Schizophrenia: Characteristics and Explanations
What Is Schizophrenia?
Schizophrenia is a severe mental health condition that affects how a person thinks, perceives the world and behaves. It is diagnosed using criteria set out in the International Classification of Diseases (ICD), a system used worldwide by clinicians.
The ICD groups schizophrenia’s clinical characteristics into three types. Positive symptoms add unusual experiences that are not normally present — such as hallucinations (hearing or seeing things that are not there) and delusions (strongly held false beliefs). Negative symptoms take something away from normal functioning, such as reduced motivation, flattened emotion and withdrawal from other people. A third group involves disorganised speech and behaviour, where thoughts and actions become jumbled and difficult to follow.
Schizophrenia is diagnosed using ICD criteria across three symptom groups: positive symptoms (hallucinations, delusions), negative symptoms (reduced motivation, withdrawal) and disorganised speech or behaviour.
Key Statistics About Schizophrenia
The specification also asks students to know key statistics about schizophrenia, including how common it is, at what age it tends to appear, and whether rates differ by sex or ethnicity. Schizophrenia is relatively rare compared with more common problems such as anxiety or depression, and it is usually first diagnosed in late adolescence or early adulthood. Diagnosis rates and recovery outcomes vary between groups, and recovery itself varies too — some people have a single episode and recover well, while others experience recurring episodes across their life.
The Dopamine Hypothesis: A Biological Explanation
The dopamine hypothesis is the main biological explanation of schizophrenia. It proposes that people with schizophrenia have an overactive dopamine system — dopamine is a neurotransmitter involved in perception and thought, and too much of it disrupts normal brain functioning.
Dopamine is released by dopaminergic neurons and crosses the gap between neurons through synaptic transmission. In an overactive dopamine system, dopaminergic neurons fire more often, or dopamine receptors become oversensitive, so more dopamine signal gets through than normal. This excess transmission is thought to overstimulate brain pathways involved in perception and thought, contributing to positive symptoms such as hallucinations and delusions.
The dopamine hypothesis states that an overactive dopamine system, caused by dopaminergic neurons and excess synaptic transmission, produces abnormally high dopamine levels linked to positive symptoms.
Brain scans show that some people with schizophrenia have differences in brain volume and brain activity compared with people without the disorder. The frontal lobes, responsible for planning, decision-making and organising thought, often show reduced activity — sometimes called hypofrontality. This reduced frontal activity is linked to negative symptoms and disorganised thinking.
The hippocampus, involved in forming and storing memories, sometimes shows reduced volume in people with schizophrenia, which may explain some of the memory and learning difficulties patients experience. The temporal lobes, which process sound and language, have also been linked to abnormalities — this may help explain why auditory hallucinations, such as hearing voices, are common in schizophrenia. Neurological damage to these regions supports the idea that schizophrenia has a physical, structural basis in the brain.
Criticisms of the Biological Explanation
A key criticism of purely biological explanations is that they focus heavily on nature (biology) and can underplay nurture (environment). Critics argue that stressful life events, family relationships and social circumstances can also trigger or worsen schizophrenia, so an explanation based only on dopamine levels and brain structure may be too simple. Most psychologists now see schizophrenia as resulting from an interaction between biological vulnerability and environmental triggers, rather than biology alone.
Core Study: Daniel, Weinberger, Jones et al (1991)
Background: Researchers wanted to test whether the prefrontal cortex — part of the frontal lobes — works differently in people with schizophrenia, and whether dopamine plays a role. Earlier research had suggested that some people with schizophrenia show reduced frontal lobe activity, particularly during tasks that require planning and problem-solving.
Method: The study compared regional cerebral blood flow, a measure of brain activity, in people with schizophrenia while they completed the Wisconsin Card Sorting Test, a cognitive task requiring participants to work out and shift between sorting rules. Each participant completed the task twice: once after receiving amphetamine, a drug that increases dopamine release, and once after a placebo. Brain activity in the prefrontal cortex was recorded during each session.
Results: When participants took amphetamine, blood flow to the prefrontal cortex increased and their performance on the card sorting task improved, compared with the placebo condition. Without amphetamine, patients with schizophrenia showed lower prefrontal activity than would be expected.
Conclusions: The findings supported a link between dopamine and prefrontal cortex functioning in schizophrenia. Increasing dopamine activity appeared to improve both brain activity and cognitive performance in the frontal lobes, providing evidence for the dopamine hypothesis and for brain dysfunction as an explanation of schizophrenia’s symptoms.
Criticisms: The study used a small sample of patients, which limits how confidently the findings can be generalised. Giving amphetamine to unwell participants raises ethical questions about protection from harm. A link between brain activity and behaviour also does not prove that dopamine directly causes schizophrenia’s symptoms — it could be a consequence of the disorder rather than a cause.
The Social Drift Theory: A Psychological Explanation
Not every explanation of schizophrenia is biological. The social drift theory argues that schizophrenia is linked to social class not because poverty causes the disorder, but because having schizophrenia causes a person’s social position to decline over time.
This happens through two processes. Rejection by society: stigma and discrimination mean people with schizophrenia are often excluded, losing jobs, friendships and housing because others react negatively to their diagnosis. Disengagement of individuals: partly as a result of this rejection, people with schizophrenia may withdraw from social contact themselves, finding it harder to maintain work, relationships and routines. Together, rejection and disengagement cause people to drift downward into poorer social and economic circumstances.
The social drift theory explains schizophrenia’s link to social class through two processes: rejection by society and disengagement of the individual, which together cause downward social movement.
Criticisms of the Social Drift Theory
The main criticism of the social drift theory is a problem of cause and effect. It is difficult to know whether lower social class leads to schizophrenia (social causation) or whether having schizophrenia causes someone to drift down the social scale (social drift), because most evidence is correlational — it shows a link between schizophrenia and social class but cannot prove which came first.