Spatial information processing in the avian hippocampus

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Spatial cognition (the ability to perceive, operate on, and recall information about spatial environments) is critical to the survival of any species. Accordingly, a wealth of research has investigated this vital form of cognition, focusing largely on mammals. This research shows that the hippocampal formation (HF) and surrounding cortical structures are critical for this kind of learning. Avian species also have the ability to solve advanced (e.g., food caching) and in many cases uniquely challenging (e.g., migration) spatial problems. Despite the sophisticated spatial repertoire that can be observed in birds, relatively little is known about the neural substrate of spatial learning in birds relative to mammals. While we know that birds have a HF and that lesions to the HF produce comparable deficits in spatial processing in both classes of animal, how spatial information is processed within the avian HF remains largely unknown. This is in part because the avian HF lacks many of the defining features of its mammalian counterpart, including clear trilaminar structure and a dominantly unidirectional tri-synaptic loop. In fact, even the subdivisions of the avian HF remain a matter of debate. We may be able to resolve this issue by defining the regions of the avian HF on the basis of their functional, rather than anatomical, homology. There are many experimental paradigms in which the pattern of activity in the HF of mammals (i.e., CA1, CA3, and the dentate gyrus) can be made to diverge. Probing activity-dependent gene expression across widespread regions of the avian HF in birds that are trained on comparable paradigms may provide critical insight into how avian species process spatial information.