Biological explanations of schizophrenia Flashcards
(19 cards)
Explanation 1: Genetic causes
Explores the level to which schizophrenia can be inherited
Prevalence rate- % of live cases within a population suffering of something at any given moment
Incidence rate- % of given cases in a given period of time
Concordance rate- the percentage of pairs of twins or other blood relatives who exhibit a particular trait or disorder
Twin studies
Looks at the development of symptoms in twins that are raised in the same home environment.
Monozygotic twins- twins that both come from the same zygote (egg) and share 100% of their DNA. Identical twins.
Dizygotic twins- twins that both come from different zygotes but develop in the womb at the same time.
Study:
Gottesman and Shields (1966)
Aim- to use the twin study method to investigate the concordance rates of schizophrenia in MZ and DZ twins.
Sample- 68 schizophrenic patients, but ended up with 57 due to various problems.
Procedure:
Each pair were assigned to either MZ or DZ conditions. 24 MZ twins and 33 DZ twins were identified.
Their mental health were measured using:
hospital notes
speech testing (to identify language problems)
psychometric testing to measure disorganized thinking
Findings:
The twins were separated into 4 distinct categories.
In every category there was a significant difference between MZ and DZ twins, with MZ twins having a higher chance of sharing a similar diagnosis of mental illness.
Concordance was stronger for female twins.
Conclusion- there is a genetic link to schizophrenia however the MZ concordance rate was significantly lower than 100% which means that despite their shared genotype they did not always share schizophrenic symptoms. This suggests that genetics is not the only cause of schizophrenia.
Strengths:
Generalizability- large sample and covers a range of ages and includes male and females, and both MZ and DZ twins.
Replicable - findings have been replicated many times elsewhere (Davis et al 1995)
Limitations:
Generalizability- sample may not be very representative as the twins were quite unusual. Many of them were admitted to a hospital after WW2 and some were even prisoners of war. Traumatic experiences may have served as extraneous variables to the study.
Adoption studies
Study that looks at the development of symptoms in twins who are raised in different home environments.
Use:
Researchers look at twins who each live with different families. This allows for genetic factors to be separated from environmental factors.
Study:
Kety et al (1968) interviewed the biological and adopted relatives of 33 schizophrenic children who were taken from a larger sample of adoptees admitted to a psychiatric hospitals.
33 mentally healthy adoptees were selected and matched to the schizophrenic patients on age, gender, social class etc.. (Matched controls)
They found that the concordance rates were higher between schizophrenics and their biological relatives than between schizophrenics and their adopted relatives. Additionally, if one of the adopted parents developed schizophrenia this did not make it likely for the adopted child to develop it as well (comparison to matched control).
Family studies
Study set out to established wether or not schizophrenia runs in the family. Usually the immediate family but can sometimes extend to others.
Co-morbidity rate
The rate at which two people show the same disorder.
Explanation 2: Brain structure/ neural correlates
Researchers have identified changes to structure of the brain that might be linked to the behavioral changes seen in schizophrenics. Neural correlates: Basal ganglia Auditory system Occipital lobe Frontal lobe Limbic system Hippocampus
Neural Correlates
Patterns of structure or activity in the brain that occur in coexistence with schizophrenia.
Schizophrenics have abnormally large ventricles in the brain.
Basal Ganglia
Role- involves in movement, emotions and combining sensory information.
Association with Sz- abnormal functioning contributes to paranoia and hallucinations.
Auditory system
Role- allows humans to hear and understand speech.
Association with Sz- overactivity in speech area (Wernicke’s area) can create auditory hallucinations.
Occipital lobe
Role- processes information about the visual world.
Association with Sz- disturbance to this area can contribute to visual hallucinations/ difficulties interpreting complex images/ reading emotions on faces.
Frontal lobe
Role- critical to problem solving and high-level reasoning.
Association with Sz- disturbances caused by Sz leads to difficulty in planning actions and organizing thoughts (disordered thinking).
Limbic system
Role- involves in emotion
Association with Sz- disturbances contribute to agitation seen in schizophrenics
Hippocampus
Role- mediates learning and memory formation.
Association with Sz- smaller hippocampus volume. Intertwined functions impaired in Sz.
Auditory hallucinations
Plaze et al. (2011)
Plaze et al. (2011) used MRI brain imaging to investigate the area of the brain responsible for auditory hallucinations.
Sample- they gathered MRI scans of 45 schizophrenic patients and 20 control participants.
Procedure:
They were split into two groups. Those who heard hallucinations internally and those who heard them externally.
Findings:
They found differences in the MRI scans in the region of the brain called the temperoparietal junction.
When they were compared to those of the controlled condition, they found a decrease in white matter (fibres carrying messages) for those who heard them externally, and an increase in white matter for those who heard them internally.
Use of MRI scans
It involves using radio waves and magnetic fields to create a 3D image of the region being scanned.
Better than X-ray due to quality of image.
A number of different brain regions can be examined at once which is an advantage when looking at a complex disorder like Sz.
Explanation 3: Neurotransmitter-related causes of schizophrenia
This section looks at the inner workings of the brain.
There are three key neurotransmitters that have been implicated in schizophrenia:
Dopamine
Glutamate
Serotonin
Dopamine hypothesis of schizophrenia
The dopamine hypothesis suggests that symptoms of Sz are associated with an imbalance of the dopamine neurotransmitter across the brain.
Dopamine- neurotransmitter and hormone that plays an important role in important body functions such as movement, memory, rewards/ motivation.
Excessive amounts of dopamine in speech centres like Broca’s area may lead to auditory hallucinations (positive symptoms)
Lower levels in areas such as the frontal cortex are thought to lead to negative symptoms like avolition or speech poverty.
This theory came from the observation that dopamine reducing drugs such as amphetamine produced schizophrenic like symptoms in patients. A drug that reduced these symptoms, called reserpine, was seen to reduce the activity of dopamine.
Other alternate neurotransmitters implicated
Glutamate- an excitatory neurotransmitter involved in learning, attention and memory. Found in low quantities in people with Sz. Leads to reduced excitation in certain regions of the brain.
Moghaddam & Javitt (2012) found that schizophrenics had a deficiency in glutamate function.
Serotonin- disruptions to serotonin by drugs have been seen to lead to hallucinations and paranoia.
Evaliation of dopamine hypothesis
Strength:
Falkali et al (1998) found increased dopamine levels in the left amygalda in post mortems of schizophrenic patients.
Antipsyhcotic drugs sich as chlorpromazine reduce the symptoms of schizophrenia by restraining dopamine transmission.
Limitation:
Cause and effect relationship- One criticism is that it is not clear wether raised dopamine levels are caused by schizophrenia or is the reason for schizophrenia.
Noll (2009) argues that 1/3 of participants do not respond to drugs that block dopamine which means other neurotransmitters may be involved.
