The Journal of Neuroscience, June 1, 1999, 19(11):4662-4673
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
Ian Q.
Whishaw and
Bogdan
Gorny
Department of Psychology and Neuroscience, University of
Lethbridge, Lethbridge, Alberta, Canada T1K 3M4
Allothetic and idiothetic navigation strategies use very different
cue constellations and computational processes. Allothetic navigation
requires the use of the relationships between relatively stable
external (visual, olfactory, auditory) cues, whereas idiothetic navigation requires the integration of cues generated by self-movement and/or efferent copy of movement commands. The flexibility with which
animals can switch between these strategies and the neural structures
that support these strategies are not well understood. By capitalizing
on the proclivity of foraging rats to carry large food pellets back to
a refuge for eating, the present study examined the contribution of the
hippocampus to the use of allothetic versus idiothetic navigation
strategies. Control rats and fimbria-fornix-ablated rats were trained
to follow linear, polygonal, and octagonal scent trails that led to a
piece of food. The ability of the rats to return to the refuge with the
food via the shortest route using allothetic cues (visual cues and/or
the odor trail available) or using ideothetic cues (the odor trail
removed and the rats blindfolded or tested in infrared light) was
examined. Control rats "closed the polygon" by returning directly
home in all cue conditions. Fimbria-fornix rats successfully used
allothetic cues (closed the polygon using visual 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 cues. The
results support the hypothesis that the hippocampal formation is
necessary for navigation requiring the integration of idiothetic cues.
Key words:
allothetic cue; dead reckoning; idiothetic cue; fimbria-fornix; hippocampus; hippocampal lesions; odor tracking; path
integration; piloting; spatial learning; spatial navigation
Copyright © 1999 Society for Neuroscience 0270-6474/99/19114662-12$05.00/0
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