Alcohol blackouts, also known as alcohol-induced amnesia, occur when individuals are unable to recall some or all of the events that occur when they are intoxicated. Large quantities of alcohol, especially when consumed rapidly, can cause a blackout. While individuals may still be able to recall new information for short periods of time while under the influence of alcohol, alcohol prevents the brain from forming new long-term memories.

Consequently, once the effects of alcohol wear off and individuals are sober, they may not be able to remember things that they said or did while under the influence. Since alcohol also decreases inhibitions and negatively impacts judgment, individuals are more likely to engage in risky behaviors and then have little or no memory the next day.

How Alcohol Interferes with Memory Formation

Alcohol interferes with the brain’s ability to form new, long-term memories, according to research published through the National Institute on Alcohol Abuse and Alcoholism. Alcohol leaves previously formed long-term memories intact, as well as the brain’s ability to keep new information active in the memory for brief periods. As the quantity of alcohol consumed increases, alcohol’s impact on memory formation worsens. Individuals may only remember bits and pieces of an experience, which is known as fragmentary memory loss, or may lose the ability to form a long-term memory altogether. This is known as blacking out.

Memory formation impairment occurs because alcohol interferes with the activity in the hippocampus, the part of the brain that is responsible for the formation of autobiographical memories. Specifically, alcohol interferes with the receptors in the hippocampus that transmit glutamate, a compound that carries receptors between neurons. Alcohol activates some receptors while preventing others from working. This disruption is what prevents the formation of new, long-term memories.

During alcohol blackouts, however, the brain is still able to function relatively normally albeit with fewer inhibitions. This means individuals may make out with a random stranger at a bar, send an ill-advised passive aggressive email to their boss, or start dancing on the bar at the club and have no memories of this behavior the next morning.

Blacking Out, Binge Drinking, and Alcoholism

While blacking out does not mean that an individual is an alcoholic, it does mean that individual was engaging in binge drinking. Research also shows that individuals who engage in binge drinking are more likely to drive under the influence, have unprotected sex, or engage in other risky behaviors when compared with individuals who do not binge drink. Frequent alcohol blackouts should never be taken lightly or written off as a rite of social passage. Any time basic brain function is altered creates vulnerabilities for long-term damage.

The Prevalence of Binge Drinking

One in six adults binge drinks approximately four times each month, consuming eight drinks during each binge drinking session, according to the Centers for Disease Control and the National Institute on Alcohol Abuse and Alcoholism. Binge drinking is most common amongst individuals aged 18 to 34 years. 92% of adults who binge drink also report doing so in the last 30 days. (CDC, 2014) Binge drinking increases the risk for unintentional injuries, sexually transmitted diseases, unintended pregnancy, liver disease, and neurological damage. Binge drinking is also associated with an increased risk for alcohol blackouts from excessive drinking, reports the CDC.

To reduce the risk for alcohol blackouts and associated health problems, drink responsibly. This includes drinking on a full rather than empty stomach, alternating alcoholic beverages with water, and spacing drinks over an extended period. Continually blacking out while drinking could be a sign of alcohol dependency. If you or a loved one may be dependent on alcohol, talk to an addiction specialist about your treatment options.


Source
http://pubs.niaaa.nih.gov/publications/arh27-2/186-196.htm
https://au.reachout.com/~/media/pdf/alcohol%20and%20other%20drugs/reachout_a4factsheet_howdoesalcoholeffectthebodyandmind.ashx
http://www.cdc.gov/alcohol/fact-sheets/binge-drinking.htm
http://gizmodo.com/5977688/what-happens-to-your-brain-when-you-get-black-out-drunk