Alcohol and Blackouts

People walking at night drunk

I’ve been reading Matthew Walker’s excellent book ‘Why We Sleep’ (about 5 years too late and I’m sure many people reading this will already have read it, but if you haven’t I would very much recommend it). I suspect I may be doing more than one blog post off the back off this but I wanted to talk in this one about alcohol induced blackouts.

When I first published Alcohol Explained (8 years ago now) I did a chapter on blackouts. In essence I said that although it is all theoretical, the prevailing theory is that we have a short and a long term memory, and alcohol prevents memories from passing from the short term to the long term memory. I was very pleased to read in ‘Why We Sleep’ details that not only validate this, but also provide a lot more detail on the mechanics of it.

The hippocampus (a long, finger shaped structure tucked deep on either side of your brain) provides an information store for new memories. But it is limited in what it can store. Another part of our brain (the cortex) contains our long-term memories and has a much greater storage capacity. Matthew Walker likens the hippocampus to a small USB stick, and the cortex to a hard drive. The hippocampus has limited storage and if you exceed its capacity you:

“…run the risk of not being able to add more information, or equally bad, overwriting one memory with another…”

So how do you transfer a memory from the hippocampus with its limited storage, to the cortex? You probably won’t be surprised to read, given the subject matter of the book, that this is done during sleep. I found this next bit fascinating:

“…we observed [during sleep] a strikingly reliable loop of electrical current pulsing throughout the brain that repeated every 100 to 200 milliseconds. The pulses kept weaving a path back and forth between the hippocampus, with its short-term, limited storage space, and the far larger, long-term storage site of the Cortex (analogous to a large memory hard drive).”

If this wasn’t enough, using MRI scans scientists can actually see where memories are being pulled from. If you teach someone something new, then ask them to recall it, before sleep the memories are pulled from the hippocampus, after sleep they are pulled from the neocortex.

So how does alcohol impact sleep? Well I deal with this is both Alcohol Explained and (in more detail) Alcohol Explained 2 but suffice to say, drinking ruins our natural sleeping patterns. To quote Matthew Walker again (this time he is talking about alcohol induced unconsciousness):

”I am very deliberately avoiding the word “sleep,” however, because sedation is not sleep. Alcohol sedates you out of wakefulness, but it does not induce natural sleep. The electrical brainwave state you enter via alcohol is not that of natural sleep; rather, it is akin to a light form of anaesthesia.”

So you don’t need to drink a lot, you just need to drink regularly, to hamper your brain’s ability to move memories from short to long-term memory, and when that happens you run out of storage space in your short term memory, and start overwriting memories as the storage space fills up. As Homer Simpson once said:

“Every time I learn something new, it pushes some old stuff out of my brain.”

We often talk about how wonderful it is to be ‘making memories’. How awful then to consume something that literally prevents us from making memories, no matter how wonderful or memorable the event in question.

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5 Responses

  1. I was going to comment on this theory, but can’t remember what I was going to say. I’m certain it would have been both pertinent and eloquent but the thoughts have been washed away on an ebbing tide of cider!

  2. That is an amazing piece of information. Thank you. I will try to remember it. The brain is incredible and to think there processes can be seen. I will keep trying to care for mine. Tanks again.

  3. This is fascinating. I’d only ever heard/read that during an alcohol-induced blackout, the brain isn’t able to “make memories” at all. But I’ve wondered why DURING a blackout period, one can often manage to have a conversation, write an email, make a sandwich, hail a taxi or somehow find their way home safely. So it makes sense that from minute to minute during a black out, the hippocampus/short term memory is working. And it also makes sense that lack of heathly, alcohol-free REM sleep makes it impossible for those memories to transfer to the long-term “hard drive”…the cortex. Thanks so much for sharing this great explanation and easy-to-understand analogy.

  4. This is fascinating! And so well explained in a quick, straightforward way. I’ve always been ‘prone’ to forgetting nights out when over drinking but over time, it had become so systematic, even when having limited drinks. This is mind opening! Thank you

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William Porter

William wrote Alcohol Explained to share his approach on recovering from alcohol dependency.

Read the first five chapters of 

Alcohol Explained

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