biological approach to explaining OCD

what does the biological approach assume?

• mental disorders are related to the physical structure & functioning of the brain

• psychopathology will be changed by the level of neurotransmitters

• mental disorders should be investigated in the same way as mental illnesses

how should mental disorders be investigated?

1. classify using symptoms

2. identify underlying cause

3. prescribe appropriate treatment/therapy

what is the genetic explanation for OCD?

individuals inherit specific genes from their parents that are related to the onset of OCD

what genes are related to OCD?

• COMT

• SERT

what is the COMT gene?

• involved in production of catechol-O-methyltransferase

• regulates production of dopamine

how is dopamine related to OCD?

high levels have been implicated to affect it

what evidence is there of the relationship between the COMT gene & OCD?

one form that produces lower activity of COMT & higher levels of dopamine has been found to be more common in OCD patients

what is the SERT gene also called?

5-HTT

how does the SERT gene affect OCD?

affects the transport of serotonin, leading to lower levels

what evidence is there of the relationship between the SERT gene & OCD?

a study found a mutation of the gene in two unrelated families where 6 out of 7 members had OCD

what is the diathesis-stress model?

there is no simple link between one gene & a complex disorder, so other facts must be considered

what other disorders is SERT gene implicated in?

• depression

• PTSD

what are the neural explanations of OCD?

• neuroanatomical explanations

• neurochemical

what is the neuroanatomical explanation for OCD?

abnormalities in areas in the frontal lobes

which areas in the frontal lobe are associated with OCD?

• caudate nucleus in the basal ganglia

• orbitofrontal cortex

what is the caudate nucleus supposed to do?

supress signals from the orbitofrontal cortex

what does the orbitofrontal cortex do?

send signals to the thalamus about worrying things

what happens when the caudate nucleus is damaged?

fails to suppress minor worry signals which creates a worry circuit

what evidence is there to support neuroanatomical explanations of OCD?

• PET scans of OCD patients - taken while symptoms are active - heightened activity in OFC

• Comer - serotonin plays key role in operation of OFC & caudate nuclei

• high levels of dopamine lead to overactivity in basal ganglia

which hormones affect the frontal lobes?

serotonin & dopamine

what is the main neurotransmitter of the basal ganglia?

dopamine

what are neurochemical explanations for OCD?

abnormal levels of neural transmitters

what neurotransmitter is abnormally high in people with OCD?

dopamine

what evidence is there to support the link between dopamine and OCD?

• animal studies - high doses of dopamine level enhancement drugs - induced stereotyped movements - resembled compulsions

what neurotransmitter is abnormally low in OCD patients?

serotonin

what evidence is there to support the link between serotonin & OCD?

• antidepressant drugs that increase serotonin - reduce OCD symptoms

• antidepressants with less effect on serotonin have no effect

what are the strengths of the biological approach to explaining OCD?

• family studies - Nestadt et al - 80 patients with OCD + 343 relatives - 73 control - people with first degree relatives with OCD 5x risk of having it themselves

• twin studies - meta-analysis - 14 studies - identical twins more than 2x likely to develop if other has it - concordance never 100%

• Paul & Leckman - tourettes/depression - OCD is one form of expression of the same gene - obsessive behaviour in both - also autism & anorexia - not one specific gene - but, predisposing factor

• research support - genetic link to abnormal levels of neurotransmitters - Menzies et al - MRI in OCD patients + family + control - OCD group had reduced grey matter in OFC - anatomical differences

• real world application - one parent w COMT - mothers fertilised eggs can be screened - gives choice - alternative gene therapy may turn genes off - presumes a simple relationship