The Biological Approach to Explaining OCD

Genetic Explanations

Genes → vulnerability to OCD. Aubrey Lewis (1936): 37% OCD patients had parents with OCD and 21% had siblings with OCD. Genetic vulnerability passed, not OCD itself. Diathesis stress model: certain genes → more likely to develop a mental disorder, but it’s not certain (environmental stress triggers it.)

Genetic Explanations: Candidate Genes

Candidate genes = vulnerability genes. Some regulate development of serotonin (e.g. 5HT1-D beta serotonin transport across synapses)

Genetic Explanations: OCD is Polygenic

OCD not caused by 1 gene, but rather a combination of variations that increase vulnerability. Steven Taylor (2013): analysed findings of previous studies & found evidence that 230 different genes may be involved (including those related to dopamine & serotonin. Neurotransmitters regulating mood.)

Genetic Explanations: Different Types of OCD

One group of genees → OCD for one person. Another group → for another person. Aetiologically Heterogeneous. Some evidence shows that diff types of OCD may be caused by particular genetic variations (e.g. hoarding, or relgious obsession.)

Neural Explanation: The Role of Serotonin

Low levels of serotonin → normal transmission of mood-related info doesn’t occur → low moods (& other mental effects.) Some cases of OCD may be a result of reduction in functioning of the serotonin system in the brain.

Neural Explanation: Decision-Making Systems

Impaired decision making → some OCD cases (e.g. hoarding.) Abnormal functioning of lateral of frontal lobes of brain are responsible for logical thinking/making decisions. Left parahippocampal gyrus (processes unpleasant emotions) → evidenced to function abnormally in OCD

Strength: Research Support

Twin studies: Gerald Nestadt (2010) → 68% of identical twins shared OCD as opposed to 31% of non-identical twins.

Family studies: Marini and Stebnicki (2012) → those with a family member with OCD are 4x as likely to have it than someone without.

Limitation: Environmental Risk Factors

OCD doesn’t appear to be fully genetic in origin, as it seems that environmental factors trigger/increase the risk of development. Kiara Cromer (2007) found that over ½ patients with OCD had a traumatic experience in the past. OCD more severe in people with 1+ traumas.

Strength: Research Support

Antidepressants that work purely on serotonin reduce OCD symptoms. Nestadt (2010): OCD symptoms form part of conditions that are known to be biological in origin (e.g. Parkinson’s disease). Bio disorder → OCD symptoms, assume biological processes underlie OCD.

LImitation: No Unique Neural System

Serotonin link may not be exclusive to OCD as many people with OCD experience clinical depression (involves, but not always caused by, disruption to serotonin). 2 disorders together = co-morbidity. Logical problem.