What Happens to Your Brain When You Blackout from Drinking?

You may have had the experience of waking up somewhere unsure how you got there. Blackouts are common during episodes of binge drinking. The more frequently you drink, the more likely you are to black out. And while heavy drinkers tend to blackout more, anyone can blackout while binge drinking. It’s alarming to not know where you’ve been or what you’ve been doing. What exactly happens when you blackout?

There are two kinds of blackouts–fragmentary and en bloc. Fragmentary blackouts are more like brownouts. You remember some bits but not others. You’re in and out. If someone reminds you what happened, you might be able to remember. En bloc blackouts are the kind where you remember walking into the bar and then you remember waking up somewhere but you have no idea what happened in between. When someone tells you what happened, you still don’t remember. It’s all a void.

Blood alcohol content is the main factor in a blackout. The faster you drink, the more quickly your blood alcohol content rises, and the more likely you are to blackout. For most people, that amount is quite high–something like 0.15 to 0.2 percent. Women’s blood alcohol content tends to rise more quickly than men’s. Not only are they smaller on average, but women metabolize alcohol less efficiently, so women typically blackout at a higher rate.

A blackout is basically a failure to turn short-term memories into long-term memories. No one can tell you are blacked out because you act more or less normally, aside from being drunk. You can carry on a conversation and you can remember things from your past, but then everything new that happens gets binned.

How that happens is a bit complicated and memory formation is still not perfectly understood. The short version is that alcohol impairs the function of the hippocampus, which is an area of the brain involved in turning short-term memories into long-term memories. Specifically, alcohol inhibits the long-term potentiation, or LTP, in specific cells in the hippocampus. LTP makes long-term memories possible by strengthening connections between specific neurons.

Think of it this way: the difference between LTP when sober and drunk is akin to the difference between following tracks on the beach at low and high tide, respectively. Alcohol is like the surf washing away new traces. The reason for this is that LTP requires the activation of a receptor called NMDA. NMDA is activated by the neurotransmitter glutamate, which alcohol suppresses. The suppression of glutamate is part of why drinking relaxes you. No glutamate means no LTP, which means no new memories.

If you find yourself blacking out often, binge drinking and are concerned that you may have an addiction, please get in touch. 

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