Schizophrenia: explanations

Psychology A2 · Clinical Psychology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

There are three explanations to know. The genetic explanation says a vulnerability is inherited. Family, twin and adoption studies show that the closer the genetic relationship to a person with schizophrenia, the higher the risk. Identical twins are never 100% concordant, so genes cannot be the whole cause.

The dopamine hypothesis links positive symptoms to too much dopamine activity in subcortical areas (the mesolimbic pathway). A later version adds too little dopamine in the prefrontal cortex, which explains negative symptoms.

The cognitive explanation (Frith) says symptoms come from faulty thinking processes. The person fails to recognise their own thoughts as their own, so inner speech is heard as an outside voice.

Rules to remember

Concordance rate: the percentage of twin pairs in which both twins have the disorder.
Higher concordance in MZ (identical) than DZ (non-identical) twins points to a genetic contribution.
Adoption studies separate genes from upbringing: the risk follows the biological parent.
Dopamine hypothesis: excess activity at D2 receptors in the mesolimbic pathway gives positive symptoms; low activity in the prefrontal cortex gives negative symptoms.
Evidence for dopamine: amphetamine raises dopamine and can cause psychosis; antipsychotics block D2 receptors and reduce symptoms.
Frith: a self-monitoring fault means self-generated thoughts are blamed on an external source.
Diathesis-stress: an inherited vulnerability plus stressful experience (nature and nurture together).

Common mistake

Students write that twin studies prove schizophrenia is genetic. MZ concordance is well below 100%, and identical twins may also be treated more alike, so the environment has a part.

Worked example

A drug that blocks dopamine D2 receptors reduces a patient's hallucinations but does nothing for his lack of motivation and flat emotion. How does the revised dopamine hypothesis explain this?

Hallucinations are positive symptoms, linked to excess dopamine in the mesolimbic pathway.
Blocking D2 receptors lowers that excess activity, so the hallucinations fade.
Lack of motivation and flat emotion are negative symptoms, linked to too little dopamine in the prefrontal cortex.
Blocking dopamine cannot correct a shortage, so these symptoms stay.

Answer: Positive symptoms come from too much dopamine (helped by blocking); negative symptoms come from too little in the prefrontal cortex (not helped by blocking).

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