Biological Explanation - Genetic Basis + Neural Correlates

Genetic Basis

Researched using family studies and studies of individual genes. Suggests that a person’s genes (which are inherited from family) cause the development of Schizophrenia.

Family Studies + Schizophrenia

These have established that schizophrenia is more common in biological relatives of schizophrenics - the greater the degree of genetic relatedness = the greater the risk of schizophrenia. Much higher % risk of diagnosis in relatives than the % risk for general population (1%).

Family Studies - Findings (Gottesman)

A large scale family study found:

Monozygotic twin of schizophrenic = 48% schizophrenia

Sibling of schizophrenic = 9% schizophrenia

General Schizophrenia risk = 1%

Studies of Individual Genes - Schizophrenia

Have found a number of candidate genes (individual genes related to schizophrenia). Schizophrenia is polygenic (unrelated to a single gene, multiple different genes configure a small increased risk of schizophrenia). Schizophrenia is Aetiologically Heterogenous (different gene combinations can cause the disorder) - one study found 108 different genetic variations were associated with an increased risk for schizophrenia.

Con - Genetic Basis of Schizophrenia - Family Studies

One weakness of the genetic explanation of schizophrenia is that family studies have a low internal validity. These studies, that are supposed to investigate whether Schizophrenia is hereditary and caused by specific genes, more significantly investigate if common rearing patters and environmental factors in households cause Schizophrenia. Therefore, these studies do not investigate the genetic basis of schizophrenia like they initially set out to.

Pro - Genetic Basis of Schizophrenia - Adoption Studies

However, one strength of the genetic explanation of schizophrenia is that some adoption studies have been conducted that suggests, regardless of if a relative of a schizophrenic lives in the same household as the schizophrenic they have an increased risk for the disorder. One study compared the percentage of schizophrenia diagnoses in children with schizophrenic mothers that had been adopted as infants and the percentage of schizophrenia diagnoses in children without schizophrenic mothers that had been adopted as infants. The study found that the adoptees with schizophrenic mothers had a 6.7% chance of disorder development whereas adoptees without schizophrenic mothers had only a 2% chance of schizophrenia. Therefore, the genetic explanation is strong as there is supporting evidence with a high internal validity.

Neural Correlates

Suggests there are specific abnormalities within the brain associated with schizophrenia. This includes the Dopamine Hypothesis.

Dopamine

A neurotransmitter operating in the brain that is widely associated with schizophrenia.

The Original Dopamine Hypothesis (high/subcortex(

This focusses on the association between high dopamine activity (hyperdopaminergia) in the SUBCORTEX, which related to the positive symptoms of Schizophrenia. These higher levels are caused by abnormally high levels of dopamine receptors on receiving neurons in areas of the subcortex - this leads to more dopamine binding and therefore more neurons firing.

Hyperdopaminergia Vs Hypodopaminergia

High levels of dopamine activity Vs Low levels of dopamine activity

The Modern Dopamine Hypothesis (low/cortex)

This focusses on the association between low levels of dopamine activity (hypodopaminergia) in the CORTEX, This relates to negative symptoms of schizophrenia. This updated hypothesis suggests that both high + low levels of dopamine activity in different brain regions are involved in schizophrenia.

Pro - Neural Correlates/Dopamine Hypothesis - Evidence

One strength of the dopamine hypothesis is that there is evidence supporting the original hypothesis. Amphetamines (which stimulate the release of dopamine) cause schizophrenia-like symptoms and antipsychotic drugs (which block dopamine activity) effectively treat the symptoms of schizophrenia. This suggests the symptoms of schizophrenia are caused by high levels of dopamine, giving evidence to support the hypothesis.

Con - Neural Correlates/Dopamine Hypothesis - Incomplete

One weakness of the dopamine hypothesis is that it does not offer a complete explanation of schizophrenia as it does not consider other neurotransmitters’ roles in schizophrenia. Some candidate genes for schizophrenia code for the function of neurotransmitters other than dopamine, such as glutamate. Therefore, it is reductionist to disregard the roles of other neurotransmitters in schizophrenia.