What is the Biological explanation for the development of OCD?

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OCD is an anxiety disorder that is associated with two symptoms. Obsessions, persistent thoughts or ideas that proceed to cause anxiety and compulsions which are repetitive behaviours that the person feels driven to perform in order to reduce anxiety.

There has been two biological factors that have been found in patients with OCD that is of genetic factors and differences in brain activity. Researchers use twin and family studies to prove that genetics do play a part in the development of OCD.

Twins are used to investigate the heritability of disorders, for example Monozygotic twins, where they both share 100% of their genes and the expected concordance rate for OCD would be 100% if the disorder was purely genetic and Dizygotic twins who share 50% of the same genes as they are both different eggs fertilised by different sperms, like any other siblings. The concordance rate in DZ twins for OCD should be 50% if the disorder was solely genetic.

A meta- analysis of 14 twin studies of OCD, including 80 MZ and 29 DZ found that identical twins were more than twice as likely to develop OCD if their twin had the disorder than non- identical twins. Slater and Shields also did a twin study on OCD and found a concordance rate of 47% for MZ twins and 18% for DZ twins. Even though this study shows that genetics do play a role in the development of OCD as the concordance rate is still higher in MZ twins however it is not purely genetic as the concordance rate isn’t 100% for MZ twins and 50% for DZ twins.

One issue with the Slater and Shields study is that it was conducted in the 1960’s where they still couldn’t scientifically identify whether or not twins were either MZ or DZ however in modern day society, new techniques can accurately determine whether twins are MZ or DZ through comparing DNA.

One strength of using twin studies is that the use of MZ and DZ twins presents researchers with naturally occurring experiments however one problem with this, even though the researcher would be of natural occurrence, MZ twins share a more similar environment compared to DZ twins, for example they are dressed the same, the same sex and are treated as one which may influence their development and cannot back up the idea the genetics play a part.

Adoption studies involve comparing a trait or characteristic of adopted children with their adoptive parents and their biological parents. The adoptive parents provide the child with the environment they grow up in whereas the biological parents pass on their genes. If a trait was genetic or heritable, then the biological parents would show more similarity with the characteristic than the adoptive parents do with the adopted child.

One disadvantage to using adoption studies is that most children aren’t adopted at birth, so it may have been the environmental factors they experienced in the presence of their biological parents that gave them the characteristic, not their genes. Another issue with adoption studies is that it may sometimes be difficult to gain access to the biological parents and even gain consent from the biological and adoptive parents.

The genetic approach to OCD is both reductionist and deterministic. It reduces the cause of OCD, such a complicated disorder down to the actions of genes that are passed on from biological parents to their offspring and completely ignores other potential factors such as the role of the environment and early childhood experiences. Simply because someone inherits a certain gene does not mean that they are set out in life to develop OCD. The approach does not account for free will, for example if you have been passed on a gene that increases the risk of you developing type 2 Diabetes, it does not mean for certain that you will get it if you look after yourself properly and keep healthy.

The approach can be applied to the life of a person if they know from an early age that they are genetically more likely to develop the disorder through the potential inheritance of genes. They could then take preventive steps in order to attempt not develop the disorder in the future.

The approach is very scientific and can provide a lot of evidence for the influence of genetics through twin and adoption studies, such as the meta-analysis of 14 twin studies of OCD, the study of Bellodi et al and Slater and Shields. All of these studies demonstrated that genetics do play a role in the development of OCD because the concordance rate for MZ twins, despite not being 100%, was still considerably higher than that of DZ twins. However it is difficult to collect a sample of MZ and DZ twins to perform studies on as there aren’t too many around.

The study of brain structure and chemistry show that there is evidence for abnormal brain structures and activity in patients with OCD. The frontal lobes are responsible for deliberation and judgement and the Basal Ganglia acts as a relay station in the planning and execution of movement. The Caudate Nuclei are areas of the Basal Ganglia that filter messages coming from the frontal lobes before passing on more important messages, that aren’t unacceptable, to other parts of the brain. These areas of the brain may be responsible for OCD because PET scans demonstrate that part of the brains circuit is damaged in people with OCD, inappropriate thoughts and images are being allowed to pass through the Caudate Nuclei which should naturally be filtered out. The patient is then overwhelmed with unpleasant thoughts and then the Basal Ganglia converts these thoughts into actions.

This explanation is viewed as deterministic and reductionist because even if someone has faulty frontal lobes it does not necessarily mean that they are set out to develop OCD, the approach does not account for the free will the an individual has over their own thoughts, feelings and actions. The explanation reduces the cause of OCD down to simple components such as the brains structure, serotonin levels and the COMT gene. It does not consider other potential factors such as psychological explanations, for example Freud’s psychoanalytical explanation.

One strength of this explanation is that there is plenty of evidence collected through scientific means such as PET scans to show the differences in brain structure between a normal brain and the brain of someone with OCD. PET scans demonstrate how inappropriate impulses get through the Caudate Nuclei and that the Basal Ganglia feels overwhelmed with these troublesome feelings and converts them into actions that can be performed as compulsions.

The chemistry of the brain and the actions of neurotransmitters have also been used to describe the disorder of OCD. Low levels of the neurotransmitter serotonin have been found in the brain of people with OCD. When serotonin is released through the synaptic terminals of the pre synaptic neuron, it stays in the synapse to allow the electrical impulse to flow between neurons. People with OCD have too little serotonin for the dendrites of the post synaptic neurons to gather the action potential effectively and thus leading to a decrease in activity within the frontal lobe of the brain. PET scans have been used to demonstrate how people with OCD have been found to have less brain activity in their frontal lobe.

Drugs such as Selective Serotonin Reuptake Inhibitors interfere with the reuptake of serotonin in the brain, by the drug blocking the reuptake channels, forcing the neurotransmitters to remain in the synapse of communicate with the receptor molecules. 50% of people show an improvement after taking SSRI, proving that the action of neurotransmitters and synapses do play a part in OCD however what about the other 50% of people who don’t improve after SSRI’s. Most studies of drug trials such as Prozac show only a 50% improvement, suggesting that there are also other causes to OCD such as psychological ones.

PET scans show lower levels of serotonin in the brains of people with OCD. This supports the explanation because after the treatment with SSRI’s, PET scans demonstrate that the brain of people with OCD return to that of a normal patients brain. Drugs which raise the levels of serotonin can improve the quality of life of the patients because it reduces the symptoms and may alleviate symptoms of Depression they may experience.

One weakness of using SSRI’s is that there is a time delay of 4-12 weeks for a clinical response from SSRI’s. Just because SSRI’s reduce the symptoms of OCD, by increasing the amount of serotonin present in the synapse, it does not necessarily mean that the lack of serotonin in the synapse was the cause of it. For example taking Paracetamol can cure a headache however it is apparent that the lack of Paracetamol didn’t initially cause the headache.

The approach is also reductionist and deterministic  because it reduces the cause of such a complex disorder to the actions between neurons, neurotransmitters and synapses instead of also considering other potentially influences such as psychological factors, environmental factors or childhood experiences. The approach is deterministic as it determines that cause and development of OCD to the actions of synapses and neurotransmitters in the brain and does not attempt to account for the free will of a person choosing to think these thoughts and have these feeling, while having the choice whether or not to perform these compulsions.

Suzanne W. A Level Psychology tutor, GCSE Psychology tutor

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is an online A Level Psychology tutor with MyTutor studying at Durham University

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