Why is it so much fun to hang out with friends? And is there really such a thing as a love hormone? New research from the Stanford University School of Medicine explains why it is pleasurable to socialize. The scientists identified processes in the brain that promote friendly behavior by producing gratifying sensations during social interactions.
“Our study reveals new insights about the brain circuitry behind social reward, the positive experience you often get when you run into an old friend or meet somebody you like,” said senior author Robert Malenka.
Dr. Malenka has focused much of his research on the brain’s reward circuitry, an assembly of interacting nerve tracts that motivate humans toward incentives.
“The reward circuitry is crucial to our survival because it rewards us for doing things that have, during our evolutionary history, tended to enhance our survival, our reproduction and the survival of our resulting offspring,” said Malenka. “It tells us what’s good by making us feel good. When you’re hungry, food tastes great. When you’re thirsty, water is refreshing.”
Dr. Malenka explained that the most critical component of the brain’s reward circuitry is a nerve tract that runs from the ventral tegmental area deep in the brain to a midbrain structure called the nucleus accumbens. Neurons in the ventral tegmental area signal the release of dopamine in the nucleus accumbens. Dopamine produces a wave of pleasure and informs the brain that the event going on is helpful for survival.
Although the researchers established that reward circuitry plays a role in social interactions, they still needed to determine how extra dopamine is released during socialization. The researchers discovered that another chemical called oxytocin is responsible.
Oxytocin is also known as the “love hormone” because it’s thought to be involved in falling in love, sexual arousal, and mating. The primary source of oxytocin is the paraventricular nucleus, which resides in the hypothalamus. The team developed tests to identify oxytocin’s role in social behavior.
The researchers found that a tract running from the paraventricular nucleus to the ventral tegmental area carries oxytocin. They demonstrated that activity in this tract’s oxytocin-secreting neurons increased during mice’s social interactions and that this neuronal activity was required for their normal social behavior.
The study revealed that oxytocin released in the ventral tegmental area by neurons originating in the paraventricular nucleus promotes sociability by binding to receptors on the dopamine-secreting neurons. This triggers the reward-circuit tract.
Dr. Malenka said that the results of this study may be able to help researchers develop medications for individuals with neurological disorders that prevent them from experiencing pleasure through connecting with other people.
Dr. Malenka also hopes the research will foster a kinder global society. “With so much hatred and anger in the world,” he said, “what could possibly be more important than understanding the mechanisms in the brain that make us want to be friendly with other people?”