biological approach explaining ocd

• obsessions

  reoccurring intrusive thoughts or impulses
• compulsions

  behaviours that are performed to reduce anxiety caused by obsessions
• neurotransmitter

  chemical substances that play an important role in the workings of the nervous system by transmitting nerve impulses across a synapse
• what neurotransmitter is regulated by the COMT gene ?

  dopamine
• what was found by Tukel et al 2013?

  all genes come in different forms (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
• what neurotransmitter is regulated by the SERT gene ?

  serotonin
• what does the SERT gene do ?

  affects transport of serotonin , creating lower levels of this neurotransmitter
• what was found by ozaki et al 2003?

  a mutation of SERT gene in 2 unrelated families where 6 / 7 family members had OCD
• diathesis-stress ,what is the idea behind it ?

  simple link between one gene and complex disorder unlikely

  e.g- SERT gene implicated in other disorders such as depression/ ptsd
• what is diathesis-stress?

  individual genes only create vulnerability(diathesis) for ocd and other conditions

  other factors(stressors) affect what condition develops or whether any mental illness develops

  so some people have COMT or SERT gene variations but no effects
• abnormal levels of neurotransmitters- dopamine

  dopamine levels high in people with ocd
• abnormal levels of neurotransmitters- serotonin

  lower levels of serotonin associated with ocd
• Jenicke 1992


  antidepressants that have less effect on serotonin do not reduce ocd symptoms
• pigott et al 1990


  low serotonin and ocd based on fact antidepressant drugs increase serotonin activity reduce ocd symptoms
• szechtman et al 1998

  high dopamine and ocd based on animal studies - high drug doses that enhance dopamine levels induce stereotyped movements resembling the compulsive behaviours found in ocd patients
• abnormal brain circuits

  several areas in frontal lobes of brain are abnormal in those with OCD
• candate nucleus as abnormal brain circuit

  In basal ganglia , suppresses signals from orbitofrontal cortex (OFC)- then sends signals to thalamus about things that are worrying
• comer 1998

  Reported serotonin plays key role in OFC operation and caudate nuclei so would appear that serotonin might cause those areas to malfunction
• strength

  evidence for genetic basis of ocd comes from studies of 1st degree relatives and twin studies
• nestadt et al 2000


  80 ocd patients + 343 1st degree relatives , compared with 73 control patients without mental illness + 300 relatives

  findings-people with 1st degree relative with ocd 5x greater risk of having it

  evidence points to genetic basis for ocd but concordance rates not 100% so environmental factors play a role
• evidence of role of genes in ocd comes from studies in people with other disorders

  Pauls+Leckman 1986 studied patients with Tourette’s and families , concluded OCD is an expression of same gene that determines Tourette’s supports view OCD does not have one specific gene but they act as a predisposing factor towards obsessive-type behaviour
• Research support for genes and OFC

  Many studies demonstrate genetic link to abnormal levels of neurotransmitters
• genes + OFC A03 link

  Menzies et al 2007 used MRI to produce activity in OCD patients and immediate family without OCD and also group of unrelated healthy people . OCD patients and close relatives had reduced grey matter in key regions of brain (OFC)
• what does menzies et al 2007 study support ?

  view that anatomical differences are inherited and those may lead to OCD in certain individuals
• alternative explanations-psychology

  E.g-two process model

  Initial learning occurs when neutral stimulus associated with anxiety , association maintained because anxiety provoking stimulus is avoided , obsession formed and link learned with compulsive behaviours that reduce anxiety

  Suggests ocd has psychological causes