jenk

Helen Fisher, an anthropologist and the author of, most recently, "Why We Love," has long studied the human brain and love. She theorizes that the brain has evolved three mating drives: lust, the craving for sexual gratification; romantic love, a focused attention on another, often compared to an opiate-like state; and attachment, the feelings of calm, security and union with a long-term partner. Each drive travels along a different pathway in the brain, Dr. Fisher and colleagues say, each associated with different neurochemicals.

"Lust is associated primarily with testosterone in both men and women," she said. "Romantic love is linked with the natural stimulant dopamine and perhaps norepinephrine and serotonin. And feelings of attachment are produced primarily by the hormones oxytocin and vasopressin, which at elevated levels can actually suppress the circuits for lust."

"I'm not so sure that sex drive diminishes when most people believe it does," she added. "Show me a middle-aged woman who says she's lost her sex drive, and I'll bet if she got a new partner, who excited her, her neurochemical levels for lust and romantic love would shoot back up."
- Quoted in The NY Times

Hm. If that's the case, it could be part of why people see threesomes as a way to 'rekindle' their sex life.