9 - Biological Approach to OCD

What are the two biological explanations of OCD?

• genetic explanation

• neural explanation

What type of vulnerability do genes cause regarding OCD?

individual vulnerability

Lewis(1936) Study

People w/ OCD:

• 37% had parents w/ OCD

• 21% had siblings w/ OCD

What is probably passed down from one generation to the next?

genetic vulnerability (not certainty of OCD)

What does the diathesis-stress model say certain genes may lead to?

certain genes leave some people more likely to develop a mental disorder (not certain)

What is necessary fo genes to trigger a mental disorder?

an environmental stressor

What are candidate genes?

genes which create vulnerability for mental disorder

What are some candidate genes of OCD involved in?

regulating the development of the serotonin system

What is an example of a candidate gene involved in OCD and what does it do?

• 5HT1-D beta

  • implicated in transport of serotonin across synapses

What is meant by OCD is polygenic?

OCD is caused by a combination of genetic variations that together significantly increase vulnerability (isn’t caused by a single gene)

How many genes did Taylor(2013) identify after his analysis of previous studies find were involved in OCD?

230

Genes found to be associated with OCD are associated with what action?

action of dopamine + serotonin

(neurotransmiters velieved to have a role in regulating mood)

What is meant by OCD is aetiologically heterogeneous?

• one group of genes may cause OCD in one person but another group could case it in a different person

What happens if a person has low levels of serotonin?

• normal transmission of mood-relevant info doesn’t take place

  • person may experience low moods

What particular case of OCD seems to be associated with impaired decision making?

hoarding disorder

What can OCD be associated with in the brain?

Abnormal functioning of the:

• lateral of frontal lobes

• left parahippocampal gyrus

What is the frontal lobe responsible for?

logical thinking + makng decisions

What is the parahippocampal gyrus associated with?

processing unpleasant emotions

Evaluation of Genetic Explanations: Research

S - RESEARCH SUPPORT

• some people more vulnerable to OCD due to genetic makeup

• Nestadt (2010) - reviewed twin studies

  • 68% MZ twins = shared OCD

  • 31% DZ twins = shared OCD

• Family Studies

  • person w/ family member diagnosed w/ OCD is 4x more likely to develop it (than someone w/o)

• suggests there is some genetic influence on the development of OCD

L - TWIN STUDIES NOT GOOD EVIDENCE

• MZ twins are commonly raised in the same environment as well as sharing majority of genes

  • OCD development could be associated w/ environmental factors

  • there is no way to differentiate environmental + genetic factors

• therefore it is not valuable as evidence of explaining genetic involvement in the development of OCD

Evaluation of Genetic Explanations: Environmental

L - ENVIRONMENTAL RISK FACTORS

• OCD doesn’t seem to be genetic in origin

• environmental risk factors can trigger/increase risk of developing OCD

• Cromer(2007)

  • ½ OCD clients experienced traumatic event

  • OCD more severe in those w/ trauma

• genetic vulnerability only provides a partial explanation

Evaluation of Neural Explanations: Research

S - RESEARCH SUPPORT

• antidepressants (regulate serotonin) effective at reducing OCD symptoms

  • serotonin may be involved in OCD

• OCD symptoms part of Parkinson’s Disease - biological in origin

• suggests biological processes underline OCD

Evaluation of Neural Explanations: Neural System

L - NO UNIQUE NEURAL SYSTEM

• serotonin-OCD link may not be unique to OCD

• many people w/ OCD also experience clinical depression

  • depression may involve disruption to serotonin

• logical problem in saying serotonin is a basis for OCD

• serotonin may not be relevant to OCD symptoms (serotonin disrupted as people w/ OCD also have depression)

Evaluation of Neural Explanations: Correlation + Causation

L - CORRELATION DOES NOT = CAUSATION

• evidence is simply a correlation between neural abnormality + OCD

• could be that OCD (or depression) cause abnormal brain functions

• could be a third factor influencing OCD + abnormal brain functions

What is co-morbidity?

having two disorders together