Biological Explanations of Schizophrenia

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There is strong evidence that biological factors play a large part in the development of schizophrenia. It has been known for a long time that sch runs in families. This could be because families share the same disadvantaged environments, but research evidence from family, twin and adoption studies suggests that genetic factors are also important.

First-degree relatives share an average of 50 per cent of their genes with each other, while second degree relatives share only 25 percent. Research evidence has looked to see if there is a correlational link between inheriting schizophrenia and genetic similarity. Kendler et al (1985) found that first-degree relatives of schizophrenics are 18 times more likely to contract the disorder than the general population.

Family studies are often inconclusive because they are conducted retrospectively, after people have been diagnosed. Therefore we can question the reliability of findings, as the relationship between genetic similarity and susceptibility to schizophrenia is not fully clear; a longitudinal study would be better
However, a longitudinal study of this nature would be hard and very time consuming to conduct.

Twin studies are another way of establishing a genetic link; they look at the difference in concordance between MA and DZ twins. Cardno et al (1999) found a 40 per cent concordance rate of sch in MZ twins, compared to only 5.3 for DZ twins.

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Twin studies are seen as reliable and significant, because MZ twins are genetically identical. However, because the concordance rate is never 100%, we can question the reliability of findings. Therefore environmental and psychological factors must also be accounted for.

Tienari et al. (1987) published results of the longitudinal Finnish adoption study that began in 1969. They found that 7 percent of adopted children with schizophrenic mothers also developed the disease, compared to 1.5 per cent of the adopted children in the control group.

This study is also seen as reliable and significant, as unlike family and twin studies it separates ...

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This study is also seen as reliable and significant, as unlike family and twin studies it separates the Ps from their original (possibly schizophrenogenic) environments, isolating the genetic factor. Also, a large enough sample was used (112 experimental and 135 control) so that individual differences could be accounted for. Therefore, the study is highly reliable, and has a positive application in society.

Zimbardo et al (1995) conducted a meta-analysis of European family and twin studies conducted between 1920 and 1987 to produce a graph of the average risks of developing schizophrenia according to your genetic similarity to a sufferer. The highest concordance rate was for MZ twins and offspring of dual matings (48% and 46% respectively). Parents were only 6%, and normal siblings were only 9%. With regards to concordance rate for second-degree relatives, percentages ranged from 2% for uncles and aunts to 6% for half siblings.

This study has high external validity; the sample was very large (being a meta-analysis) and is not context-bound as the date-range of the studies spans almost 7 whole decades. However, presenting the data in this way tells us nothing about the procedure of any of the individual studies. Therefore, the reliability of findings can be questioned.

Like many similar studies, Zimbardo’s study is correlational. While this allows for a large amount of data to be easily collected, there is no cause-effect relationship between the two variables, and the IV cannot be controlled. Thus we cannot establish causality or draw firm conclusions from this research.

Another aspect of the biological approach to schizophrenia is neurobiological/biochemical explanations. Research evidence has looked at both high and low levels of neurological activity. The high level aspect looks at the role of dopamine. Drugs which increase dopamine levels in the brain, such as L-dopa which is used to treat Parkinson’s, cocaine and cannabis, often produce schizophrenic symptoms in “normal” individuals. Wong et al suggested that persons who suffer from schizophrenia may have more dopamine receptors than others. It has also been noted that dopamine receptors decrease with age, perhaps this could be responsible for the decrease in schizophrenic symptoms in older people.

Unlike many psychological theories, neurobiological explanations are supported by objective scientific research. Findings such as levels of dopamine are measurable and hard to refute. Therefore, an advantage of neurobiological research is that is has high internal validity, hence causality can be inferred.

The “dopamine” hypothesis accounts for positive symptoms of schizophrenia, such as hallucinations and delusions. However, it does not account for negative symptoms, which are thought to have been caused by low levels of neurological activity. Buchsbaum et al (1992) found that individuals with schizophrenia had lower levels of frontal lobe activity. Therefore, we must also look at low levels of neurological activity to fully account for schizophrenia.

Another neurological explanation is structural abnormalities. For example, Andereasen (1988) found that ventricles (cavities in the brain) were 20% to 50% higher in schizophrenic individuals.

Like the dopamine hypothesis, research into structural abnormalities is highly reliable, as evidence is derived from PET and MRI scans, which are objective and almost impossible to argue against. However, the cost of these scans has meant that almost all studies are retrospective; conducted after diagnosis of schizophrenia. Therefore, it is hard to establish if these abnormalities are a cause or an effect, so the explanation can be questioned.

It is clear that biological explanations of schizophrenia are important and must always be considered. It is worth noting that schizophrenia is a disorder that is always treated biologically in the form of medication. However, in genetic studies the concordance rate is never anywhere near 100% and biological symptoms do not always result in schizophrenia being diagnosed. Therefore, in order to fully understand the disorder, we must also consider psychological factors, and also the arguments of the constantly raging nature-nurture debate; clearly nurture also plays an important part.