Explaining OCD

• What is the genetic explanation for OCD?

  • OCD is not genetic itself but genes are involved in individual vulnerability to it (predispositions)
  • Lewis (1936) observed that of his patients, 37% had OCD parents and 21% had OCD siblings, suggesting OCD runs in families
  • Diathesis-stress model - certain genes leave some people more likely to develop OCD but is not certain and some environmental stress is necessary to trigger it
• What other aspects are there to the genetic explanation for OCD?

  • Candidate genes: genes that create vulnerability for OCD and can be involved in regulating the development of serotonin e.g. 5HT1-D beta is implicated in the transport of serotonin across synapses
  • Polygenic: not caused by one single gene but a combination of genetic variations that together increase vulnerability
  • Taylor (2013) found up to 230 different genes that may be involved in OCD
  • Aetiologically heterogeneous: origins of OCD vary from one person to another explaining different types like hoarding disorder and religious obsession
• What genes are associated with OCD?

  • COMT gene regulates the production dopamine associated with mood, satisfaction, sleep, etc.
  • A mutation of this reduces its' ability to break down dopamine, leading to higher levels of dopamine in the brain and overactivity in areas like the prefrontal cortex
  • Turk et al. found that a variation of the COMT gene leads to lower levels of it's activity -> leading to higher dopamine levels
  • Found that it is more common amongst people with OCD than clinically normal people providing evidence that OCD has a genetic basis
• What is one strength of the genetic explanation of OCD?

  • Research support from twin studies: Nestadt et al. (2010) found that 68% of monozygotic identical twins shared OCD compared to only 31% of dizygotic non-identical twins
  • Family studies: Marini and Stebnicki (2012) found that a person with an OCD family member is 4x more likely to develop it than someone without
  • Suggests there must be some genetic influence on the development of OCD
• What is one limitation of the genetic explanation of OCD?

  • Environmental risk factors: Cromer et al. (2007) found that over half of the OCD clients in their sample had experienced a traumatic event in their past and OCD was actually more severe in those with one or more traumas
  • Means that OCD does not appear to be entirely genetic in origin and environmental factors can also trigger/increase risk, meaning genetic vulnerability is a partial explanation
• What is the neural explanation for OCD?

  • Suggests the genes associated with OCD are likely to affect levels of key neurotransmitters as well as structures of the brain
• What is the role of serotonin in OCD?

  • During synaptic transmission, presynaptic neurons release neurotransmitters which are detected by receptors on the postsynaptic neuron - once the message is passed on the neurotransmitters detach are taken back to the presynaptic neuron through a process called reuptake
  • Low levels of serotonin are caused by premature removal from the synapse before it has been able to transmit its' signals to the postsynaptic cell, thought to cause obsessive thoughts and lead to poor mood regulation, explaining OCD characteristics
• What is the worry circuit?

  • The caudate nucleus (located in the basal ganglia) usually suppresses minor worry signals from the orbitofrontal cortex (OFC), which then sends signs to the thalamus about things that are actually worrying
  • A damaged caudate nucleus cannot suppress minor worry signals, meaning the thalamus becomes overactive with irrational worries and sends signals back to the OFC, becoming stuck in a worry cycle
  • Leads to obsessions and compulsions as the brain struggles to turn off the worry response, explaining OCD
• What is one strength of the neural explanation for OCD?

  • Research support for serotonin: Pigott et al. (1990) found that anti-depressant drugs that increase serotonin activity have reduced OCD symptoms successfully
  • Jenicke (1992): found that anti-depressant drugs that do NOT have a strong impact on serotonin DO NOT reduce OCD symptoms
  • Suggests low levels of serotonin are implicated in the development of OCD symptoms
• What is another strength of the neural explanation for OCD?

  • Research support for worry circuit: Comer (1998) found that serotonin plays a key role in the orbitofrontal cortex and the caudate nuclei, meaning low levels of serotonin may cause these areas to malfunction
  • Sukel (2007): dopamine is the main neurotransmitter in the basal ganglia (where the caudate nuclei reside) and high levels lead to overactivity in this region of the brain which can explain why people with OCD have so many irrational worries - the part of the brain that suppresses these has abnormal neurotransmitter levels that can lead to dysfunction
• What is one limitation of the neural explanation?

  • No unique neural system: serotonin-OCD link may not be unique to OCD as many people who have it also experience clinical depression, called co-morbidity
  • Depression involves disruption to the actions of serotonin, meaning we cannot establish that this is the cause of OCD as it could just be an effect of depression
  • Means serotonin may not be exclusively relevant to OCD symptoms leaving us uncertain what the root cause is