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Drunk Flies Can Learn, As Long As They Keep Drinking

You learn something new everyday—even if you’re a really drunk insect. In a new study out today in Current Biology, researchers at the University of Texas at Austin demonstrate that short-term alcohol consumption impairs learning, but that chronic...

by Kelly Bourdet
Nov 29 2012, 1:47pm

You learn something new everyday—even if you’re a really drunk insect. In a new study out today in Current Biology, researchers at the University of Texas at Austin demonstrate that short-term alcohol consumption impairs learning, but that chronic consumers adapt in ways that allow them to learn as well as their sober counterparts.

The animals were trained to associate a pleasant smell—well, pleasant to the fly larvae—with a heat-shock; associative learning would mean that animals would become less attracted to the smell. Researchers then fed half of the larvae an ethanol-enriched food source, while allowed the others to remain sober. The drunken larvae had internal alcohol concentrations equivalent to BACs of 0.05 to 0.08 for a human, enough to make you tipsy but not all-out wasted. All the larvae were then retested on their learned behaviors.

As you might expect, at first the drunken larvae performed worse than the sober ones, but after chronic exposure to alcohol, they eventually adapted to their inebriation and performed as well at this learning task as ethanol naïve larvae. To test for alcohol dependence, withdrawal, and learning, the researchers divided the drunk larvae into three groups: the first group stayed intoxicated with no change to their alcohol diet, the second group had their alcoholic food completely withdrawn, and the third group had their alcoholic food withdrawn but was later given alcoholic food for the short time period of one hour.

The perennially intoxicated larvae continued to learn as well as the sober ones. The group completely withdrawn from their chronic alcohol consumption learned less well, which is expected. But the group that had alcohol withdrawn and then given back continued to learn as well as the sober ones, despite the fact that their alcoholic consumption was now acute instead of chronic. Interestingly, alcohol naïve larvae given boozy food for one hour learned significantly worse than the group that had alcohol withdrawn then reinstated for one hour, despite the fact that both groups’ internal alcohol concentrations were the same. Further, the alcohol concentrations in these two groups were higher than that of the chronic drinkers.

According to the study, acute alcohol withdrawal is detrimental to learning, which we would expect—who wants to learn when you’re suffering from withdrawal, which, by some theories, is what powers hangovers. By halting withdrawal (with alcohol consumption), therefore, you can assuage symptoms of withdrawal and restore learning faculties. Nervous system hyperexcitability is a well-documented effect of alcohol withdrawal, and this manic condition may well hinder learning. But it’s likely that neural adaptation has also occurred in these larvae, producing changes in cognition that cannot be easily undone without reintroduction of alcohol. It’s perhaps a bit of evidence for the “hair of the dog” approach to hangovers: rather than try to sober up, wash it down with another Bloody Mary.

While it’s been shown that things learned in one environment are best recalled when that environment is reinstated—also known as “state-dependent learning”—the authors claim that the behavior they’re seeing "cannot be attributed to state-dependent learning, because the [approximately] 20 min training and testing assay for all treatment groups occurs on nonethanol plates.” It is instead theorized to be a neural adaptation that has developed in response to chronic alcohol exposure that does not hinder larvae when chronically exposed, but does hinder those who are suffering from acute withdrawal.

This isn’t the same thing as being better at a foreign language when you’re drunk—chalk that up to lower inhibitions or boosted confidence. And it doesn’t imply that learning is qualitatively better when the larvae are drinking. In humans, drunken states have been shown to inhibit the proper functioning of the hippocampus, which is an integral part of the brain’s memory ability. Still, some types of seemingly debilitating states have been shown to increase learning and memory: people under deep hypnosis, for instance, have been shown to perform better on learning tasks than people who have undergone lesser types of hypnosis.

In a meta-analysis of studies on human alcoholics published this year in Addiction Biology, researchers found that “cognitive dysfunction may linger for up to an average of 1 year post-detoxification from alcohol.” Clearly, here, acute withdrawal cannot account for such far-reaching cognitive effects. In any case, these studies might help provide insight into why alcoholics have such a hard time abstaining from alcohol in the long-term. If the process of re-adapting to a sober existence is so protracted, it’s not difficult to see why, once they’ve had a lot to drink, it’s hard for both humans and larvae to stay on the wagon.