Whether it happened to you or someone else, everyone knows what blackout drunk means. It’s probably ruined countless relationships and friendships, but what exactly causes it? Obviously, alcohol is the culprit, the process itself is quite complex. According to science, blackouts are the result of alcohol blocking the brain’s ability to form new memories due to an increase in inhibition stemming from changes in neurotransmitter levels.
Before we look at what alcohol does to the brain during a blackout, we first need to look at how memory works in the human brain. Many researchers believe in the general model of memory formation proposed by Atkinson and Shiffrin in 1968. This model (depicted below) suggests that all sensory input is encoded into a short-term memory that – after the process of rehearsal – is then consolidated into a long-term memory.
Where alcohol comes in
Research shows that alcohol primarily inhibits the ability of the brain to encode information in short-term memory storage into long-term memories. Typically, someone who is very intoxicated can remember information immediately after they are exposed to it because it is kept active in their short-term memory for around one minute or more. However, the encoding process that consolidates this short-term memory into a long-term memory is inhibited by alcohol. In short, alcohol inhibits our ability to form new memories – each experience of the night simply passes through our conscious experience without ever leaving a lasting impact.
You might be asking yourself why someone who is blackout drunk can still remember their name and where they went to school as a child. Although alcohol affects the consolidation of short-term memories, it doesn’t affect long-term memories that were encoded prior to intoxication, making the recall of these memories possible even in states of extreme inebriation.
Alcohol primarily acts as a gamma-Aminobutyric acid (GABA) agonist, meaning that it increases the levels of the GABA neurotransmitter throughout the brain by binding to GABA receptors. As the main inhibitory neurotransmitter in the human brain, activation of these receptors reduces the rate of neuronal firing in standard cellular processes.
When alcohol concentrations reach very high levels – such as those seen during blackouts – it also acts as an N-methyl-D-aspartate (NMDA) antagonist, in turn decreasing the levels of the glutamate, the neurotransmitter that acts on these receptors. Since glutamate is an excitatory neurotransmitter, blocking its receptors further inhibits neuronal firing.
After alcohol causes a widespread inhibition of brain activity through its action on GABA and NMDA receptors, it inhibits long-term potentiation – the cellular process that consolidates short-term memories into long-term memories through the strengthening of connections between neurons in the brain. This strengthening occurs specifically in areas of the brain associated with memory, such as the hippocampus.
The hippocampus is a structure in the brain located in the medial temporal cortex that plays a large role in the formation of memories. Long-term potentiation is known to occur primarily in this brain region and NMDA receptors in particular are known to play an important role in this process, which is why receptor blockage by alcohol is connected to its inhibition.
How much is too much?
Although it seems safe to assume that drinking large quantities of alcohol causes blackouts – and indeed blackouts almost always happen during periods of heavy drinking – heavy drinking alone is not enough to cause a one. Other factors such as the speed of drinking and drinking on an empty stomach are necessary to cause blackouts due to their connection to rapid increases in blood alcohol content (BAC). Even social drinkers can fall victim to alcohol blackouts by letting their BAC increase too fast.
“They were inexperienced,” said Daniel Goodwin, a researcher who has conducted numerous studies on the effects of alcohol on memory, in reference to first-year medical students that reported experiencing at least one blackout. “They drank too much too quickly, their blood levels rose extremely quickly, and they experienced amnesia.”
Ultimately, pacing the speed at which you drink and ensuring that you keep some food in your stomach will lessen the likelihood that you will experience a blackout after consuming large amounts of alcohol. Without paying attention to these factors, you risk waking up with no memory of your night, or worse – with alcohol poisoning.