Self-stimulation behavior can be elicited from various 'aversive' brain structures

Electrical stimulation applied to various brain regions of the negative motivational system: the dorsal part of the mesencephalic central gray area (CG) the medial hypothalamus (MH), the medial lemniscus (ML), the lateral tegmentum (LT) and the reticular formation (RF), produces vigorous escape responses in mice. In spite of their highly aversive consequences, stimulation of all these regions also elicits self-stimulation behavior. This paradoxical approach response was clearly observed when the animals were placed in a Y-maze where they could successively trigger and turn off continuous electrical stimulation. In effect, mice stimulated in 'aversive' structures, similarly to animals stimulated in the lateral hypothalamus (LH), were able to discriminate between the reinforced arm and the non-reinforced arm of the Y-maze in order to self-administer the stimulation. When the mice were placed in a lever press box which delivered 0.2 s of electrical stimulation, an evident self-stimulation behavior was observed in LH and in some animals implanted in RF or MH. On the other hand, the very low response rates recorded in CG, LT, ML and in other RF or MH implanted mice do not permit a description of the motivational properties of these different stimulation sites. These results show that stimulation of brain structures of the negative reinforcement system has an approach component which, however, shows up clearly only in certain experimental situations.