When I arrived late to pre-drinks during my first year at university, it seemed important to catch up to others’ level of inebriation before braving the cold of the line outside the club and the exorbitant alcohol prices charged inside it. So I free-poured a very tall shot of vodka in my friend’s college room.
Waking up the next morning, I had almost no memory of the night. I assumed I must have passed out during pre-drinks before my friends brought me back to my room.
When I asked my friend to tell me what happened, I learned I had made it as far as the line for the club. There, I proceeded to hug the bouncer as my friends tried to persuade him to let me in.
The embarrassment I felt was akin to hearing about the questionable behaviour of a relative, only so much worse, because it was my own.
But even more disconcerting was realising I had been interacting with the world around me, yet I had no memory of any of it.
The experience made me wonder: what happens to our brains when we drink alcohol?
Disrupting the delicate balance of the brain
Alcohol’s effect on the brain is complex.
While other drugs may have a very specific effect on only one receptor in the brain (for example heroin increasing the brain’s natural opioid receptors), alcohol can act on several, Shalini Arunogiri, an associate professor and chair of the Royal Australian and New Zealand College of Psychiatrists’ Faculty of Addiction, says.
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Alcohol reaches the brain fast because it is a small, simple molecule that can pass directly through cell membranes, including the blood-brain barrier. It doesn’t need to be digested first, so enters the bloodstream within minutes. The brain receives a large share of blood flow, so its effects may be felt quickly.
Once in the brain, alcohol affects two key chemical messengers, GABA (gamma-aminobutyric acid) and glutamate. The former slows down brain activity, while the latter stimulates it, says Dr Rachel Visontay, a postdoctoral research fellow from the Matilda Centre for Research in Mental Health and Substance Use.
When we first start drinking, alcohol disrupts the balance between the two, increasing the effects of the calming GABA chemical that makes you feel relaxed, she says, while other feelgood chemicals such as serotonin, dopamine, and endorphins are also getting a boost.
As you drink more, the stimulatory effects of glutamate are dampened, further slowing down activity across all the regions of the brain, Visontay says.
As blood-alcohol levels rise, it further affects the frontal lobe, the part of your brain associated with thinking, planning, decision-making and judgment.
“If you were having a conversation, without alcohol on board, you usually think through what you’re going to say, what the implications might be,” Arunogiri says.
Add alcohol and “that’s when we start to get people making decisions that they might not normally have made, and might come to regret later”, Visontay says.
What happens as blood-alcohol levels rise?
As the level of alcohol in the blood – called the blood alcohol concentration (BAC) – rises above 0.08g per 100ml, people may lose their balance, reflexes and coordination as the cerebellum, which is the part of the brain responsible for control, is affected.
Once BAC rises beyond 0.15g, alcohol strongly affects the hippocampus, hampering the brain’s ability to turn short-term memories into long-term ones.
“We’re able to still form short-term memories and engage in a conversation with somebody around us where we remember what was just said to us, but we have the failure of transferring that to long-term memory, which is why we may wake up the next day not remembering the conversation,” Visontay says.
Some people’s memories will be fragmented, while others may struggle to remember whole periods of time, she says.
Known as “blackouts”, this disruption to memory is different to passing out. At about the same BAC of 0.15g , difficulty breathing may occur as the signals between the brain and body are diminished. It’s why at a BAC above 0.30g, people can go into comas or die as vital functions are suppressed, Visontay says.
Why biology and genetics matter
These effects can vary widely from person to person, Arunogiri says, due to differences in how quickly alcohol levels rise in the bloodstream, and in brain and body chemistry.
Drinking in quick succession, a low weight, or drinking on an empty stomach can all cause blood-alcohol levels to rise more quickly, making the acute effects of alcohol more pronounced, Arunogiri says.
Sex also makes a big difference. Women drinking the same amount as men reach higher blood-alcohol levels and experience more impairment, for a range of biological reasons, Visontay says.
This is true even for men and women of the same body weight, she says.
“This is because women have less body water per kilo of weight, meaning women disperse the alcohol less throughout the body, and also because women metabolise alcohol differently,” Visontay says. “Men are actually better able to break it down quickly when it first reaches the stomach.”
Genetics also make a difference. Some people’s genetic makeup makes them feel more pleasure from alcohol than others because they have an increased dopamine response in the brain reward’s centre, increasing the risk of heavy drinking and developing alcoholism.
It is not known why some people with a given blood-alcohol level will experience blackouts while others won’t, and Visontay says – while there may be genetic factors driving it – blood-alcohol levels rising very quickly is known to increase the risk.
Blackouts are also more common when people start drinking: research shows almost one in two adolescents who have started drinking experience one by age 19.
‘Disorienting and destabilising’ – the psychological effects
There are also a range of psychological effects people may experience after drinking, says Rachel Samson, a director of the Australian Association of Psychologists.
Waking up with fragments of memory is in itself very “disorientating and destabilising” and this is exacerbated when others are affected. For example, those who black out may receive text messages from people angry because of behaviour while drinking, Samson says.
“You might find out from someone you’re with about the embarrassing things you’ve done,” Visontay says.
Dr Kelsey Perrykkad, a cognitive scientist and philosopher at the Monash Centre for Consciousness and Contemplative Studies, says finding out about acting out-of -character or experiencing something “horrible” can be “impactful on your sense of self”.
She says these changes in how we see ourselves aren’t just emotional and psychological but lead to changes in the brain at the neural level.
“A lot of people think that, in young adulthood, your brain stops changing … but one of the great discoveries of the last 50 years is that the brain changes constantly through adulthood,” she says.
The significance of adolescent development is why young people under 18 are advised they should not drink, Visontay says.
While there is no safe level of drinking, adults should look at the national guidelines, which, Visontay says, “don’t recommend people abstain totally, because people aren’t going to do that, especially over the festive season”.
“We really normalise drinking alcohol,” Samson says. “We’re not necessarily seeing it as a drug that impacts our brain chemistry but that is what is happening.”
