Spontaneous object recognition and object location memory in rats: the effects of lesions in the cingulate cortices, the medial prefrontal cortex, the cingulum bundle and the fornix.

The first experiment assessed the effects of neurotoxic lesions in either the anterior cingulate cortex (ACc) or the retrosplenial cortex (RSc) on a test of object recognition. Neither lesion affected performance on this task, which takes advantage of the rat's normal preference to spend more time investigating novel rather than familiar stimuli. In response to this negative result, a second experiment assessed the effects of much more extensive cingulate lesions (Cg) on both object recognition and object location memory. The latter task also used a preference measure, but in this case it concerned preference for a novel location. For comparison purposes this second study included groups of rats with lesions in closely allied regions: the fornix (Fx), the cingulum bundle (CB) and the medial prefrontal cortex (Pfc). Comparisons with sham-operated control rats showed that none of the four groups (Cg, Fx, CB, Pfc) was impaired on the object recognition task, adding further weight to the view that these structures are not necessary for assessing stimulus familiarity. The Fx and Cg groups were, however, impaired on the object location task, suggesting that these regions are necessary for remembering other attributes of a stimulus (spatial location).