biological explanation of ocd: neuroanatomical

Question 1

what is one explanation for ocd related to brain neuro-circuitry?

Answer 1

• ocd may be caused by neuro-circuitry in the brain not functioning properly
• to understand this theory, you need to know about certain parts of the brain

Question 2

what role does the thalamus play in ocd?

Answer 2

• the thalamus contains primitive checking and cleaning behaviours hardwired in the brain
• if overactive, it triggers a compulsion to engage in these behaviours

Question 3

what role does the orbitofrontal cortex play in ocd?

Answer 3

• the orbitofrontal cortex alerts the brain to potential worries in the environment
• if overactive, it causes anxiety

Question 4

what role does the cingulate gyrus play in ocd?

Answer 4

• the cingulate gyrus connects the orbitofrontal cortex to the thalamus

Question 5

what role do the basal ganglia play in ocd?

Answer 5

• basal ganglia nuclei are strongly interconnected with the cerebral cortex, thalamus, and other brain areas

Question 6

what components of the basal ganglia are important in ocd?

Answer 6

• globus pallidus fibres act as a braking mechanism, controlling activity in the thalamus
• the caudate nucleus inhibits the action of the globus pallidus fibres
• if the caudate nucleus is overactive, this inhibition does not occur

Question 7

how does overactivity in the basal ganglia relate to ocd?

Answer 7

• in ocd, the caudate nucleus is overactive, so it doesn’t inhibit the globus pallidus fibres (which should dampen activity of thalamus)
• this means the thalamus becomes overactive, triggering compulsions like checking and cleaning behaviours
• the overactive thalamus causes a cascade reaction in the orbitofrontal cortex, making it overactive
• the orbitofrontal cortex alerts the brain to perceived threats, causing anxiety and leading to obsessions

Question 8

what evidence supports the idea that brain structure explains ocd? (supporting - brain scans + Menzies)

Answer 8

• brain scans show differences in brain structure between people with OCD and healthy controls
• Menzies (2007) found that people with OCD have less grey matter in the orbitofrontal cortex
• other studies show people with OCD have a smaller caudate nucleus

Question 9

what research supports a genetic explanation for ocd?

Answer 9

• Feng et al. (2007) bred mice showing OCD-like symptoms (e.g. excessive grooming) when a targeted gene was missing
• this gene is linked to brain areas involved in planning and action initiation, showing a link to compulsions
• although humans and mice share 97% of DNA, differences in gene expression may make extrapolation to humans unreliable
• Murphy et al. (1997) found evidence of a genetic marker for early onset OCD in humans

Question 10

what do brain scans show in people with ocd?

Answer 10

• brain scans show differences in brain functioning between people with OCD and healthy controls
• in OCD, the cingulate gyrus, basal ganglia, and orbitofrontal cortex are active at rest
• these areas become even more active when OCD symptoms are triggered (Whiteside et al., 2004)

Question 11

why is it difficult to show cause and effect in the brain activity model for ocd? (weakness)

Answer 11

• brain activity differences in OCD may be a symptom rather than the cause
• drugs affect serotonin levels almost immediately, but symptom relief can take up to 12 weeks
• this suggests that the role of serotonin is more complex than a simple cause-and-effect relationship

Question 12

how does surgical lesioning relate to the faulty feedback loop theory of ocd? (strength + CA)

Answer 12

• surgical lesioning of the cingulate gyrus has been successful in treating OCD
• supports the theory that OCD results from a faulty feedback loop between the thalamus and orbitofrontal cortex
• however, lesioning doesn’t always work, suggesting OCD is more complex
• Kireev et al. (2013) found that other brain areas can take over the functions of the cingulate gyrus
• this makes the explanation reductionist and oversimplified