Biological explanations Flashcards
what does the biological explanation say is the cause of SZ?
Genetics (heredity)
There is a genetic component that predisposes individuals to the illness.
Higher risk of development if you are related to someone with SZ
what do family studies look for/find?
Key study
look for individuals with SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives
Gottesmann found that children with 2 SZ parents have a concordance rate of 46%,
Children with 1 SZ parent = 13%
Children with 1 SZ sibling = 9%
General population = 1%
The greater the genetic relatedness, the greater the risk of development
what do twin studies look for/find?
Key study
Monozygotic twins (MZ) = identicle. Dizygotic twins (DZ) = non-identicle.
Joseph calculated that all the pooled data into SZ twins before 2001 showed that the concordance rate for MZ twins was 40.4%, and for DZ twins: 7.4%
what do adoption studies look for/find?
Key study
look for the influence of environmental factors (no shared genes)
Tienari:
164 adoptees with schizophrenic biological mums. 11/164 (6%) went on to develop SZ
197 adoptees with no relation to SZ.
4/197 (2%) went on to develop SZ
what is the dopamine hypothesis?
an excess of the neurotransmitter dopamine in certain regions of the brain is associated with the positive symptoms of SZ.
messages from neurones that transmit dopamine fire too easily/often, leading to (positive) symptoms such as hallucinations and delusions.
schizophrenics are thought to have abnormal levels of the D2 receptor, resulting in more dopamine binding and so more neurones firing.
Evidence for dopamine:
amphetamine
Amphetamine is a dopamine agonist- it stimulates nerve cells containing dopamine, causing the synapse to be flooded with the neurotransmitter.
‘Normal’ individuals who are exposed to large doses of dopamine-releasing drugs such as amphetamines can develop the characteristics of a schizophrenic episode, such as hallucinations/delusions. disappears when stop taking drug
Evidence for dopamine:
L-Droga
Parkinson’s disease is characterized by low levels of dopamine.
L-Droga increases levels of dopamine.
It has been found that schizophrenic symptoms can appear alongside higher levels of dopamine
Evidence for dopamine:
Anti-psychotic drugs
anti-psychotic drugs are dopamine antagonists which block the activity of dopamine in the brain. by reducing the stimulation of the dopamine system, hallucinations and delusions are eliminated. By alleviating many of the SZ symptoms, anti-psychotic drugs are strong support that dopamine plays an important, contributory factor in the development of SZ.
what is the revised dopamine hypothesis?
Davis and Kahn proposed that positive symptoms are a result of an excess of dopamine in subcortical areas of the brain, in particular the mesolimbic pathway.
Negative/cognitive symptoms arrise due to a defecit of dopamine in the pre-frontal cortex areas.
evidence for the revised dopamine hypothesis?
NEURAL IMAGING= Patel et al used PET scans to assess levels of dopamine in schizophrenic and normal individuals. Found lower levels of dopamine in the dorsolateral pre-frontal cortex in schizophrenic patients.
ANIMAL STUDIES= Wang and Deutch induced dopamine depletion in pre frontal cortex in rats. This caused cognitive impairement i.e. memory deficit.
