Mediodorsal thalamic lesions and object recognition in rats

Rats with bilateral electrolytic or sham lesions of the mediodorsal thalamic nucleus (MD) were tested on a nonrecurring-items delayed nonmatching-to-sample (DNMS) task—a test of object recognition. In Experiment 1, naive rats with MD lesions required more trials to solve the DNMS task at a 4-sec retention delay than did sham-lesion controls, and after they had done so, their performance was worse than that of the controls at delays ranging from 30 to 300 sec. In Experiment 2, rats with MD lesions that had received extensive DNMS training prior to surgery required more trials to remaster the task than did sham-lesion controls, and subsequently, their performance was worse than that of the controls at delays ranging from 4 to 300 sec. These findings resemble those reported in monkeys and humans with MD lesions, and they suggest that DNMS deficits in rats with MD lesions may be a useful component of a rat model of diencephalic amnesia.