Path integration absent in scent-tracking fimbria-fornix rats: Evidence for hippocampal involvement in "sense of direction" and "sense of distance" using self-movement cues

Allothetic and idiothetic navigation strategies use very different cue cons tellations and computational processes. Allothetic navigation requires the use of the relationships between relatively stable external (visual, olfact ory, auditory) cues, whereas idiothetic navigation requires the integration of cues generated by self-movement and/or efferent copy of movement comman ds. The flexibility with which animals can switch between these strategies and the neural structures that support these strategies are not well unders tood. By capitalizing on the proclivity of foraging rats to carry large foo d pellets back to a refuge for eating, the present study examined the contr ibution of the hippocampus to the use of allothetic versus idiothetic navig ation strategies. Control rats and fimbria-fornix-ablated rats were trained to follow linear, polygonal, and octagonal scent trails that led to a piec e of food. The ability of the rats to return to the refuge with the food vi a the shortest route using allothetic cues (visual cues and/or the odor tra il available) or using ideothetic cues (the odor trail removed and the rats blindfolded or tested in infrared light) was examined, Control rats "close d the polygon" by returning directly home in all cue conditions. Fimbria-fo rnix rats successfully used allothetic cues (closed the polygon using visua l cues or tracked back on the string) but were insensitive to the direction and distance of the refuge and were lost when restricted to idiothetic cue s. The results support the hypothesis that the hippocampal formation is nec essary for navigation requiring the integration of idiothetic cues.