Furthermore, it is near impossible to distinguish between genetic and environmental factors if the twins share the exact same environment. As well as this, even twins reared apart shared the same environment in the womb before birth; this includes receiving the same nutrients, oxygen and being affected if the mother becomes unwell. Schizophrenia could be due to certain complications in the womb impeding development which would be classified as an environmental influence rather than a genetic one. Moreover, many longitudinal studies are problematic as the diagnostic criteria for schizophrenia is constantly being updated and changed.
The genetics theory is a biological approach that supports the nature side of the nature/nurture debate. However, it is reductionistic to suggest that either nature or nurture solely influences the development of schizophrenia. It is likely that a diathesis-stress model is at work; a biological predisposition for schizophrenia is the cause but the disorder only develops if there are enough environmental stressors to trigger it. The diathesis-stress relationship combines both nature and nurture. Furthermore, the majority of studies are non-scientific as they are not conducted in a lab so extraneous variables which are not controlled could be a contributing factor in the development of schizophrenia.
Another biological explanation for schizophrenia is the dopamine hypothesis. Dopamine is a vital neurotransmitter in the brain which controls a persons ability to guide attention and an abnormal amount could therefore result in problems with attention, perception and thought. The dopamine hypothesis states that the messages from the neurons that transmit dopamine fire too frequently resulting in an access of dopamine. Schizophrenics are thought to have an abnormally high number of D2 receptors on receiving neurons resulting in more dopamine binding and consequently more neurons firing.
The evidence for the influence of dopamine in the development of schizophrenia derives from the use of anti-psychotic drugs and Parkinson's Disease. The majority of anti-psychotic medications block the activity of dopamine in the brain by reducing stimulation of the dopamine system. This also results in the reduction of schizophrenic symptoms like hallucinations and delusions.
Parkinson's patients suffer from low levels of dopamine so are prescribed the drug L-dopa which is a dopamine agonist and thus raises dopamine levels. As a result patients were experiencing similar symptoms to that of a schizophrenic. As the drug causes increased dopamine levels it's easy to deduce that the increase in dopamine is causing the schizophrenic-like symptoms and therefore schizophrenia is due to excess dopamine. However, L-dopa could stimulate other parts of the brain which scientists are not aware of. It would therefore not be the increased dopamine levels causing the schizophrenic-like symptoms.
A major problem with the dopamine hypothesis is that a lot of evidence does not find a clear link between dopamine and schizophrenia. For example, Haracz (1982) received post-mortem studies of schizophrenics and found most of those studied who showed elevated dopamine levels had received anti-psychotic medication shortly before death. This could be due to the fact that the drugs blocking dopamine activity can sometimes increase dopamine levels as the neurons struggle to compensate for the sudden deficiency. He also found that the post-mortems of schizophrenic patients who hadn’t been prescribed medication showed normal levels of dopamine.
Moreover, the development of advanced neuroimaging techniques, like PET scans, have allowed scientists to investigate dopamine activity more closely than previous studies which relied on metabolites of the dopamine system. Despite this, studies have failed to provide enough convincing evidence to support the claim that excess dopamine is the cause of schizophrenia. A possible explanation for the results of recent studies not being consistent enough could be a problem with the classification of schizophrenia. Many psychologists are in disagreement as to what schizophrenia actually is and although the DSM-IV-TR clearly states the features of schizophrenia, many patients nowadays are often incorrectly diagnosed with the disorder.
The dopamine hypothesis is also reductionistic, which is the case with most biological approaches, as it suggest that schizophrenia is solely due to an increase of dopamine in the brain. However, the hypothesis is a scientific approach which is a positive as the theory can be supported by the use of scientific studies. Despite this, a lot of scientific evidence is not convincing enough, for example the PET scans, and extraneous variables are not controlled.
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psya42 (student)
