Subtle but distinct impairments of rats with chemical lesions in the thalamic mediodorsal nucleus, tested in a radial arm maze.

Tested the performance of 18 hybrid BD9?×?BD10 rats trained in a radial arm maze before and after chemical lesions of the thalamic mediodorsal nucleus or the ventral tegmental area. Their behavior was compared with that of 18 sham-operated controls. Lesions were produced with ibotenic acid, a compound that selectively destroys neurons while apparently leaving fibers of passage intact. Results revealed no intergroup differences in the number of errors performed when all 6 trials were given in 1 session without interruption. The group with mediodorsal lesions, however, made significantly more errors than either of the other 2 groups when a delay of 1 hr was interposed between the 1st 4 and the last 2 trials. Furthermore, these Ss differed from Ss of the other groups in the number of sessions necessary to reach criterion, in the time needed to finish a session, and in the directness with which a goal was approached. Ss with lesions of the ventral tegmental area did not differ from Ss of the sham-operated control group in any of the measures taken. It is suggested that the deficits of rats with mediodorsal lesions resemble qualitatively those found in human patients with lesions of the mediodorsal nucleus. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)