Inhibition, the final frontier: the impact of hippocampal lesions on behavioral inhibition and spatial processing in pigeons.

Two commonly accepted functions of the mammalian hippocampus are the processing of spatial information and behavioral inhibition. Although there is clear evidence that the avian hippocampus is also critical for the processing of spatial information, there is a dearth of evidence that it plays a role in behavioral inhibition. In Experiment 1, the effect of hippocampal lesions on behavioral inhibition in pigeons was assessed. Control and hippocampal lesioned pigeons were trained to peck stimuli that were associated with one of three probabilities of reinforcement (40%, 70%, or 100%). The number of pecks that control pigeons distributed to each stimulus was directly related to its respective probability of reinforcement. In contrast, hippocampal lesioned pigeons distributed their pecks evenly across the three stimuli. In Experiment 2, we tested whether these pigeons also displayed the well-accepted spatial deficit. Consistent with previous work, control pigeons acquired the radial arm maze in significantly fewer trials than the hippocampal lesioned pigeons. Together, Experiments 1 and 2 demonstrate that, much like the mammalian hippocampus, the avian hippocampus is critical to behavioral inhibition and spatial processing.