Biological approach to explaining OCD

Biological approach

A perspective that emphasises the importance of physical processes in the body like genetic inheritance and neural function

Genetic explanations

Genes make up chromosomes and consist of DNA that codes the physical and psychological features of an organism.

Genes are transmitted from parents to offspring

Neural explanations

The view that physical and psychological characteristics are determined by the behaviour of the nervous system, in particular the brain as well as individual neurons

COMT gene

Important in understanding OCD

An allele of this gene is more common in OCD patients.

A variation of this gene produces lower levels of the COMT gene and higher levels of dopamine

SERT gene

Involved in OCD symptoms

Involved in transport of serotonin and may lead to lower levels of this. Leads to OCD symptoms

Diathesis-stress

Unlikely for 1 gene to be responsible for OCD.

SERT gene may have a role in depression. Some people with this gene may not develop the disorder

States that genes make a person vulnerable to the disorder but that ‘stresses’ affect whether the mental illness develops or not

Brain circuits

PET scans have shown that people with OCD have abnormal areas in their brains

Orbitofrontal corext sends signals to the thalamus about worries.

Usually these are suppressed by the caudate nucleus.

If this is damaged the worry is not suppressed and the thalamus sends the signals to the OFC. Creates a ‘worry circuit’. Leads to obsessive thoughts

Serotonin and dopamine are linked to these regions of the frontal lobe and may be the cayse of the damaged caudate nucleus

Neurotransmitters

Low serotonin and high dopamine levels are linked to OCD

G S Twin studies

Twin research reveals that people with a first-degree relative with OCD are 5x more likely to get OCD themselves.

Monozygotic twins are found to be twice as likely to develop OCD if their twin had it than a dizygotic twin would be.

MZ twins share 100% genetic makeup but only 50% for DZ.

Supports genetic basis of OCD

G W Lack of candidate genes

Pomohaibo

Concluded that OCD is polygenic (a number of genes contribute a small degree of vulnerability)

We are still unsure which genes these are or how they lead to OCD

Suggests we don’t understand the link between genes and OCD.

G W Other factors

Environment may play a role.

Concordance rates are never 100% so there must be other factors than genetics that cause OCD to appear.

Specific OCD symptoms vary so genetics may lead to increased likelihood of developing OCD but not necessarily specific symptoms.

It would be reductionist to assume that only genetics lead to OCD

N S Support for OFC

Saxena

Reviewed research using PET, fMRI and MRI scans.
Found there was consistent support for association with OFC and OCD symptoms

Scans are objective and use scientific methods

Adds reliability and validity to the theory.

N S Menzies

Supported OFC. Conducted MRIs on patients with OCD and their immediate families that didnt have OCD. Compared scans to healthy people.

Reduced grey matter found in OFCs of OCD patients and close relatives

Supports the view that neural mechanisms are involved in OCD

N W Unique neural system

Serotonin-OCD link may not be unique to OCD.

People with OCD may have clinical depression. Having 2 conditions together is co-morbidity. This depression may involve disruption to serotonin action.

Serotonin activity could be disrupted in many people with OCD because they are depressed as well.

Doesn’t support serotonin being relevant to OCD