Biological Explanations for Schizophrenia Flashcards
what are biological explanations?
4
emphasise the role of inherited factors and dysfunction of brain activity in the development of a behaviour or mental disorder such as schizophrenia
genetics = inherited factors make certain individuals more likely to develop a behaviour or mental disorder such as schizophrenia
neural correlates = changes in neuronal events and mechanisms that result in the characteristic symptoms of a behaviour or mental disorder such as schizophrenia
biological explanations; genetic + neural factors
what explanations for schizophrenia have received the most research support?
3
it is the biological explanations of schizophrenia that have received the most research support to date
in particular, the role of genetics and neural correlates such as dopamine in schizophrenia has been supported
however, the importance of biological explanations of schizophrenia does not deny the important role that psychological factors play in the onset of the disorder
what do psychologists currently believe in terms of biological influences in schizophrenia?
2
a diathesis-stress relationship exists
an individual may have a biological predisposition (the diathesis) for schizophrenia but the disorder only develops if other significant psychological stressors are present in the person’s life
genetic factors in schizophrenia
6
one possible cause of schizophrenia may be heredity, which involves genetics
genetics = inherited factors make certain individuals more likely to develop a behaviour or mental disorder such as schizophrenia
schizophrenia tends to run in families, but only among individuals who are genetically related rather than related by marriage
the risk of developing the disorder is higher for individuals who have family members with schizophrenia than it is for those who do not
no single gene is thought to be responsible for schizophrenia, it is more likely that different combinations of genes make individuals more vulnerable to the disorder
having these genes does not necessarily mean an individual will definitely develop schizophrenia, they simply have a genetic predisposition for it and will be more likely to
genetic factors: family studies
6
family studies find individuals with schizophrenia and determine whether their biological relatives are similarly affected more often than non-biological relatives
family studies have established that schizophrenia is more common among biological relatives of a person with schizophrenia
they have also found that the closer the degree of genetic relatedness, the greater the risk of developing the disorder
for example, Gottesman (1991) found that children with two schizophrenic parents had a concordance rate of 46%
whereas children with one schizophrenic parent only had a concordance rate of 13% and siblings (where a brother or sister had schizophrenia) had a concordance rate of only 9%
this suggests that schizophrenia is genetically influenced
genetic factors: twin studies
5
twin studies allow researchers to investigate the relative contribution of genetic and environmental influences on schizophrenia
if monozygotic (genetically identical) twins are more concordant/similar than dizygotic (who only share 50% of their genes) twins, then this suggests that the greater similarity is due to genetic factors
Joseph (2004) calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and only 7.4% for DZ twins
more recent studies that use ‘blind’ diagnoses (where researchers do not know whether the twin they are assessing is MZ or DZ) have tended to report a lower concordance rate for MZ twins than earlier studies
however, such studies still support the genetic explanation of schizophrenia because they show a concordance rate for MZ twins that is many times higher than that for DZ twins
genetic factors: adoption studies
7
it is difficult to determine whether schizophrenic individuals who share the same genes and environment are more influenced by their genes or their environment
so adoption studies are often used, which involve studies of genetically related individuals who have been separated
Tienari et al (2000) conducted a study in Finland using 164 adoptees whose biological mothers had been diagnosed with schizophrenia
they compared this group to a control group of 197 adoptees whose biological mothers were non-schizophrenic
of the 164 adoptees, 6.7% also received a diagnosis of schizophrenia compared to just 2% of the 197 control adoptees
this suggests that there are genetic factors involved in schizophrenia
the researchers concluded that these findings showed that the genetic liability to schizophrenia had been “decisively confirmed“
neural correlates in schizophrenia (the dopamine hypothesis)
5
the dopamine hypothesis claims that an excess of the neurotransmitter dopamine in certain regions of the brain is associated with the positive symptoms of schizophrenia
messages from neurons that transmit dopamine fire too easily or too often, leading to hallucinations and delusions that are the characteristic positive symptoms of schizophrenia
schizophrenics are thought to have abnormally high numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing
the key role played by dopamine was highlighted in two sources of evidence…
• drugs that increase dopaminergic activity
• drugs that decrease dopaminergic activity
other features of the neural explanation of schizophrenia…
• the revised dopamine hypothesis
• neural imaging
• animal studies
neural correlates: drugs that increase dopaminergic activity
5
amphetamine is a dopamine agonist
it stimulates nerve cells containing dopamine, causing the synapse to be flooded with this neurotransmitter
normal individuals who are exposed to large doses of dopamine-releasing drugs such as amphetamines can develop the characteristic hallucinations and delusions of a schizophrenic episode
this generally disappears with abstinence from the drug
likewise, some people who suffer from Parkinson’s disease (a neurodegenerative disease characterised by low dopamine levels) who take the drug L-dopa to raise their levels of dopamine have been found to develop schizophrenic type symptoms
neural correlates: drugs that decrease dopaminergic activity
4
there are many different types of antipsychotic drug that all block the activity of dopamine in the brain
these drugs are known as dopamine antagonists because they block its action
by reducing activity in the neural pathways of the brain that use dopamine as the neurotransmitter, these drugs eliminate symptoms such as hallucinations and delusions
the fact that these drugs alleviated many of the symptoms of schizophrenia strengthened the case for the important role of dopamine in this disorder
neural correlates: the revised dopamine hypothesis
3
Davis and Kahn (1991) proposed that the positive symptoms of schizophrenia are caused by an excess of dopamine in subcortical areas of the brain, particularly in the mesolimbic pathway
whereas the negative and cognitive symptoms of schizophrenia are caused by a deficit of dopamine in areas of the prefrontal cortex, particularly the mesocortical pathway
support for this revised hypothesis comes from….
• neural imaging
• animal studies
neural correlates: neural imaging
2
Patel et al (2010) used PET scans to assess dopamine levels in schizophrenic and normal individuals
they found lower levels of dopamine in the dorsolateral prefrontal cortex of schizophrenic patients compared to the normal individuals
neural correlates: animal studies
3
Wang et al (2008) induced dopamine depletion in the prefrontal cortex of rats
this resulted in cognitive impairment (such as memory deficits) that the researchers were able to reverse using olanzapine
which is an atypical antipsychotic drug thought to have beneficial effects on negative symptoms of schizophrenia in humans
x3 evaluation points for genetic factors
common rearing patterns may explain family similarities
MZ twins encounter more similar environments
research support
GENETIC EVALUATION
common rearing patterns may explain family similarities
3
research has shown that schizophrenia appears to run in families, supporting the argument for genetic basis of the disorder
however, many researchers now accept that the fact that schizophrenia appears to run in families may be more to do with common rearing patterns and other factors that have nothing to do with heredity
for example, research on expressed emotion has shown that the negative emotional climates in some families may lead to stress beyond an individual’s coping mechanisms, thus triggering a schizophrenic episode
GENETIC EVALUATION
MZ twins encounter more similar environments
6
the assumption underlying all twin studies is that environment of monozygotic twins and dizygotic twins are equivalent
therefore, it is assumed that the greater concordance for schizophrenia between MZ twins is a product of greater genetic similarity rather than greater environmental similarity
however, as Joseph (2004) points out, this assumption may be false as MZ twins may have more similar environments than DZ twins
MZ twins are treated more similarly than DZ twins, encounter more similar environments, are more likely to do things together and experience more ‘identity confusion’ in which they frequently treated as ‘the twins’ rather than as two distinct individuals
as a result, there is reason to believe that the differences in concordance rates between MZ and DZ twins are due to MZ twins having more similar environments rather than simply having more similar genetics
this suggests that there is an environmental influence in schizophrenia and to suggest that it is entirely genetically determined is over simplistic
GENETIC EVALUATION
research support
6
for example, Gottesman (1991) found that children with two schizophrenic parents had a concordance rate of 46%
whereas children with one schizophrenic parent only had a concordance rate of 13% and siblings (where a brother or sister had schizophrenia) had a concordance rate of only 9%
this suggests that schizophrenia is genetically influenced and supports the notion that the closer the degree of genetic relatedness, the greater the risk of developing the disorder
twin studies also support the genetic basis of schizophrenia
Joseph (2004) calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and only 7.4% for DZ twins
as MZ twins are genetically identical while DZ twins only share 50% of their genes, the greater similarity must be partly due to genetic factors
x3 evaluation points for neural correlates (the dopamine hypothesis)
support from treatment
inconclusive supporting evidence
challenges to the dopamine hypothesis
NEURAL EVALUATION
support from treatment
5
much of the evidence supporting the dopamine hypothesis comes from the success of drug treatments that attempt to change levels of dopamine activity in the brain
antipsychotic drugs reduce the effects of dopamine and so reduce the symptoms of schizophrenia
for example, Leucht et al (2013) carried out a meta-analysis of 212 studies that had analysed the effectiveness of different antipsychotic drugs compared to a placebo
they found that all the drugs tested were significantly more effective than the placebo in the treatment of positive and negative symptoms of schizophrenia
this supports the idea that dopamine plays a role in schizophrenia as symptoms of schizophrenia are reduced when levels of dopamine are altered
NEURAL EVALUATION
inconclusive supporting evidence
5
Moncrieff (2009) claims that evidence for the dopamine hypothesis of schizophrenia is far from conclusive
for example, although stimulant drugs such as cocaine and amphetamine have been shown to induce schizophrenic episodes, such stimulants are also known to affect many neurotransmitters other than dopamine
therefore, researchers cannot be certain that the neurotransmitter linked to schizophrenia is definitely dopamine, it could be another neurotransmitter that is affected these stimulants
likewise, evidence of dopamine concentrations in post-mortem brain tissue has either been negative or inconclusive and other confounding sources of dopamine release, such as stress and smoking, have rarely been considered
therefore, this suggests that the idea that symptoms of schizophrenia are caused by the overactivity of the dopaminergic system is not supported by current evidence
NEURAL EVALUATION
challenges to the dopamine hypothesis
5
Noll (2009) claims that there is strong evidence against both the original dopamine hypothesis and the revised dopamine hypothesis
he argues that antipsychotic drugs do not alleviate hallucinations and delusions in about one third of people experiencing these symptoms
he also points out that, in some people, hallucinations and delusions are present despite levels of dopamine being normal
blocking the D2 receptors of these individuals has little or no effect on their symptoms
this suggests that rather than dopamine being the sole cause of the positive symptoms of schizophrenia, other neurotransmitter systems acting independently of the dopaminergic system may also produce these symptoms
neural correlates: abnormal brain structures
2
a further biological explanation for schizophrenia concerns neurological factors, such as abnormal brain structure
this explanation involves…
• ventricular differences
• grey matter
• white matter
neural correlates: ventricular differences
5
people with schizophrenia have abnormally large ventricles in their brains, which are brain cavities filled with cerebral spinal fluid — this means that the brains of schizophrenics are lighter than normal
researchers have found that many with schizophrenia, particularly those displaying negative symptoms, have enlarged ventricles
enlarged ventricles suggest damage to the central brain areas and pre-frontal cortex, which could account for the negative symptoms of those with schizophrenia
enlarged ventricles are thought to be a consequence of nearby parts of the brain not developing properly or being damaged
Johnstone et al compared the size of ventricles in the brains of people with schizophrenia to the brains of those without — he found that those with schizophrenia had enlarged ventricles, suggesting schizophrenia is linked to a reduction in the temporal and frontal lobe volume
neural correlates: grey matter
2
those with schizophrenia have a reduced volume of grey matter in their brain, especially in the temporal and frontal lobes
grey matter differences are found in schizophrenia patients over time
