biological explanations for OCD Flashcards
genetic explanations
Some mental disorders appear to have a stronger biological component than others, and OCD is a good example of a condition that may be largely understood as biological in nature. One form of biological explanation is the genetic explanation.
Genes are involved in individual vulnerability to OCD. In a classic study, Aubrey Lewis
(1936) observed that of his OCD patients, 37% had parents with OCD and 21% had siblings with OCD. This suggests that OCD runs in families, although what is probably passed on from one generation to the next is genetic vulnerability not the certainty of OCD.
According to the diathesis-stress model certain genes leave some people more likely to develop a mental disorder but it is not certain. Some environmental stress (experience) is necessary to trigger the condition.
candidate genes
Researchers have identified genes, which create vulnerability for OCD, called candidate genes. Some of these genes are involved in regulating the development of the serotonin system. For example, the gene 5HT1-D beta is implicated in the transport of serotonin across synapses.
OCD is polygenic
However, like many conditions, OCD seems to be polygenic. This means that OCD is not caused by one single gene but by a combination of genetic variations that together significantly increase vulnerability.
Steven Taylor (2013) has analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD. Genes that have been studied in relation to OCD include those associated with the action of dopamine as well as serotonin, both neurotransmitters believed to have a role in regulating mood.
OCD is polygenic
However, like many conditions, OCD seems to be polygenic. This means that OCD is not caused by one single gene but by a combination of genetic variations that together significantly increase vulnerability.
Steven Taylor (2013) has analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD. Genes that have been studied in relation to OCD include those associated with the action of dopamine as well as serotonin, both neurotransmitters believed to have a role in regulating mood.
different types of OCD
One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person. The term used to describe this is aetiologically heterogeneous, meaning that the origins (aetiology) of OCD vary from one person to another (heterogeneous).
There is also some evidence to suggest that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession.
neural explanation-role of seratonin
One explanation for OCD concerns the role of the neurotransmitter serotonin, which is believed to help regulate mood. Neurotransmitters are responsible for relaying information from one neuron to another. If a person has low levels of serotonin then normal transmission of mood-relevant information does not take place and a person may experience low moods (and other mental processes may also be affected). At least some cases of OCD may be explained by a reduction in the functioning of the serotonin system in the brain.
neural explanations-decision making system
Some cases of OCD, and in particular hoarding disorder, seem to be associated with impaired decision-making. This in turn may be associated with abnormal functioning of the lateral (side bits) of the frontal lobes of the brain. The frontal lobes are the front part of the brain (behind your forehead) that are responsible for logical thinking and making decisions.
There is also evidence to suggest that an area called the left parahippocampal gyrus (see diagram on left), associated with processing unpleasant emotions, functions abnormally in OCD.
strength-genetic explanation-research support
One strength of the genetic explanation for OCD is the strong evidence base.
There is evidence from a variety of sources which strongly suggests that some people are vulnerable to OCD as a result of their genetic make-up. One source of evidence is twin studies. In one study Gerald Nestadt et al. (2010) reviewed twin studies and found that 68% of identical twins (MZ) shared OCD as opposed to 31% of non-identical (DZ) twins. Another source of evidence for a genetic influence on OCD is family studies. Research has found that a person with a family member diagnosed with OCD is around four times as likely to develop it as someone without (Marini and Stebnicki 2012).
These research studies suggest that there must be some genetic influence on the development of OCD.
limitation-genetic explanation-environmental risk factors
One limitation of the genetic model of OCD is that there are also environmental risk factors.
There is strong evidence for the idea that genetic variation can make a person more or less vulnerable to OCD. However, OCD does not appear to be entirely genetic in origin and it seems that environmental risk factors can also trigger or increase the risk of developing OCD. In one study for example, Kiara Cromer et al. (2007) found that over half the OCD clients in their sample had experienced a traumatic event in their past. OCD was also more severe in those with one or more traumas.
This means that genetic vulnerability only provides a partial explanation for OCD.
extra strength-It has proved difficult to find candidate genes i.e. genetic variations that are possible causes of OCD. There is evidence though from animal studies showing that particular genes are associated with repetitive behaviours in other species, for example mice (Ahmari 2016).
However, although mice and humans share most genes, the human mind and brain are much more complex, and it may not be possible to generalise from animal repetitive behaviour to human OCD.
strength-neural explanation-research support
One strength of the neural model of OCD is the existence of some supporting evidence.
Antidepressants that work purely on serotonin are effective in reducing OCD symptoms (see next spread for evidence) and this suggests that serotonin may be involved in OCD. Also, OCD symptoms form part of conditions that are known to be biological in origin, such as the degenerative brain disorder Parkinson’s disease, which causes muscle tremors and paralysis (Nestadt et al. 2010). If a biological disorder produces OCD symptoms, then we may assume the biological processes underlie OCD.
This suggests that biological factors (e.g. serotonin and the processes underlying certain disorders) may also be responsible for OCD.
limitation-neural explanation-no unique neural system
One limitation of the neural model is that the serotonin-OCD link may not be unique to OCD.
Many people with OCD also experience clinical depression. Having two disorders together is called co-morbidity. This depression probably involves (though is not necessarily caused by) disruption to the action of serotonin. This leaves us with a logical problem when it comes to serotonin as a possible basis for OCD. It could simply be that serotonin activity is disrupted in many people with OCD because they are depressed as well.
This means that serotonin may not be relevant to OCD symptoms.
extra evaluation-There is evidence to show that some neural systems (such as serotonin) do not work normally in people with OCD. According to the biological model of mental disorder this is most easily explained by brain dysfunction causing the OCD.
However, this is simply a correlation between neural abnormality and OCD, and such correlations do not necessarily indicate a causal relationship. It is quite possible that the OCD (or its accompanying depression) causes the abnormal brain function or both are influenced by a third factor.
