title: Directional learning, but no spatial mapping by rats performing a navigational task in an inverted orientation.
abstract: Previous studies have identified neurons throughout the rat limbic system that fire as a function of the animal's head direction (HD). This HD signal is particularly robust when rats locomote in the horizontal and vertical planes, but is severely attenuated when locomoting upside-down (Calton & Taube, 2005). Given the hypothesis that the HD signal represents an animal's sense of directional heading, we evaluated whether rats could accurately navigate in an inverted (upside-down) orientation. The task required the animals to find an escape hole while locomoting inverted on a circular platform suspended from the ceiling. In Experiment 1, Long-Evans rats were trained to navigate to the escape hole by locomoting from either one or four start points. Interestingly, no animals from the 4-start point group reached criterion, even after 29 days of training. Animals in the 1-start point group reached criterion after about six training sessions. In Experiment 2, probe tests revealed that animals navigating from either 1- or 2-start points utilized distal visual landmarks for accurate orientation. However, subsequent probe tests revealed that their performance was markedly attenuated when navigating to the escape hole from a novel start point. This absence of flexibility while navigating upside-down was confirmed in Experiment 3 where we show that the rats do not learn to reach a place, but instead learn separate trajectories to the target hole(s). Based on these results we argue that inverted navigation primarily involves a simple directional strategy based on visual landmarks.
authors.affiliation: Department of Psychological and Brain Sciences, Dartmouth College, 6207 Moore Hall, Hanover, NH 03755, USA.
authors.forename: Stephane
authors.initials: S
authors.lastname: Valerio
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Clark
authors.forename: Jeremy H M
authors.initials: JH
authors.lastname: Chan
authors.forename: Carlton P
authors.initials: CP
authors.lastname: Frost
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Harris
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Taube
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003463:Cues; D005260:Female; D007858:Learning; D018782:Maze Learning; D008568:Memory; D009043:Motor Activity; D009483:Neuropsychological Tests; D055696:Olfactory Perception; D010775:Photic Stimulation; D051381:Rats; D020318:Rats, Long-Evans; D013028:Space Perception; D013997:Time Factors; D014796:Visual Perception