Why does alcohol cause memory loss

Why does too much alcohol trigger a blackout?

Every now and then someone drinks so much alcohol that when they wake up they don't know what actually happened while they were intoxicated. Such a blackout is also called a film tear. The person concerned then has only vague memories or no memories at all for a period of a few minutes to several hours. According to a 2015 survey, 30 percent of English teenagers who have ever drank alcohol have experienced such a memory gap by the age of 15. At 19 it was even 75 percent.

Medically speaking, it is a temporary anterograde amnesia: the ability to form new memories is temporarily impaired. So you can no longer remember the period in question because you didn't even remember it. In contrast, with retrograde amnesia, access to what has already been stored would be blocked.

Scientists have long believed that alcohol kills cells in the brain

Neuroscientists do not yet fully understand how the blackout occurs. It is clear, however, that processes in the hippocampus are disrupted. This area of ​​the brain is crucially involved in the fact that we form, store and retrieve memories and learn new things. Apparently alcohol affects the so-called long-term potentiation of the synapses on the pyramidal cells in the hippocampus. This mechanism strengthens the synaptic transmission of information between neurons and forms the basis of memory formation.

Researchers have long assumed that alcohol weakens memory because it kills brain cells. In fact, long-term alcohol abuse can damage nerve cells and permanently impair memory and learning. However, it is unlikely that there is brain damage behind an acute blackout. Instead, the intoxicant apparently changes the activity of certain glutamate receptors and thus boosts the production of certain steroid hormones. These in turn slow down the long-term potentiation of the synapses in the hippocampus. In experiments on rodents, my colleagues and I checked how much alcohol it takes. The blood alcohol concentration must be dangerously high, around 300 milligrams per deciliter - this corresponds to around 2.4 per thousand.

The amount of alcohol that triggers a blackout varies from person to person. However, those who drink large quantities quickly are more likely to experience it. In addition, drugs such as benzodiazepines and other drugs that have a similar effect on the brain also weaken memory formation and can cause a blackout even without or in combination with small amounts of alcohol.

We are currently investigating which substances strengthen the long-term potentiation under the influence of alcohol and thus support the formation of memories. As an antagonist, AP5 blocks certain glutamate receptors and thus prevents alcohol from exerting its negative effect. Likewise, the 5-alpha reductase inhibitor - a drug that is often used for enlarged prostates - partly counteracts the negative effects of alcohol because it prevents the formation of new steroid hormones.