BBC – Future – Why do only some people get blackout drunk?

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It was another regrettably familiar wake-up for Sarah Hepola. Much of her memory from the previous night was blank. She remembers talking to people at a party, but then after that a shadow drops over her memories.

How did she get there, where was the stamp on her hand from? Who bought the pizza? Who was the man beside her?

“I was like, well that’s weird, I don’t know what happened… I just kind of laughed it off, it just seemed normal to me,” she recalls.

This sort of memory loss happened time and again to Hepola – and from a very early age. It often felt like “a trap door had opened underneath me… I would wake up the next day and I would be in a different place,” she says.

She was experiencing alcohol-fuelled blackouts – a colloquial term with potentially serious consequences. As the word suggests, in this state all memories of the night turn dark after a point. Some drinkers experience less severe, fragmentary blackouts where only pieces of memory are lost.

Hepola’s regular blackouts didn’t ring alarm bells for her at the time. It was only looking back that she realised she had a “messed up” relationship with alcohol, experiences she has written about in a book

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If this type of amnesia after drinking alcohol sounds familiar, that’s because blackouts are surprisingly common: one analysis suggests that over half of university-aged drinkers have experienced some level of blackout when asked about their drinking habits, while a survey of more than 2,000 adolescents recently out of secondary school found that 20% had experienced a blackout in the previous six months.

“Fifteen years ago, the field didn’t accept these were common phenomenon,” says Aaron White of the National Institute on Alcohol Abuse and Alcoholism in the US, who spends most of his career studying blackout drunkenness. “Now we are all aware that [many] people black out.”

Scientists are now revealing more about why blackouts occur and why it affects some more than others – helping them to better understand and hopefully prevent the many negative consequences.

Until recent studies showed otherwise, for many decades it was believed that only alcoholics reached the state of being blackout drunk. A bizarre series of experiments – which never would be ethically approved today – revealed some startling insights.

In the late 1960s, a researcher called Donald Goodwin recruited alcoholics in hospitals and job centres to identify what happens when a drunken memory disappears.  

When they answered, he told them that the pan had dead mice inside

He found that out of 100 alcoholics, more than 60 experienced regular blackouts, some total and some fragmentary. He also revealed that individuals experiencing a blackout can act in a remarkably coherent manner. For instance, he showed that during intoxication subjects revealed “no impairment” of immediate memory and even were able to perform simple calculations. But 30 minutes later, these events were forgotten.

In follow-up experiments, he plied alcoholics with whiskey (up to 18oz – or half a litre – in four hours) and presented them with situations that were set up to “provide memorable experiences, which sober persons have no difficulty remembering”.

In one he showed participants pornography, then asked detailed questions about what they had seen. In another, with a frying pan in hand, he asked individuals if they were hungry. When they answered, he told them that the pan had dead mice inside. The drunk subjects had forgotten these memories after 30 minutes and could still not recall the events the following day. They could, though, recall these events up to two minutes later, revealing that their short-term memory was working.

Though these experiments were performed with alcoholics, they set the stage for understanding how even non-alcoholics act during a blackout. They remain influential in part because today – for obvious ethical reasons – scientists cannot ply participants with alcohol to induce memory loss. They must largely rely largely on questionnaires of past events instead.

It’s like a temporary gap in the tape

That chunks of memory are completely lost during a blackout goes some way into revealing what is going on in the brain. It’s believed that the hippocampus is momentarily impaired – this is the structure of the brain important for weaving together incoming information to create our memories of everyday events. People with severe damage to this area cannot create new memories.

Alcohol therefore shuts off brain circuits central to making episodic memories (memories of specific times and places), explains White, who has studied the process on a cellular level with rodent brains.

“We think a big part of what’s happening is that alcohol is suppressing the hippocampus, and it’s unable to create this running record of events,” he says. “It’s like a temporary gap in the tape.”

In rats, White showed that there are doses of alcohol where brain cells “still kind of work”, and higher doses where they are completely off – which explains partial blackouts where only fragments are lost. At the same time, two other important brain areas that feed the hippocampus information about what’s happening in the world are also suppressed when we drink alcohol, explains White. These are the frontal lobe, the reasoning area of the brain that we use when we’re paying attention to something, and the amygdala, the area that warns us about danger.

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