Biological explanations for schizophrenia Flashcards
What are the biological explanations for schizophrenia?
genetics and neural correlates, including the dopamine hypothesis.
What are the three biological explanations of SZ
Genetics
The dopamine hypothesis
Neural correlates
What are the two main arguments when it comes to
the genetic explanation of schizophrenia?
- Sufferers have inherited a predisposition from
their parents to inherit schizophrenia: family,
twin and adoption studies - A specific genes causes schizophrenia .
What is included in genetics?
The genetic basis of behaviour
Family studies
Candidate genes
The role of mutation
How does the genetic basis of behaviour link to schizophrenia?
There is evidence, which indicates that schizophrenia runs in families and is in part, genetic.
What do family studies indicate?
family studies indicate that the closer the genetic relationship to someone with schizophrenia, the greater the chance of developing the disorder. (supported by Gottesman)
GIVE GOOD SUPPORT FOR THE IMPORTANCE OF GENES IN SCHIZOPHRENIA
What did Gottesman do/find?
Did a large scale family study and found:
- if you have an aunt with sz you have a 2% chance of developing it
- this increases to 9% if you have a sibling with sz
- increases to 48% if you have an identical twin with sz
- both parents = 46% risk
- one schizophrenic parent = 16% risk
- if a grandparent has schizophrenia = 5%
What is concordance rate?
the extent to which twins/family members are similar and they show the likelihood of family members developing a particular disorder.
What evidence is used to study genetic explanations?
Family studies
Twin studies
Adoption studies
Who did studies on twins?
Gottesman + Shields
What did Gottesman + Shields find?
Research has found much higher concordance rates in MZ twins in comparison to DZ twins. Gottesman + Shields found a concordance rate of 42% for MZ and 9% for DZ twins
What do adoption studies allow?
Allow researchers to look at people who were born to schizophrenic mothers but brought up by adoptive parents with no history of the disorder.
What did Heston do?
Compared 47 children of schizophrenic mothers who have been fostered or adopted during the first month of their life with a control group of 50 children who had been raised in the same homes as these children.
What did Heston find?
None of the control group developed schizophrenia but 17% of the children with a schizophrenic biological mother did. This shows that having a biological mother with sz increased a child’s chances of developing it, even when not being raised by her or sharing the same environment.
What does Heston’s study show?
This study shows that having a schizophrenic mother i.e. having some of her genetic material, increased a child’s chances of having schizophrenia and other mental illnesses, even when not being raised by her or sharing the same environment.
How is schizophrenia caused by different genes?
- schizophrenia may be polygenic (i.e. it requires a number of factors to work in combination).
-because different studies have identified different candidate genes, it also appears schizophrenia is aetiologically heterogeneous (i.e. schizophrenia may be caused by many different genes).
What did Ripke do?
Ripke et al. (2014) studied 37,000 patients and found 108 separate genetic variations associated with increased of Schizophrenia. Many of which were involved in the functioning of dopamine
What did Sherrington do?
Sherrington et al. (1988) found a gene located on
chromosome 5, which has been linked in a small number of extended families with the disorder.
What is dopamine?
Dopamine is one of the chemicals i.e. a neurotransmitter in the brain, which causes neurons to fire; it is one of the chemicals that is responsible for transmitting signals between the neurons in the
brain.
Explain the original dopamine hypothesis
Hyperdopaminergia in the subcortex
- The original dopamine hypothesis stated that schizophrenia was caused by excessive activity of dopamine.
- This causes the neurons that respond to dopamine to fire too often
and transmit too many messages. - This message ‘over load’ may produce many symptoms of schizophrenia.
- It focuses on the possible role of high levels or activity of dopamine
in the subcortex i.e. the central areas of the brain. - For example, an excess of dopamine receptors in Broca’s area might be associated with poverty of speech and/or the experience of auditory hallucinations (Broca’s area is responsible for speech production).
Explain the new dopamine hypothesis
Hypodopaminergia in the cortex
- The (new) dopamine hypothesis suggests that schizophrenia is caused by a high density of dopamine receptors, and by a high level of sensitivity in dopamine receptors.
- This causes the messages from neurons that transmit dopamine to fire too easily or too often. According to Snyder (1976) if too much dopamine is released into the synapse it can lead to the onset of schizophrenia.
- Focused on abnormal dopamine systems in the brain’s cortex- particularly the pre-frontal cortex, which is responsible for thinking and decision making- this could explain negative symptoms.
- Goldman-Rakic et al. (2004) identified a role for low levels of dopamine (hypodopaminergia)
What are neural correlates?
Neural correlates are measurements of the structure or
function of the brain that correlate with an experience, in
this case schizophrenia. Both positive and negative symptoms have neural correlates.
Neural correlates of negative symptoms
one negative symptom avolition involves the loss of motivation.
Motivation involves the anticipation of a reward, and certain areas of the brain (Ventral striatum) are believed to be involved. Therefore abnormality to areas of the brain like the ventral striatum can cause avolition.
A03 – Juckel et al found a negative correlation between ventral striatum activity and the negative symptoms of schizophrenia.
Neural correlates to positive symptoms
Allen et al (2007)
- scanned the brains of patients with auditory hallucinations and compared them with a control group.
- patients experiencing auditory hallucinations recorded lower activation levels in the superior temporal gyrus and anterior cingulate gyrus.
- therefore reduced activity in these two areas of the brain is a neural correlate of auditory hallucinations.
