Biological Explanations For Schizophrenia

Question 1

What are the 3 main points?

Answer 1

1- genetic basis of schizophrenia
2- the dopamine hypothesis
3- neural correlates of schizophrenia

Question 2

Explain the genetic basis of schizophrenia

Answer 2

• schizophrenia tends to run in families

- schizophrenia is polygenic and aetiologically heterogenous

Question 3

Explain how schizophrenia tends to run in families

Answer 3

• there is a strong relationship between genetic similarity between family members and the likelihood of both family members developing schizophrenia
• for example, Gottesman’s large-scale family study found that monozygotic twins (share 100% of same alleles for genes) have a 48% shared risk of developing schizophrenia
• in contrast, siblings who share approximately 50% of the same alleles for genes have a 9% shared risk
• and first cousins only 2% shared risk

Question 4

Explain how schizophrenia is polygenetic and aetiologically heterogenous

Answer 4

• different studies have identified different candidate genes for the development of schizophrenia indicating:
  A- each individual gene confers a small increased risk of developing schizophrenia I.e. schizophrenia is polygenic
  B- different combination of factors can lead to schizophrenia I.e. schizophrenia is aetiologically heterogenous
• Ripke et al found in 37,000 patients that 108 separate genetic variations were associated with an increased risk; many coded for the functioning of the dopamine transmitter

Question 5

Explain the dopamine hypothesis

Answer 5

• neurotransmitters appear to work differently in patients with schizophrenia- in particular, dopamine is widely believed to be involved
• dopamine is a neurotransmitter that generally has an excitatory effect and is associated with the sensation of pleasure
• dopamine hypothesis suggested that hyperdopaminergia (high levels or activity of dopamine) in the subcortex (central areas of the brain) may be associated with hallucinations and speech poverty
• for example, excess of dopamine receptors in Broca area
• more recent versions have focused on hypodopaminergia (low levels in the pre-frontal cortex responsible for thinking and decision making

Question 6

Explain neural correlates of schizophrenia

Answer 6

• neural correlates are measurements of the structure or function of the brain that correlate with positive or negative symptoms of schizophrenia
• ventral striatum is believed to be particularly involved in the anticipation of reward which is related to motivation
• the loss of motivation (avolition) in some schizophrenic patients may be explained by low activity levels in this area
• Juckel et al found a negative correlation between activity levels in the ventral striatum and the severity of overall negative symptoms
• positive symptoms also have neural correlates- Allen et al found that patients experiencing auditory hallucinations recorded lower activation levels in the superior temporal gyrus and anterior cingulate gyrus

Question 7

What are the evaluation points for biological explanation of schizophrenia?

Answer 7

✅very strong evidence for genetic vulnerability to schizophrenia (Gottesman and Tienari)
❌ mixed support for dopamine hypothesis
❌ correlation-causation problems with neural correlates neural correlates explanation for schizophrenia
❌ clear the environment is also involved

Question 8

Explain how there is very strong evidence for genetic vulnerability to schizophrenia (Gottesman and Tienari)

Answer 8

• the Gottesman family study clearly shows how genetic similarity and shared risk of schizophrenia are closely related- Gottesman’s large-scale family study found that monozygotic twins (share 100% of same alleles for genes) have a 48% shared risk of developing schizophrenia
• in contrast, siblings who share approximately 50% of the same alleles for genes have a 9% shared risk
• and first cousins only 2% shared risk
• adoption studies such as Tienari et al (19,000 Finnish children) clearly show that children of people with schizophrenia are still at heightened risk of schizophrenia if adopted into families with no history of schizophrenia
• providing overwhelming evidence for the idea that genetic factors make some individuals more vulnerable to schizophrenia
  ❌ HOWEVER all Finnish

Question 9

Explain how there is mixed support for dopamine hypothesis

Answer 9

• in support, dopamine agonists e.g. amphetamines that increase levels of dopamine can induce schizophrenic-like symptoms in people without the disorder
• in addition, dopamine antagonists such as Chlorprozamine that lower dopamine activity have been effective in reducing symptoms
• e.g. Thornley et al reviewed studies comparing Chlorpromazine and placebo control conditions. Data from 13 trials with over 1000 participants found that Chlorpromazine was associated with improved functioning and reduced symptom severity
• however, some of the identified candidate genes code for the production of other neurotransmitters such as glutamate
• suggesting that dopamine cannot provide a complete explanation for schizophrenia, but it is still a possible significant factor, just perhaps not a sole explanation

Question 10

Explain how a limitation is correlation-causation problems with neural correlates neural correlates explanation for schizophrenia

Answer 10

• the question that remains is whether unusual activity in the brain causes the symptoms or whether there are other possible explanations for the correlation
• for example, the negative correlation between activity in the ventral striatum may suggest that low activity causes avolition
• alternatively it could be that negative symptoms means that less information passes through the striatum resulting in low activity
• therefore, although neural correlates exist, they tell us relatively little about the causes of schizophrenia

Question 11

Explain how it is clear that the environment is also involved

Answer 11

• ultimately, the probability of developing schizophrenia, even if your identical twin has the disorder, is less than 50%
• there is evidence that environmental factors such as family functioning during childhood can also play a role in the development of schizophrenia
• this suggests that schizophrenia may be the result of a combination of biological and psychological factors which is acknowledged by the interactionist approach: a much more holistic approach to explaining schizophrenia