Biological Explanation Of OCD Flashcards
What areas of the brain are believe to be involved in OCD?
- Orbitofrontal cortex (OFC) - involved in decision making and worrying about social and other behaviour.
- The thalamus - cleaning, checking and other safety behaviours
Neural explanations include
Brain structure
Brain chemistry
What parts of the brain are overactive in OCD?
The OFC and the thalamus are believe to be overactive.
What would an overactive thalamus result in?
An overactive thalamus would result in an increased motivation to clean or check for safety. If the thalamus was overactive the OFC would also become overactive as a result.
What would an overactive OFC result in?
Increased anxiety and increased planning to avoid anxiety.
The worry circuit
The OFC and Thalamus’ overactive with each other becomes a worry circuit
The worry circuit: abnormal
1.) Identifies worries (Orbitofrontal cortex)
2.) If damaged it fails to filter out minor worry signals (Caudate Nucleus)
3.) Transfers major and minor worry signals from CN to OFC, the circuit becomes overactive (Thalamus)
4.) Individual obsesses over minor worries and act in a way that is disproportionate to the worry - compulsions (Orbitofrontal cortex)
What are neurotransmitters?
Brain chemicals that enable communication between different parts of the brain
How are brain chemicals transited?
These are transmitted as electrical impulses using neurons, through a process called synaptic transmission.
How does information get passed?
Information gets passed between neurons at the synapse.
What is the synaptic cleft?
The gap between 2 neurons is called a synaptic cleft.
What direction do neurotransmitters travel?
Axon-dendrite, you always send from the end of an axon and receive from a dendrimer as axons have vesicles and dendrites only have receptors.
What neuron sends the neurotransmitter?
The pre-synaptic neuron which is before the synapse.
What neuron received the neurotransmitter?
The post-synaptic neuron.
Pre-synaptic neuron
Has vesicles in the axon terminal - ‘pockets’ which transport neurotransmitters
Where do the neurotransmitters go to get transported and released in synaptic transmission?
These will go to the pre-synaptic membrane and release the neurotransmitter into the synaptic cleft.
What will the neurotransmitter bind to?
The receptors which are on the post-synaptic membrane which causes a response
Seratonin - effect
Inhibitory effect: they reduce the activity levels in the post-synaptic neuron
Dopamine - effect
An excitatory effect: they increase the activity levels in the post-synaptic neuron
Seratonin - mood neurotransmitter
Use
Contributes to well-being and happiness.
Helps sleep cycle and digestive system regulation
Affected by exercise and light exposure
Dopamine - Pleasure neurotransmitter
Use
Feelings of pleasure, and also addiction, movement and motivation. People repeat behaviours that leas to dopamine release.
What does too much dopamine lead to for those with OCD?
When too much dopamine is transmitted it leads to increased levels of activity and leads to compulsive behaviour.
Main transmitter in this part of the brain and it causes over activity in the affected brain structures.
Seratonin - for those with OCD
Not enough serotonin is release in the same parts, therefore the dopamine excess is not controlled and anxiety is increased.
Thought that it affects the function of both the OFC and Caudate Nucleus.
Genetic component to OCD
Proposed there is a genetic component to OCCD which predisposes some individuals to the illness
Genetic explanations
It has been proposed that there is a genetic component to OCD which predisposes some to the illness.
Why is OCD polygenic?
This is because more than 1 specific gene has been identified in the onset of OCD
Taylor (2013)
Carried out a meta-analysis, finding as many as 230 different genes implicated in developing OCD called candidate genes
How can we investigate genetic explanations?
Twin studies with monozygotic twins or dizygotic twins
Nestadt (2010)
Reviewed previous twin studies:
MZ OCD concordance = 68%
DZ OCD concordance = 31%
What is concordance rate?
The extent to which both twins share the same characteristic
What is the COMT Gene?
- Helps to reduce the action of dopamine
- The variation in the COMT gene decreases the amount of COMT available
- Means dopamine is not controlled and there is too much dopamine which associates with OCD
What is the SERT gene?
Affects the transport of serotonin
Creates lower levels of Seratonin therefore
Low levels of serotonin which have been implicated with OCD
Diathesis-stress model
Suggests that people gain a vulnerability towards OCD through genes but also an environmental stressor is also required. This could be a stressful event, for example a bereavement.
