Drug reward

Brain stimulation reward (BSR) is a phenomenon in which direct stimulation of regions of the brain through either electrical or chemical means is rewarding and can serve as an operant reinforcer. The stimulation activates the reward system and establishes response habits similar to those established by natural rewards such as food and water. BSR experiments soon demonstrated that stimulation of the lateral hypothalamus and other regions of the brain associated with natural reward was both rewarding as well as drive inducing.Electrical brain stimulation and intracranial drug injections are among the most powerful rewards because they activate the reward circuitry directly rather than through the peripheral nerves. BSR has been found in all vertebrates tested, including humans, and it has provided a useful tool for understanding how natural rewards are processed by the brain as well as the anatomical structures and the neurochemistry associated with the brain's reward system.

Intracranial self-stimulation (ICSS) is the operant conditioning method used to create the BSR response.

In 1953, James Olds and Peter Milner observed that rats preferred to return to the region of the test apparatus where they received direct electrical stimulation to the septal area of the brain. From this demonstration, Olds and Milner inferred that the stimulation was rewarding, and through subsequent experiments, they confirmed that they could train rats to execute novel behaviors, such as lever pressing, in order to receive short pulse trains of brain stimulation. Olds and Milner discovered the reward mechanisms in the brain involved in positive reinforcement and their experiments led to the conclusion that electrical stimulation could serve as an operant reinforcer. According to B.F. Skinner, operant reinforcement occurs when a behavior is followed by the presentation of a stimulus, and it is considered essential to the learning of response habits. Their discovery enabled motivation and reinforcement to be understood in terms of their underlying physiology, and it led to further experimentation to determine the neural basis of reward and reinforcement. Since the initial discovery, the phenomenon of BSR has been demonstrated in all species tested, and Robert Heath similarly demonstrated that BSR can be applied to humans.

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