Your Brain in a ‘Blackout’
Alcohol and Memory
When you drink alcohol, it travels through your bloodstream to your brain, where it has numerous effects. Aside from the euphoric effects that often motivate drinking, these effects include changes in the normal function of the hippocampus, a part of your brain that plays a primary role in your basic capacity to create, store and recall your short- and long-term memories. Particularly, alcohol interferes with your ability to transfer your memories from short-term recall to long-term recall. The initial impact of this interference is detectable after the average person has a couple of drinks. As alcohol intake increases, changes in the normal function of the hippocampus grow more and more profound.
What Happens During a Blackout?
During an alcohol blackout, memory interference reaches a critical stage. Technically, your mental state while experiencing one of these episodes qualifies as a form of amnesia. This is true because disruption of normal hippocampus function grows so extensive that the ability to turn short-term memories into long-term memories largely or completely breaks down. When this occurs, you literally cannot complete the required transfer process, and your brain fails to make durable memories of what you think, say or do while a high level of intoxication continues.
The exact extent of the lost ability to form long-term memories varies from person to person, and also depends on exactly how high your blood-alcohol content (BAC) rises. If your BAC rises past a certain point, you may totally lose the capacity to complete the transfer process inside the hippocampus. This means that you will not have any memories of what happened during an alcohol blackout. (Doctors and researchers sometimes call this state an “en bloc” blackout.) More often, people who drink heavily over a short span of time experience partial or fragmented blackouts, which allow for some memory formation and later memory recall. Generally speaking, partial blackouts occur at lower blood-alcohol levels than en bloc blackouts.
Behavior During a Blackout
During a blackout, your hippocampus retains its ability to form short-term memories. This fact explains why a person experiencing a blackout episode can appear to function more or less normally (at least normally for an intoxicated individual). Essentially, during an episode, you can do anything that you would otherwise do. At the time, you will have no way of knowing that the normal transfer of information is not taking place inside your brain’s hippocampus. Only when you emerge from a blacked-out state will you notice the partial or complete disruption of your ability to remember what happened.
Risks for Blacking Out
Research indicates that you have a higher chance of experiencing an alcohol blackout if you regularly drink too much alcohol and qualify for an alcohol abuse diagnosis. However, blackouts are not uncommon among social drinkers who only get drunk occasionally. This is especially true for periodic binge drinkers, who knowingly or unknowingly consume enough alcohol to reach a legally intoxicated state in two hours or less.
National Institute on Alcohol Abuse and Alcoholism: What Happened? Alcohol, Memory Blackouts and the Brain https://pubs.niaaa.nih.gov/publications/arh27-2/186-196.htm
Columbia University – Go Ask Alice: Alcohol Use and Memory Loss – Blackouts? http://www.goaskalice.columbia.edu/answered-questions/alcohol-use-and-memory-loss-%E2%80%94-blackouts