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For millennia, humans have enjoyed using alcohol as a social lubricant. The reasons seem obvious at first. Most of us have had a drink or two that's put us at ease, helped us lose our inhibitions, lifted our mood. And yet, literally for decades through the last century, psychologists and other scientists struggled to find evidence for what they termed the "tension reduction theory" that proposed alcohol was rewarding because of its relaxing, mood-enhancing effects. In the lab, alcohol often had no effect or even made people feel worse.

A new review in Behaviour Research and Therapy helps make sense of this mismatch between real life and the lab. Too much of the early research presumed alcohol's effects are straightforward, that if you give a dose of alcohol to a person sat alone in a psych lab, that its pharmacological effects will kick in and make them feel jollier and less anxious.

The reality, as Michael Sayette of the University of Pittsburgh explains in his review, is that alcohol's rewarding effects interact in complex ways with our thoughts and emotions and the social situations we find ourselves in. To uncover why social drinking is so rewarding, researchers have had to develop more sophisticated, realistic experiments. Here I've pulled out five of the key insights from Sayette's review that help explain why so many of us find alcohol the perfect companion when we're socialising.

Alcohol makes us stay in the moment

With moderate doses of alcohol we seem less affected by past experiences, our mood is more connected to the immediate moment. One study to show this involved researchers filming small groups of strangers interacting. Comparing the changing facial emotions of those participants who'd drunk modest amounts of alcohol with those who'd drunk a non-alcoholic beverage or placebo (they thought it was alcohol but it wasn't) showed that alcohol seemed to reduce "emotional inertia" - that is, the intoxicated participants' current emotions were less affected by their earlier emotions. As Sayette writes in his review, alcohol "increases the ability to experience the present moment unbound by past experience."

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Alcohol reduces anxiety, but not fear

Moderate intoxication doesn't seem to help reduce our fear of a threat that we know is definitely coming, but it does reduce our anxiety about unpredictable threats, which could help explain its appeal in social situations.

An unpredictable threat is more analogous to the challenge of a social situation where you never know when you might next suffer a snub or awkward exchange.

Researchers demonstrated this effect of alcohol by measuring participants' startle response to loud noises during a task in which they knew they were definitely going to receive mild electric shocks, or another in which there was uncertainty about whether they would receive a shock or not.

Drinking alcohol reduced participants' startle reaction and their subjective feelings of anxiety only when the shock threat was uncertain. "This experiment provides clear evidence that the magnitude of alcohol stress reduction is greater when there is uncertainty about the severity of the upcoming threat than when the threat is well defined," the researchers said.

Alcohol narrows our attention focus, making it easier to ignore worries and threats

When we're mildly intoxicated we seem to have less spare mental capacity which means that as long as we're currently distracted by a pleasant or non-threatening task - such as chatting with friends - our minds are less likely to have the resources left over to worry about other things. For a study published in 1988, participants were either mildly intoxicated or sober, and either looked at art slides or sat quietly, after being told that they would soon have to give a speech.

Being intoxicated and looking at art slides helped reduced the anxiety about the upcoming speech consistent with the "attention-allocation" model of alcohol's effects - that is, presumably the tipsy participants were unable to fret about the upcoming speech because the artwork occupied their diminished powers of attention. Alcohol or artwork on their own did not have the same benefit.

Nights like these often end at the kebab shop.
kaicho20 / Pixabay

Alcohol boosts social bonding and the catchiness of positive emotions

It's little wonder that early research struggled to pin down the rewarding effects of alcohol: so many of these studies involved testing participants on their own when some of alcohol's most relevant effects seem to manifest specifically in social situations.

Recent research has begun to capture these social effects. For example, when psychologists filmed small groups of strangers getting to know each other, they found that those groups who were mildly intoxicated reported increased feelings of closeness with their new acquaintances and they displayed more genuine "Duchenne" smiles, as compared with sober groups or groups drinking placebo. What's more, alcohol increased the frequency of "golden moments" when all three members of the group were showing Duchenne smiles at once.

Men and extroverts are especially likely to experience the social benefits of moderate drinking

Other research that's used the same format, of filming groups of strangers getting to know each other, has found that extraverts are especially likely to report mood-enhancing and social bonding effects of alcohol, which might partly help explain why extraverts are more likely to develop problems with drinking to excess. Similarly, men seem especially receptive to alcohol's social effects.

For instance, other research that's used conversation volume to gauge the merriment of social gatherings has found that small groups of sober women seem merrier than small groups of sober men, but this gender difference disappears when participants have had an alcoholic drink. The researchers said this shows "greater alcohol reward for male groups and thus identifies a mechanism that may support heavy drinking in male drinking contexts."

Concluding his review, Michael Sayette says that that there is still a lot more we need to know about social drinking: for example, a lot of the social group research has so far involved strangers, but of course much of the time we drink socially with friends in which case the precise effects of alcohol might be quite different.

He also notes that these findings on social drinking could help inform new ways to help people who have problems with controlling their alcohol consumption. For instance, by better understanding the rewarding psychological effects of alcohol, clinicians might be better placed to help clients find different, potentially healthier ways to increase their enjoyment of socialising.