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.