BINGMAN, V.P.*; SIEGEL, J.J.; HOUGH III, G.E.; KAHN, M.C.: Adaptive Variation in the Hippocampal Representation of Environmental Space

Behavioral, anatomical and neurochemical data demonstrate that the hippocampus of birds and mammals are homologous structures playing a critical role in the memory representation of environmental space used for navigation. Uncertain at the electrophysiological level is whether the hippocampus of birds and mammals employ similar neural representational strategies to capture the spatial information known to be dependent on the hippocampus. Although an oversimplification, the hippocampus of the nocturnal, poor vision rat is characterized by a robust feed-forward processing network (the trisynaptic pathway), and the presence of “place” neurons and “head direction” neurons thought to be critical elements in their hippocampal spatial memory system. Perhaps surprisingly, data accumulating from the diurnal, highly visual homing pigeon suggest at least a somewhat different electrophysiological representational organization. The existing data have yet to reveal a robust feed-forward processing network within the homing pigeon hippocampus, and although recordings from isolated hippocampal neurons in freely moving homing pigeons display some spatial sensitivity, homing pigeon hippocampal neurons display response profiles clearly different from the prototypical place neurons of rats. If confirmed by ongoing experiments, the data from homing pigeons would suggest that while some anatomical and neurochemical characteristics of the hippocampus may be conserved during the course of evolution, critical aspects of the electrophysiological representation of space within the hippocampus may show considerable inter-species variability; inter-species variability that may reflect adaptive variation in the organization of the hippocampus to match the natural history and ecology of a particular species.