The effects of mammillary body lesions on delayed matching and delayed non-matching to place tasks in the mice.

This study was designed to investigate the effects of different recognition procedures on memory performance in Balb/c mice. To this end, mice were submitted to spontaneous or contingently reinforced delayed non-matching (DNMTP) and delayed matching (DMTP) to place tasks in a T-maze. Results indicate that mammillary bodies (MM)-lesioned subjects are significantly impaired in the DNMTP tasks at the long (6 h) but not the short (5 min) delays; in contrast, they did not exhibit deficits in the DMTP task, whatever the delay considered. We stress the importance of task difficulty as a major factor explaining the different effects of the lesion in the two tasks.