Schizophrenia in the Brain

Schizophrenia is a condition in which perception and belief separate from shared reality — most often hallucinations and fixed false beliefs — alongside a loss of drive, expression and the ability to organise thought.

Also called: Schizophrenia spectrum disorder, Psychosis.

ICD-10 F20 · ICD-11 6A20

Signals lose their source.

The picture most people have is a chemical one: too much dopamine in the brain, fixed by medicines that block it.

The research shows that story is partly true. Underneath it is a brain doing two things wrong. It gives meaning to the wrong things. And it loses track of which signals it made itself. Genes set the stage during the teenage years, and stress decides when it spills over.

Here are five findings. They run from the least settled to the most useful.

Simply too much dopamine

Evidence: contested

This is the explanation you will hear most. It is part of the truth. It is not all of it.

Every medicine that treats hallucinations and delusions blocks dopamine. Brain scans show that many people with schizophrenia make more dopamine in one deep part of the brain.

But not everyone does. About one in three people respond poorly to these medicines. In many of them, dopamine is at a normal level. Something else is driving their symptoms.

The picture shows nine people as fountains, with a dashed line at a typical level. Six of them run high. Medicine brings those six down and their symptoms go quiet. Three were never high, and medicine does little for them.

Dopamine blockers also do little for the negative and cognitive symptoms. Those are often the ones that shape a life the most.

Turning down a speaker

If the music is too loud, turning it down helps. But if the problem is that the wrong song is playing, turning it down only makes the wrong song quieter.

Why the story is sticky

It is neat. It matches how the medicines work. And for many people it does fit. It simply does not fit everyone. The people it misses are often the ones who struggle most.

Connections cut back too far

Evidence: proposed

This is a leading idea about why the illness so often starts in the late teens.

During the teenage years the brain cuts itself back. It removes unused connections between nerve cells, which are called synapses. This makes the brain work more efficiently.

One of the strongest genetic findings in schizophrenia involves a gene called C4. It is part of the immune system, and it marks synapses for removal. Versions that make more of it raise the risk.

The idea is that in some people this cutting back goes too far. The brain's thinking areas are left with too few connections, exactly as adult life begins. Brain scans do show thinning in those areas.

In the picture, spines on two nerve cells are marked in amber and then removed. The cell on the right loses far more of them.

Cutting back a bush

A light trim keeps it healthy and helps it grow. Cut it right down to the stem and it takes years to fill out again. Sometimes it never does.

Ordinary things feel meaningful

Evidence: established

This is a way to understand how delusions begin.

Dopamine is not only about reward. It also flags what is worth noticing. It gives things importance, and scientists call that importance salience.

When dopamine signalling runs too high, ordinary things get flagged. A number plate. A word overheard. A stranger's cough. They all feel charged, as if they must mean something.

The mind then does what minds do with meaningful things. It connects them into an explanation. That explanation is a delusion. To the person, it feels like a discovery.

The picture shows a field of ordinary objects. As salience rises, more of them light up. Threads then join them into a pattern that is not really there.

Seeing faces in clouds

Everyone does this now and then. Now imagine you could not stop doing it. And every face seemed to be looking straight at you.

Your own inner speech, without its label

Evidence: established

This explains why the voices can sound so real.

When you speak, or even think in words, your brain sends a copy of the signal ahead to the hearing areas. The copy says one thing. This is your own. It is the same reason you cannot tickle yourself.

Recordings of brain activity show this signal is weaker in schizophrenia. That is true both for speaking out loud and for thinking in words. The weaker it is, the more severe the hallucinations tend to be.

So a thought arrives in the hearing areas without its label attached. The person experiences it as a voice coming from somewhere else.

In the picture, a thought travels from where speech is made to where it is heard. When the copy arrives first, the thought is recognised as your own. When the copy fails, it lands as a voice from outside.

A voice note with no name on it

You recorded it yourself and forgot about it. When it plays back, it does not sound like you. So it feels like someone else is talking.

Many small risks, then stress

Evidence: established

This is the most useful finding on the page. Treatment and prevention are both built on it.

Schizophrenia is strongly inherited, but not through one gene. Hundreds of common genetic differences each add a tiny amount of risk.

Life then adds more risk on top. Trauma in childhood. Migration and discrimination. Living in a city. And cannabis. Using strong cannabis daily is linked to about five times the odds of a psychotic disorder.

The picture shows a container filling with many tiny drops, then a few big ones, until it spills over into an episode. Then protection is added. Medicine, support and less stress raise the rim, and the level falls.

This is why relapse often follows stress, or follows stopping medicine. It is also why treatment is about much more than a pill.

A cup under a tap

Some cups start fuller than others. Whether a cup overflows depends on two things. How much more is poured in, and how fast.

Why this is the useful one

Nobody can change their genes. But stress, sleep, cannabis, support and medicine all change how full the container gets.

The same thing, without the vocabulary

Too much dopamine is part of schizophrenia for many people, but not for everyone, and it does not explain the quieter symptoms.

Ordinary things can start to feel meaningful, which is how many delusions begin. And the brain can fail to mark its own inner speech as its own, so it is heard as a voice.

Risk builds from many genes and life stresses. Treatment lowers the level and raises the protection around it.