A Tale of Monogamy and Dopamine

In a recent hack, private information from nearly 30 million users was leaked from Ashley Madison, a “dating” website intended to facilitate extramarital affairs.  The sheer number of Ashley Madison users on this website raises some age-old questions of monogamy: is it instinctual, or even healthy?  What is it about our brains that cause some to seek monogamy and others to reject it?

A previous Knowing Neurons article postulated that our attractions are largely based on associations between physical traits and emotional satisfaction.  However, we know that adultery is not only present among those unhappy or unsatisfied with their partners.  Scientists model this “adultery” behavior by studying the Coolidge effect, which describes the reinstatement of sexual behavior when a sexually satiated animal is exposed to a novel and receptive mate.

The Coolidge effect, as the name implies, was coined from an anecdote involving former President Calvin Coolidge.  It’s said that as Mr. and Mrs. Coolidge were visiting a government farm, Mrs. Coolidge noticed a rooster that was mating recurrently.  Mrs. Coolidge asked how often the rooster copulated, to which the attendant replied, “Dozens of times each day.”  When the President heard of this story, he asked, “Same hen every time?”  This time, the attendant replied, “Oh, no, Mr. President, a different hen every time.”  President Coolidge, finding this quite funny, asked for the message to be relayed to his wife.  And thus, this phenomenon was aptly named the Coolidge effect.

This phenomenon might seem surprising in light of my previous article, which focused on preferring familiarity.  In building positive associations between physical traits and emotional satisfaction, one is more likely to stick to an accustomed mate.  How these two processes – associative conditioning, favoring familiarity, versus the Coolidge Effect, favoring novelty – function together in mate preference is still unknown.

This effect was first seen in the 1960s and has been observed in a variety of different mammalian species.  Through a series of experiments, scientists have shown this effect can be reversed through drugs that act upon different neurotransmitter systems, including dopamine.  Dopamine is a key player in the mesolimbic reward system, which is also implicated in phenomena such as addiction and depression.  This system, consisting of the ventral tegmental area and the nucleus accumbens, dictates pleasure, reward, and motivation.

In a classic study, Fiorino and colleagues studied dopaminergic activity within the mesolimbic system of a male rat during copulation, sexual satiety, and the reinstatement of sexual behavior with a novel mate in order to understand the motivation behind this reinstatement. Unsurprisingly, sexual behavior was associated with a robust increase in dopamine within the nucleus accumbens.  When the animal reached sexual satiety with its mate, these dopamine concentrations drastically declined back to the baseline seen prior to initiation of sexual behavior.  Interestingly, when this sexually satiated animal was presented with a novel mate, dopamine levels spiked again!

Other studies have demonstrated that animals allowed to mate until satiety will not reinstate sexual behaviors, even when tested 24 hours later.  However, Fiorino et al. show that these sexually satiated animals mate with a novel partner within a very brief time span following satiety, and this change in behavior was associated with a substantial release of mesolimbic dopamine.

Evolution has shaped a delicate balance between craving security from the familiar and excitement from the unfamiliar.  Whether it’s deciding to eat at your favorite restaurant or to branch out to a brand new eatery – or, the undoubtedly more complex decision of whether to stay faithful to one’s partner or to create an Ashley Madison account – the neuroscience behind motivational behaviors is closely tied into mesolimbic dopamine release.  While we have far from answered the question of whether monogamy is instinctual, the Coolidge effect gives us insight into the way your brain perceives and decides to seek novelty with a mate.

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Images made by Jooyeun Lee.

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References:

Fiorino, Dennis F., Coury, Ariane, & Phillips, Anthony G. (1997). Dynamic Changes in Nucleus Accumbens Dopamine Efflux During the Coolidge Effect in Male Rats, The Journal of Neuroscience, 17 (12) 4849-4855. PDF