Biological Explanations for Schizophrenia

Detailed Revision Cards regarding the biological explanations for schizophrenia

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The Biological Explanations

Biological Explanations are explanations which believe schizophrenia is caused by abnormalities within the body itself and its biological make up. There are three main explanations that can be used in the exam. These are:

  • The Genetic Hypothesis
  • The Biochemical Explanation (Dopamine Hypothesis)
  • The Brain Structure Explanation (Differences in Brain Shape and Structure)

All of these can be used in a question regarding biological explanations for psychology. In addition to this, if the question asks for explanations in psychology without defining what sort, the following explanation can also be used.

  • Diathesis-Stress Model
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The Genetic Hypothesis

Research, such as twin studies, shows that schizophrenia appears to run in families. Studies found the following in their research:

  • MZ Twins (identical) risk if twin has Sz = 48%
  • DZ Twins (non-identical) risk if twin has Sz = 17%
  • Risk if one parent has Sz = 17%
  • Risk if both parents have Sz = 46%
  • General risk for population = 1%

These figures show a clear genetic link however if schizophrenia was entirely due to genetics MZ twins would have a 100% risk, suggesting that there are other factors which impact on whether or not a person develops schizophrenia. Further twin and adoption studies have looked to tease out the relative influences of genes and the environment on development of schizophrenia.

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Twin Studies: The Genetic Hypothesis

Most twin studies have generally shown a higher concordance rate for MZ twins that for DZ twins, suggesting an obvious genetic link. Cardno et al used the Maudsley Twin Register which uses very strict diagnostic criteria and found a concordance rate of 26.5% in MZ twins and 0% in DZ twins. There are problems however with this kind of research:

  • Methodological issues: not all twin studies have used the same diagnostic criteria and so direct comparisons between different twin studies cannot always be made.
  • In the past it was difficult to ensure whether or not twins were MZ or DZ. Nowadays this is a lot more accurate thanks to scientific advances however older studies may have used less accurate methods and so gained unreliable results.
  • Concordance rates appear to relate to the investigation's scientific rigour. The more rigourous a study is the lower the concordance rates appear to be. 
  • It is impossible to tease out the relative influences of environmental factors as MZ twins tend to be treated more similarly than DZ twins and so this could have produced the higher concordance rates rather than the genetic link.
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Adoption Studies: The Genetic Hypothesis

Adoption studies allow researchers to look at children born to schizophrenic mothers but raised by adoptive families with no history of the disorder. This helps to deal with the nature/nurture debate.

  • Kety found high rates of schizophrenia in individuals whose biological parents had schizophrenia despite having been adopted by psychologically healthy families.
  • Tienari, in a Finnish adoption study, matched 155 adopted children who had schizophrenic biological mothers with a group of children with no family history of Sz. He found those with Sz mothers had a 10% risk of developing schizophrenia in comparison to the 1% in the control group.
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The Biochemical Explanation

The biochemical explanation refers to biochemical abnormalities and in particular abnormality in neurotransmitter activity. The main neurotransmitter linked to schizophrenia is dopamine. Neurotransmitters carry nerve impulses across the synaptic gap and imbalances in these neurotransmitters can cause the impulse to be affected. Early theories suggested that schizophrenia was down to an excess production of dopamine in the brain and this was backed up by:

  • post- mortem studies finding increased amounts of dopamine in schizophrenics
  • Amphetamine Psychosis  has similar symptoms to Sz and is down to excess production of dopamine in the brain. Amphetamines have also been shown to worsen Sz symptoms.

Now however it is suggested that the brain doesn't produce excess but rather utilises dopamine to a greater extent. This may be because a.) post-synaptic receptors are more sensitive to dopamine or b.) the schizophrenic has more dopamine neuroreceptors in their brain. This was backed up by:

  • Seeman et al finding that the density of the D4 receptoy was 6 times greater in the brain tissues of schizophrenics suggesting that for every bombardment of dopamine there is six times as much message transmitted, correlating with the idea of delusions and hallucinations.
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Evaluation of the Biochemical Explanation


  • Use of phenothiazines. This medication blocks dopamine receptors. It has been shown to alleviate some of the major symptoms of Sz.
  • L-dopa is used to treat sufferers of Parkinson's disease, which is down to low levels of dopamine. If sufferers are administered too much L-dopa they sometimes show symptoms similar to those of Schizophrenia such as hallucinations. Conversely Schizophrenics who have too much medication can also experience symptoms of Parkinson's disease such as involuntary shaking. 
  • Post-mortem examinations have shown increased levels of dopamine in schizophrenics.
  • Howes et al. found that dopamine levels were elevated in people who were experiencing very early symptoms of Sz, suggesting dopamine is a cause and not a result of the disorder.


  • Phenothiazines do not work for everyone and appears only to alleviate positive symptoms, not the negative ones.
  • Post-mortem examination results may be due to the deceased having taken a wide range of neuroleptics during treatment.
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The Brain Structure Explanation

MRI scans show many Sz patients to have quite definite structural abnormalities in their brains, these include:

  • Enlarged ventricles
  • Decreased brain weight
  • Abnormalities in the prefrontal cortex 
  • Abnormalities in the basal ganglia
  • Reduced cerebral fluid (Reduced cerebral fluid can lead to altered gait and posture as well as abnormal eye movements.)

Enlarged ventricles and decreased brain weight can impact intellectual functioning and the ability to express oneself fluently.

The prefrontal cortex is in charge of planning and goal directed behaviour. If it is damaged it can cause lack of insight and the inability to alter behaviour in order to make it appropriate for the situation.

The basal ganglia is in charge of memory and emotional expression. Damage to this part of the brain can impact these functions.

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Evaluation of the Brain Structure Explanation

  • MRI Studies appear to provide conclusive evidence for structural abnormalities however different studies tend to find different areas of the brain to be affected.
  • Structural abnormalities correlate more with the presence of negative symptoms rather than postivie symptoms. This has led to the suggestion that there are 2 different types of Sz. Type 1: genetically inherited and associated with dopamine dysfunction. Type 2: neurodevelopmental disorder due to problems in the womb or in birth. The problem with this however is that many sufferers who begin with positive symptoms then develop negative symptoms later on.
  • It is uncertain as to whether or not the structural abnormality causes the disorder or that the disorder results in the structural abnormality.
  • Castner did a study on monkeys in which he subjected them to brain damaging x-rays whilst in the womb. There was no ill effects until the monkeys hit puberty and they developed Sz symptoms. This suggests that brain damage precedes the onset of the disorder and that puberty triggers the symptoms. The study however was highly unethical and cannot be generalised to humans as it was done on monkeys.
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