The Neuroscience of Pleasure

I know what you're thinking: What does it feel like for a human to have his or her medial forebrain reward circuitry stimulated with an electrode? Does it produce a crazy pleasure that's better than food or sex or sleep or even "Seinfeld" reruns?
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In the 1930s, the psychologist B. F. Skinner devised the operant conditioning chamber, or "Skinner box," in which a lever press by an animal triggered either a reinforcing stimulus, such as delivery of food or water, or a punishing stimulus, such as a painful foot shock. Rats placed in a Skinner box will rapidly learn to press a lever for a food reward and to avoid pressing a lever that delivers the shock.

In the 1950s, the psychologists James Olds and Peter Milner modified the chamber so that a lever press would deliver direct brain stimulation through deep implanted electrodes. What resulted was perhaps the most dramatic experiment in the history of behavioral neuroscience: Rats would press the lever as many as 7,000 times per hour to stimulate their brains. This was a pleasure center, a reward circuit, the activation of which was much more powerful than any natural stimulus.

A series of subsequent experiments revealed that rats preferred pleasure circuit stimulation to food (even when they were hungry) and water (even when they were thirsty). Self-stimulating male rats would ignore a female in heat and would repeatedly cross foot-shock-delivering floor grids to reach the lever. Female rats would abandon their newborn nursing pups to continually press the lever. Some rats would self-stimulate as often as 2000 times per hour for 24 hours, to the exclusion of all other activities. They had to be unhooked from the apparatus to prevent death by self-starvation. Pressing that lever became their entire world.

Further work was done to systematically vary the placement of the electrode tips and thereby map the reward circuits of the brain. These experiments revealed that stimulation of the outer (and upper) surface of the brain, the neocortex, produced no reward -- the rats continued to press the lever at chance levels. However, deep in the brain, there was not just a single discrete location underlying reward. Rather, a group of interconnected structures, all deep within the brain and distributed along the midline comprised the reward circuit.

I know what you're thinking: What does it feel like for a human to have his or her medial forebrain reward circuitry stimulated with an electrode? Does it produce a crazy pleasure that's better than food or sex or sleep or even "Seinfeld" reruns? We do in fact know the answer to that question. The bad news, however, is that it comes, in part, from some deeply unethical experiments.

Perhaps the most egregious example was reported in a paper entitled "Septal stimulation for the initiation of heterosexual behavior in a homosexual male," published in 1972. The rationale behind this experiment was that because stimulation of the septal area evoked pleasure, if it was combined with heterosexual imagery it could "bring about heterosexual behavior in a fixed, overt homosexual male."

And so Patient B-19, a 24-year-old male homosexual of average intelligence who suffered from depression and obsessive-compulsive tendencies, was wheeled into the operating room. Electrodes were implanted at nine different sites in deep regions of his brain, and three months were allowed to pass after the surgery to allow for healing. Initially stimulation was delivered to all nine electrodes in turn. However, only the electrode implanted in the septum produced pleasurable sensations. When Patient B-19 was finally allowed free access to the stimulator, he quickly began mashing the button like an 8-year-old playing Donkey Kong. According to the paper,

"During these sessions, B-19 stimulated himself to a point that, both behaviorally and introspectively, he was experiencing an almost overwhelming euphoria and elation and had to be disconnected despite his vigorous protests."

Lest anyone think that it is only men -- creatures of inherently base urges -- who would respond in this manner, another recorded case, performed by a different group, involved a woman who received an electrode implant in her thalamus, an adjacent deep brain structure, to control chronic pain. This technique has proven effective for some patients whose severe pain is not well-controlled by drugs. However, in this patient the stimulation spread to nearby brain structures, producing an intense pleasurable and sexual feeling:

"At its most frequent, the patient self-stimulated throughout the day, neglecting her personal hygiene and family commitments. A chronic ulceration developed at the tip of the finger used to adjust the amplitude dial and she frequently tampered with the device in an effort to increase the stimulation amplitude. At times she implored her family to limit her access to the stimulator, each time demanding its return after a short hiatus."

So, not to put too fine a point on it, these patients responded just like Olds and Milner's rats. Given the chance, they would stimulate their pleasure circuits to the exclusion of all else.

Back to patient B-19: Before his brain stimulation began, he was shown a "15 min long 'stag' film featuring sexual intercourse and related activities between a male and female." Not surprisingly, he was sexually indifferent to this material and even a bit angry about being made to view it. Following pleasure circuit self-stimulation, however, he readily agreed to re-view the film," ... "and during its showing became sexually aroused, had an erection and masturbated to orgasm." All this in the decidedly unsexy environment of the lab.

So, with the patient starting to exhibit heterosexual tendencies, what were the experimenters to do? Would he ever have an actual sexual relationship with a woman? After careful consideration of all the options and with the well-being of the patient foremost in their minds, the investigators, whose names were Drs. Moan and Heath made a sober medical and scientific decision: Upon getting approval from the attorney general of the state of Louisiana, they hired a hooker to come to the lab at Tulane and attempt to seduce him. She succeeded -- they had sexual intercourse. The concluding sentence to the lengthy, overly descriptive paragraph describing their 2-hour long sexual encounter reads, "Then, despite the milieu and the encumbrance of the electrode wires [poor B-19 was attached to an EEG machine the whole time], he successfully ejaculated [in her vagina]."

Did patient B-19 actually become heterosexual? Following discharge from the hospital, he had a sexual relationship with a married woman for several months, much to the delight of Drs. Moan and Heath, who found this development quite encouraging. His homosexual activity was reduced during this period, but did not stop completely: He still liked to turn tricks with men to earn money. Long-term follow-up information was not available. Writing in the discussion section of their scientific report, Moan and Heath were enthusiastic about the prospects for this therapy: "Of central interest in the case of B-19 was the effectiveness of pleasurable stimulation of new and more adaptive sexual behavior."

While it's clear that patient B-19 found the brain stimulation to be intensely pleasurable, I'm not convinced that he truly became heterosexual, even temporarily. It should also be cautioned that this report concerns only a single individual, not a population (with a control group).

This study is morally repugnant on many different levels -- the profound arrogance of attempting to "correct" someone's sexual orientation, the medical risk of unjustified brain surgery, the gross violations of privacy and human dignity. Fortunately, homosexual conversion therapy with brain surgery and pleasure circuit stimulation was soon abandoned.

Many years later, experiments in both humans and critters have revealed that most experiences in our lives that we find transcendent -- whether illicit vices or socially sanctioned ritual and social practices as diverse as exercise, meditative prayer, or even charitable giving -- activate this pleasure circuit in the brain. Shopping, orgasm, learning, highly caloric foods, gambling, prayer, dancing 'till you drop, and playing on the Internet: They all evoke neural signal that converge on this same brain circuit activated in Olds and Milner's rats and in Patient B-19. This dopamine-using pleasure circuitry can also be co-opted by some psychoactive substances, like cocaine, nicotine, heroin, marijuana or alcohol. Evolution has, in effect, hardwired us to catch a pleasure buzz from a wide variety of substances and experiences from crack to cannabis, from meditation to masturbation, from Bordeaux to beef.

This piece is an excerpt from David J. Linden's new book, The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good. He is a professor of neuroscience at The Johns Hopkins University School of Medicine and Chief Editor of the Journal of Neurophysiology.

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