Response properties of avian hippocampal formation cells in an environment with unstable goal locations.

The response properties of 48 right (n=24) and left (n=24) hippocampal formation (HF) cells were examined by recording from freely moving homing pigeons as they foraged in an open-field environment with unstable goal locations. Compared to previous results based on HF recordings from environments with stable goal locations, the spatial signal of the HF neurons recorded in the present study was substantially diminished; there was little indication of PATH cells found in previous HF recordings and nothing resembling place cells routinely recorded in rat hippocampus under similar conditions. However, lateralized response properties were detected. Right HF cells dramatically reduced their firing rates during a foraging session, resulting in very low reliability scores. By contrast, left HF cells maintained firing rates throughout sessions and displayed modestly higher reliability scores compared to right HF neurons. Notable was one striking group of cells (n=13), predominantly found in the right HF, that displayed rate maps characterized by numerous, discrete areas of above baseline firing rates, overall very low firing rates and higher specificity than other cells recorded in this study. Overall, the data emphasize the importance of stable goal locations in shaping the spatial response profile of homing pigeon HF neurons and demonstrate the persistence of lateralized response properties under conditions when space explains little of the temporal variation in firing rate.