2. the biological explanation Flashcards
GENETIC EXPLANATION
FAMILY STUDIES
Have confirmed that the risk of schizophrenia increases in line with genetic similarity to relative with the disorder.
Gottesman’s large scale family study shows the chance of developing schizophrenia increases as
shared genetic material increases: someone with a sibling with schizophrenia has 9% chance of developing it, increasing to 48% if they are an identical twin.
This means schizophrenia is at least partly genetic.
GENETIC EXPLANATION
THE ROLE OF MUTATION
Mutation in parental DNA can be caused by radiation, poison, or viral infection.
Brown et al found
a positive correlation between paternal age (associated with an increased risk of sperm mutation) and risk of schizophrenia, increasing from 0.7% with fathers over 25 to over 2% in fathers over 50.
GENETIC EXPLANATION
CANDIDATE GENES
Schizophrenia is polygenic - many genes are potential candidate genes causing it.
The most likely genes would be those coding for neurotransmitters like dopamine.
Ripke et al. did a meta-analysis of genome wide studies of schizophrenia
and compared the genetic makeup of 37,000 people with schizophrenia to 113,000 controls.
He found 108 separate genes that were associated with a slightly increased risk of schizophrenia.
GENETIC EXPLANATION
AO3: strength of genetic explanation
RESEARCH SUPPORT - Tienari
Strong research evidence for the genetic explanation.
Family studies such as Gottesman show that risk increases with genetic similarity a family member with schizophrenia. Adoption studies such as Tienari et al. show that biological children of parents with schizophrenia are at heightened risk even if they grow up in an adoptive family.
This shows that sine people are more vulnerable to schizophrenia because of their genetic makeup.
GENETIC EXPLANATION
AO3: limitation - genetic explanation
ENVIRONMENTAL FACTORS - Morkred
There is clear evidence to show that environmental factors also increase the risk of developing schizophrenia.
For example, birth complications cause a higher chance of developing schizophrenia and smoking cannabis in teenage years also increases the risk. In one study by Morkred, 67% of people with schizophrenia reported at least one childhood trauma compared to 38% of a matched group with non-psychotic mental health issues.
This means that genetic factors alone cannot provide a complete explanation of schizophrenia.
NEURAL CORRELATES
NEURAL CORRELATES are brain structures of functions that cause the symptoms of schizophrenia.
The best-known neural correlate of schizophrenia is
dopamine
NEURAL CORRELATES
THE ORIGINAL DOPAMINE HYPOTHESIS (SEEMAN)
Dopamine is a neurotransmitter that has an excitatory effect, and unusually high levels of dopamine are associated with schizophrenia, particularly the positive symptoms.
Messages from neurons that transmit dopamine fire too easily or too often. It is also thought that there are abnormally high levels of dopamine receptors on post synaptic neurones, resulting in more dopamine binding. This is called hyperdopaminergia, and an excess of dopamine receptors found in subcortical areas like the Broca’s area may explain the positive symptoms of schizophrenia, such as auditory hallucinations. (Broca’s area deals with speech production)
NEURAL CORRELATES
THE UPDATED DOPAMINE HYPOTHESIS (DAVIS)
Not all schizophrenics have high levels of dopamine, as the modern antipsychotic drug clozapine (very little dopamine blocking activity) works effectively against schizophrenia.
Hypodopaminergia (too little dopamine) in the cortical areas of the brain e.g. prefrontal cortex can explain negative symptoms of schizophrenia. (prefrontal cortex deals with rational thinking). It has also been suggested that cortical hypodopaminergia leads to subcortical hyperdopaminergia.
NEURAL CORRELATES
AO3: strength of neural correlates
EVIDENCE FOR DOPAMINE - drugs
There is support for the idea that dopamine is involved in schizophrenia.
Amphetamines increase dopamine and worsen symptoms in people with schizophrenia and induce symptoms in people without. Antipsychotic drugs reduce dopamine activity and reduce the intensity of symptoms.
Some candidate genes act on the production of dopamine or dopamine receptors.
This strongly suggests that dopamine is involved in the symptoms of schizophrenia.
NEURAL CORRELATES
AO3: limitation of neural correlates
GLUTEMATE
There is evidence for a central role of glutamate.
Post-mortem and live scanning studies have consistently found raised levels of the neurotransmitter glutamate in several brain regions of people with schizophrenia. In addition, several candidate genes for schizophrenia are believed to be involved in glutamate production or processing.
This means that an equally strong case can be made for a role for other neurotransmitters.
