LOVE is no longer a privileged topic for literature and fiction. Findings on hormones affecting social behavior have just given science a chance at love.

Scientific studies reveal that key brain areas and body fluids are involved in the ability to love and bond with others. Dr. Thomas Insel, Emory University neuroscientist in Georgia and director of the Yerkes Regional Primate Research Center, explains these “mysteries” of love.

Using a Midwestern rodent called a vole, Insel developed the best laboratory model for a study on behavior. He employed prairie and montane voles, species that are 99 per cent genetically identical, but with the last per cent resulting in radically different social behaviors.

Insel and his team discovered that prairie voles are highly social and monogamous while montane voles prefer seclusion, breed promiscuously, and abandon offspring soon after birth. Also, a widowed prairie vole prefers staying single than taking a new mate, in contrast with a montane vole’s polygamous behavior.

The team determined two hormones responsible for the behavior of the prairie voles: oxytocin, which is more active in females, and vasopressin, which is more active in males. The research team associated the hormones with behaviors such as parenting, social memory, territorial behavior, and aggression, all of which can be found in most mammals.

Oxytocin is a mammalian hormone that acts as a neurotransmitter. According to Maria Gina Macaranas, professor from the Department of Biochemistry, Molecular Biology, and Nutrition of the UST Faculty of Medicine and Surgery, oxytocin’s physiologic function is to induce labor.

“Oxytocin causes the contraction of the uterus to push the baby outward during a woman’s labor,” Macaranas said. It is also produced only during the laboring period of a pregnant woman to prepare lactation for breastfeeding the baby.

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In the brain, oxytocin is involved in social recognition and bonding, and even in the formation of trust between people. It is also responsible in female sexual arousal, monogamous bonding with the male partner, and maternal behavior. Plasma concentrations of oxytocin have been reported to be higher among people who are in love.

On the other hand, vasopressin released within the brain can affect memory formation, including delayed reflexes, mental imagery, and short- and long-term memory retention. It is involved in aggression, blood pressure regulation, and temperature regulation, mostly experienced at the peak of falling in love.

When vasopressin is released into the brain during sexual activity, it initiates and sustains patterns of activity that support the bonding between sexual partners, and the male’s aggression toward other males. A study published in the Journal of Neuroscience in 1997 on golden hamsters provide evidence that increased volume of vasopressin in the brain increases offensive aggression toward rival males, while maintaining protective behavior toward its partner.

Other love potions

There are other “love hormones” that affect other bodily systems as well.

Able to control love-struck feelings, serotonin regulates body temperature, mood, sleep, vomiting, sexuality, and appetite, all of which are experienced when in love. According to Macaranas, it is one of the “feel-good” hormones that might be heightened when a person in love encounters weird feelings.

In a 1999 study by Donatella Marazziti of the University of Pisa, Italy, levels of the neurotransmitter serotonin, which has a calming effect, is below normal in those who say they are in love as well as in people with obsessive compulsive disorder.

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Both men and women in love also have considerably higher levels of the stress hormone cortisol, indicating that courtship can be somewhat stressful.

“But the most intriguing finding is related to testosterone,” says Marazziti in her study. Testosterone, secreted from the male’s testicles, affects not only the physical body but also the brain, which is usually accompanied by the “sexual” advancement instinct. “Being an androgen, it is also related to sexual libido of males,” Macaranas said.

Men who are in love have lower levels of testosterone than other men. Love-struck women, in contrast, have higher levels of testosterone than their counterparts.

“Men, in some way, become more like women, and women become like men,” says Marazziti in her study. “It’s as if nature wants to eliminate what can be different in men and women, because it’s more important to survive (and mate) at this stage.”

Meanwhile, estrogen stimulates desire in females. As testosterone is to males, estrogen develops the female body with secondary characteristics at puberty stage. This greatly affects their menstrual cycle that favors fertility and procreation.

“When ovulating, during the times when women are fertile, they tend to be in estrus and overflowing with libido,” Macaranas said. “Estrus” refers to the phase when the female is sexually receptive, or in lay man’s term, “in heat.” But humans, like gibbon monkeys, have no specific estrus when they can only be sexually available. This is one reason why both species have been found to be monogamous, as one female partner is enough to satisfy the “needs” of her partner.

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In the course of falling in love and the chemical reactions involved in it comes the brain’s reward system. Commonly associated with pleasure, the neurotransmitter dopamine is released during naturally rewarding experiences such as love and sex, motivating a person to always perform activities aimed at those goals.

And that’s love actually. It has its magic and its puzzle science alone can solve.


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