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Researchers have always attributed positive emotions to the brain chemical, dopamine. Different levels of dopamine are responsible for controlling the levels of joy and pleasure in the brain, which is why drugs that raise dopamine can be so addictive. Dopamine, however, is not the only brain chemical responsible for joy and laughter. Researchers concluded that hypocretin, also known as oretin, is also involved in regulating positive emotions in the brain.

According to a study done by Jeremy Siegel, a professor at the University of California in Los Angeles, the chemical hypocretin, which has two types in the brain, is responsible for pleasure and reward. Hypocretin-1 levels rise simultaneously with increases in positive emotions, social interactions, and strangely, also anger. The researchers looked at the levels of hypocretin-1 and the hormone MCH in eight epileptic patients that received brain implants that would help them with tracking their seizures and possibly prevent them. The researchers monitored the levels of hypocretin-1 and MCH in these patients who were told that they qualified for the brain implants. Siegel and his colleagues found that patients who received good news had higher levels of hypocretin-1. The researchers also found that hypocretin-1 levels rose when the patients talked to their family members and friends and when they laughed.

"These patients are experiencing a lot of emotion. Sometimes they are in pain. If the surgery is successful, they'll be seizure-free. [In other cases], there's nothing we can do. This is a golden opportunity to get some deeper understanding of [these chemicals]," Siegel stated.

Siegel also studied the effects of hypocretin back in 2000 where he found that it was linked to daytime sleepiness and sudden muscle weakness, which are symptoms of narcolepsy. In that study, Siegel found that people who suffer from narcoleptic symptoms did not have the brain neurons that regulate hypocretin. The combination of both these studies reveals the effects of hypocretin when it is either absent or present in the brain. Researchers found that genuine laughter can trigger an attack of cataplexy, which is a common symptom of narcolepsy that causes the victim to lose muscle movements. Since these people suffering from narcolepsy do not regulate hypocretin-1 normally, the researchers suggested that the chemical might be responsible for preventing muscle loss during high levels of laughter and happiness in normal people. It is, however, unclear as to why hypocretin is linked to narcolepsy, cataplexy, and happiness.

"This is to my knowledge the first study that has measured these [substances] in humans under a variety of quite complex behavioral situations," Dr. Antonello Bonci, who was not a part of the study, stated. Dr. Bonci is the scientific director of the National Institute on Drug Abuse.

The overlapping functions of hypocretin might help researchers in developing new treatment options for patients who suffer from a wide range of complications from narcolepsy to depression and addiction. However, more research surrounding the role of hypocretin needs to be done before scientists can really understand how changing the levels of the chemical affects different aspects of the brain.

The study was published in Nature Communications.