Mediodorsal nucleus and behavior regulation in the rat.

Twelve electrodes aimed at the mediodorsal thalamic nucleus were implanted in 6 rats. In 5 of these animals intracranial stimulation was effective in punishing a bar press response on a baseline schedule of water reinforcement. The sixth animal was not tested. In all 6 animals lesions produced through these electrodes disrupted response suppression to punishing electric shock superimposed on the same baseline. Those animals in which both parts of the mediodorsal thalamic nucleus were damaged showed a more marked and graded punishment effect of intracranial stimulation and a more profound disruption of the quantitative shock intensity-response relationship than those in which only the rostromedial part of the nucleus was damaged. Three other animals had electrodes implanted in the rostromedial hypothalamus or the midline thalamus. They showed neither the punishing effect of intracranial stimulation nor the dusruptive effect on response suppression of electrocoagulative lesions.