1. Methods Experiment 1 Conclusions Does the home base anchor spatial mapping? *D.G. Wallace 1 ; D.A. Hamilton 2 ; A.D. Choate 1 1 Department of Psychology, Northern Illinois University, De Kalb, IL, USA 2 Department of Psychology, University of New Mexico, Albuquerque, NM, USA Rat exploratory behavior in an open field is organized around a single location, or home base. The home base appears to anchor spatial exploration in that animals spend a great deal of time there and return to the home base after exploratory trips. Recent work has suggested that both exteroceptive visual (allothetic) cues and self-movement cues contribute to this organization. Under normal light conditions, salient allothetic cues exhibit control over the location of the home base. A home base is also established under dark conditions suggesting that self-movement cues contribute to the organization of exploratory behavior. Considering that both place cells and head direction cells exhibit parallel response characteristics to manipulations of allothetic cues, and that place field firing rate maps established under light conditions are maintained in the dark by self- movement information, the home base may anchor the representation of relationships between allothetic and self- movement navigational systems. Whereas previous studies of home base behavior have utilized large table-tops, the current study examined home base formation and the control of the home base location by allothetic cues in an apparatus traditionally used in place cell and head direction cell studies. Rats were disoriented and placed in a transparent Plexiglas cylinder (91.5 cm) in which stimulus characteristics of the wall could be manipulated by wrapping different segments with black, white, or gray poster board. The animals were free to explore the cylinder for 60 minutes during each daily session. Figure 1: Diagram of the apparatus used in the current study. Location and visual characteristics of the cue card can be manipulated without altering the cylinder. Home base establishment and stability was examined in a cylinder with black walls and a white cue card. During the first 60 minute session the cue card was in the same position for all rats (n=21). On the second day, the cue remained in the same position for the rats in the stable group (n=9) and was rotated 90o for rats in the rotate group (n=12). Figure 2: A representative rat’s total time (A), cumulative change in heading (B), rearing frequency (C), and inverse of the mean linear speeds (D) are plotted for each 22.5o zone from a single session. Home base establishment is a ubiquitous characteristic of rat behavior in traditional place cell apparati. Visual and spatial characteristics of the cylinder influence home base location. Highly salient visual cues polarize home base location. Less salient visual cues weakly control home base location. This work is consistent with a role for the home base in anchoring a spatial mapping system to an idiothetic cue based system. 66.9/Z26 Introduction N : 180 o S : 0 o W : 270 o E : 270 o A.B. C. D. Figure 3: A representative rat’s path and distribution of time spent in different regions of the cylinder are plotted for one session (left). The mean parameter of concentration for the cumulative time measure is plotted for each group across both sessions (right). Figure 4: Average correlations between cumulative time and change in heading (left), rearing (middle), and inverse of speed (right) are plotted for each group across both days. Figure 5: Polar graphs plot home base location for stable (left) and rotate (right) groups across both days (Day 1: blue; Day 2: red). Clockwise (dotted lines) and counter-clockwise rotations (solid lines) are indicated for each rat. The bottom panel plots the mean difference in heading direction of home base for each group. This experiment examined the effects of manipulating visual characteristics of the cylinder wall on home base location. Each group of rats explored a cylinder for four 60-minute sessions. During the first three sessions the cylinder remained stable. On the forth day, the cylinder was rotated 90o. Figure 6: Illustrations provide a schematic of the cylinders explored by the Black-White (left), Gray-White (middle), and White-Black (right) groups. Experiment 2 Figure 7: Parameter of concentration for the cumulative time measure are plotted for each group across the four daily sessions (A). Average correlations between cumulative time and change in heading (B), rearing (C), and inverse of speed (D) are plotted for each group. A.B. C. D. Figure 8: Home base locations are plotted for each rat in the black- white (left), gray-white (middle), and white-black (right) groups. The background of each graph represents the visual and spatial characteristics of the cylinder across sessions. Figure 9: The second order circular statistics were used to examine whether home base locations were random for each group across sessions. (Rayleigh uniform distribution test, *p<.05). Acknowledgments: We would like to thank Megan Martin for her assistance in data collection related to the current project. Correspondence should be addressed to Douglas G. Wallace: dwallace@niu.edu or www.niu.edu/user/tj0dgw1.