brain Research, 93, 185-190. Grön, G., Wunderlich, A. P., Spitzer, M., Tomczak, R., & Riepe, M. W. (2000), Brain activation during human navigation: gender-different neural networks as substrate of performance. Nature Neuroscience, 3, 404-408. Sandstrom, N.J., Kaufman, J., & Huettel, S.A. (1998). Differential cue use by males and females in a virtual environment navigation task. Cognitive Brain Research, 6, 351-360. O'Keefe, J., & Nadel, L. (1978). The hippocampus as a cognitive map. Oxford University Press. Colby, C.L., & Goldberg, M.E. (1999). Space and attention in parietal cortex. Annual Review Neuroscience, 22, 319-349. A large sex difference was observed: men had significantly faster swim latencies across stationary blocks F(1, 308) = 42.94, p <.01 than women performing the Morris water maze. This differences vanished, or became non-significant, when only the performance in the first trials of the stationary blocks was compared, p =.10. Design Independent variables: sex, platform stability, block, environment Dependent variables: swim latency to find target Procedure: The experiment consisted of 14 blocks, 7 stationary platform blocks interleaved with 7 non- stationary platform blocks, with 4 trials in each block. The starting positions within the pool was randomly determined for each trial. Stationary platform block : the platform was tied to the same location within the pool over all blocks Non-stationary platform trial : the location was randomly reassigned for each block The two conditions used different sets of distal cues (abstract objects vs. concrete objects) which made it possible for the subject to discriminate between the conditions, though they were not told about the design. The association of stationary and non-stationary blocks with either abstract and concrete cues were evenly distributed over the subjects. A possible interpretation: use of different spatial representations. Men are more effective in construction and use of an allocentric representation of the environment (cognitive map) relying on geometrical and distal cues, while women, at least initially, rely instead on an egocentric representation. This leads to an advantage of men in spatial navigation tasks. The advantage turns into disadvantage, when differential environments are alternating. The cognitive maps are interfering with each other, maybe due to an automatic process of generalization based on similar geometric cues. Women, on the other hand, were less affected by the change of the environment, as the egocentric representation is based on the use of clearly distinguishable distal cues. Assuming egocentric representation to be mainly supported by parietal cortex (Colby & Goldberg, 1999), and allocentric representations by the hippocampus (O'Keefe & Nadel, 1978), differential brain activations, with women showing stronger activation in prefrontal and right parietal areas and men in the left hippocampus (Grön et al., 2000), indicate the use of differential representations. Additional support for differential representation use comes from studies exploring sex differences in cue use (Sandstrom, Kaufmann, & Heuttel, 1998), with women relying mainly on distal cues and men on distal and geometric cues. A classical Morris water task Subjects are supposed to find a stationary hidden platform in a circular pool filled with opaque water. Orientation is only possible by the use of distal cues distributed around the pool. The subjects are finding the target faster with every trial, indicating a continuous learning process. This is thought to indicate the construction of an cognitive map of the environment. To navigate through the environment subjects initially have to rely on egocentric representations. By continuous exposure to the environment, it becomes possible to form relations between the various cues. An allocentric representation (cognitive map) is built and refined gradually, supporting the navigation process. Fig. 1 Male example of an stationary platform block demonstrating learning