Question: What is it that makes some people the life of the party, others recluses and still others shoulder-shruggingly indifferent to the delights of social interaction? Answer: We don't know. The biological forces driving sociability or, in some disorders, its absence remain a puzzle.

That said, a new study in Science begins to provide an answer, pinpointing places and processes in the brain that promote socialization by providing pleasurable sensations when it occurs.

Much has been written and said about a substance called oxytocin, produced in the brain and inappropriately touted by some scientists as the "love hormone" because because it’s thought to be involved in falling in love, mother-child bonding and female sexual arousal as well as lifetime pair-bonding of sexual mates among some species. But other investigators have thrown a wet blanket on the "love hormone" hype by showing that oxytocin can also increase one's distrust of outsiders. That's human nature, folks. It makes biological sense, because throughout our evolution as hunter-gatherers traveling in small bands in competition with other bands for scarce resources, the best defense of self and family or clan was no doubt a strong offense against individuals who didn't bear characteristic features (looks, language, style) of one's own group.

There's obviously still a lot to learn about what this multifaceted chemical does in the brain that makes it. In the new study, Stanford neuroscientist Rob Malenka, MD, PhD -- a renowned expert at teasing apart the brain's convoluted circuitry and figuring out how its components work together -- and his colleagues revealed the function of a specific nerve tract that runs from the hypothalamus, deep in the brain, to the origin of another tract famous among scientists as the most important component of what's called the "reward circuitry."

Quoting Malenka from my news release about the study:

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... 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. Sex is great pretty much most of the time. Hanging out with your friends confers a survival advantage, too, by decreasing your chances of getting eaten by predators, increasing your chances of finding a mate and maybe helping you learn where food and water are.

Because the reward system is so critical to survival, it’s been carefully conserved over evolution and in many respects operates just the same way in mice as it does in humans, making mice good experimental models for studying it. The researchers showed in mice that the newly identified tract secretes oxytocin from the tips of projections it sends to the better-known reward-circuit tract, tripping off activity there -- with behavioral consequences: Boosting oxytocin secretion in the latter region, sophisticated experiments demonstrated, makes mice more socially curious; inhibiting oxytocin's binding to receptors for it on nerve cells there diminishes mice's social curiosity.

The findings could lead to potential therapies for people, such as those with autism or schizophrenia, who are painfully averse to socializing.

Previously: "Love hormone" may mediate wider range of relationships than previously thought, The two faces of MDMA: Drug of abuse, and promising therapeutic and research tool and Obscure chemical indicted in chronic-pain-induced "Why bother?" syndrome

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