Changes in hippocampal volume and neuron number co-occur with memory decline in old homing pigeons (Columba livia)

The mammalian hippocampus is particularly susceptible to age-related structural changes, which have been used to explain, in part, age-related memory decline. These changes are generally characterized by atrophy (e.g., a decrease in volume and number of synaptic contacts). Recent studies have reported age-related spatial memory deficits in older pigeons similar to those seen in older mammals. However, to date, little is known about any co-occurring changes in the aging avian hippocampal formation (HF). In the current study, it was found that the HF of older pigeons was actually larger and contained more neurons than the HF of younger pigeons, a finding that suggests that the pattern of structural changes during aging in the avian HF is different from that seen in the mammalian hippocampus. A working hypothesis for relating the observed structural changes with spatial-cognitive decline is offered.