A COMPARISON OF THE EFFECTS OF ANTERIOR THALAMIC, MAMILLARY BODY AND FORNIX LESIONS ON REINFORCED SPATIAL ALTERNATION

The effects of cytotoxic lesions in either the anterior thalamic nucle i or the mamillary bodies were compared with those of fornix lesions o n a test of spatial working memory. All three lesions impaired acquisi tion of a forced alternation task in a T-maze, but the disruptive effe cts of the mamillary body lesions were significantly less than those f ollowing either fornix or anterior thalamic damage. When the alternati on task was changed, so as to increase proactive interference, the imp airment associated with mamillary body damage became more evident and was now equal in severity to that in the animals with anterior thalami c lesions. The fornix lesion group were the most impaired. In contrast , all three groups performed normally on a test of object recognition. The results add weight to the view that hippocampal - anterior thalam ic connections are critical for normal spatial memory and that the rel ative contribution of the mamillary bodies is task dependent.