The biological approach to explaining OCD - TBC

Question 1

What are biological explanations for OCD interested in?

Answer 1

Biological explanations of OCD are particularly interested in how an individual’s vulnerability to OCD may be affected by their genetic makeup, and how the brain functioning of a sufferer of OCD may differ from that of someone without the condition.

Question 2

What are the two biological explanations for OCD?

Answer 2

Genetic explanations
Neural explanations

Question 3

What do genetic explanations suggest about OCD?

Answer 3

Genetic explanations suggest OCD is inherited and that individuals inherit specific genes which cause OCD.

Question 4

What is an example for genetic explanations?

Answer 4

For example, Lewis (1936) found that 37% of his OCD patients had parents with OCD and 21% had siblings with OCD.

Question 5

What does Lewis’ research suggest?

Answer 5

For example, Lewis (1936) found that 37% of his OCD patients had parents with OCD and 21% had siblings with OCD.

Question 6

What does the diatheses stress model suggest?

Answer 6

environmental stressors may be necessary to trigger OCD in those with genetic vulnerability.

Question 7

What are candidate genes?

Answer 7

Candidate genes are genes that are believed to be related to a particular trait, such as a disease or a physical attribute.

Question 8

What are the types of candidate genes for OCD?

Answer 8

SERT gene
COMT gene

Question 9

What is the SERT gene?

Answer 9

Implicated in the efficiency of transport of serotonin across synapses

Question 10

What is the COMT gene?

Answer 10

Regulates the production of dopamine

Question 11

What does the SERT gene do?

Answer 11

The SERT gene (also called 5-HTT) affects the transport of serotonin across the synapse, creating lower levels of this neurotransmitter.
Low levels of serotonin have been implicated in OCD.

Question 12

What did Ozaki et al. (2003) fine about the SERT gene?

Answer 12

He found a mutation of this gene in two unrelated families where six out of the seven family members had OCD.

Question 13

What does the COMT gene do?

Answer 13

The COMT gene regulates the production of dopamine, which has been implicated in OCD.

Question 14

What did Tukel et al. 2013 fine about the COMT gene?

Answer 14

All genes come in different forms (known as alleles) and one form of the COMT gene has been found to be more common in OCD patients than people without the disorder. This variation produces lower activity of the COMT gene and higher levels of dopamine.

Question 15

What does polygenic mean for OCD?

Answer 15

This means that OCD is not caused by one single gene but several genes are involved.

Question 16

How does Taylor’s (2013) support the idea that OCD is polygenic?

Answer 16

His meta-analysis found that 230 different genes may be involved in OCD. Genes that have been studied in relation to OCD include those associated with the action of dopamine as well as serotonin - neurotransmitters associated with mood.

Question 17

What does aetiologically heterogeneous mean for OCD?

Answer 17

One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person.

Question 18

What is the evidence for different types of OCD?

Answer 18

There is some evidence to suggest that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and those who carry out cleaning rituals. Different groups of genes cause different types of OCD in different people.

Question 19

What do neural explanations suggest about OCD?

Answer 19

Neural explanations suggest that physical and psychological characteristics are determined by the behaviour of the nervous system, in particular the brain as well as individual neurons.

Neural explanations of OCD suggest that abnormal levels of neurotransmitters, in particular serotonin and dopamine, are implicated in OCD.

Neural explanations of OCD also suggest that particular regions of the brain, in particular the basal ganglia and orbitofrontal cortex, are implicated in OCD.

Question 20

What are the different areas of the brain?

Answer 20

Frontal lobe
Parietal lobe
Occipital lobe
Cerebellum
Brain stem
Temporal lobe

Question 21

What is the frontal lobe used for?

Answer 21

Speech, thought, personality and learning

Question 22

What is the parietal lobe used for?

Answer 22

Sensory information e.g. temperature and pain

Question 23

What is the occipital lobe used for?

Answer 23

Visual information

Question 24

What is the cerebellum used for?

Answer 24

Motor skills, balance, muscle coordination

Question 25

What is the brain stem used for?

Answer 25

Regulates automatic functions such as breathing, heartbeat and swallowing

Question 26

What is the temporal lobe used for?

Answer 26

Hearing and memory

Question 27

What are the brain areas implicated to OCD?

Answer 27

Orbitofrontal cortex (OFC)
Thalamus
Parahippocampul gyrus
Frontal lobes

Question 28

How is the orbitofrontal cortex implicated in OCD?

Answer 28

The orbitofrontal cortex is a prefrontal cortex region in the frontal lobes of the brain. It sits just above the orbits (eye sockets).

The orbitofrontal cortex is responsible for generating feelings of anxiety.

In OCD patients, this area has been found to be overstimulated and will continue to provoke anxiety until it is acted on.

Question 29

How is the thalamus implicated in OCD?

Answer 29

The thalamus lies at the top of the brain stem near the centre of the brain. It’s known as a relay station of all incoming motor and sensory information — hearing, taste, sight and touch (but not smell) — from your body to your brain.

The thalamus is responsible for safety behaviours such as checking and cleaning.

In OCD patients, this brain area is often enlarged.

Question 30

How is the parahippocampul gyrus implicated in OCD?

Answer 30

The parahippocampal gyrus lies along the edge of the temporal lobe adjacent to the hippocampus. It is an important part of the limbic system and plays an important role in memory, encoding and retrieval.

This area is associated with processing unpleasant emotions, and is thought to function abnormally in patients with OCD.

Question 31

How are the frontal lobes implicated in OCD?

Answer 31

The frontal lobes are associated with decision making and logical thinking. The frontal lobe can be divided into lateral, polar, orbital and medial parts.

In cases of OCD, abnormal functioning of the lateral frontal lobes may be associated with behaviours such as hoarding.

Question 32

What happens in the ‘worry circuit’?

Answer 32

The caudate nucleus (located in the basal ganglia) normally suppresses signals from the orbitofrontal cortex (OFC). In turn, the OFC sends signals to the thalamus about things that are worrying, such as a potential germ hazard.

When the caudate nucleus is damaged, it fails to suppress minor ‘worry’ signals and the thalamus is alerted, which in turn sends signals to the OFC, acting as a worry circuit.

Question 33

What are some supporting research for the worry circuit?

Answer 33

PET scans of patients with OCD, taken while their symptoms are active (e.g. when a person with a germ obsession holds a dirty cloth) have shown heightened activity in the OFC.

Comer (1998) reports that serotonin plays a key role in the operation of the OFC and the caudate nuclei, and it would appear that abnormal levels of serotonin might cause these areas to malfunction.

Dopamine is the main neurotransmitter of the basal ganglia, with high levels of dopamine leading to overactivity of this region
(Sukel, 2007)

Question 34

What is the role of serotonin for OCD?

Answer 34

Low levels of serotonin mean that normal transmission of mood-relevant information does not take place and mood – and sometimes other mental processes – are affected.

Some cases of OCD may be explained by reduction in the functioning of the brain’s serotonin system.

Question 35

What is the role of dopamine for OCD?

Answer 35

High levels of dopamine have been found to play a role in the development of OCD.

While it is unknown exactly what part dopamine plays in the disorder, PET scans reveal that patients have higher than normal levels of the neurotransmitter.