Flashcards in Biological Explanations Deck (67)
How many genetic explanations of SZ are there?
What are the 3 genetic explanations of SZ?
1) Family studies
2) Twin studies
3) Adoption studies
What are family studies for SZ?
They find individuals who have SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives
What have family studies found for SZ?
Established SZ more common among biological relatives of person with SZ, and the closer the degree of genetic relatedness, the greater the risk - children with SZ parents have a concordance rate of 46%, children with 1 have 13% and siblings is 9%
Outline twin studies for SZ
If MZ twins who share 100% of their genes are more concordant in terms of SZ than DZ twins who only share 50% of genes, suggests greatest similarity is due to genetic factors
Name the 2 studies for twin studies for SZ
1) Gottesman (91)
2) Joseph (04)
Outline Gottesman (91)
Suggests SZ inherited through genes - studied 40 pairs of twins and found concordance rate for MZ twins was 48% and only 17% for DZ twins
Outline Joseph (04) for twin studies
Calculated that pooled data for all SZ twin studies carried out prior to 2001 shows concordance rate for MZ as 40.4% and for DZ twins as only 7.4%
What have twin studies shown recently for SZ?
More recently, methodologically sound studies (blind diagnoses) tended to report lower concordance rates for MZ twins - despite this, researchers still argue even these findings support the genetic position as provide a MZ concordance rate many times higher than DZ concordance rate
Outline adoption studies for SZ
Due to difficulties of disentangling genetic and environmental influences for individuals who share genes and environment, studies of genetically related individuals who have been reared apart can be used
What is the main study for adoption studies for SZ?
Outline Tienari (00)
Of the 164 adoptees whose biological mothers diagnosed, 11 (6.7%) also received diagnosis compared to just 4 (2%) of the 197 control adoptees born to non-SZ mothers - concluded showed genetic liability to SZ had been 'decisively confirmed'
What are the other 2 biological explanations for SZ besides the genetic ones?
1) The dopamine hypothesis
What does an agonist mean?
A drugs that binds to and alters the activity of a receptor
What does an antagonist mean?
A drug that binds to a receptor but which does not alter the activity of the receptor
What is dopamine?
A neurotransmitter found in the brain
Outline the dopamine hypothesis
States brains of SZ patients produce more dopamine - states messages from neurons that transmit dopamine fire too easily or too often, leading to characteristic symptoms of SZ - SZs thought to have abnormally high numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing
Name a big study relating to the dopamine hypothesis
Outline Comer (03)
Dopamine neurons play a role in guiding attention so disturbances in process may lead to the problems relating to attention, perception and thought found in people with SZ
What are the 4 sources of evidence which support the role of dopamine in SZ?
2) Antipsychotic drugs
3) Parkinson's disease
4) Post-mortem studies
What are amphetamines relating to dopamine?
Outline how amphetamines support the dopamine hypothesis
It is a drug which stimulates nerve cells containing dopamine, causing the synapse to be flooded with the neurotransmitter - large doses can cause characteristic hallucinations and delusions of SZ episode
What are antipsychotic drugs relating to dopamine?
Outline how antipsychotic drugs support the dopamine hypothesis
There are many different types but all block the activity of dopamine in the brain - by reducing stimulation of dopamine system, drugs eliminate symptoms like hallucinations and delusions - the fact that these drugs alleviated many symptoms of SZ strengthened the case for dopamine being a significant contributory factor in this disorder
Outline how Parkinson's disease supports the dopamine hypothesis
Those with the disease have low levels of dopamine and Grilly (02) found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms
Outline Grilly (02)
Found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms
What is the main post-mortem study supporting the dopamine hypothesis?
Outline Falkai (88)
Looked at autopsies and found SZs had larger than normal numbers of dopamine receptors - there was an increase of dopamine in brain structures and receptor density so concluded dopamine production was abnormally high in SZs
Outline the role of neuroanatomy in SZ
There is growing evidence that SZ is associated with physical abnormalities in the brain - Szesko found asymmetry that was found in normal brains and that SZs tend to have symmetrical brains - also tend to have abnormally large ventricles in the brain which means brains of SZs are lighter than normal