L’experiment de Olds i Milner
https://en.wikipedia.org/wiki/Brain_stimulation_reward, http://alfre.dk/the-pleasure-center/]
In 1953, James Olds and Peter Milner, of McGill University, 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.[7] 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.[7] 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.[7][8] 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.[9] 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.[8] 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.
http://alfre.dk/the-pleasure-center/]
In a highly controversial experiment by Robert Heath in the 1950s, patients with violent tendencies had electrodes implanted in their brains in the hopes that stimulation would calm them down. Patients reported mild euphoric or pleasant feelings in response to the stimulus, but nothing close to the intense sensation that drove the rats to extreme behavior and exhaustion. These experiments were not specifically looking for areas of pleasurable brain stimulation, however, so it may be the case that targeting other areas or combinations of areas would result in a more intense sensation.
Either way, even without direct neural stimulation, we may still be susceptible to behavior analogous to that of the rat, continuously pushing a lever for more self-stimulation. Indeed, some scientists believe that addictions (such as alcohol or drug abuse) result from a reward deficiency syndrome, in which a deficiency in the brain’s reward centers results in a constant craving for relief in the form of substance abuse.