Schizophrenia is a mental health disorder that affects a person's perception of reality, thought processes and social behaviors. According to the National Institute of Mental Health, schizophrenia is a chronic and disabling disorder that impacts brain functioning in approximately 1 percent of the American population. Different forms of schizophrenia are recognized, including paranoid type, disorganized type or catatonic. While general symptoms occur in each type of schizophrenia, specific symptoms differentiate one subtype from another. Symptoms are grouped into positive--characterized by a loss of reality based on hallucinations, false beliefs or disorganized thinking, or negative--characterized by a lack of emotional expression. Different factors are thought to contribute to the development of schizophrenia, such as genetics and brain injury. However, a prominent yet controversial theory called the dopamine hypothesis offers a promising clue to a major chemical cause of schizophrenia.
Dopamine Hypothesis
According to the "Journal of Psychiatry and Neuroscience," the dopamine hypothesis proposes that schizophrenia is caused by excessive production of dopamine. Dopamine is a neurotransmitter, or chemical messenger produced in the brain. It has several functions in regulating the central nervous system, such as interpreting external reward and motivation. Dopamine helps to regulate thought, perception, memory and learning in addition to playing a role in movement, attention and sleep patterns. PsychCentral notes that dopamine is prominent in certain brain regions such as the thalamus and striatum. Altered levels of dopamine in these areas tend to have a significant impact in terms of changes in behavior and thinking.
Evidence of Dopamine Cause
According to a study reviewed in the "Schizophrenia Bulletin" in 2007, critical evidence that elevated levels of dopamine cause schizophrenia is demonstrated by the efficacy of dopamine-receptor-blocking drugs that treat schizophrenia psychosis. Medications termed antipsychotics reduce symptoms such as hallucinations and delusions through blocking the dopamine receptor D2. Another point of evidence supporting the dopamine hypothesis comes from users of amphetamines. The 2001 review in the "Journal of Psychiatry and Neuroscience" explains that use of amphetamines causes an influx of dopamine in the brain, which produces psychotic-type symptoms, much like the symptoms exhibited by people with schizophrenia.
Discrepancy of Evidence
The dopamine hypothesis is seriously questioned by the authors of study published in a 2009 issue of the "Harvard Review of Psychiatry." They pose an alternative explanation for initial results backing excessive dopamine levels as a major cause of schizophrenia based on the efficacy of antipsychotic drugs in reversing the underlying disease. The drugs may work by inducing neurological suppression, whereby the symptoms are rendered less intense rather than eliminated, these researchers suggest. As for the amphetamine-induced psychosis evidence, they further note that dopamine is not the only chemical impacted by the amphetamine; therefore singling out dopamine as a cause is not substantiated. Moreover, the 2007 "Schizophrenia Bulletin" study points out that in the case of antipsychotic medication aiding in symptom reduction and amphetamine-induced psychosis, the positive symptoms were impacted but not the negative symptoms. Overall, research on schizophrenia and dopamine is in agreement that the neurotransmitter plays a role in the disorder, yet there is no consensus that dopamine is the only cause of schizophrenia.
References
- "Journal of Psychiatry and Neuroscience"; Apomorphine and the Dopamine Hypothesis of Schizophrenia: A Dilemma; Lana Depatiei, B.A., and Samanthji Lal, M.D.; 2001
- National Institute of Mental Health: What Causes Schizophrenia
- "Harvard Review of Psychiatry"; A Critique of the Dopamine Hypothesis of Schizophrenia and Psychosis; J. Moncrieff; 2009
- PsychCentral: The Dopamine Connection Between Schizophrenia and Creativity
- "Schizophrenia Bulletin"; Dopamine Modulation of Emotional Processing in Cortical and Subcortical Neural Circuits; Steven R. Laviolette; 2007
