Pharmacological evidence is consistent with a prominent role of spatial memory in complex navigation

The ability to learn about the spatial environment plays an important role in navigation, migration, dispersal, and foraging. However, our understanding of both the role of cognition in the development of navigation strategies and the mechanisms underlying these strategies is limited. We tested the hypothesis that complex navigation is facilitated by spatial memory in a population of Chrysemys picta that navigate with extreme precision (+/-3.5 m) using specific routes that must be learned prior to age three. We used scopolamine, a muscarinic acetylcholine receptor antagonist, to manipulate the cognitive spatial abilities of free-living turtles during naturally occurring overland movements. Experienced adults treated with scopolamine diverted markedly from their precise navigation routes. Naive juveniles lacking experience (and memory) were not affected by scopolamine, and thereby served as controls for perceptual or non-spatial cognitive processes associated with navigation. Further, neither adult nor juvenile movement was affected by methylscopolamine, a form of scopolamine that does not cross the blood-brain barrier, a control for the peripheral effects of scopolamine. Together, these results are consistent with a role of spatial cognition in complex navigation and highlight a cellular mechanism that might underlie spatial cognition. Overall, our findings expand our understanding of the development of complex cognitive abilities of vertebrates and the neurological mechanisms of navigation.