Enhanced preference for perceptual novelty in the monkey after section of the fornix but not after ablation of the hippocampus.

Previously uncovered discrepancies between the behavioral effects of fornix sections and hippocampal ablations in the monkey suggested that damage to the fornix but not that to the hippocampus may result in a motivational post-operative change. To test this notion, control monkeys and those with damage to either hippocampus or fornix were given an opportunity to choose freely between presentations of novel or repetitive stimuli in two modalities. In the visual mode, the choice was between viewing color slides which changed on every trial or repeated presentations of a geometric pattern (experiments 1 and 1a). In the auditory mode, the choice was between trains of identical clicks and different sound patterns (experiments 2 and 2a). Monkeys with sections of the fornix, but not those with ablations of hippocampus, showed an abnormally marked preference for novel stimuli in both modalities, even when perceptual novelty was designed to compete unfavorably with food reward (experiments 1b and 2b). These findings (a) provide another instance of functional dissociation between the effects of fornix and hippocampal damage and caution against assuming safely that data obtained with sections of the fornix will always mirror the behavioral consequences of hippocampal ablations; and (b) suggest that the hippocampus of primates may participate in the mediation of cognitive-motivational aspects of behavior which should be taken into account when the role of the hippocampus in memory processes is considered.