Fimbria-fornix lesions in young rats impair acquisition in a 14-unit T-maze similar to prior observed performance deficits in aged rats

Bilateral electrolytic lesions were made in the fimbria-fornix of 3-month-old male Fischer-344 rats. One week after surgery, acquisition in a shock-motivated 14-unit T-maze was assessed in these experimental animals and compared with that of sham-operated and unoperated controls. All animals were pretrained to criterion in one-way active avoidance in a straight runway before receiving two 10-trial daily sessions in the complex maze task in which the response requirement was to negotiate each of five maze segments within 10 sec to avoid footshock. All groups showed high levels of performance in pretraining. In the complex maze, rats sustaining damage to the fimbria-fornix exhibited learning impairments compared with controls in all analyzed performance measures including errors, run time, number of shocks, duration of shock, and alternation errors. The latter measure, which reflected the rat’s tendency to maintain a strategy of alternating responses at the choice-points, showed no evidence of change with training among lesioned animals, whereas control animals demonstrated a dropout of this response strategy. The impairment in maze performance associated with the fimbria-fornix lesions appeared to parallel those previously observed in scopolamine-treated young rats and in aged rats.