OCD explanation and evaluations

what does the approach believe

• Approach assumes that all behaviour can be related to physical changes in the body

• Focus is on nervous system - the brain particularly

• Views psychological abnormality as an illness and as a disease (in the same way as physical illness or disease)

genetic explanation

 

• Genetic explanation suggests that OCD is inherited in the genetic material which is passed down from parents

• Genes are said to be involved in individual vulnerability to OCD

  • Lewis 1936 observed that of his OCD patients, 37% had parents with OCD and 21% had siblings with OCD - suggests that it runs in the family

  • What is passed on is vulnerability to OCD not certainty

  • Diathesis-stress model - certain genes leave some more likely to develop a mental disorder but it is not certain and environmental stress is necessary to develop OCD

what are the two types of gene

• Everyone has the same genes but they just vary slightly which triggers different things

• Candidate genes: researchers have identified genes which create vulnerability for OCD

  • COMT gene

  • SERT gene

  • Disorders including OCD may be influenced by a lot of genes - polygenic

• Taylor 2013 analysed findings of previous studies and found evidence that up to 230 genes may be involved with OCD

  • Main genes studied have association with role of mood regulating neurotransmitters - serotonin and dopamine

 

• COMT gene is involved in the production of the enzyme COMT - catechol-methyltransferase

  • Regulates the production of dopamine, a neurotransmitter, in the synapse

  • Dopamine - involved in reward, motivation and motor control

• The form of the COMT gene that is more common in those with OCD is low level activity of the gene which results in higher levels of dopamine

 

• SERT gene - shorter form of serotonin transporter gene = 5-HTT

  • Regulates the transport of serotonin in a synapse

  • Involved in feelings of well being and happiness

• Form of SERT gene more common in OCD individuals is high level activity of the gene which results in lower levels of serotonin as reuptake mechanism works too hard

different types of OCD

• One group of genes may cause OCD in one person but different group of genes will cause this in another

• Aetiologically heterogenous - origins of OCD vary from one to another

• Some evidence to suggest that different types of OCD may be the result of particular genetic variations - hoarding disorder and religious obsession

neural explanation what is the worry circuit

• People with OCD tend to have relatively high levels of neural activity in the orbital frontal cortex (OFC)

• OFC sends 'worry' signals to the thalamus, thalamus is alerted and confirms the 'worry' back to the OFC, creating a circuit

• In a 'neurotypical' brain, the 'worry' signal would be suppressed/intercepted by the caudate nucleus however, in an 'atypical' brain the caudate nucleus is impaired allowing this neural activity (worry gets to thalamus and the thalamus will reconfirm the worry and send it back to the OFC)

• Caudate nucleus' inability to filter small worries in people with OCD result in worry circuit being overactive

neurotransmitters and neuroanatomy

• Serotonin plays a key role in operation of the OFC and the caudate nucleus - abnormally low levels of serotonin might cause this area to malfunction

• Dopamine - main neurotransmitter of the basal ganglia (caudate nucleus, putamen and globus pallidus), high levels of dopamine leads to overactivity of this region - associated with OCD

what are some decision making systems

• Some cases - associated with impaired decision making

• Frontal and lateral lobes are abnormally functioning - frontal lobes are responsible for logical thinking and decisions

• Evidence suggests that left parahippocampal gyrus which is associated with processing unpleasant emotions, functions abnormally in OCD

strengths of neural explanation

• Piggot et al 1990 - serotonin agonists and several selective serotonin uptake inhibitors are effective at reducing the symptoms of OCD

• Anxiety reducing drugs that do not affect serotonin are not effective for those with OCD

• Supports the idea that lower levels of serotonin are involved in exhibition of OCD symptoms

 

• Szechtman et al 1999 - gave rats a dopamine agonist (stimulates production) and they started to experience repetitive behaviours that were compulsive

• They then gave rats anti-OCD drugs (antagonists) and the repetitive behaviour was reduced as this slows dopamine production

• Supports idea that dopamine systems are involved in OCD as it resembles ritualistic behaviour in humans

 

• Saxena and Rauch 2000 - reviewed studies of OCD that used PET, fMRI  and MRI neuro-imaging techniques

• Found consistent evidence of an association between the orbital frontal cortex and OCD symptoms

• Suggests that specific neural mechanisms in the OFC are involved with the explanation of OCD

 

• Antidepressants are useful to reducing OCD symptoms - these symptoms are seen in conditions that are biological in origin such as the degenerative Parkinson's disease which is a brain disorder

• If biological disorders produce OCD symptoms it can be assumed that biological processes underlie OCD

weaknesses of neural explanation

• Many people who have OCD also have depression (co-morbidity), this is thought to involve disruption of the serotonin system

• Leaves us with a logical problem when it comes to serotonin system as possible basis for OCD

• Simply be that serotonin activity is disrupted in many people with OCD as they are depressed as well

• Serotonin may not be relevant to symptoms

 

• Not clear what neural mechanisms are involved in OCD

• Studies show that neural systems involved in decision making are the ones that malfunction in OCD (Cavedini et al 2002)

• Some research also identified various other brain systems that may be involved in OCD

• Cannot claim to understand the neural mechanisms in OCD

strengths of genetic explanation

• Nestadt et al 2010 reviewed twin studies of OCD and it was found that concordance for MZs was 68% compared to 31% for DZ

• Concordance rate is the percentage of pairs of twins that both showed the disorder

• Person with a family member diagnosed with OCD is around 4 times more likely to develop the disorder than someone without - Marini & Stebnicki 2012

weaknesses of genetic explanation

• OCD is polygenic so the COMT and SERT genes are not the only ones that contribute to OCD

• Our understanding of the human genome advances all the time and more genes being discovered which contribute to OCD

• Many of the genes contribute small risk of OCD and many have other functions

 

• Genetic vulnerability is not the only factor in determining whether someone will develop OCD as there are also environmental risk factors

• Cromer et al 2007 - sample of 265 diagnosed with OCD given structured clinical interviews

• 54% reported experiencing one traumatic life event

• Those with traumatic life events had more severe OCD symptoms - the correlation remained despite variables such as age, OCD age-of-onset, comorbidity and depressive symptoms