Biological Explanations of OCD Flashcards
Explain the genetic explanation for OCD
This explanation suggests that OCD is a result of genetic factors. It is based on the idea that our genetic code is not only responsible for physiological characteristics, but also behavioural characteristics, including mental disorders. It proposes that the genes we inherit from our biological parents are the main cause of OCD. It suggests that the sequence for a gene or set of genes is in some way different to those who do not develop OCD. It suggests that the sequence for a gene or set of genes is in some way different to those who do not develop OCD and that this difference is the reason for some individuals developing it. These genes may then have an impact on a physiological function in the brain which leads to OCD. For example, there may be a link between OCD and a gene responsible for producing an enzyme called COMT (catechol-O-methyltransferase). Some individuals have a variation in the expression of this gene which reduced the production of COMT. COMT helps terminate the action of the neurotransmitter dopamine which has been linked (in high amounts) to OCD. Trichotillomania (compelling urge to pull one’s hair out) has also been linked to a gene called Hoxb8. Mice bred without this gene nibble their fur until they are bald (Wood and Twohig).
Explain family studies for the biological explanation
First-degree relatives (parents, children, siblings) share 50% of their genes. Therefore studies compare rates of OCD in relatives of diagnosed cases compared to relatives of people without the disorder i.e. controls. If there is greater prevalence rate in the relatives of those with OCD compared to controls, this provides support for the genetic hypothesis.
Pauls et al - reported up to 10% of first-degree relatives of those with OCD were more likely to develop the disorder compared with approximately 2% prevalence in the general population. This finding is supported by Nestadt et al - performed a family study comparing 80 patients with OCD and 73 patients without mental illness (controls). They found that first-degree relatives of those with OCD has an 11.7% risk of developing the condition at some time in their lives. First degree relatives of the control patients had only a 2.7% risk. However one of the problems with family studies is that they do not control for the effects of the environment on the development of OCD. First degree relatives may have similar life events or learning experiences which could also be involved in the development of the disorder. For this reason twin studies may offer more convincing evidence.
Explain twin studies into the genetic explanation for OCD
Twin studies compare concordance rates (the likelihood of both twins being affected with the disorder) for identical (MZ) and fraternal (DZ) twins. Only MZ twins have identical genetic make-up. DZ twins are no more similar genetically than siblings. Lambert and Kinsley - in a review of studies found 53% concordance in MZ twins and 23% in DZ twins.
Explain the neuroanatomical (brain abnormalities) explanation for OCD
It has been suggested that some kind of dysfunction in the orbito-frontal cortex (OFC) (an area in the frontal lobe just above the eye) and the caudate nuclei (structures located in the basal ganglia) may be responsible for OCD. These form a circuit who function is to convert sensory information into thoughts and actions. Information arising in the OFC is passed to the caudate nuclei which act as filters screening out or irrelevant or unimportant information. The most powerful pieces of information are then passed on to the thalamus. It is only when the information reaches the thalamus that the person thinks more about it and take action. Researchers believe that parts of the brain circuit are damaged in people with OCD, so inappropriate information is not suppressed and the individual is overwhelmed by troublesome thoughts and actions. When the caudate nuclei is damaged it fails to suppress minor worry signals and the thalamus is alerted which in turn sends signals back to the OFC, acting as a worry circuit. As a feedback loop of worry signals reverberates throughout the system, the OFC resorts to compulsive defences to control it.
Evaluate the Genetic explanation
- This research provides strong evidence of a genetic component for OCD, but there are no studies that show 100% concordance in MZ twins, suggesting that other factors must be involved. This is consisted with the diathesis model with brings nature and nurture together, suggesting that genetic factors predispose an individual to developing OCD, but environmental factors (e.g. life events/learning) are needed to trigger the disorder.
- It is difficult to separate the effects of nature and nurture. MZ twins may be treated more similarly than DZ twins which may partly account for Lambert and Kinsley’s findings.
- Twin and family studies have not all found the same concordance rates. For example Andrews et al - found no difference in the concordance rate of MZ and DZ twins. This could be because of difference studies use different diagnostic criteria to others.
- Genetic research is a relatively new area, and it is still not known exactly which gene of combination of genes is relevant. Research into the COMT gene has established a link, but findings are not consistent.
- The genetic explanation is reductionist. It tries to explain a very complex disorder in terms of one causal factor. This has the advantage that it is scientific and thus allows for testable predictions but in reducing complex behaviours down to the simplest explanation meaning and significance are lost. A more holistic approach would consider biological environmental and psychological factors when explaining OCD.
