Biological Explanations Flashcards
Family Studies
Gottesman demonstrated a positive correlation between the increasing genetic similarity of family members and their increased risk of developing schizophrenia. The concordance rates are as follows = Monozygotic twins (48%), dizygotic twins (17%), siblings (9%) and parents (6%). This strongly suggests a genetic basis and the existence of candidate genes for schizophrenia.
Candidate genes
Ripke et al conducted a genome-wide study
of 5,001 cases of Swedish nationals with SZ and compared them to 6243 healthy controls. The researchers found 22 loci 4
associated at genome-wide significance; 13 of these are new, and 1 was previously implicated in bipolar disorder, alongside 8300 separate candidate genes. Each candidate gene represents a genetic variation which marginally increases the risk of developing SZ. Therefore, SZ is a polygenic disorder i.e. has multiple, contributing candidate genes.
Dopamine hypothesis - neurotransmitters
Chemical messengers that have an excitory effect.
Dopamine hypothesis - hyperdopaminergia in the subcortex
High levels of dopamine in the subcortex, e.g. an excess of dopamine receptors in Broca’s area (which is responsible for speech reduction) may be associated with speech poverty and/or auditory hallucinations.
Dopamine hypothesis - hypodopaminergia
Goldman-Racik identified a role of low activity of dopamine in the prefrontal cortex (responsible for thinking and decision making) in the negative symptoms of schizophrenia.
Neural correlates
Measurements of the structure of function of the brain that correlate with an experience.
Neural correlates of positive symptoms
Allen et al. scanned the brains of people experiencing auditory hallucinations and compared them to a control group whilst they identified pre-recorded speech as theirs or others. Lower activation levels in the superior temporal gyrus and the anterior cingulate gyrus were found in the hallucination group, who also made more errors than the control group. Reduced activity in these two areas of the brain is a neural correlate of auditory hallucination.
Neural correlates of negative symptoms
Occurs in the ventral striatum. Abnormality of areas like ventral striatum may be involved in the development of Avolition. Juckel et al. has measured activity levels in the ventral striatum in schizophrenia and found lower levels of activity than those observed in controls. Moreover, they observed a negative correlation between activity levels in the ventral striatum and the severity of overall negative symptoms. Thus activity in the ventral striatum is a neural correlate of negative symptoms of schizophrenia.
+ P - Research support
E - Brown et al found that the risk of having offspring with SZ increased by over 1.3% if the father was over 50 years old, compared to if the father was under the age of 25.
E - Therefore, this suggests that mutations in the sections of DNA containing the candidate genes, such as those coding for serotonin and dopamine production specifically, means that SZ is likely to have a strong heritability coefficient and biological basis.
L - This supports the use of family studies and neural correlates as ways of studying and explaining incidence rates of SZ.
- P - Evidence can be described as ‘mixed’
E - Tauscher et al found that antipsychotics, which act as dopamine antagonists and so reduce dopamine activity by binding to complementary receptors on the post-synaptic membrane, alleviated the symptoms of SZ, suggesting that dopamine has a key role in its development, in line with the predictions of the dopamine hypothesis.
E - Moghaddam and Javitt have criticised the dopamine hypothesis and biological explanations of SZ as emphasising the role of dopamine too far. For example, the
neurotransmitters glutamate and serotonin may also play a key role, as evidenced by the antipsychotic Clozapine acting upon both of these substances and being more effective than other atypical antipsychotics in reducing SZ symptoms.
L - Therefore, biological explanations of schizophrenia have contradictory research reducing its validity.
- P - Ignores the third variable problem
E - The evidence is correlational and a third unstudied factor could be affecting both outcomes.
E - Taking the example of the link
between lower levels of activation in the superior temporal gyrus and anterior cingulate gyrus, and the experience of auditory hallucinations, one explanation would be the lowered activation levels causing the hallucinations, or the hallucinations themselves causing the lowered activation levels. A third
possible explanation would be the third variable problem.
L - Therefore, this demonstrates that
correlational research cannot be used to reliably demonstrate a ‘cause and effect’ relationship between two variables.
