Dead reckoning (path integration) requires the hippocampal formation: evidence from spontaneous exploration and spatial learning tasks in light (allothetic) and dark (idiothetic) tests

Animals navigate using cues generated by their own movements (self-movement cues or idiothetic cues), as well as the cues they encounter in their envi ronment (distal cues or allothetic cues). Animals use these cues to navigat e in two different ways. When dead reckoning (deduced reckoning or path int egration), they integrate self-movement cues over time to locate a present position or to return to a starting location. When piloting, they use allot hetic cues as beacons, or they use the relational properties of allothetic cues to locate places in space. The neural structures involved in cue use a nd navigational strategies are still poorly understood, although considerab le attention is directed toward the contributions of the hippocampal format ion (hippocampus and associated pathways and structures, including the fimb ria-fornix and the retrosplenial cortex), In the present study, using tests in allothetic and idiothetic paradigms, we present four lines of evidence to support the hypothesis that the hippocampal formation plays a central ro le in dead reckoning. (1) Control but not fimbria-fornix lesion rats can re turn to a novel refuge location in both light and dark (infrared) food carr ying tasks. (2). Control but not fimbria-fornix lesion rats make periodic d irect high velocity returns to a starting location in both light and dark e xploratory tests. Control but not fimbria-fornix rats trained in the light to carry food from a fixed location to a refuge are able to maintain accura te outward and homebound trajectories when tested in the dark. (3). Control but not fimbria-fornix rats are able to correct an outward trajectory to a food source when the food source is moved when allothetic cues are present . These, tests of spontaneous exploration and foraging suggest a role for t he hippocampal formation in dead reckoning. (C) 2001 Elsevier Science B.V. All rights reserved.