In 1953, two postdoctoral researchers, Peter Milner and James Olds, worked in the laboratory of the acclaimed Canadian neuropsychologist Donald Hebb. Their research involved surgically implanting electrodes into the brains of rats and observing the animals’ responses to an electrical impulse stimulating different areas of their brains. The rats recuperated in a few days and behaved more or less normally, the only difference being that they now had wires “growing” out of their heads.

Discovery of the brain’s pleasure centre

With one of these experiments the scientists hoped to study a part of the brain they thought was connected with sleep cycles, but the electrodes in the rats’ brains accidentally slipped away from their intended location. Initially the scientists activated the implanted electrodes every time a rat went to stand in a particular corner of the cage, but later modified the mechanism so that the rats pushed the button themselves and thus sent electric impulses to their own brains. This modification in the way the impulses were administered contributed to one of the most dramatic results in the history of behavioral neuroscience.

The rats that were sending electrical impulses to their own brains got caught in a bizarre obsession. They pushed the stimulation button up to seven thousand times an hour. The rats were pushing the button so fanatically they even forgot to eat and drink. Even the nursing females suddenly forgot all about their offspring and kept pushing the button non-stop, twenty-four hours a day. Milner and Olds were quick to realize that this experiment was no longer targeting the brain center that controls the sleep/wake cycle, but had led to the discovery of the pleasure center in the mammalian brain.

The next question naturally was the extent to which this experiment applied to the human brain when stimulated in the same fashion through surgically implanted electrodes. The idea may sound preposterous since this experiment today probably would not be authorized by any ethics committee in the world, but it was indeed carried out only a few decades ago.

American psychiatrist Robert Galbraith Heath attempted treating patients suffering from severe depression and schizophrenia by implanting electrodes deep into their brains. In 1972 he published a curious article on reconstructing the Milner and Olds experiment on a twenty-four-year-old male patient, referred to in the paper as B-19.

The results observed in the patient were as shocking as those seen in the rats. When his brain was electrically stimulated in the newly identified area, patient B-19 experienced strong feelings of euphoria and exaltation. When the stimulus was withdrawn, the patient strongly protested and demanded that the treatment continue. A similar experiment was conducted on a woman suffering from chronic pain symptoms. When the electrodes were inserted, she pushed the stimulation trigger with such zeal that she developed sores on her finger and started neglecting herself and her family.

The chemistry of happiness and satisfaction

Today it is no longer a secret that the source of intimate feelings of joy lies in the secretion of so-called happiness chemicals in the brain. It is less known however, that these happy feelings are caused by four different kinds of chemicals, producing four different kinds of happiness. In all the examples mentioned above, the area of the brain being stimulated was the one responsible for producing dopamine, with similar effects resulting from enhanced secretions of serotonin, oxytocin and endorphins.

Endorphins are nature’s painkillers and are used to block the feeling of pain. The mechanism evolved to enable wounded wild animals to run from predators. If our brain could release endorphins all the time, we would be able to run with a sprained ankle, which occasionally happens to high performance athletes when they fail to notice an injury. But this mechanism is only intended to resolve life-threatening situations because masking the pain can easily aggravate the injury and possibly even cause death.

The brain starts releasing endorphins when it receives a signal from pain, either physical or emotional. A slight amount of pain is triggered when we run, causing a release of endorphins which can eventually addict us to running. But there aren’t many activities where self-injury is small enough to be overridden by the benefits of endorphin production. Opiates have a similar chemical structure to endorphins and unsurprisingly have similar effects, manifesting strong feelings of euphoria.

Oxytocin is a chemical related to trust. It is triggered when we bond with people around us. Dubbed the “cuddle” chemical, it promotes trust, love and companionship. It is a form of reward sent to us by our brains when we successfully form new trustworthy social bonds. The same chemical is released during orgasm and breastfeeding.

The mammalian brain starts releasing increased amounts of oxytocin immediately after a baby is born and reunited with its mother. This keeps the baby close to a safe family environment. Unlike mammals, reptile species haven’t developed this mechanism, which prevents offspring from becoming attached to their parents. In regulating their behavior, reptiles rely solely on the feeling of pain or similar sensations. If for instance they don’t get enough sun, they feel pain, which wears off when they get warm again. But even when they succeed in reducing the pain, they can’t feel happy because their brains don’t possess a chemical structure that would induce happiness. The benefit of this pain-avoiding system is that it functions well on a very low energy intake. Since it requires fewer neurons, it is more energy efficient. Mammals’ and humans’ brains, however, are much more complex and require greater amounts of energy.

When growing up, the child-mother bond in mammals transforms into an attachment to a larger group, the herd in animals and family in humans, eventually leading to a bond with a nation, a political party, a football club or any other group we identify with. When out of sight with other group members, herd animals typically start releasing cortisol, a chemical triggered by stress and an “antidote” to happiness-inducing chemicals.

Cortisol release signals danger, while the secretion of serotonin indicates the danger has passed. Serotonin gives a green light to normal behavior. It lets us know that whatever we are currently doing is safe and that we can continue doing it.

If people around you pay you respect, their behavior triggers a dose of serotonin in you. This is done spontaneously, even if we are not aware of the reason for their respect. Those mammals that occupy a higher position in their group have higher levels of serotonin and are less prone to aggression; low levels of serotonin being the cause of impulsive and asocial acts. Serotonin has two important functions: it lets us know we are out of a danger zone and that it is safe for us to feed.

Dopamine, the last of the four “happiness chemicals”, keeps mammals motivated to exert themselves until they reach their goals. It causes excitement about the expectation of something good coming our way. It signals the anticipation of reward but not the reward itself. The release of dopamine is a sign that we are coming closer to the finish line, while oxytocin and serotonin mark the reward we actually get. Dopamine promotes both learning and pleasure in order to make us remember how pleasure was achieved. The highest doses of dopamine are released when the final reward exceeds our expectations, but at the same time it is precisely in the dopamine system that addictions develop.

If we take love as an example of a complex emotional state in terms of brain chemistry, we can identify several chemical components. Dopamine is released in the state of expectation of future pleasures, oxytocin accompanies the formation of trust and serotonin signals security. And in unrequited love endorphins tune in, which makes our concoction of “happiness” about as perfect as it gets.