Dorsal/ventral hippocampus, fornix, and conditioned place preference

Conditioned place preference (CPP) is a learning paradigm requiring formati on of associations between reward and particular locations. White and McDon ald (Behav Brain Res 1993;55:269-281) demonstrated that amygdala (AMG) lesi ons impair, while fornix (Fx) lesions enhance learning of this task. In the present experiments, we replicated the effects of AMG and Fx lesions, but we also found that complete hippocampal (HPC) lesions interfere with normal performance. Thus, the effects of Fx and HPC lesions on CPP are opposite. This is in contrast with spatial learning in the water maze. Because it has been demonstrated that damage of dorsal HPC interferes to a greater extent with spatial learning than damage of ventral HPC, we also tested animals w ith either dorsal or ventral HPC disruptions on CPP. Lesions limited to dor sal HPC were followed by impairment on this task. In contrast, lesions limi ted to ventral HPC resulted in enhanced learning. We argue that Fx and HPC lesions do not have interchangeable effects in all learning paradigms. To e xplain the complex pattern of results presently obtained, we propose a nove l hypothesis regarding behavioral functions of HPC neural circuits. Implica tions regarding the interaction between memory systems are also considered. Hippocampus 2001;11:187-200. (C) 2001 Wiley-Liss, Inc.