L2 - Biological Explanations of Schizophrenia Flashcards
what two factors are biological explanations based on?
BIOLOGICAL EXPLANATIONS ARE BASED ON TWO FACTORS:
- THE GENETIC BASIS AND NEURAL CORRELATES (including the DOPAMINE HYPOTHESIS)
how are genetic factors normally tested?
genetic factors are normally tested through FAMILY, TWIN and ADOPTION STUDIES
how do family studies show genetic basis for sz?
FAMILY STUDIES find individuals who have SZ and determine WHETHER THEIR BIOLOGICAL RELATIVES are SIMILARLY AFFECTED MORE OFTEN THAN NON BIOLOGICAL RELATIVES.
Family studies have shown that THE CLOSER THE GENETIC RELATEDNESS, THE GREATER THE RISK.
GOTTESMAN found that IF BOTH PARENTS WERE SCHIZOPHRENIC, the likelihood of the OFFSPRING having SZ was 46%, if ONE PARENT was schizophrenic, the likelihood dropped to 13% and if a sibling had sz the likelihood was 9% - this research clearly shows there is a genetic basis for schizophrenia
how do TWIN STUDIES show genetic basis for sz?
When comparing monozygotic (100% identical) and dizygotic (50% identical genes) twins the concordance rate showed there is a genetic basis for schizophrenia.
GOTTESMAN found a 48% concordance rate for MZ twins and a 17% CONCORDANCE RATE for DZ TWINS.
This study shows that the more genetically similar you are then the more likely you are to get SZ, hence suggesting there is a genetic basis for SZ.
how do ADOPTION STUDIES show genetic basis for SZ?
Adoption studies are used to understand the INFLUENCE OD NATURE AND NURTURE as genetics can be taken out of the equation.
TIENARI ET AL carried out a study in FINLAND. Of 164 adoptees whose BIOLOGICAL MOTHERS had been DIAGNOSED WITH SZ. 6.7% 11 were ALSO DIAGNOSED WITH SZ compared to a CONTROL GROUP of 197 ADOPTEES where only 4 were diagnosed with SZ.
This study showed that there is once again a clear genetic explanation and basis for developing SZ.
candidate genes and SZ
there are SPECIFIC GENES that seemed to be associated with SZ although it is now agreed that it is POLYGENIC (can be caused by a combination of genes)
RIPKE ET AL compared the GENETIC MAKEUP of 37000 SZ patients worldwide with 113000 controls. They found that 108 SEPARATE GENETIC VARIATIONS were associated with an INCREASED RISK OF SZ.
The genes that were particularly vulnerable were the ones that had some connection to the FUNCTIONING OF CERTAIN NEUROTRANSMITTERS SUCH AS DOPAMINE.
+ research evidence (genetic basis)
There is lots of research evidence to support the genetic basis of SZ such as that from GOTTESMAN AND TIENARI, thus there is a link between genes and SZ.
This is a strength because it shows that if a child grows up in a family where schizophrenia has been diagnosed in the parents, the children are more likely to be also be diagnosed with it, highlighting the genetic basis for the condition.
- nature nurture (genetic basis)
However, the problem with TWIN AND FAMILY STUDIES is SEPARATING NATURE (genes) from NURTURE (the environment).
E.g MZ twins are normally REARED TOGETHER and sent to the same school etc so their nurture is very similar - this makes it very hard to separate upbringing from genes.
Even if we look at adoption studies that attempt to SEPARATE NATURE AND NURTURE, children tend to be ADOPTED BY RELATIVES who may STILL REAR THE CHILD SIMILARLY TO THE BIOLOGICAL PARENTS - adoption studies may not always be a good comparison for the effects of nature and nurture.
- can occur randomly (genetic basis)
a weakness of the genetic basis is that SZ can take place in the ABSENCE OF A FAMILY HISTORY OF THE CONDITION. There can be a MUTATION IN YOUR PARENTS DNA which can be completely random and this will be passed onto offspring.
BROWN ET AL’s study showed a POSITIVE CORRELATION between PATERNAL AGE and INCREASED RISK OF SZ, increasing from around 0.7% with FATHERS UNDER 25 to OVER 2% IN FATHERS ABOVE 50.
This suggests that although no direct genes are involved, a person can still get SZ if father was OLDER AT THE TIME OF FERTILISATION. Thus the role of NATURE AND NURTURE may both play a part rather than genes.
- diathesis stress model
The diathesis stress model states that there is a GENETIC VULNERABILITY in SZ but this vulnerability is only LIKELY TO BE TRIGGERED IF THERE IS A STRESS TRIGGER IN THE INDIVIDUALS LIFE.
You may be born with a gene which makes you particularly vulnerable to SZ, but if your life is RELATIVELY STRESS FREE, then you may not end up having the disorder at all - once again suggesting that nurture can have a big impact on an individual developing the condition.
what are NEURAL CORRELATES?
NEURAL CORRELATES are MEASUREMENTS OF THE STRUCTURE OR FUNCTION OF THR BRAIN that have a RELATIONSHIP WITH SZ, especially different regions of the brain.
Neural correlates also refers to how DIFFERENT NEUROTRANSMITTERS such as DOPAMINE and SEROTONIN in different areas of the brain can also play a part in SZ developing.
what is the neural correlates DOPAMINE HYPOTHESIS?
NEUROTRANSMITTERS are the BRAINS CHEMICAL MESSENGERS - these appear to WORK DIFFERENTLY in the BRAINS OF SCHIZOPHRENICS.
In particular, DOPAMINE seems to have an important role since it’s necessary in the FUNCTIONING OF SEVERAL BRAIN SYSTEMS, dopamine has also been implicated in SZ.
what is dopamine?
Dopamine is one of the brains neurotransmitters - a CHEMICAL that transmits MESSAGES BETWEEN NEURONES. Dopamine contributes to FEELINGS OF PLEASURE AND SATISFACTION, it also plays a part in ADDICTION. Dopamine is heavily involved in the MOTOR SYSTEM too.
The activity of the DOPAMINE SYSTEM depends on the STATE OF ONE’s DOPAMINE RECEPTORS.
The dopamine hypothesis claims that an EXCESS OF DOPAMINE in CERTAIN REGIONS OF THE BRAIN is associated with the POSITIVE SYMPTOMS OF SZ
How does an excess of dopamine cause SZ?
When dopamine receptors are overactive, messages from NEURONES THAT TRANSMIT DOPAMINE FIRE TOO EASILY and OFTEN, LEADING TO HALLUCINATIONS AND DELUSIONS .
Schizophrenics are thought to have particularly HIGH LEVELS OF D2 RECEPTORS ON RECEIVING NEURONES, resulting in MORE DOPAMINE BINDING and therefore MORE NEURONES FIRING.
what are two consequences of the dopamine hypothesis?
HYPERDOPAMINERGIA IN THE SUBCORTEX - this refers to the levels of activity of dopamine in the area of the brain known as the SUBCORTEX BEING TOO HIGH, this can cause SPEECH ISSUES.
HYPODOPAMINERGIA IN THE CORTEX - this refers to dopamine levels in the area of the brain called the CORTEX BEING TOO LOW, this can lead to JUMBLED THOUGHT PROCESSES.
