Selectivity of the spatial learning deficit after lesions of the mammillary region in rats

Rats with lesions of the mammillary region (MB-R) or a control group (C) we re trained on a visual-spatial conditional associative learning task in whi ch they had to learn to go to one of two locations depending on the particu lar visual cue presented on each trial; the rats approached the cues from d ifferent directions. The animals were subsequently tested on a spatial work ing memory task, the eight-arm radial maze. Rats with damage to the MB-R we re able to acquire the conditional associative task at a rate comparable to that of the C animals. By contrast, lesions of the MB-R led to a severe im pairment on the radial maze. The present finding of a dissociation between the effects of MB-R lesions on two different classes of behavior suggest th at the spatial learning deficit following damage of this region may be spec ific to remembering one or more places over a given time but not the abilit y to form associations between visual and spatial stimuli. (C) 2000 Wiley-L iss, Inc.