The effects of mammillary body and combined amygdalar-fornix lesions on tests of delayed non-matching-to-sample in the rat.

A series of experiments compared the effects of mammillary body lesions with those of combined damage to the amygdala and fornix on 2 tests of working memory, both of which used the delayed non-matching-to-sample rule. This comparison was based on evidence of the involvement of these regions in anterograde amnesic syndromes. The mammillary body lesions had no effect on the acquisition or subsequent performance of a non-spatial recognition task and had only a mild effect on the acquisition of a spatial forced-alternation task. Although the animals with combined amygdalar plus fornix lesions were able to master the non-spatial recognition task they were impaired when the levels of proactive interference were increased. The same animals were also severely impaired on the forced-choice alternation task. The overall pattern of results is seen as mirroring those found in primates and points to an underlying similarity in the mnemonic roles of these limbic regions.