Causes of Schizophrenia
What causes schizophrenia is essentially unknown. Several risk factors seem to prefigure it, the most notable of which are genetics and brain structure. And a combination of these is probably most influential.
In addition to these, schizophrenia occurs with changes in brain chemistry, specifically, excessive levels of dopamine. Also, significant changes in the activation of the brain's frontal and parietal lobes have been associated with schizophrenia.
Schizophrenia & The Dopamine Hypothesis
Dopamine is a neurotransmitter that transports signals between nerve endings in the brain. It is thought that the brains of people with schizophrenia and other psychotic disorders produce too much dopamine. There is evidence that supports and counters the dopamine hypothesis.
The main support for the theory that too much dopamine causes schizophrenia is the fact that antipsychotic medications, which are used to treat schizophrenia, block dopamine receptors. The medications are designed to bind to dopamine receptors in the brain, and their effects have helped many people cope with symptoms. Secondly, drugs that increase levels of dopamine, like amphetamines, often cause psychotic symptoms and a schizophrenic-like paranoid state.
However, several factors challenge the dopamine hypothesis. For example, dopamine-related psychosis occurs in many disorders, not exclusively in schizophrenia. People with schizophrenia are not the only ones who respond to antipsychotic medication.
Antipsychotic medication may not significantly affect the negative symptoms of schizophrenia, which suggests that there is more involved than abnormal dopamine levels alone. Moreover, dopamine levels might actually be lower rather than higher in the frontal lobes of the brain. At any rate, antipsychotic medication only treats the symptoms of schizophrenia; it does not eliminate its underlying causes.
The theory that schizophrenia is partly a result of abnormal brain function is useful in understanding its biological basis. Underactive frontal lobes and overactive parietal lobes are thought to cause some of schizophrenia's associated symptoms. For example, when frontal lobes are underactive, planning, organization, and volition are all impaired. Frontal lobe abnormalities are probably related to schizophrenia's negative symptoms.
Parietal lobes are involved in sensory perception, like voice recognition, the ability to distinguish patterns, and spatial orientation. Overactive parietal lobes may cause distortion of these senses, which is seen in many people with schizophrenia. Parietal lobe abnormalities are probably more closely related to positive symptoms.