What Alcohol Does to the Brain | Alcohol
Alcohol affects the brain, body and mental health, with repeated use changing reward, stress and inhibitory systems.
Alcohol is usually described as a central nervous system depressant, meaning that its overall effect is to reduce or disrupt activity within the brain and nervous system.
That description can seem confusing because early intoxication may look anything but depressed. Someone may become louder, more confident, more sociable or more impulsive.
The apparent contradiction makes sense once inhibition is considered.
Parts of the brain normally restrain impulses, monitor consequences and regulate behaviour. Alcohol can interfere with these control systems. Reducing the brain's “brakes” may temporarily make behaviour appear more energetic or uninhibited even while nervous-system function is being impaired.
GABA and glutamate
Two signalling systems are particularly important.
GABAÂ is the brain's major inhibitory neurotransmitter. It helps reduce neuronal activity.
Glutamate is the major excitatory neurotransmitter and helps neurons activate one another.
Alcohol alters both systems, including enhancing important aspects of inhibitory GABA signalling and suppressing excitatory glutamate signalling. These effects contribute to relaxation and sedation, but also to slowed processing, poor coordination, impaired memory and reduced judgement.
This is more complicated than alcohol simply “switching GABA on” and glutamate off. Different receptors, brain regions and alcohol concentrations are involved. The useful everyday principle is that alcohol shifts the balance of neural activity toward suppression while disrupting the precision with which brain networks communicate.
Reward and learning
Alcohol can also activate reward-related pathways.
Dopamine signalling within reward circuitry helps the brain learn that an experience is worth seeking again. With alcohol, that learning can extend beyond the drink itself.
A certain pub, glass, friend, song, Friday evening or feeling of stress may gradually become linked with the expectation of alcohol. Eventually, those cues can generate desire or craving before any alcohol has been consumed.
Dopamine is therefore not simply a “pleasure chemical.” It also participates in motivation and learning about cues that predict important outcomes.
Judgement and inhibition
Alcohol interferes with frontal brain systems involved in planning, decision-making, attention, behavioural inhibition and evaluating consequences.
This is why intoxication can produce behaviour that appears out of character. The person has not necessarily developed completely different values. The systems that normally allow those values and future consequences to guide behaviour are functioning less effectively.
Greater intoxication can impair speech, balance, coordination and reaction time. Memory formation may also be disrupted.
During an alcohol-related blackout, a person can remain awake, speak and interact but fail to form normal lasting memories for part of the episode. A blackout is therefore not the same thing as becoming unconscious.
At still higher exposure, alcohol can profoundly suppress brain function. Severe intoxication can interfere with breathing, heart rate, temperature control and protective reflexes and can become fatal.
How much alcohol produces a particular effect varies with factors including drinking speed, body composition, tolerance, food intake, other drugs or medicines and individual biology. Visible drunkenness is not a reliable measure of whether someone is approaching danger.