The hippocampus is engaged in the processing of visual (allothetic) and self-motion (idiothetic) information for spatial memory function. Beyond memory, it is involved in cognitive coordination processes (Wesierska at al. 2005). We hypothesised that the hippocampus is also critical for the reorganization of spatial representations. To study this we used a place avoidance (PA) method to create homogenous allothetic (Room: R+) or idiothetic (Arena: A+) spatial representations. We then rearranged these representations according to the A+ or the R+. In the PA task hippocampal lesioned (HL) and intact (I) rats learn to avoid a place on the arena where shocks are administered. In the R+ variant this place was in a fi xed position according to the room frame (lit room, rotating arena, waterdissolved proximal cues); the A+ variant was represented by a fi xed position according to the arena information (dark, rotating arena). The HL rats were impaired during acquisition of avoidance in the R+ (F1, 14=13.97; P<0.002) but not in the A+ variant. When spatial conditions were rearranged all lesioned rats showed impaired learning (from R+ to A+: F1, 13=12.04; P<0.004; from A+ to R+: F1, 14=10.59; P<0.005). Our results suggest that acquisition of allothetic representation, compared to idiothetic representation is more highly hippocampal-dependent. Conversely, an unimpaired hippocampus seems to be necessary for the reorganisation of spatial representation. Supported by grant 3120/B/P01/2007/33.
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