These notes explain how brain activity and dopamine function have been used to account for schizophrenia, focusing on symptom-specific findings and the main strengths and limitations of biological evidence.

Neural correlates

Neural correlates are important because they connect particular symptoms of schizophrenia to identifiable patterns of brain structure or brain activity.

Researchers do not usually look for one single “schizophrenia area” in the brain. Instead, they investigate whether different symptoms are linked to different neural systems.

Examples of neural correlates

One well-known example concerns auditory hallucinations, especially hearing voices. Brain-scan studies have found unusual activity in areas involved in speech perception and self-monitoring, such as the superior temporal gyrus and the anterior cingulate cortex. If these regions process internally generated thoughts as though they came from an outside source, this could help explain why a person experiences voices as real.

A second example concerns avolition, the reduced motivation to begin or continue goal-directed activity. This has been linked to lower activity in the ventral striatum, a brain area involved in reward anticipation.

Educational figure illustrating an fMRI task design and example activation in the striatum during reward anticipation (the “waiting” period) versus reward receipt. It helps students connect the ventral striatum’s role in anticipating reward with motivational processes, making the avolition discussion more concrete. Source

If the brain responds weakly to expected reward, everyday actions may feel less worthwhile, contributing to a lack of motivation.

These findings suggest that schizophrenia may be better understood in relation to specific symptoms than as one uniform condition. Different symptoms may have different neural correlates.

Evaluating neural correlates

A strength of neural correlates research is that it uses relatively objective scientific methods, such as fMRI and PET scans, to measure brain activity. This reduces reliance on self-report alone and allows psychologists to compare people with schizophrenia to control groups.

Another strength is that the approach can help explain why symptoms differ. Neural correlates of hallucinations are not necessarily the same as neural correlates of avolition. This makes the explanation more precise than a broad claim that the whole brain is simply abnormal.

However, neural correlates are mainly correlational. If a brain difference is associated with a symptom, that does not prove the brain difference caused the symptom. It is also possible that long-term illness, medication, or lifestyle factors helped produce the observed brain changes.

A further limitation is that findings are not always completely consistent. Schizophrenia is a very varied disorder, so not every person shows the same symptoms or the same pattern of brain activity. This makes it difficult to identify one set of correlates that applies to every case.

The dopamine hypothesis

The dopamine hypothesis is one of the best-known biological explanations of schizophrenia. It argues that abnormal dopamine activity in the brain contributes to schizophrenic symptoms.

The original dopamine hypothesis

The earliest version of the hypothesis stated that schizophrenia was caused by hyperdopaminergia, meaning too much dopamine activity. In particular, overactivity at D2 receptors in subcortical areas was thought to produce positive symptoms such as hallucinations and delusions.

Support came from the effects of drugs that increase dopamine activity. For example, amphetamines can produce symptoms resembling psychosis, especially in high doses or with repeated use. This suggests that unusually high dopamine activity may contribute to positive symptoms.

There is also support from evidence in the opposite direction. Many antipsychotic drugs block dopamine receptors, and this often reduces hallucinations and delusions. This pattern supports the idea that excessive dopamine transmission is involved.

The revised dopamine hypothesis

The modern version is more complex.

Schematic diagram of the brain’s major dopaminergic pathways, highlighting projections from the ventral tegmental area (VTA) to limbic structures (mesolimbic pathway) and to the frontal cortex (mesocortical pathway). This is a useful visual for understanding how dopamine dysregulation could differ by pathway, helping to link “subcortical” dopamine activity to positive symptoms and “prefrontal” dopamine activity to negative/cognitive symptoms. Source

It suggests that schizophrenia is not simply caused by too much dopamine everywhere. Instead, there may be too much dopamine activity in subcortical regions and too little dopamine activity in the prefrontal cortex.

This matters because different pathways appear to be related to different symptoms:

• Hyperdopaminergia in subcortical areas, especially the mesolimbic pathway, is linked to positive symptoms.

• Hypodopaminergia in cortical areas, especially the mesocortical pathway and prefrontal cortex, is linked to negative symptoms and cognitive difficulties.

The revised version is stronger because it can explain a wider range of symptoms than the original account. It also fits better with evidence that schizophrenia involves both excess and reduced functioning in different neural systems.

Evaluating the dopamine hypothesis

A major strength is the amount of supporting evidence from drug research. If increasing dopamine can trigger psychotic experiences and blocking dopamine can reduce them, dopamine clearly plays an important role.

However, dopamine may not be the whole explanation. Some people with schizophrenia do not show clear dopamine abnormalities, and symptoms are not always removed simply by altering dopamine activity. Also, some newer antipsychotic drugs affect serotonin as well as dopamine, suggesting that more than one neurotransmitter may be involved.

Another criticism is that dopamine blockade happens quickly, but clinical improvement can take days or weeks. This means dopamine disruption may be part of the process, but not the only process involved in producing symptoms.

Research on neural correlates also suggests that dopamine explanations work best when linked to specific brain circuits rather than treated as a single global imbalance. This makes the revised hypothesis more convincing than the original version.