The Biological Approach to Explaining OCD

• the COMT gene regulates the production of dopamine
• all genes come in different forms (alleles) and one form of the COMT gene is more common in OCD patients than those without the disorder
• this variation produces lower activity of the COMT gene and higher levels of dopamine

• affects the transport of serotonin- creating lower levels
• lower levels are associated with OCD
• Ozaki et al. (2003) found that a mutation of this gene in two unrelated families where 6 of the 7 family members had OCD

• one gene cannot determine complex behaviours
• the SERT gene is also implicated in a number of other mental disorders e.g. depression and PTSD
• the diathesis-stress suggests a vulnerability of OCD (and other mental disorders). Other factors (stressors) affect what condition develops (if any)
• some people may posses the variatons but suffer no ill effects

HIGH DOPAMINE LEVELS

• based on animal studies- high doses of drugs that enhance dopamine induce stereotyped movements resembling the compulsive behaviours found in OCD patients (Szechtman et al., 1998)

LOW SEROTONIN LEVELS

• antidepressant drugs which increase serotonin levels have been shown to reduce OCD symptoms (Pigott et al., 1990)
• antidepressants that have less effect on serotonin do not reduce OCD symptoms (Jenicke, 1992)

THE WORRY CIRCUIT

• the caudate nucleus normally surpresses signals from the orbitofrontal cortex (OFC)
• in turn, the OFC sends signals to the thalamus about things that are worrying
• when the caudate nucleus is damaged, it fails to surpress the minor 'worry' signals and the thalamus is altered, which in turn, sends signals back to the OFC

EVIDENCE FOR

• Billet et al. (1998) meta analysis of twins found 68% concordance with identical twins (MonoZygotic- MZ) compared to 31% concordance in non-identical twins (DiZygotic-DZ)
• Pauls et al. (2005) found 10% of people with an immediate relative with OCD also suffered the disorder in comparison to 2% of the general population

EVIDENCE AGAINST

• no study has found a 100% concordance rate, so there must be other factors e.g. learning

EVIDENCE FOR

• by using MRI/ other brain scanning techniques to produce images of the activity in the brain of OCD patients and their immediate family members without OCD- reduced grey matter in key regions of the brain (inc. OFC). Supports the view that anatomical differences are inherited and may lead to OCD in certain individuals.

EVIDENCE AGAINST

• Aylward et al. (1996) did not find any significant difference in basal ganglia impairment between OCD patients and controls
• Basal ganglia damage hasn't been found in 100% of people with OCD so cannot be the full story

PSYCHOLOGICAL EXPLANATION

• two process model can be applied to OCD (intiation and maintenance)
• initial learning occurs when a neutral stimulus e.g. dirt is associated with anxiety
• this association is maintained because the anxiety-provoking stimulus is avioded, then the link is learned with compulsive behaviours, e.g. hand washing