biological explanations for schizophrenia Flashcards
what is dopamine?
a neurotransmitter level associated with the experience of pleasure which has an excitatory effect on neighbouring neurons
what are neural correlates?
patterns or structures in the brain that occur in conjunction with an experience and may be implicated in the origins of that experience
gottesman (1991)
great genetic similarity is associated with a higher likelihood of developing sz
reviewed over 40 other studies and found similar results to gottesman and shields
-they found that the average concordance rate of sz in Mz to be 48% and in DZ 17%
gottesman and shields (1972)
- examined medical records of 57 twins with schizophrenia
- approximately 23 were MZ and 34 DZ
-found MZ had a concordance rate of 42% compared to DZ who had 9% concordance rate
Joseph (2004)
- found concordance rates amongst monozygotic twins to be 40.4% for schizophrenia development and for dizygotic twins to be 7.4%
- more recent evidence reports an even lower concordance rate for monozygotic twins in relation to schizophrenia development
-states that Mz are raised more similarly than DZ and suffer from identity confusion due to encountering similar environments
-therefore, such assumptions mean concordance rates are not a genetic outcome but that of the environment.
family studies?
- studies have found that schizophrenia is more prevalent in individuals who are closely related genetically with someone who already has schizophrenia
- children with 2 schizophrenic parents have a 46% chance to develop sz
- those with one parent have 13% and siblings 9%
adoption studies?
- Tienari conducted a study in Finland of 164 adoptees who has schizophrenic mothers, of which 11 (6.7%) were also diagnosed with sz, compared with 4 cases in 197 control adoptees with no schizophrenic parents.
- they concluded this evidence confirmed the genetic position within sz development.
kety (1988)
- studied over 5000 danish children between 1923 and 1947 compared to a control group of 18%,
-sz was developed in 32% of adoptees separated from biological parents who had the disorder.
-furthermore, children born with no biological relatives with sz yet raised by sz parent were no more likely than the general population to develop sz.
condradictory point of kety?
however, in the study the concordance rate of 32% included related disorders, not purely schizophrenia
-therefore, this reduces the validity of the findings for a genetic basis of sz
what are candidate genes?
these are genes which create vulnerability.
candidate genes contributing to schizophrenia?
a number of genes appear to contribute a small increased risk of sz making it polygenic - a combination of different factors is needed.
why could schizophrenia be considered aetiologically heterogeneous?
as many different genetic DNA combinations or multiple factors can lead to the condition.
Ripke et al (2014)
- compared the genetic makeup of 37,000 sz with 113,000 controls
- found that 108 separate genetic variations were associated with increased risk of sz
-genes associated with increased risk were those that code for neurotransmitter function, including dopamine.
what are the strengths and issues with studies such as gottesman, tiernari, kety and ripke?
a wealth of strong evidence from studies supports this explanation. however, many of these are correlations so causality cannot be inferred.
one limitation of the genetic explanation?
environmental factors may play a role such as smoking cannabis in teenage years and psychological childhood trauma.
this means that genetic explanations alone cannot provide a complete explanation of schizophrenia.