Spatial memory in a virtual arena Human virtual analogue of the Morris water maze I. Fajnerová, M. Rodriguez, L. Konrádová, P. Mikoláš, K. Dvorská, M. Ungrmanová, J. Horáček
K. Vlček, D. Levčík, A. Stuchlík
Neurophysiology of Memory Institute of Physiology, Academy of sciences CR Prague, Czech Republic
Prague Psychiatric Center Affiliated with 3rd Faculty of Medicine Charles University Prague, Czech Republic
[email protected]
C. Brom
Department of Software and Computer Science Education Faculty of Mathematics and Physics Charles University Prague, Czech Republic Abstract—The assessment of cognitive functions represents a crucial step in the diagnostics and therapy of mental disorders such as schizophrenia. To assess spatial learning, mental flexibility and working memory using a test applicable in clinical research, we designed virtual analogue of the spatial animal task: the Morris water maze (MWM). The task of the tested subject was simply to find and remember several hidden goal positions placed in an enclosed circular arena. Data obtained in 30 schizophrenia patients show cognitive deficit in the newly-developed virtual task in comparison to healthy volunteers, indicating its possible application as a tool for diagnostics or remediation of cognitive functions.
II.
A. Participants A group of 30 first-episode schizophrenia patients (diagnosed as acute psychotic episode or schizophrenia) were recruited in Prague Psychiatric Center. A comparable group of healthy volunteers was recruited from students, academic workers and medical staff and their family (matched for age, sex and education level). B. Apparatus and Software The three-dimensional virtual environment was presented in a first-person view on a 24" LCD monitor. The game engine Unreal Tournament (UT2004; Epic Games) was used to visualize the virtual scene to the respondents. The java software toolkit called “SpaNav” was connected to the game engine UT2004 to control the experiment and collect online data. Subjects controlled the movements of their avatar within the virtual arena using one joystick of the gamepad device. Prior to the spatial task, all participants underwent a short pre-training session in complex virtual maze, which served as a training of movement control.
Keywords—cognition; spatial memory test; schizophrenia; virtual reality environment, Morris water maze protocols
I.
INTRODUCTION
The assessment of cognitive functions represents a crucial step in diagnostics and in therapy of mental disorders such as schizophrenia. Various methods of cognitive remediation are introduced to improve the cognitive deficit accompanying schizophrenia. A computer-based cognitive remediation, focused on individual problems of participating psychotic patients, takes place also in the Prague Psychiatric Center. The team of therapists is currently working on new methods useful to train cognitive functions online (neurokog.pcp.lf3.cuni.cz) or in complex navigation tasks which could present a more natural way of cognitive training. To use such navigational tasks as training tool, first we need to assess the overall performance of healthy population and schizophrenia patients using comparable method. To assess the spatial cognition, we have created a navigation task in virtual reality environment. The task paradigm is based on the traditional spatial task used in rats to test spatial memory, the Morris water maze [1] displayed on Fig.1.
C. Design and Procedure of the spatial task Prior to the experiment all participants completed the standard cognitive tests battery. The newly-developed virtual task was performed in a virtual model of the Blue Velvet Arena apparatus (see Fig. 1) used to test navigation in humans [2]. The created virtual Four Goals Navigation (vFGN) task required of the participant to find and remember the hidden goal position.
The study was supported by IGA MH CR grant NT13386 and the institutional support from Academy of Sciences (RVO: 67985823) and by Prague Psychiatric Center by MH CZ -DRO (PCP, 00023752).
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METHODS
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Figure 1. Morris water maze -the hidden platform paradigm: (a) model of the original MWM apparatus for rats; (b) real human analogue called Blue Velvet Arena (BVA); (c) virtual analogue.
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Figure 3. Performance of both tested groups (schizophrenia vs. controls) expressed in parameters of path efficiency (minimal / real path) or goal quadrant preference (% time spend in the correct arena quadrant) in individual phases of the vFGN task: (a) Training.session, (b) Reversal session, (c) Recall session, and (d) Probe session.
• Recall session (delayed matching-to-place protocol), • Probe session (probe trials with removed goal position). III.
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The performance in the Probe session was disturbed as well (p < 0.01), showing lower place preference represented by the time spent in the correct arena quadrant (Figure 3d).
RESULTS
The task showed significant differences in all four tested sessions (tested by two-way ANOVA for repeated measures).
IV.
CONCLUSIONS
The presented results show significant cognitive impairment in schizophrenia patients measured using the spatial vFGN task, corroborated by the standard cognitive test battery. This spatial navigation task confirmed sensitivity toward the cognitive deficit measurable in schizophrenia in all four sessions. Such cognitive task could be used in two possible ways. First, the performance measured in the vFGN task can be used as a tool for translational research to identify cognitive deficit in neuropsychiatric disorders. Secondly, variants of the vFGN task can be used as a tool for remediation of cognitive functions in neuropsychiatric disorders.
The learning in the Training session was slower (less precise) in schizophrenia patients (p < 0.01) and did not achieve the asymptotic level of the control group (Fig. 3a). In the Reversal session the group of patients showed disturbed flexibility (p < 0.05) while learning the sequence of the three goal positions (Fig. 3b). The repetition of the spatial sequence (ABC) in the Recall session showed working memory deficits in decreased performance in the first repetition round of the spatial sequence (p < 0.05) followed by improvement of the performance in the second recall of the sequence, less evident in controls (Fig. 3c).
ACKNOWLEDGMENT We are grateful first of all to our former head of the department Jan Bureš (deceased in 2012) for scientific inspiration and valuable advice especially in the beginnings of the project. We thank Zbyněk Krulich for designing the virtual environment and Michal Bída for modifications done in SpaNav software. REFERENCES [1] [2]
Figure 2. Design of the virtual Four-Goals Navigation (vFGN) task: (a) Training session with stable goal position over 11 trials; (b) Reversal session with changing goal position, each position (A,B,C) repeated in 3 consecutive trials; (c) Recall session with 2 repetitions of the previously learned sequence ABC; (d) Probe session with 1 sequence repetition with inactivated goal position.
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R.G.M Morris, “Morris water maze.” Scholarpedia, vol. 3, pp. 6315, 2008. K. Stepankova, E. Pastalkova, E. Kalova., M. Kalina., and J. Bures, “A battery of tests for quantitative examination of idiothetic and allothetic place navigation modes in humans.” Behav Brain Res, vol. 147, pp. 95-105, 2003.
