Effects of Hippocampus and Medial Caudate Nucleus Lesions on Memory for Direction Information in Rats

A delayed matching-to-sample task was designed to assess memory for direction information in rats. During the study phase, rats traversed a maze arm oriented in 1 of 3 directions. After a delay period, a test phase was presented that required a choice between the study phase direction and a foil direction. Once rats reached a learning criterion, probe trials suggested that normal rats favor the use of direction, rather than turning response, information and use vestibular feedback. Rats were then given hippocampus, medial caudate nucleus (MCN), or cortical control lesions. Unlike control rats, those with hippocampus and MCN lesions exhibited marked impairments when retested. However, all rats were able to learn a direction discrimination task. These results suggest that the hippocampus and MCN support processes associated with short-term memory for direction information.