Of molecules, memories and migration: M1 acetylcholine receptors facilitate spatial memory formation and recall during migratory navigation

Many animals use complex cognitive processes, including the formation and recall of memories, for successful navigation. However, the developmental and neurological processes underlying these cognitive aspects of navigation are poorly understood. To address the importance of the formation and recollection of memories during navigation, we pharmacologically manipulated turtles ( Chrysemys picta ) that navigate long distances using precise, complex paths learned during a juvenile critical period. We treated freely navigating turtles both within and outside of their critical learning period with a specific M1 acetylcholine receptor antagonist, a drug known to disrupt spatial cognition. Experienced adult turtles lost all navigational ability under the influence of the drug, while naive juveniles navigated successfully. We retested these same juveniles the following year (after they had passed their critical period). The juveniles that initially navigated successfully under the influence of the antagonist (but were unable to form spatial memories) were unable to do so subsequently. However, the control animals (who had the opportunity to form memories previously) exhibited typical navigational precision. These results suggest that the formation of spatial memories for navigation occur during a critical period, and successful navigation after the critical period is dependent upon the recall of such memories.