3.8. OCD Explanation: Biological Approach

Question 1

What are the two explanations?

Answer 1

Genetic explanation
Neural explanation

Question 2

What are candidate genes in relation to OCD? (ge)

Answer 2

Specific genes have been identified that create a vulnerability for OCD

Question 3

What are serotonin genes?

Answer 3

Implicated in transmission of serotonin across synapses

Question 4

What are dopamine genes?

Answer 4

Implicated in OCD and may regulate mood

Question 5

What are serotonin and dopamine examples of?

Answer 5

Neurotransmitters

Question 6

The COMT gene:

Answer 6

• Helps to reduce the action of dopamine
• The variation in the COMT gene decreases the amount of COMT available and therefore, dopamine is not controlled and there is probably too much dopamine (associated with OCD)

Question 7

The SERT gene:

Answer 7

• Affects the transport of serotonin, creating lower levels of this neurotransmitter
• Low levels of serotonin have been implicated with OCD

Question 8

Polygenic:

Answer 8

• OCD isn’t caused by one single gene but several genes
• Taylor found evidence that up to 230 different genes may be involved in OCD

Question 9

Aetiologically heterogenenous:

Answer 9

• One group of genes may cause OCD in one person but a different group of genes may cause OCD in another person
• Different types of OCD may be the result of a particular genetic variation e.g. hoarding disorder and religious obsession

Question 10

What are neurotransmitters?

Answer 10

Chemical messengers that transmit nerve impulses from one cell across the synapse to another cell.

Question 11

Serotonin:

Answer 11

Lower levels found in OCD sufferers

Question 12

Dopamine:

Answer 12

Levels are high in people with OCD

Question 13

Abnormal levels of dopamine in OCD sufferers:

Answer 13

• Dopamine levels are thought to be abnormally high in people with OCD.
• This is based on animal studies -> high doses of drugs that enhance levels of dopamine induced stereotyped movements of resembling the compulsive behaviours found in OCD patients.

Question 14

Abnormal levels of serotonin in OCD sufferers:

Answer 14

• Lower serotonin -> someone with low levels of serotonin, then normal transmission of mood-relevant information doesn’t take place and mood is affected (sometimes along with other mental processes)
• Piggot found the fact that antidepressants that increase serotonin activity have proven to reduce OCD symptoms

Question 15

What is it thought that serotonin and other neurotransmitters help the functioning of?

Answer 15

The OFC and worry circuit

Question 16

What is the process of the OFC?

Answer 16

• Serotonin deficiency initiates faulty signals from OFC
• OFC send worry signal to thalamus
• Caudate nucleus monitors signals
• Thalamus sends filtered version of danger back
• Circuit begins again

Question 17

Abnormal brain circuits:

Answer 17

• Several areas in the frontal lobes of the brain are thought to be abnormal in people with OCD, the orbitofrontal cortex (OFC) sends ‘worry’ signals to the thalamus
• These are normally suppressed by the caudate nucleus but, if this is damaged, the thalamus is alerted and confirms the ‘worry’ to the OFC creating a worry circuit
• Then the individual is driven to think more (anxiety) about them and take action (compulsive behaviour).

Question 18

Frontal lobes:

Answer 18

• Responsible for decision making/ logical thinking
• Some cases of OCD are associated with impaired decision making e.g. hoarding disorder
• May be associated with abnormal functioning of the lateral frontal lobes

Question 19

parahippocampal gyrus:

Answer 19

• The left parahippocampal gyrus is associated with processing unpleasant emotions
• Evidence to suggest this functions abnormally in people with OCD

Question 20

Strength: evidence for genetic explanations:

Answer 20

• Nestadt compared to the general population people with first degree relatives with OCD have 5x higher risk of having the illness at some point in their life
• Billet: MZ twins are more than twice as likely to develop OCD if their co-twin has OCD
• This means that people who are egenetically similar are more likely to share OCD, supporting a role for genetic vulnerability
• However, concordance rates aren’t 100%, therefore, there must be other factors, such as environmental as the twins grow up in the same environment and they may observe and imitate.

Question 21

Strength: Research support for the OFC

Answer 21

• Menzies compared to the unrelated healthy people, OCD patients and their immediate relatives had reduced grey matter in key regions of the brain, including OFC.
• This supports the views that anatomical diffs are inherited and may lead to OCD.

Question 21

Strength: support for neurotransmitters

Answer 21

• Piggot et al -> antidepressant drugs that increase serotonin activity has been seen to reduce OCD symptoms -> this suggests that serotonin may be involved in OCD

Question 22

Weakness: alternative explanations

Answer 22

• As not one gene has been identified, it’s clear the environment may play a part- The two process model is a credible alternative, behaviourist explanations for OCD e.g. a link between dirt and anxiety persists because compulsions such as hand-washing reduce anxiety.

Question 23

Weakness: Tourette’s syndrome and other disorders

Answer 23

• Genes may merely predispose individuals towards obsessive-type behaviour
• Pauls and Leckman argued that OCD is one expression of the same gene that also determines Tourette’s
• Rasmussen-> OCD symptoms are also present in autism and anorexia nervosa, and 2/3 OCD patients also experience one episode of depression
• There is therefore no one gene directly and exclusively responsible for OCD.

Question 23

Weakness: existence of environmental risk factors

Answer 23

• Genetic variation affects vulnerability to OCD, but there are environmental risk factors that can trigger it.
• Cromer et al found that over half of OCD patients in their sample had a traumatic event in their past
• This means that genetic vulnerability is only a partial explanation for OCD
• The diathesis stress model may be a better explanation -> a genetic vulnerability but has to be triggered by an environmental factor

Question 24

Weakness: no unique neural system

Answer 24

• Many people who experience OCD also experience depression
• Depression likely involves disruption to the action of serotonin
• Therefore, serotonin may not be relevant to OCD symptoms, as it could just be disrupted due to the depression they’re experiencing, not the OCD.