ocd

• the biological model is the most widely respected model due to its emphasis on scientific investigation and understanding
• the biological model suggests that mental illness is caused by underlying biological or physical factors, including structural abnormalities, bio-chemical imbalances and genetic predispositions
• the biological model is also sometimes known as the medical model
• the biological model assumes that mental illness has a physiological cause
• obsessive compulsive disorder is classed as an anxiety disorder
• what are obsessions?

  persistent thoughts, often automatic and / or difficult to control
• what are compulsions?

  repetitive behaviours, often with a sense of imperative
• what are emotional characteristics of ocd?

  someone with ocd will feel anxious and distressed

  they are aware that their behaviour is excessive which can lead to embarrassment

  disgust e.g. about germs
• what are behavioural characteristics of ocd?

  compulsive behaviours are performed to reduce the anxiety created by the obsessions

  they are repetitive and can be behavioural or mental

  patients often feel that they have to perform them to stop something bad from happening

  often behaviours do not relate logically to the problem and are excessive
• what are cognitive characteristics of ocd?

  recurrent and intrusive thoughts which can be frightening or embarrassing

  not just excessive worries, but uncontrollable impulses - causes anxiety

  awareness that these thoughts are the product of their mind

  irrational beliefs / catastrophic thinking / selective attention

  cognitive strategies to deal with their obsessions

  some people do not have obsessions
• ocd is caused by genes - polygenic - several genes are involved
• what is a gene?

  a part of the chromosome of an organism that carries the information in the form of dna
• some people inherit genes that make them vulnerable to the development of ocd
• the concordance rate from twin study research varies significantly but suggests that inherited genes are a significant cause of ocd
• family of ocd patients are ten times more likely to have ocd
• twin studies suggest some inheritence of ocd (shields and slater) - 47% for monozygotic twins and 18% for dizygotic twins
• research has attempted to identify specific genes that cause ocd. 2 have been linked:

  1. the comt gene (catechol-o-methyltransferase)
  2. the sert gene (5-htt)
• what does the comt gene do?

  regulates the production of dopamine, which is a neurotransmitter that has been linked to ocd
• 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 with people without the disorder
• it has been found (according to tukel et al, 2013) that one form of the comt gene produces lower activity of the gene and higher levels of dopamine
• comt is responsible for clearing dopamine from synapses (enzymatic breakdown)
• what does the sert gene do?

  affects the transport of serotonin, decreasing levels
• the sert gene comes in two lengths, or two “alleles”, and a person with even one short version is at higher risk for mental health issues
• the long version of the sert gene makes more serotonin transporters. this ultimately leads to more serotonin being available for use by neurons and other serotonergic cells in the body. research has shown that a person who has two long alleles has the capability to utilise up to twice as much serotonin as a person with two short alleles
• serotonin is a neurotransmitter which regulates mood
• when serotonin levels are normal you feel happier, calmer, more focussed and less anxious
• when levels of serotonin are abnormal you feel anxious, unfocussed, unable to concentrate and not in control of your thoughts
• people with ocd have low levels of serotonin
• ssris (which increase serotonin) alleviate symptoms of ocd in about half of cases
• low serotonin levels could be an effect of ocd, not a cause
• neurotransmitters are responsible for relaying information from one neuron to another
• people with ocd have higher levels of dopamine
• dopamine is involved in motor control
• higher levels of dopamine have been associated with some of the symptoms of ocd, in particular the compulsive behaviours
• dopamine is the main neurotransmitter of the basal ganglia, high levels of dopamine lead to over activity in this region
• serotonin plays a key role in the operation of the orbitofrontal cortex and the caudate nucleus, and it would therefore appear that abnormal levels of serotonin might cause those areas to malfunction
• frontal lobe areas are abnormal in ocd
• 1. the caudate nucleus (in basal ganglia) suppresses signals from the orbitofrontal cortex
  2. orbitofrontal cortex sends signals to the thalamus about things that are worrying
  3. when the caudate nucleus is damaged, it fails to stop these minor ‘worry’ signals and the thalamus is alerted
  4. this in turn sends signals back to the orbitofrontal cortex
  5. creates a worry circuit
• pet scans show basal ganglia to be involved in repetitive motor behaviours
• it is suggested that brain abnormalities in ocd patients may be the result of abnormal levels of dopamine and serotonin