Rewarding and punishing effects from stimulating the same place in the rat's brain.

Delgado, Roberts, and Miller (1) found that electrical stimulation in hypothalamic structures of the cat brain would motivate the learning and performance of escape and avoidance habits. In another line of research, Olds and Milner (7) and Olds (6) reported a positive reinforcing effect from electrically stimulating septal and hypothalamic areas in the rat's brain. Finally, Roberts (8) discovered areas in the posterior hypothalamus of cats in which electrical stimulation would motivate the cats to learn the correct turn in a T maze to escape (i.e., terminate) the stimulation, but would not motivate them to learn to leave a distinctive starting box in time to avoid the stimulation. One hypothesis that Roberts suggested to explain this odd effect was that the onset of stimulation in these structures may actually be rewarding, although it becomes punishing quickly thereafter. To support this hypothesis, Roberts (9) tested his cats in a Skinner box and found indeed that they would press the bar to receive brief electrical stimulation of the brain (ESB). On the basis of this and other allied results, he inferred that brief stimulation in these structures produced a positive reinforcing effect. His hypothesis, then, was that the onset of stimulation in these structures was rewarding and that it became punishing only after it had been on for a few seconds. With this in mind, we can understand why his 5s might never learn to avoid the stimulation, although they would learn to do something to turn it off (escape) after it had been on for several seconds. The present study further investigates this hypothesis using albino rats as 5s, The over-all plan of the experiment is to start with a heterogeneous group of reward rats and to give several behavioral tests which will differentiate 5s having reward and aversion