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Love leaves a chemical imprint on the brain, and being apart for too long causes that imprint to disappear

Throughout history, love has been a constant theme for mankind. Biologically in nature, human consciousness stems from a series of electrochemical activities in the brain, and love is no exception. When you go on a date with your sweetheart, your brain produces more dopamine, a pleasure-inducing neurohormone that makes you eager to interact with each other and create the feeling of being "in love".

Interestingly, dopamine-induced pleasure is also produced by eating, as well as by addictions to substances such as smoking and drinking. Therefore, love is in fact an alternative "poison" that affects us subconsciously, leaving an indelible mark on our bodies, memories, and even our souls and making us fall in love without even realizing it.

On January 12, 2024, researchers at the University of Colorado at Boulder published a paper entitled "Nucleus accumbens dopamine release reflects the selective nature of pair bonds" in the journal Current Biology.

The study suggests that the brain produces more dopamine and a special "chemical imprint" when dating a "sweetheart". If you are in a normal relationship, the production of dopamine is much lower, like a flood (in a romantic relationship) versus a trickle (in a normal relationship).

Interestingly, this unique "chemical imprint" fades away after a breakup, suggesting that the brain works through an internal mechanism to remove the negative effects of love and move forward in a positive way, a discovery that could point the way to a new direction in the treatment of people with emotional disorders who have been hurt by love.

Monogamous prairie vole

In this study, prairie voles were used as subjects. Unlike most rodents, prairie voles are "monogamous" and usually love only one mouse in their lifetime. Like humans, prairie voles tend to form long-term partnerships, grooming each other, sharing nesting and parenting responsibilities, and even displaying sadness when they lose a partner. Such partnerships are so strong that, interestingly, the vole's English name, "vole," can be changed into the word for love with only a slight variation.

Therefore, the prairie vole is an excellent animal model for studying human love. By testing prairie voles, the research team sought to explore what happens in the human brain during love, which makes intimate relationships possible, and how we neurochemically overcome lost love when such relationships are broken.

How does love 'light up' the brain?

In the new study, the team used neuroimaging techniques to record, in real time, the changes that occur in the brains of prairie voles when they are close to their partners. The team first separated two mated prairie voles, and in subsequent tests, if the couple wanted to meet, they had to press a lever to open a door to their partner's room or climb over a fence in order to be reunited with each other.

Meanwhile, a tiny fiber-optic sensor tracked neural activity in the prairie vole's nucleus accumben in milliseconds, detecting the release of brain dopamine and glowing in real time. The nucleus accumben, located at the junction of the brain's basal nucleus and limbic system, is thought to be the brain's pleasure center, which responds to addictive substances such as food, alcohol, and tobacco and pleasurable stimuli such as sex.

According to first author Dr. Anne Pierce, "The fiber-optic sensors light up like glow sticks at a rave party when prairie voles press a lever or climb over a fence to meet a partner! Not only that, but human neuroimaging studies have shown that the nucleus accumbens also glows when we hold our partner's hand, like a light in the dark."

In contrast, if a stranger prairie vole appears on the other side of a door or wall, the fiber-optic sensor does not fluoresce. Furthermore, when dopamine secretion decreases, prairie voles will lose their strong desire to be reunited with their partner. This suggests that dopamine plays a key role in keeping love alive and that the brain's nucleus ambiguus secretes much more dopamine when we are with a partner than when we are with a stranger.

The research team conducted another experiment. The prairie vole couple will be separated for four weeks—the prairie vole's life expectancy in the wild is less than a year—four weeks for them is equivalent to "goodbye", and this time is also enough for them to find another partner.

Unfortunately, when the prairie vole couple was reunited after the 4-week separation, they still remembered each other, but their signature dopamine surge had almost disappeared. By the very nature of the brain's biology, the dopamine-based imprint of love disappeared, and the once-compatible partners were now strangers, no different from any other prairie voles.

All in all, this study shows for the first time that the neurotransmitter dopamine plays a key role in keeping love alive. When you are with your sweetheart, the nucleus ambiguus, the brain's reward center, releases large amounts of the hormone dopamine, prompting a strong and secure romantic relationship. However, when lovers are separated for a long period of time due to various factors, the imprint of love planted by dopamine in the brain fades away, and the relationship is sadly brought to an end.

Of course, the team also emphasized that more research is needed to determine whether these findings in prairie voles are also applicable to humans with more developed brains.