Why do we “black out” after drinking alcohol?

Alcohol Black OutHow is it possible to “black out” after drinking alcohol – where you can still walk, talk (and perhaps send embarrassing texts) that you don’t recall doing the morning after? Does it have to do with oxygen in the brain?  (via email)

As a “hard-working” student, I feel that I am well placed to answer this question (due to my medical and biochemical studies, not personal experimentations of course). And as I’m sure you’re aware, alcohol affects how well your brain works and, in particular, how well you remember things. While alcohol influences many parts of the brain, some areas are affected more than others.

One part of the brain that does feel the effects of alcohol is called the ‘hippocampus’ – a region crucial for making memories. Seated deep within the brain, it is a place where there are many junctions between nerve cells from many different parts of the brain – a bit like a switchboard for telephone lines. The hippocampus somehow ties information from different parts of the brain together – strengthening junctions – and in doing so helps form memories as events happen.

Interestingly, alcohol affects how well we can make long term memories much more than short term ones. This means that you will be able to remember what drink you ordered, but you won’t be able to remember standing up and singing karaoke the next day.

For a bit more detail: brain signalling at the junctions within the hippocampus relies on a chemical messenger (neurotransmitter) called glutamate, which is detected by a receptor called ‘NMDA’. Alcohol stops the brain cells’ NMDA receptors from working as well as they should, meaning less information is transmitted though the hippocampus and so memories are harder to form.

This is a simple view of what happens as the brain is very complicated and alcohol will affect many different parts in different ways. Let’s just be thankful that we can’t remember the horrors from the night before!

Answered by James Crewdson.

Image credit: Martin Mutch on flickr

Article by James Crewdson

July 24, 2014

James Crewdson is a Clinical Medicine student at Imperial College London, having already completed a BA in Biological and Biomedical Science at Gonville and Caius College, University of Cambridge. He has a keen interest in all of biological sciences and in the happenings of Manchester City Football Club, the best team in the land and all the world. You can get in touch with him on Twitter at @JamesCrewdson1.


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