Compare genetic, dopamine and cognitive explanations of schizophrenia
Compare the syllabus explanations, distinguish group-level risk from individual causes, and evaluate what each account can and cannot explain.
Original StudyForA teaching mapped to the Cambridge 2028–2030 syllabus. Research summaries describe population-level evidence and theories; they do not diagnose or predict an individual outcome. This is not Cambridge material or an official mark scheme.
Before you begin
- This is Clinical Psychology topic 1.1.2 in the 2028–2030 Version 1 syllabus. It follows the syllabus section on diagnostic criteria and does not replace clinical assessment.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which conclusion is justified by a large genome-wide association study?
What you will learn
- Describe genetic explanations as risk or vulnerability rather than a single inherited cause
- Explain the dopamine hypothesis and why contemporary accounts are more specific than ‘too much dopamine everywhere’
- Describe a cognitive account using self-monitoring and source attribution as examples
- Compare biological and cognitive explanations using the syllabus issues and debates
Genetic explanations describe vulnerability, not destiny
Genetic explanations propose that inherited differences can contribute to a person's vulnerability to schizophrenia. Family and twin patterns can be consistent with genetic influence, but relatives may also share environments. A family pattern alone cannot separate inherited factors from shared experience.
Large genome-wide studies support a complex, polygenic picture: many genetic variants may each contribute small amounts of risk. A 2014 Psychiatric Genomics Consortium study reported associations across 108 loci in a large case-control sample. An association is not a single-gene cause, a personal prediction or a diagnostic test; risk reflects many influences and no result in this lesson can tell whether an individual will develop a disorder.
This account can be evaluated through nature versus nurture and reductionism versus holism. Genes may be one part of a wider explanation, while an account that focuses only on inheritance can omit developmental, social and situational influences. Heritability describes variation in a studied population; it does not state that a fixed percentage of one person's experience is genetic.
The dopamine hypothesis links biochemical processes to psychosis
The dopamine hypothesis proposes that differences in dopamine signalling are relevant to schizophrenia, especially some psychotic experiences. A simple early version described general dopamine excess. Later formulations are more specific: Howes and Kapur (2009), for example, discuss increased presynaptic striatal dopaminergic function and how aberrant salience might contribute to psychosis.
The account is supported by converging evidence, including the effects of dopamine-receptor-blocking medicines on some symptoms and imaging findings. Neither observation proves that one chemical imbalance is the sole cause. Medication effects may be incomplete or delayed, and a treatment response cannot establish that a single neurotransmitter difference caused an individual's experiences.
A biochemical account can be criticised as reductionist if it treats a complex pattern as only a chemical event. It can also connect biological processes to experience: altered salience could help explain why an otherwise ordinary event feels unusually significant. State the version of the hypothesis you are evaluating instead of using ‘too much dopamine’ as a complete explanation.
Cognitive explanations describe how experiences may be interpreted
Cognitive accounts focus on processes such as attention, reasoning, beliefs and source monitoring. One example proposes that difficulty monitoring self-generated speech or actions may contribute to some experiences being attributed to an outside source. This is a proposed psychological process, not a claim that a person chooses or invents symptoms.
Cognitive explanations can be evaluated through individual versus situational explanations and reductionism versus holism. They can describe a route between an experience and its interpretation, but a single process cannot explain every symptom or every person's situation. The relationship between cognition, biology and context may be complex and can run in more than one direction.
Frith and Done (1987) proposed a neuropsychological account connecting self-monitoring with some positive symptoms. Later research and competing models continue to test and refine such accounts. Use a named account to explain a mechanism, then evaluate its evidence and limits rather than treating a theory as settled fact.
Compare explanations against the same evidence
A useful comparison asks what each account explains, what evidence could support it, and what it leaves out. A genetic account describes inherited vulnerability; a dopamine account proposes a biochemical mechanism; a cognitive account describes how information or experience may be processed and interpreted. They operate at different explanatory levels and need not be treated as mutually exclusive.
For a balanced evaluation, link a strength and limitation to the actual explanation. For example, a large genetic association study can support a polygenic contribution but cannot identify a single cause for a particular person. A cognitive process model can make a testable prediction, yet findings from one task may not generalise to every context or symptom.
The syllabus also asks students to consider nature versus nurture, reductionism versus holism, determinism versus free will, individual versus situational explanations, and idiographic versus nomothetic approaches. These are lenses for evaluating evidence, not labels that automatically prove one explanation is correct.
Sources for this lesson
- Cambridge International AS & A Level Psychology 9990 syllabus, 2028–2030
- Schizophrenia Working Group of the Psychiatric Genomics Consortium (2014), Nature
- Howes and Kapur (2009), The dopamine hypothesis of schizophrenia, version III · PubMed
- Frith and Done (1987), Towards a neuropsychology of schizophrenia · PubMed
Pause and explain
Why does a response to a dopamine-receptor-blocking medicine not prove that dopamine differences are the sole cause?
Worked example
A student writes, ‘Schizophrenia is caused by a faulty gene that creates too much dopamine, so cognitive explanations are unnecessary.’ Improve the comparison.
Show the worked solution
- Separate inherited vulnerability from a single-gene cause.
- State the dopamine hypothesis with its limits.
- Explain what a cognitive account adds and why the explanations need not be mutually exclusive.
Answer Genetic research supports a complex contribution to risk, not one faulty gene that determines an individual's outcome. The dopamine hypothesis concerns differences in dopamine signalling, not a complete explanation of every symptom. Cognitive accounts examine how experiences may be monitored and interpreted; these explanations work at different levels and should be compared with evidence rather than treated as mutually exclusive.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A family study reports that schizophrenia is more common among relatives of people with the diagnosis. Evaluate the claim: ‘This proves schizophrenia is entirely inherited.’
Give me a hint
Separate a pattern of risk from a complete causal explanation.
Compare my reasoning
- The family pattern is consistent with inherited vulnerability, so it may support a genetic contribution.
- Relatives may also share environmental conditions; the finding alone cannot separate genes from shared experience.
- A complex disorder may involve multiple influences, so the evidence does not show that inheritance is the sole cause.
The family pattern can support genetic influence, but it does not prove that schizophrenia is entirely inherited. Relatives can share environments, and the observation does not identify one cause or predict an individual's outcome.
Look for these in your work
- Evidence linked to a limited claim
- Shared environment considered
- No deterministic conclusion
A study links increased presynaptic striatal dopamine activity with psychosis. Explain how this can support the dopamine hypothesis and identify one limitation.
Give me a hint
Use the proposed biochemical mechanism, then state what an association cannot establish.
Compare my reasoning
- The finding is consistent with the hypothesis that altered dopamine signalling is relevant to some psychotic experiences.
- An association does not show that dopamine differences are the only cause or explain every symptom.
- Other biological, cognitive and situational processes may contribute; the evidence should be interpreted at the level and in the sample studied.
The result supports a link between dopamine activity and psychosis, consistent with the biochemical explanation. It does not establish a sole cause, explain all symptoms or show that the same process accounts for every person.
Look for these in your work
- Mechanism accurately stated
- Association not overstated
- At least one alternative or scope limit
A fictional research team measures source-monitoring accuracy and dopamine activity in a group of volunteers. Results show a relationship with unusual perceptions. Explain how cognitive and biochemical explanations might interpret the result, and give one caution.
Give me a hint
Explain both levels without converting correlation into a diagnosis or cause.
Compare my reasoning
- A cognitive account could examine whether source-monitoring differences relate to how internally generated experiences are interpreted.
- A biochemical account could examine whether dopamine activity is associated with the measured experiences.
- Because the variables were measured rather than manipulated, the correlation does not establish direction or cause; volunteers' results cannot diagnose anyone.
The same pattern can be discussed at cognitive and biochemical levels: source monitoring concerns interpretation, while dopamine activity concerns a proposed biological process. If both were only measured, the association cannot establish causation or diagnose a participant. A stronger explanation would consider context and alternative variables.
Look for these in your work
- Both explanations applied
- Different explanatory levels distinguished
- Causal and diagnostic limits stated
Common mistakes
- Treating family similarity as proof that environment played no role
- Calling a genetic association a single-gene cause or an individual prediction
- Reducing the dopamine hypothesis to ‘too much dopamine everywhere’
- Claiming that medication response proves the cause of a disorder
- Describing cognitive explanations as blaming or voluntary
- Presenting a theory as a complete or settled explanation
What can you explain now?
What does a large genetic association study show, and what does it not show about one person?
Compare with the explanation
It can identify population-level associations consistent with a genetic contribution to risk.
It does not identify a single cause, predict an individual's outcome or provide a diagnosis.
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Make it stick
State the genetic, dopamine and cognitive explanations in one sentence each, then give one limit on each account.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.