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Biological Explanations for Schizophrenia

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Biological Explanations for Schizophrenia

How we think and behave may be due to either psychological or physiological factors. Is it the structure of our brains that dictates how we think? Or is there something else governing our thoughts? And if there is a dysfunction or failure in that structure, what effects will that have on our brains?

Biological explanations for schizophrenia (and disorders, in general) assume that our thoughts and behaviours are due to certain aspects of our biology. There are three major biological causes of schizophrenia that we will discuss in this article: genetics, the dopamine hypothesis, and neural correlates.

Biological explanations for schizophrenia: genetic basis

One explanation for schizophrenia is that it may have a genetic basis. Schizophrenia tends to run in families. This means that the closer the relationship to a person with schizophrenia, the more likely they are to have it.

However, schizophrenia is a polygenic disorder not caused by a single ‘schizophrenia gene’. Many genes contribute to the development of schizophrenia, but each gene increases a person’s risk of developing schizophrenia by only a tiny amount.

This genetic predisposition is supported by a 1991 study by Gottesman, which found that in identical twins (monozygotic, MZ) who share 100% of their DNA, the concordance rate (the rate that one twin will develop schizophrenia if the other twin also has the disorder) is 48%. This is significantly higher than non-identical twins (dizygotic, DZ), who share only 50% of their DNA. The concordance rate for DZ twins was 17%.

This study suggests that there must be a genetic component in the development of schizophrenia. However, it is unlikely that schizophrenia is entirely genetic, as the concordance rate for MZ twins was not 100%.

Biological Explanations for Schizophrenia Genetic component in the development of schizophrenia StudySmarterThe genetic component in the development of schizophrenia, Pixabay

Biological causes of schizophrenia: the dopamine hypothesis

Another biological explanation for schizophrenia is the dopamine hypothesis. The dopamine hypothesis states that schizophrenia results from an imbalance of the neurotransmitter dopamine in the brain.

Neurotransmitters are chemicals that allow the brain to transmit messages between neurons. Small, specialized receptors receive them, and there are different types for each neurotransmitter. Dopamine is a neurotransmitter associated with the reward system in our brain and some areas of the brain that are important for speech and movement.

The dopamine hypothesis states that too much or too little dopamine or dopamine receptors in the brain develops schizophrenia. Too much dopamine is associated with positive symptoms such as hallucinations and delusions. Too little dopamine is related to negative symptoms such as poor speech.

Biological causes of schizophrenia: neural correlates

Neural correlates is a term used when a particular structural difference in the brain is associated with a psychological disorder.

Concerning schizophrenia, the main neural correlate we focus on is the difference in ventricle size between schizophrenic and control participants. Ventricles are small hollow vessels in the brain that transport cerebrospinal fluid to, from, and around the brain. The cerebrospinal fluid helps supply the brain with vital nutrients and also helps remove toxins and waste products from the brain.

A 2002 study by Torrey found that the ventricles of schizophrenia patients are on average 15% larger than those of people without schizophrenia.

The dopamine hypothesis and its evidence support the biological approach to schizophrenia because it shows that biological factors such as brain structure can influence the onset of schizophrenia.

Evidence for biological explanations for schizophrenia

Here are some critical studies that support the idea that biological factors have at least some influence on the development of schizophrenia. Many of these studies are discussed in more detail in our articles on individual biological explanations of schizophrenia.

Gottesman ( 1991)

Gottesman (1991) determined using the twin study mentioned earlier, that there must be a genetic component to schizophrenia. Since MZ twins had higher concordance rates than DZ twins and other family members, it was demonstrated that genetics must have some influence.

Tienari et al. (2004)

According to Tienari et al. (2004), adopted children with schizophrenic biological mothers were more likely to develop schizophrenia than control participants. A genetic (ie, biological) component to schizophrenia is thus also suggested.

Seeman and Kapur (2000)

This study found that people with schizophrenia had more dopamine receptors in their brains on post-mortem examination than control participants, supporting the dopamine hypothesis. This supports the biological approach as the dopamine hypothesis provides a biological explanation for schizophrenia.

Suddath et al. (1990)

Suddath et al. (1990) found differences in ventricle size in 12 out of 15 pairs of twins, one of which had schizophrenia, and the other did not. This supports the biological approach, as it clearly shows how a biological factor (eg, brain structure) presents differently in people with and without mental disorders.

Biological Explanation for Schizophrenia Twin studies StudySmarterTwin studies in schizophrenia research, Cottonbro, Pexels

Evaluation of biological explanations for schizophrenia

In evaluating biological explanations for schizophrenia, we ought to consider their main limitations. Let us have a look.

Determinism

Biological explanations such as those in this article are usually deterministic. Deterministic research and theories are characterized by the idea that factors we cannot choose control our thoughts and behaviour. Biological determinism states that we cannot choose our neurobiology and how it shapes our thoughts and behaviour, just as we cannot choose the color of our eyes or skin colour.

This is a limited view because it contradicts our typical societal belief that we have free will and can control our actions. Without this belief, our justice systems and other ways in which our society functions would not work.

Biological explanations of schizophrenia are evidence of biological determinism. They assume that biological factors (e.g., our genes or brain structure) determine schizophrenia, which does not consider free will.

Nature vs nurture

Biological approaches often favour the side of ‘nature’ in the ‘nature vs nurture’ debate.

The ‘nature’ side of this debate holds that people’s behaviour is due to their nature (biological factors, evolutionary factors, etc.) rather than how they were raised (education, external factors, life experience).

Twin studies of schizophrenia show that we cannot rely entirely on nature’s explanation. The concordance rate in identical twins (sharing 100% of DNA) was not 100% (Gottesman 1991), suggesting that there must be some influence from external factors.

Applications of biological explanations for schizophrenia

A significant application of these biological explanations is antipsychotic drugs. These drugs are widely used to help schizophrenic patients manage their symptoms through typical and atypical antipsychotic drugs.

Antipsychotics can help patients regain control of their daily lives, improve their quality of life, and in some cases, support non-biological treatment plans. However, they do not ‘cure’ schizophrenia.

Biological Explanations for Schizophrenia - Key takeaways

  • There are three primary biological explanations for schizophrenia: genetics, neural correlates, and the dopamine hypothesis.

  • The genetic explanation states that schizophrenia tends to run in families. The closer a person’s relationship is to someone with schizophrenia, the more likely they are to develop the illness.

  • The dopamine hypothesis states that schizophrenia results from an imbalance of the neurotransmitter dopamine in the brain.

  • Neural correlates is the idea that specific structural differences in the brain are associated with schizophrenia.

  • There is much research for biological approaches, but they do not fully explain how and why schizophrenia develops.

Frequently Asked Questions about Biological Explanations for Schizophrenia

We can narrow down the biological causes of schizophrenia to three potential explanations: 


  1. Genetics, for instance, the concordance rates (despite not being 100%) in MZ twins supports this.
  2. Dopamine hypothesis, which states dopamine imbalances are associated with schizophrenia.
  3. Neural correlates, which suggests specific structural differences in the brain, are associated with the development of schizophrenia. 

Schizophrenia has both biological and psychological causes. People can be genetically predisposed to developing schizophrenia and have structural and chemical differences in their brains. However, they can also be more susceptible to developing schizophrenia due to psychological reasons. For instance, hostile family environments, dysfunctional thought processing issues (e.g., faulty attention systems) and issues with central control and meta-representation are also associated with developing and maintaining schizophrenia.

It is somewhat reductionist since it dismantles the complex disorder and states that simple components such as genetics cause schizophrenia. Reductionism often offers physiological explanations without considering all the variables that have been proven to influence disorders such as schizophrenia.

The three biological risk factors for schizophrenia are genetic predispositions, such as schizophrenia running in the family, neural correlates (differences in brain structure), and dopamine imbalances. 

Dopamine is both an excitatory and inhibitory neurotransmitter. When too much dopamine exists in the limbic regions of the brain, it increases the activation of dopamine two receptors (D2), and positive symptoms such as hallucinations begin to develop. Similarly, negative symptoms develop when the function of dopamine receptors is reduced in the prefrontal cortex.

Final Biological Explanations for Schizophrenia Quiz

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What is dopamine?

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Answer

 A neurotransmitter associated with the rewards system of our brains.

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How was the dopamine hypothesis developed?

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Studies into the effects of amphetamines in the 1960s and 1970s discovered that dopamine can cause schizophrenic symptoms in neurotypical individuals. This sparked research that resulted in psychologists finding links between dopamine levels and schizophrenia.

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What is a synapse?


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A small gap between neurons across which messages are fired.

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Who first proposed the dopamine hypothesis?

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Van Rossum.

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Where is dopamine produced in the brain?

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The substantia nigra and ventral tegmental area.

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What did later revisions of the dopamine hypothesis include?

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Later revisions of the hypothesis state that it may be excess dopamine in the mesolimbic areas of the brain and low dopamine in the prefrontal cortex of the brain that cause positive and negative symptoms.

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Why must we be careful when establishing cause and effect in schizophrenia using this hypothesis?

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Because it is unclear whether high levels of dopamine cause schizophrenia or schizophrenia causes high levels of dopamine.

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What did Farde et al. (1990) find in their study into the dopamine hypothesis?

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No difference in dopamine levels between schizophrenic and non-schizophrenic participants.

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The dopamine hypothesis is a deterministic theory. Why is this a limitation?

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Deterministic theories have their limitations, as they are not compatible with societal notions of responsibility and self-control, on which many of our legal and moral norms are based.

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What is the strength of the dopamine hypothesis?

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Some patients are given levodopa when treating Parkinson’s disease, a drug that increases dopamine levels in the brain. These patients are reported to experience psychotic side effects similar to schizophrenia symptoms. This supports the role that dopamine plays in the development of schizophrenic symptoms.

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What is the difference between typical and atypical antipsychotic medications that impacts why they work differently for different people?

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Typical antipsychotics only target dopamine, whereas atypical antipsychotics also affect other neurotransmitters such as serotonin and glutamate.

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Which type of antipsychotic tends to have more severe side effects?

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 Typical.

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Are antipsychotics able to cure schizophrenia for good?

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No, they can only help reduce symptoms so that patients can return to normal life.

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What positive effect do antipsychotics have on the economy and healthcare providers?

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Using antipsychotics to treat schizophrenia is good for the economy because they are relatively easy to produce and administer while allowing people to return to work. For healthcare providers, it is also beneficial as it frees up space in hospitals to treat more people.

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What are neural correlates?

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Neural correlates are instances where brain structure differences correlate with some psychological disorders or symptoms.

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In which brain areas are abnormalities linked to schizophrenia?

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The ventricles, basal ganglia, medial temporal lobe, prefrontal cortex, and thalamus.

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What is a correlation?

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 A relationship or link between two factors.

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 Does correlation equal causation?


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No.

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 Who conducted a meta-analysis of 65 studies into neural correlates related to schizophrenia?

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E. Fuller Torrey.

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What were the results of the 2002 study into neural correlates by E. Fuller Torrey?

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Torrey found links between structural abnormalities in multiple brain areas and the development of schizophrenia. One such link is the relationship between the size of ventricles and the onset of schizophrenia.

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 How does ventricle size link to schizophrenia?

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 Larger ventricles usually correlate with the development of schizophrenia.

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What did Suddath et al. (1990) find in their study?

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In monozygotic twins, the twin with schizophrenia was more likely to have larger ventricles than their neurotypical twin. This finding supports the theory of neural correlates.

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Why is this theory biologically deterministic?


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Because the theory states that if you have these specific structural abnormalities in your brain, you will develop schizophrenia. This stance leaves no room for free will or individual differences, making it deterministic.

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Why is determinism a limitation of this theory?

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Determinism can negatively impact attempts to treat harmful behaviours and mental disorders. Suppose someone is undergoing family therapy for schizophrenia but believes that their neurology dictates their condition. In that case, they may not even try the treatment that could have helped them.

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 How does Vilain et al.'s 2013 study refute neural correlates as an explanation for schizophrenia?

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The 2013 study by Vilain et al. found that some environmental factors influence the onset of schizophrenia. This is a limitation of neural correlates because the latter does not consider these factors.

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Why is it hard to produce treatments for schizophrenia from this theory?

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No proven causal link between neurophysical differences and schizophrenia exists, making the concepts of this approach difficult to apply.

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What method did Torrey (2002) use in the meta-analysis?

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MRI brain scans.

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 Why are MRI scans reliable?

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Because they are objective and highly controlled.

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Why is the use of a twin study by Saddath et al. a strength of this explanation?

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Because, in twin studies, it is reasonable to assume that schizophrenia is either caused by or is the cause of these neurophysical differences. It is unlikely to be due to biological differences or external factors (as twins are genetically identical and typically raised in similar environments).

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What is a genotype?

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 A piece of DNA that tells our cells how to behave and build our body in the womb/as we grow.

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What is a genotype?

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A person's genetic makeup.

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Which of the following are genotypes?

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Blue eyes.

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What is a phenotype?


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A phenotype is a way that a gene is expressed, which external factors can affect.

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Which of the following is a phenotype?

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Dyed pink hair.

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Who carried out a study investigating concordance rates in schizophrenia?

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Gottesman.

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What is a phenotype?

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A phenotype is the physical expression of genes. Phenotypes can be affected by external factors.

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Who found that children whose biological mother had schizophrenia were more likely to develop the disorder, even when adopted by mentally healthy parents?

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Tienari et al.

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Who argued that schizophrenia wasn't a disease, but instead a result of stress and social pressures?

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Bateson.

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What is the term for disorders that multiple genetic mutations or abnormalities cause?

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Polygenic disorders.

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What was the concordance rate for monozygotic twins in Gottesman's 1991 study?

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48%.

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What was the concordance rate for dizygotic twins in Gottesman's 1991 study?

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17%.

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What was the rate of schizophrenia for the general population in Gottesman's 1991 study?


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1%.

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What do concordance rates in monozygotic twins being higher than that of dizygotic twins tell us about schizophrenia?

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They tell us that genes influence schizophrenia, but it is not fully genetic

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Which of the following is a valid criticism of Gottesman (1991)?

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Monozygotic twins are likely to be raised in similar environments, meaning their concordance rate may be due to this instead.

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What percentage of our genetic information comes from our father?

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50%.

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Why might Bateson's claims that schizophrenia was not a disease be affected by bias?

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He was against psychiatry.

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What do biological approaches to understanding psychological disorders assume?

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Biological explanations for disorders assume our thoughts and behaviours are due to certain aspects of our biology.

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What are the three main biological explanations for schizophrenia?

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There are three major biological causes of schizophrenia: genetics, the dopamine hypothesis, and neural correlates.

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True or false: Schizophrenia tends to run in families.

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True.

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True or false: A singular ‘schizophrenic gene’ causes schizophrenia.

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False.

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