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Saturday, 12 p.m., the light burns, your head throbs, and you have no recollection of how you got back home.
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Don't worry, you're not alone.
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More than half of college students experience blackouts, according to several studies.
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And let's be clear, blacking out doesn't mean passing out.
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You were probably awake and aware the entire night.
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So then, where did all those memories go?
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Let's rewind to Friday night.
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Normally, whenever you have an experience, like a conversation, a part of your brain called the prefrontal cortex stores that information in short-term memory.
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Then, another part of your brain called the hippocampus weaves those experiences together, so they can be stored away as long-term memories.
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So the next day, you remember the party as a whole, instead of the smell of sweat, house music, Jen was there.
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But here's the key part.
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Storing these episodes in long-term memory requires special neurotransmitters.
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But your liquor shots prevent the neurotransmitters from working properly.
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So instead of remembering the party, all you have is an incomplete, or even empty file.
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And the amount of alcohol in your system at the time influences how much you remember.
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Let's say you're a 73-kilogram adult man, and you've done eight shots in one hour.
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Your blood alcohol content is probably around 0.2% by this point, more than twice the legal limit for driving a car.
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And your brain may still be able to store some memories, so you end up with islands of memories separated by missing sections.
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That's called a fragmentary blackout, aka a grayout or brownout.
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But if you keep pounding those shots, it gets worse.
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Within the next half hour, you pound back another four shots.
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Now your blood alcohol content hits around 0.3%, and your hippocampus goes dark, and full amnesia sets in.
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This is called an en bloc blackout, and once you wake up, that entire night could be blank.
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Push your BAC much higher than that, and you might die.
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And yet your friends might not even realize you're in the middle of a blackout, since the alcohol didn't delete your long-term memories already safe in storage before the night began.
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So you can still carry on conversations and behave more or less like a typical person, to an extent.
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Blackouts aside, alcohol can still interfere with other regions of your brain, including those responsible for reasoning and decision-making.
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So during blackouts, people have crashed cars, gotten into fights, and committed or been the victims of sexual assault.
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They might just not remember it.
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That being said, not everyone gets blackouts.
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Your sex, body weight and family history all play a role.
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So that could explain why your friends recall the entire night, despite downing just as much tequila.
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But it won't save them from a wicked hangover the next morning.