the biological approach to explaining OCD

what is concordance rate?

• a measure of genetic similarity.

• In a sample, for example, 100 twins, one twin of each pair has a phobic disorder. The number of times their other twin also shows the illness determines the concordance rate, so if 40 have phobic disorder the concordance rate is 40%

what is dopamine?

one of the key neurotransmitters in the brain, with effects on motivation and 'drive'

what is a gene?

a part of the chromosome of an organism that carries information in the form of DNA

what is a neurotransmitter?

chemical substances that play an important part in the workings of the nervous system by transmitting nerve impulses across a synapse

what are the 2 genes involved in the genetic explanation of OCD?

• COMT

• SERT

what are the 2 explanations as part of the biological approach to explaining OCD?

• genetic explanations

• neural explanations

is OCD caused by one gene or many?

• many - it is polygenic

• over 230 genes connected to the disorder

what does the COMT gene do?

• involved in the production of COMT

what does COMT do?

• regulates the production of neurotransmitter dopamine

what do people with OCD have with their COMT gene?

• One form of the COMT gene has been found to be more common in those with OCD than those without

• the variation produces lower activity of the COMT gene and higher levels of dopamine

what does the SERT gene do?

• SERT gene affects the transport of serotonin, creating lower levels of this neurotransmitter

• lower levels of serotonin are also implicated in OCD

what is Diathesis-stress in terms of OCD?

• Idea of a simple link between one gene and a complex disorder like OCD is unlikely

• Unlike something like eye colour that may have one gene to determine it - complex behaviours don't

• Genes such as SERT gene are also implicated in a number of other disorders such as depression and PTSD

• This suggests each individual gene only creates a vulnerability (diathesis) for OCD as well as other conditions like depression

• Other factors (stressors) affect what condition develops or whether any illness develops

• Therefore, some could have COMT or SERT gene variations but not suffer any effects

what is a strength of using genetic explanations for OCD?

Strong research support

• Researcher found 68% of identical twins both had OCD compared to 31% of non-identical twins

• Increases validity of theory, suggesting OCD can be partly explained by genetics

what is a limitation of genetic explanations for OCD?

 ignoring environmental factors

• Ignoring role of environment in development of mental illness means that a genetic explanation is prone to biological reductionism

• Twins are brought up in same environment, which means they are likely to respond to upbringing and family life similarly

• If the environment also contributes to OCD then a genetic explanation lacks fully explanatory power

what are the 3 important parts of the brain when looking at the neural explanations of OCD?

• Orbitofrontal Cortex

• Basal Ganglia

• Caudate Nucleus

what does the Basal Ganglia do in a normal brain vs an OCD brain?

Normal = Controls movements, thinking and judgement

OCD = Causes reflexive or repetitive behaviours

what does the orbitofrontal cortex do in a normal brain vs an OCD brain?

Normal = Integrates sensory information, make decisions, anticipates rewards and punishments

OCD = Detects an error where there isn't one, and sends 'worry' signals

what does the caudate nucleus do in a normal brain vs an OCD brain?

Normal = Processes and filters information, removes unwanted thoughts

OCD = Fails to filter anxious thoughts

what is the brain circuit of someone who has OCD?

1. Orbital frontal cortex detects minor worries as significant threats, generates intense worry signals

2. Caudate nucleus fails to filter out minor worry signals. A damaged or hyperactive caudate nucleus lets too many signals through to the thalamus

3. Thalamus receives amplified unfiltered signals and transfers all (major and minor) back to the orbital frontal cortex, creating vigorous cycle of hyperactivation

4. OCD response - individual obsessively focusses on unfiltered worries (obsessions) and performs compulsions to temporarily reduce anxiety 

what do neural explanations suggest?

• link between genetic factors and uncommon levels of certain neurotransmitters

• genetic factors affect certain brain circuits that may not be typical

what are the 2 parts that constitute the neural explanations of explaining OCD?

• variation in levels of neurotransmitters

• differing brain circuits

what do variation in levels of neurotransmitters show in context of OCD?

• dopamine levels = uncommonly high in people with OCD

• based on animal studies - high doses of drugs that enhance levels of dopamine induce stereotyped movements resembling the compulsive behaviours found in patients with OCD

• contrast with dopamine, lower levels of serotonin are associated with OCD

what is the OCD cycle?

what does the diathesis stress model look like?

how do brain circuits differ for those who have OCD?

Several areas in the frontal lobes are thought to function differently in people with OCD

• The orbitofrontal cortex (OFC) integrates sensory information, helps with decision-making and anticipates rewards and punishments

• The OFC sends signals to the thalamus about potential threats, e.g. germ hazards

• The caudate nucleus (in the basal ganglia) normally filters information and suppresses unnecessary signals from the OFC

• In OCD, the caudate nucleus may malfunction and fail to suppress minor worry signals. The thalamus is unnecessarily alerted and sends signals back to the OFC, creating an overactive 'worry circuit'

• This may contribute to obsessive thoughts and repetitive behaviours

what are 2 strengths of neural explanations as a way to explain OCD?

Strength: antidepressants

• Antidepressants such as SSRIs which regulate serotonin levels have been effective in reducing OCD symptoms

• Findings support idea that irregular levels of serotonin are linked to the development of OCD, increasing validity of theory

Strength: high reliability

• Research into neural explanations tend to use objective, clinical methods such as fMRI scanning and so is high in reliability

what is a limitation of neural explanations as an explanation of OCD?

Weakness: external validity

• Not all OCD suffers respond positively to SSRIs, which reduces external validity of the study

• If SSRIs can't treat all individuals with OCD, then the cause may not be solely neural