Biological explanations of schizophrenia Flashcards
genetics definition
genes consist of DNA stands. DNA produces instructions for general physical features of an organism (such as eye colour and height) and also specific physical features (such as neurotransmitter levels and size of brain structures). these may impact on psychological features (such as intelligence and mental disorder). genes are transmitted from parents to offspring (inherited)
neural correlates definition
patterns of structure or activity in the brain that occur in conjunction with an experience and may be implicated in the origins of that experience
dopamine definition
a neurotransmitter that generally has an excitatory effect and s linked to the sensation of pleasure. unusually high levels are associated with schizophrenia and usually low levels are associated with Parkinson’s disease
genetic basis of schizophrenia- evidence by family studies
confirmed schizophrenia increases in line with genetic similarity to a relative with the disorder
genetic basis of schizophrenia- Gottesman’s findings on family studies showing the genetic basis of schizophrenia
-2% chance of developing if their aunt has it
-9% if a sibling has it
-48% if identical twin has it
genetic basis of schizophrenia- what does the correlation between family and schizophrenia also show
correlation represents genes and environments as family members tend to share aspects environemnt and many of their genes, so correlation represents both (but still give good indication for importance of genes)
genetic basis of schizophrenia- are lots of genes involved in schizophrenia
yes there are lots of candidate genes making it polygenetic
genetic basis of schizophrenia- what are the candidate genes most likely involved in
coding for neurotransmitters such as dopamine
genetic basis- candidate genes what did Ripke et al study involve
combined all previous data from genome-wide studies. he used genetic make up of 37,000 people with a schizophrenia diagnosis and compared to 113,000 controls and 108 separate variations were also associated with slightly increased risk of schizophrenia –> ateilogically hetrogengeous
genetic basis of schizophrenia- what have studies finding different candidate genes lead to
schizophrenia has been found to be aetiologically heterogeneous so different combinations of factors, including genetic variation can lead to the condition
genetic basis of schizophrenia- why can schizophrenia have a genetic origin even if there is no family history
mutation in parental DNA which can be caused by radiation, poison or viral infection
genetic basis of schizophrenia- what did Brown et al find about paternal age and risk of developing schizophrenia
positive correlation between paternal age and risk of schizophrenia which is 0.7% with fathers under 25 to over 2% in fathers over 50
strength of the genetic basis of schizophrenia as a biological explanation for schizophrenia - research support
-strong evidence base
-family studies such as Gottesman show that risk increases with genetic similarity to a family member with schizophrenia. Adoption studies such as Tienari et al showed that biological children of parents with schizophrenia are at heightened risk even if they grow up in their adopted family. Hilker et al showed concordance rate of 33% for identical twins and 7% for non identical twins
limitation of the genetic basis of schizophrenia as a biological explanation for schizophrenia - environmental factors
-clear evidence to show that environmental factors also increase the risk of developing schizophrenia
-these environmental factors include both biological and psychological influences. Morgan et al suggested the biological factors include birth complications and Di Forti et al suggests smoking THC-rich cannabis in teenage years.
- Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems in general but there is evidence for a particular link with schizophrenia. Morkved et al found 67% of people with schizophrenia and related psychotic disorders reported at least one childhood trauma as opposed to 38% of a matched group with non-psychotic mental health issues –> means genetic factors cannot alone provide a complete explanation for schizophrenia
neural correlates of schizophrenia - what is a neural correlate
brain structure or function
neural correlates of schizophrenia - what is the best known neural correlate for schizophrenia
neurotransmitter dopamine which is involved in important functions of several brain systems related to symptoms of schizophrenia - dopamine hypothesis
neural correlates of schizophrenia - what was original dopamine hypothesis based of
based on discovery that drugs used to treat schizophrenia (antipsychotic which reduce DA) cased symptoms similar to those in people with parkinson’s (which has low DA levels)
neural correlates of schizophrenia - dopamine hypothesis
-might be result if high DA (which is hyperdopaminergia) in subcortical areas of the brain
neural correlates of schizophrenia - hyperdopaminergia in Broca’s area
excess of DA receptors in pathways form the subcortex to Broca’s area may explain specific symptoms such as speech poverty and or auditory hallucinations
neural correlates of schizophrenia - what is hyperdopaminergia
high levels of dopamine in subcortical areas of the brain
neural correlates of schizophrenia - updated dopamine hypothesis (hypdodopaminergia)
David et al proposed addiction of hypodopaminergia which is abnormally low DA in prefrontal cortex .
-as prefrontal cortex is responsible for thinking this could explain cognitive problems which is a negative symptom
-suggested that cortical hypodopaminergia leads to subcortical hyperdopaminergia
-both low and high levels of DA in different areas of the brain
neural correlates of schizophrenia - updated dopamine hypothesis on explaining schizophrenia
-try and explain origins of abnormal DA function
-seems both genetic variations and early experiences of stress (psychological and physical) make some people more sensitive to cortical hypodopaminergia and hence subcortical hyperdomainergia (howes et al)
strength of neural correlates for schizophrenia as a biological explanation for schizophrenia - evidence for dopamine
-support that DA is involved in schizophrenia
-Curran et al amphetamines increase DA and worsen symptoms in people with schizophrenia and induce symptoms in people without
-Tauscher et al antipsychotic drugs that reduce DA activity and also reduce the intensity of symptoms
-some candidate genes act on production of DA or DA receptors –> suggests dopamine is involved in symptoms of schizophrenia
limitation of neural correlates for schizophrenia as a biological explanation for schizophrenia - glutamate
-evidence for the central role of glutamate limits the dopamine hypothesis
-McCutcheon et al found post-mortem and live scanning studies have consistent found raised levels of the neurotransmitter glutamate in several brain regions of people with schizophrenia
-several candidate genes for schizophrenia are believed to be involved in glutamate production or processing –> means that an equally string case can be made for a role of other neurotransmitters
