biological explanations for schizophrenia

Question 1

genetic basis of schizophrenia - family studies

Answer 1

• studies confirmed that risk of schizophrenia increases in line with genetic similarity to relatives with disorder (Irving Gottesman)
• family members tend to share aspects of environment as well as genes, correlation represents both
• family studies still give good support for importance of genes in schizophrenia

Question 2

genetic basis of schizophrenia - candidate genes

Answer 2

• early research looked for a single genetic variation, belief that one faulty gene could explain schizophrenia
• however, appears that number of different genes are involved
• most likely genes would be those coding for neurotransmitters, such as dopamine
• Stephen Ripke combined all previous data from genome-wide studies of schizophrenia
• genetic makeup of 37K people with schizophrenia was compared to 113K controls
• 108 separate genetic variations were associated with slightly increased risk of schizophrenia
• different studies have identified different candidate genes, so it appears tat schizophrenia is aetiologically heterogeneous (different combinations of factors, including genetic variation, can lead to the condition)

Question 3

genetic basis of schizophrenia - role of mutation

Answer 3

• schizophrenia can also have genetic origin in absence of family history
• one explanation for this is mutation in parental DNA which can be caused by radiation, poison or viral infection
• evidence for mutation comes from positive correlations between paternal age and risk of schizophrenia, increasing from 0.7% in fathers under 25 to 2% in fathers over 50

Question 4

neural correlates of schizophrenia

Answer 4

• we do not know exact cause of symptoms on biological level
• research has identified some neural correlates (brain structure or function etc.)
• best know neural correlate is dopamine (DA)
• important in functioning of several brain systems related to schizophrenia symptoms

Question 5

neural correlates of schizophrenia - original / historical dopamine hypothesis

Answer 5

• based on discovery that drugs used to treat schizophrenia caused symptoms similar to those in people with Parkinson’s, which is associated with low DA levels
• schizophrenia may therefore be result of high levels of DA in subcortical areas of the brain
• eg. excess of DA receptors in pathways from subcortex to Broca’s area may explain symptoms of schizophrenia such as poverty of speech
• abnormally high number of D2 receptors, resulting in more dopamine binding and therefore more neurons firing
• receptors may also be oversensitive

Question 6

neural correlates of schizophrenia - updated versions of dopamine hypothesis

Answer 6

• Kenneth Davis proposed addition of cortical hypodopaminergia (abnormally low DA in brain’s cortex)
• this can explain symptoms of schizophrenia
• eg. low DA in prefrontal cortex could explain cognitive problems
• also suggested that cortical hypodopaminergia leads to subcortical hyperdopaminergia, so both high and low levels of DA are part of updated version
• current versions of dopamine hypothesis also try to explain origins of abnormal DA function
• seems that both genetic variations and early experiences of stress make some people more sensitive to cortical hypodopaminergia and hence subcortical hyperdopaminergia

Question 7

evaluation strength for genetic basis - research support

Answer 7

• family studies show that risk increases with genetic similarity to family member with schizophrenia
• adoption studies show that biological children of parents with schizophrenia are at heightened risk even if they grow up in adoptive family
• recent twin study showed concordance rate of 33% for identical twins and 7% for non-identical twins
• some people more vulnerable to schizophrenia as result of genetic makeup

Question 8

evaluation limitation for genetic basis - environmental factors

Answer 8

• environmental factors include both biological and psychological influences
• study by Nina Morkved showed that 67% of people with schizophrenia and related psychotic disorders reported at least one childhood trauma, compared to 38% of matched group with non-psychotic mental health issues
• genetic factors alone cannot provide complete explanation for schizophrenia

Question 9

evaluation strength for neural correlates - evidence for dopamine

Answer 9

• amphetamines increase DA and worsen symptoms in people with schizophrenia and induce symptoms in people without
• antipsychotic drugs reduce DA activity and also reduce intensity of symptoms
• some candidate genes act on production of DA or DA receptors
• suggests that dopamine is involved in symptoms of schizophrenia

Question 10

evaluation limitation for neural correlates - glutamate

Answer 10

• evidence for central role of glutamate
• post-mortem and live scanning studies have found raised levels of neurotransmitter glutamate in brain regions of people with schizophrenia
• several candidate genes for schizophrenia believed to be involved in glutamate production or processing
• equally strong case can be made for role of other neurotransmitters