Biological Approach - Explain OCD

Genetic Explanation

Individuals inherit specific genes from their parents that are related to the onset of OCD

COMT gene

Regulates production of dopamine

What type of COMT gene is found to be more common in patients w. OCD

A particular allele (form/variation of the gene)

• This allele produces lower activity of COMT gene & higher levels of dopamine (Tukel et al, 2013)

SERT gene

Affects transport of serotonin

What does the underactive allele of SERT gene do?

Slows transportation of serotonin in brain

• Creates lower levels of serotonin

  • Common in OCD patients

Diathesis Stress Model

Genes such as COMT or SERT only create a vulnerability for OCD, as well as other conditions e.g. depression

• Other factors (environmental factors), e.g. stressors, need to be present to trigger the development of the disorder

Neural Explanations

The idea that people w. OCD have abnormal levels of neurotransmitters & brain circuits

Abnormal Levels of Neurotransmitters

• Abnormally high levels of dopamine found in some people w. OCD

  • Based on animal studies (Szechtman et al) - high doses of drugs induce behaviour resembling that of OCD patients

• Low levels of serotonin found in some people w. OCD

  • Antidepressant drugs have shown to reduce OCD symptoms (Pigott et al)

Abnormal Brain Circuits

• Several areas in frontal lobe are abnormal in people w. OCD

• Caudate nucleus usually suppresses signals from OFC reaching thalamus

  • When caudate nucleus damaged, can’t suppress minor ‘worry’ signals, causing thalamus to be alerted

  • In turn, sends signals back to OFC, acting as a worried circuit

• Supported by PET scans of OCD patients

  • Shows heightened activity in OFC

AD1 GEN: Research Support

P: A strength of the genetic explanation for OCD is the strong evidence base

Ev: 1 source is twin studies. Nestadt et al reviewed twin studies & found 68% of identical twins shared OCD as opposed to 31% of non-identical twins. Family studies. Person w. family member diagnosed w. OCD is approx. 4x as likely to develop it as someone w.out (Marini & Stebnicki)

Ex: Suggests some people are vulnerable to OCD as a result of their genetic make up

L: These research suggest there must be some genetic influence on development of OCD

AD1 NEU: Supporting evidence

P: A strength of the neural model of OCD is the existence of some supporting evidence

Ev: Antidepressants that work purely on serotonin are effective in reducing OCD symptoms & this suggests serotonin may be involved in OCD. Also, OCD symptoms form part of conditions that are known to be originally biological, e.g. Parkinson’s, which causes muscle tremors + paralysis (Nestadt)

Ex: If a biological disorder produces OCD symptoms, we may assume the biological processes underline OCD

L: This suggests that biological factors (e.g. serotonin & processes underlying certain disorders) may also be responsible for OCD

AD1: Research support OFC & genes

P: Many studies demonstrate the genetic link to abnormal levels of neurotransmitters

Ev: Menzies et al used MRI to produce images of brain activity in OCD patients & their immediate family w.out OCD & group of unrelated healthy people

Ex: OCD patients & their close relatives had reduced grey matter in key regions of the brain including the OFC

L: Supports view that anatomical differences are inherited & these may lead to OCD in certain individuals. Brain scans may be used to detect OCD risk

DIS1: Environmental Risk Factors

P: A limitation of genetic model is there are also environmental risk factors

Ev: Cromer et al found over half of OCD clients in sample had experienced traumatic event in their past. OCD was more severe in those w. 1 or more traumas

Ex: Environmental risk factors can trigger or increase risk of developing OCD

L: This means that genetic vulnerability only provides a partial explanation for OCD