Genetic factors: Family studies + Evaluation
Family studies: Gottsman: find individuals who have schizophrenia and determine whether their biological relatives are similarly affected. Family studies have established that schizophrenia (sz) is more common among biological relatives of a person with sz, and that the closer the relative, the greater the risk.
Children with 2 schizophrenic parents have a concordance rate of 46%, children with one schizophrenic parent have a rate of 13% and siblings 9%
Research shows that schizophrenia runs in families, supporting the arguments for a genetic basis. However many researchers now accept the fact that sz and its appearance in families may be nothing more to do with common rearing patterns or other factors that have nothing to do with heredity.
Expressed emotion has shown that the negative emotional climate in some families may lead to stress beyond an individuals coping mechanisms, therefore triggering a schizophrenic episode.
Genetic factors: Twin studies + Evaluation
Twin studies: opportunity for researchers to investigate the contributions of genetic and environmental influences. If MZ (identical) twins, who share 100% of their genes, are more concordant in terms of a trait like sz, than DZ (non-identical) twins who share 50% of their genes, then this suggests that the greater similarity is because of genetic factors.
Joseph - concordance rate for MZ twins 40%, and for DZ twins 7.4%.
More recent blind studies (researchers don't know whether the twins are MZ or DZ) have tended to report a lower concordance rate of MZ twins.
However still argued there is a genetic basis because of the still higher concordance rate in MZ twins than DZ twins
MZ twins also have a greater environmental similarity than DZ twins, they are treated more similarly. They are also more likely to experience more identity confusion. This shows that there is reason to believe that the differences in concordance rates between MZ and DZ twins reflect nothing more than the environmental differences
Genetic factors: Adoption studies + Evaluation
Adaption studies: Help to detangle environmental and genetic factors in behaviour.
Tienari - Finland - Of 164 adoptees whose biological mothers had been diagnosed with sz, 11 (6.7%) also received a diagnosis, compared to just (2%) of the control adoptees.
Potential parents in countries such as Denmark and the US are informed of the genetic background of the child prior to selection. Kringlen - 'because adoptive parents evidently received information about the child's biological parents, one might wonder who would adopt such a child'
The dopamine hypothesis
The dopamine hypothesis states that messages from neurons that transmit dopamine fire too easily or too often, leading to the characteristic symptoms of sz. They are thought to have abnormal numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing.
- Amphetamines - It is a dopamine agonist, stimulating nerve cells containing dopamine causing the synapse to be flooded with this neurotransmitter. Large doses of the drug can cause characteristic hallucinations and delusions of a schizophrenic episode.
- Antipsychotic drugs - They block the action of dopamine in the brain. By reducing stimulation of the dopamine system, these drugs can eliminate symptoms such as hallucinations and delusions.
- Parkinson's disease - Low levels of dopamine activity are found in people who suffer from this disease. It was found that some people who were taking the drug L-dopa to raise their levels of dopamine were developing schizophrenic symptoms (Grilly)
The dopamine hypothesis - Evaluation
Post-mortem studies - Haracs - found that schizophrenics who had received anti-psychotics shortly before death had higher dopamine levels while those who had not received the drug had normal levels of dopamine. - By blocking dopamine activity can actually increase it as neurons struggle to compensate of the sudden deficiency
Evidence from neuroimaging research - PET scans has allowed researchers to investigate dopamine activity more precisely than in the past by looking at waste products of dopamine. However neuroimaging studies, as yet, failed to provide convincing evidence of altering dopamine activity in the brains of sz patients (Copolov and Crook)