Drunken Prairie Voles Help Explain Alcohol’s Demons

Why do some people become more prone to attachment and sentimentality when drunk, while others tend to stray?

Could it be true vole love, or just a casual encounter? Depends on whether booze is involved. Photo: Dave Challender

Ladies: So, you’re at a party and are several drinks in. Suddenly, you are overwhelmed by a sudden desire to get close to your boo, who is hanging out with his boys on the other side of the room. You approach him, bat your eyes, and coo, “We need to talk about us.”

“But baby,” he says, barely looking up, “I’m playing beer pong.”

This story—based on an actual interaction as told to the author—can wildly vary in interpretation, depending on your point of view. Women might assume that the guy in this story is being a jerk, while males might be more inclined to think that the lady is being a bit overly needy. According to science, however, both sides could be justified in having these respective reactions thanks to their underlying biology.

This, at least, was part of the findings of a new study published in Proceedings of the National Academy of Sciences. The authors decided to investigate the dueling nature of intoxication—“in some cases, it erodes social relationships; in others, it facilitates sociality,” the authors write. Specifically, they wanted to see whether social attachment differed between males and females who willingly consume alcohol.

But rather than turn to humans, they relied on prairie voles: wide-eyed little fuzz balls renowned for their romantic faithfulness. Prairie voles’ life-long commitment to one another is so strong, in fact, that scientists regularly recruit these rodents as subjects of social monogamy experiments.

The researchers behind this new study decided to throw something of a prairie vole party in the lab. They introduced pairs of young adult male and female prairie voles who were still seeking that special someone, and recorded bonding-related rituals such cuddling and mating. Next, they provided the rodents with a couple beverage options in their cage: a water and ethanol mixer (essentially, vodka) and plain water. Then, they left the rodents alone for 24 hours to see what would happen.

They had a pretty good idea that the voles would choose to imbibe. “We previously demonstrated that prairie voles voluntarily self-administer substantial amounts of alcohol (ethanol) and can influence the drinking patterns of a social partner, similar to social drinking in humans,” they write. Sure enough, at the end of the 24 hours, they returned to find a bunch of drunken voles. The prairie voles went for the booze more than half the time, and consumed about 12.5 grams of alcohol per kilogram of their body weight.

The research team, led by scientists from the Oregon Health and Science University in Portland, then separated the two lovebirds and subjected them to the partner preference test—an experimental set-up previous studies have established to be remarkably sensitive for assessing everything from the effects of genetic influence to pharmaceuticals on social bond formation.

This test entailed introducing the boozed-up males and females to new potential partners for three-hour periods, and then reintroducing them to their old party pal. For comparison, they also did the same with another set of prairie voles who were not invited to the party and had been stuck together all night with only water. Importantly, both the drunken prairie voles and the sober ones mated with the same frequency during their 24 hour initial alone-time period, indicating that having or not having sex wasn’t the reason behind the prairie voles later reactions to their overnight partners. Likewise, the authors found no evidence that alcohol-related aggression, impaired locomotor activity (e.g., stumbling) or passing out played a role in determining whether two voles became a steady couple.

Nearly 100 percent of female prairie voles who had partaken in the ethanol festivities, they found, preferred interacting with their partner in crime rather than the new guy. In contrast, two-thirds of the sober females liked their overnight partners best, but the others did not care one way or the other or else liked the stranger better.  

Males were a different story, doing just the opposite. Upon being reunited, the soused males oftentimes shunned their prior paramours, instead tending to show significant interest in the intriguing new strangers they were introduced to. The sober guys, on the other hand, were hopeless romantics. All of them preferred their original partner to the stranger.

These results alone were quite telling, but the authors decided to dig deeper into the neural underpinnings of alcohol and bonding tendencies (unfortunately, some of the lovers were star-crossed and had to be sacrificed for this part of the experiment). They examined the brains of two sets of nine pairs of voles, some which had gotten drunk and others that had stuck with water.

Alcohol, they found, affected the neuropeptide systems in the rodents’ brains—areas that influence social behaviors and anxiety. In males only, it increased the density of fibers in the amygdalar, which other experiments have shown reduces anxiety. But in females, the team thinks, alcohol promoted more anxious feelings, leading the gals to want to shack up and establish a bond with someone. By contrast, alcohol seemed to have the opposite effect on males, relaxing them and making them less inclined to commit.

While prairie voles, of course, cannot be directly compared with human pairs like the beer pong-clashing lovers described earlier, there are some interesting parallels. “The enhancement of attachment in female prairie voles parallels to prosocial effects of alcohol in humans,” they team writes. So people, too, can become both more amorous and more expressive of their feelings, as anyone who has ever drunk-texted or has been on the receiving end of inebriated expressions of love knows.

But on the other hand, they point out that “the inhibition of bond formation in males is reminiscent of the negative effects of alcohol on long-term attachments and marital happiness, which occur for both men and women.”

In other words, unlike prairie voles, human men and women can fall on either side of the alcohol bonding reaction, becoming either more attached or disinclined toward attachment. So where you might fall may stem from what your brain looks like when you're drunk.

Luckily, for humans there's more at play to being a jerk or a cling-on than a mere biological reaction. We have the ability to change and control our behavior, which might mean setting limits on our bar tabs or just scrapping the beer pong.

Get the latest Science stories in your inbox.