Biological Explanations for Schizophrenia Flashcards
What are the two factors that biological explanations of schizophrenia are based on?
Genetic basis and neural correlates (dopamine hypothesis)
How are genetic factors of schizophrenia usually tested?
Family, twin and adoption studies
How do family studies test genetic factors of schizophrenia?
Find individuals who have SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives
What have family studies shown overall?
The closer the genetic relatedness, the greater the risk
What did Gottesman (1991) find from family studies about the genetic basis of schizophrenia?
If both partners are schizophrenic, the likelihood of the offspring also having SZ was 46%, if one parent was schizophrenic then the likelihood was 13% and if a sibling had it then it was 9%
What are twin studies an opportunity for in studying the genetic basis of SZ?
For researchers to investigate the nature/nurture debate in terms of the contribution of hereditary and emotional influences in having SZ
What did Gottesman (1991) find from twin studies into the genetic basis of schizophrenia?
48% concordance rate for MZ twins and 17% for DZ
Who reviewed the twin studies into the genetic basis of schizophrenia until 2001?
Joseph (2004)
What did Joseph (2004) find from reviewing twin studies into schizophrenia?
Overall concordance rate for MZ twins as 40% and DZ as 7.4% supporting the genetic basis of SZ
Why are adoption studies useful for understanding the genetic basis of SZ?
it is difficult to separate genetic from environmental influences in twin and family studies so it is used to understand nature/nurture
Who carried out adoption studies into the genetic basis of SZ?
Tienari et al (2001) in finland
Who was involved in Tienari et al (2001)?
164 adoptees whose biological mother had been diagnosed with SZ and a control group of 197 adoptees
What were the results of Tienari et al (2001)?
11/164 (6.7%) adoptees with a mother with schizophrenia were also diagnosed. and 4/197 (2%) adoptees in control group were diagnosed
What does Tienari et al (2004) show?
Overall percentage of children adopted by non schizophrenic parents was low and there was a small link between genes
What are candidate genes in schizophrenia?
genes associated with schizophrenia (its polygenic)
what does it mean for schizophrenia to be polygenic?
There is a combination of different genes that have been implicated in SZ
Gurling et al (2006)
Used evidence from family studies indicating that schizophrenia is associated with chromosome 8p21-22 to identify a high-risk sample. Gene mapping showed that the PCM1 gene made people susceptible to
Benzel et al (2007)
used gene mapping to find evidence suggesting that NRG3 gene variants interacts with both NRG1 and ERBB4 gene variants to create susceptibility
Ripke et al (2014)
compared genetic makeup of 37000 SZ patients worldwide with 113000 controls. They found that 108 separate genetic variations increasing the risk of SZ
What are the advantages of the genetic basis of SZ?
Research evidence from Gottesman, Joseph and Tienari
What are the disadvantages of the genetic basis of schizophrenia?
- Separating nature and nurture in family and twin studies - Can happen in the absence of a family history - Biologically reductionist - Diathesis stress model
How can SZ happen in the absence of family history?
May be a mutation in parental DNA, evidence from Brown et al (2002)
Brown et al (2002)
Showed a positive correlation between paternal age and increased risk of SZ from 0.7% in fathers under 25 to over 2% in fathers over 50
diathesis-stress model
If there is a genetic vulnerability in SZ it may only be triggered by an event.
What are neural correlates?
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
Torrey (2002)
Using brain imaging techniques researchers have discovered that many schizophrenics have enlarged ventricles (15% bigger)
What are people with SZ who have enlarged ventricles like?
Display more negative than positive symptoms and respond poorly to typical antipsychotics
What may enlarged ventricles be a result of?
poor brain development or tissue damage
Weinberger and Gallhofer (1997)
Prefrontal cortex is the main area of the brain involved in executive control and research has shown that this is impaired in schizophrenic patients
Conrad et al (1991)
The hippocampus is an area of the brain in the temporal lobe and several studies have reported anatomical changes in the hippocampus in schizophrenic patients. Deficits in the nerve connections between the hippocampus and prefrontal cortex have found to correlate with the degree of memory impairment in schizophrenics
What are the strengths of neural correlates?
Research evidence to support structural changes in the brain and the use of brain scanning evidence
What are the weaknesses of neural correlates?
- Individual differences - different brain regions so hard to pinpoint the issue
dopamine hypothesis
an excess of dopamine causes positive symptoms of schizophrenia
What are the two consequences of the dopamine hypothesis?
Hyperdopaminergia and hypodopaminergia
Where is hyperdopaminergia?
subcortex
What is hyperdopaminergia in the subcortex?
Based on the original version of the DA hypothesis and says there are high levels of activity in the subcortex
What is hypodopaminergia in the cortex?
Focuses of lower levels of dopamine in the cortex causing negative symptoms
What does cortical hypodopaminergia lead to?
subcortical hyperdopaminergia
What are the strengths of the Dopamine hypothesis?
- Evidence from drug research - Antipsychotics act like antagonists so supports it (Tauscher et al (2014)) - Lindstroem (1999)
Lindstroem et al (1999)
Found chemicals needed to produce dopamine are taken up faster in sz brains showing that they produce more dopamine
What are the weaknesses of the dopamine hypothesis
- Biologically determinist (Moghadamm and Javitt (2012)) - correlation-causation problem
Moghaddam and Javitt (2012)
High levels of glutamate contibute to symptoms of schizophrenia. The dopamine hypothesis is reductionist as it doesn’t consider other neurotransmitters
