Lesson 12: Biological Explanations Of OCD Flashcards
Genetic explanations of OCD
- abnormalities in the brain can be the result of genetic inheritance i.e. passed on from parents to child
Twin studies
- often psychologists focus on identical twins (also known as MZ) who share 100% genes who have been separated at birth, so been bought up in completely different environments. If concordance rates for a psychological disorder are high this suggests that genes play an important part in the development of that disorder.
- alternatively psychologists can compare to concordance rates for psychological disorders for identical twins and then non-identical twins (who only share 50% of their genes). If the concordance rates for identical twins is higher this suggests that genes do play a role in the disorder.
Family studies
-genetics has been shown to play a role in a variety of psychological disorders including obsessive compulsive order. Genes are involved in individual vulnerability to OCD. Lewis (1936) observed that of his OCD patients, 37% had parents with OCD, 21% had siblings with OCD which suggests that OCD runs in families. According to the diathesis stress model, certain genes leave some people more likely to suffer a mental disorder, but it is not certain and some environmental stress may be necessary to trigger the condition.
Adoption studies
- if OCD is in the genes, then adoption studies are a good way to test this as if a baby is born with an OCD gene but adopted by parents who do not have OCD, will the baby end up with OCD as an adult? If OCD is genetic, then the baby could end up with OCD as an adult but if it is not genetic then the baby will not end up with OCD as an adult as the environment that the baby will be reared in will not have parents that have OCD.
Candidate genes
- genes that create vulnerability for OCD are called candidate genes. Some of these genes regulate the development of the serotonin system. For example, 5GT1-D beta is implicated in the efficiency of transport of serotonin across synapses.
- SERT gene - involved in the regulation of serotonin activity in the brain. There is some evidence that some individuals with OCD have a mutated version of this gene leading to reduced serotonin activity.
- COMT gene - involved in the regulation of dopamine activity. There is some evidence that some individuals with OCD have a mutated version of this gene which this time leads to increased dopamine activity
OCD is polygenic
- OCD seems to be polygenic which means that OCD is not caused by a single gene, but rather several genes are involved. Taylor (2013) analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD. Many of these genes are associated with the actions of dopamine and serotonin, which are both believed to play an important role in regulating mood.
Different types of OCD
- one group of genes may cause OCS in one person but a different group of genes may cause the same disorder in another person. The term aetiologically heterogenous means that the origin of OCD has different causes. Some evidence suggests that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession.
Strengths of genetic explanations
+ there is good supporting evidence. There is evidence from a variety of sources particular,y twin studies, for the idea that people are vulnerable to OCD as a result of their genetic makeup for example, twin studies show us whether OCD is due to genetics or the environment through concordance rates - the higher the concordance rates, the higher the chance that OCD is genetic for example Nestadt et al (2010) reviewed previous twin studies and found that 68% of identical twins shared OCD as opposed to 31% of non-identical twins which strongly suggests a genetic influence on OCD.
Supporting evidence through Lewis (1936) who observed that of his OCD patients, 37% had parents with OCD, 21% had siblings with OCD with suggests that OCD runs in families and this may be through genes.
Weaknesses of genetic explanations
- too many candidates genes, psychologists have not been successful at identifying all the genes involved in OCD. It appears that several genes are involved and they only increase your risk of OCD by a fraction, consequently the genetic explanation for OCD is not very useful because it provides little predictive value.
- Environmental risk factors (diathesis stress model) - environmental risk factors can also trigger or increase the risk of developing OCD. Cromer et al (2007) found that over half the OCD patients in their sample had a traumatic event in their past and that OCD was more severe in those with more than one trauma, which suggests that OCD cannot be entirely genetic in origin.
- twin studies are flawed as genetic evidence, twin studies overlook the fact that identical twins may be more similar in terms of shared environmental for example even though twins may be genetically identical, they may also share the same environment e.g. go to the same school, wear the same clothes etc. this then makes it very difficult to separate the nature and nurture on whether the OCD was indeed due to genes or the environment
Neural explanations of OCD
- neural explanations are based on brain chemicals and abnormal brain circuits. Messages are carried across gaps between neurones in the brain by neurotransmitters. Low or high levels of neurotransmitters in the brain have been linked to mental disorders. The main neurotransmitter associated with OCS is serotonin.
The role of serotonin
- the neurotransmitter serotonin is believed to help regulate mood. As neurotransmitters are responsible for relaying information from one neuron to another, if a person has low levels of serotonin then normal transmission of mood relevant information does not take place. This may mean that mood and other mental processes may be affected. Some cases of OCD can be explained by a reduction in the functioning of the serotonin system in the brain. In other words, the fact that OCD patients feel sad and generally have a low mood, this may be linked to low levels of serotonin.
Neuroanatomical explanations
These explanations focus on specific parts of the brain being responsible for specific behaviours. Two main brain regions have been implicated in OCD, including the basal ganglia and orbitofrontal cortex,
Basal ganglia
- the basal ganglia is a brain structure involved in multiple processes, including the coordination of movement, and abnormalities in the basal ganglia have been linked to OCD. Rapport and Wise have proposed that hypersensitivity of the basal ganglia leads to repetitive motor behaviours as seen in OCD for example, repetitive washing. In support patients who suffer head injuries in this region often develop OCD-like symptoms, following their recovery suggesting that if the basal ganglia is damaged, then OCD may occur.
- Max et al (1994) found that when the basal ganglia is disconnected from the frontal cortex during surgery, OCD-like symptoms are reduced. This clearly suggests a link between the basal ganglia and OCD.
The Orbitofrontal Cortex (OFC)
- the OFC is found on the frontal lobes and is thought to be involved in higher level cognitive processing including decision making and worrying about social and other behaviours
- it has significant connections to the thalamus, an area whose functions including controlling, checking and other safety behaviours. When the OFC detects something is wrong, it sends a ‘worry’ signal to the thalamus
- in OCD, the OFC and thalamus are believed to be overactive, 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. An overactive OFC would result in increase anxiety and increased planning to avoid anxiety.
- In a study by Whitehead (2004), he reviewed brain-imaging research into OCD and found hyperactivity in the orbital region was consistently found in OCD patients compared to healthy controls. After treatment, activity reduces to a level comparable to that of controls, as found by Saxena and Rauch showing supporting evidence.
Strengths of neural and Neuroanatomical explanations
- neural explanations are supported by the effectiveness of biological treatments of OCD. Anti-depressants typically work by increasing levels of serotonin, such drugs are effective in reducing OCD symptoms which suggest that OCD is linked to low levels of serotonin. However anti-depressants are not effective in all patients suffering from OCD and are rarely completely effective. Furthermore, there is a time delay between taking drugs and improvements in symptoms and yet SSRIs increase serotonin levels within hours. This suggests that low levels of serotonin alone cannot explain OCD.
