Inhibition of cell proliferation in black-capped chickadees suggests a role for neurogenesis in spatial learning

Following development, the avian brain continues to produce neurons throughout adulthood, which functionally integrate throughout the telencephalon, including the hippocampus. In food-storing birds like the black-capped chickadee (Poecile atricapillus), new neurons incorporated into the hippocampus are hypothesized to play a role in spatial learning. Previous results on the relation between hippocampal neurogenesis and spatial learning, however, are correlational. In this study, we experimentally suppressed hippocampal neuronal recruitment and tested for subsequent effects on spatial learning in adult chickadees. After chickadees exhibited significant learning, we treated birds with daily injections of either saline or methylazoxymethanol (MAM), a toxin that suppresses cell proliferation in the brain and monitored subsequent spatial learning. MAM treatment significantly reduced cell proliferation around the lateral ventricles and neuronal recruitment in the hippocampus, measured using the cell birth marker bromodeoxyuridine. MAM-treated birds performed significantly worse than controls on the spatial learning task 12 days following the initiation of MAM treatment, a time when new neurons would begin functionally integrating into the hippocampus. This difference in learning, however, was limited to a single trial. MAM treatment did not affect any measure of body condition, suggesting learning impairments were not a product of non-specific adverse effects of MAM. This is the first evidence of a potential causal link between hippocampal neurogenesis and spatial learning in birds.