Electrical hypothalamic stimulation in rats induces hyperthermia if and only if they learn to self-stimulate

Handling and exposure to a novel environment has been shown to produce an emotional fever in rats. Electrical stimulation of lateral hypothalamus sites produced a rise of intracranial temperature not different from this emotional fever. Once the rats learned to self-stimulate, the same electrical stimulation produced a rise of the intracranial temperature significantly higher than the emotional fever. During the autoshaping for self-stimulation a significant relationship was found between the rise of the intracranial temperature and time expressed as successive days of self-stimulation training, or between the rise of intracranial temperature and the increasing frequency of operant responses. This seems to indicate that when the rats learned to self-stimulate, an initially nonsense signal, without specific thermal effect, was transformed into a neural or neurochemical code producing a new or modified effect which was a significantly higher fever.