Biological Explanations of Phobic Disorders

  • Created by: JessDyer
  • Created on: 12-10-14 18:48

Genetic Explanations

  • Fear and anxiety have evolutionary advantages for survival because they trigger our 'fight or flight' mechanisms.
  • Not all humans develop such extreme fears that they become phobias and most phobias are related to things that are potentially harmful.
  • Genetic research is attempting to establish whether the tendency to develop phobias is hereditary. 
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Family History Studies

  • Solymon et al - 47 phobic patients. Found a family history of psychiatric disorder in 45% of cases. Only 19% in families of non-phobic control group of patients.
  • Noyes et al - Found a higher than normal rate of agoraphobia and panic disorder in first-degree relatives. Family members were interviewed to see if they reported symptoms of agoraphobia and panic disorder.
  • Fyer et al - 49 first-degree relatives of people with a specific phobia. Found that 31% relatives were also diagnosed with phobias. Only two people had the same type. 
  • Fyer et al - 16% of first-degree relatives also had social phobias. 5% in control group. The disorder was more common in siblings than in parents. 
  • Mannuza et al - extension of Fyer's study. Made a distinction between generalised and non-generalised social phobias. Found that 16% of first-degree relatives also had social phobia in the generalised group, compared to 6% in the non-generalised group.
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Twin Studies

  • Torgerson - 31% concordance in 13 MZ twins for panic disorder and agoraphobia. 0% concordance rate in 16 DZ twins. None of the concordance twins shared the same phobia. 
  • Kendler et al - Interviewed 722 female twins with a lifetime history of phobia. MZ twins had significantly lower concordance rate for agoraphobia than DZ twins. 
  • Kendler et al - study of over 2000 female twin pairs where one had been diagnosed with a social phobia. Found 24% concordance for MZ twins compared with 15% concordance in DZ twins. 
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Evaluation of Genetic Explanations Part 1

  • Family Studies

+ Have found links - most of them show that the relatives of those with phobias are more likely to suffer phobias themselves compared with relatives of non-phobic controls. 

- Methological difficulties - in most instances family members share the same environment and could equally have learned the behaviour

- Data collected using the family interview method are vulnerable to memory and demand characteristics. 

  • Twin Studies

+ More reliable data to test the hypothesis

- Very few have been controlled

- Adoption studies would be more convincing but these are sparse. 

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Evaluation of Genetic Explanations Part 2

  • Role of genetic factors

+ Some evidence for genetic factors in the development of phobias

- More likely to be a tendency to inherit a physiological predisposition towards anxiety in general

- Not sure what exactly is passed on genetically?

  • Diathesis Stress Model

- Even at the highest rates it is clear that phobic disorders are not solely genetic and have some experiential component. 

- Genetic factors predispose an individual to develop phobias but life experiences play an important role in triggering responses. 

- Comorbidity between phobias and depression. Means that genetic factors may predispose to a range of mental disorders.

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Evaluation of Genetic Explanations Part 3

  • Cultural Differences

- Brown et al - phobic disorders are more common among African American than white Americans when socioeconomic factors were controlled. This shows that environment/social factors are important. 

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Neurochemical Explanations

  • If genetic facors are important they are likely to work by exerting an influence on the hardware of the brain. 
  • Structural or biochemical abnormalities should be detectable in the brains of those diagnosed with genetic disorders.

The Role of GABA

  • Research indicates that people who develop phobias are those who generally maintain a high level of physiological arousal which makes them particularly sensitive to their external environment. 
  • It has been suggested that phobias arise because of a dysfunction in the neurones that inhibit anxiety. 
  • Dysfunction caused by low levels of GABA (neurotransmitter)
  • Neurotransmitters are chemicals that act as messengers to transmit impluses from one nerve cell to another across the synapse.
  • GABA is the neurotransmitter that is automatically released in response to high levels of arousal. It binds to receptors on the excited neurons which underlie the experience of anxiety and inhibits their activity. Produces a reduction of arousal levels and a decrease in anxiety.
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Evaluation of Neurochemical Explanations

+ Evidence to support the role of GABA hypothesis comes from studies of people treated with benzodiazepines such as Valium and Librium. 

- Rob- Byrne and Cowley - The effects of benzodiazepines in adults have only been found to be short term. 

- Taylor - in children benzodiazepines produce only marginally better relief than placebos. 

- Suggests that there are other factors that contribute to the development of phobias.

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Neuroanatomical Explanations

  • The amygdala is a part of the brain that is activated in response to the threat. 
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Evaluation of Neuroanatomical Explanations

  • Research evidence

+ Tilfors et al - evidence from PET scans that people with phobias have increased blood flow in the amygdala when they experience anticipatory anxiety compared with controls. 

+ Frederickson and Furmark - when people with specific phobias were exposed to the phobic stimulus they had a startled response and increased activity was observed in the amygdala and the hippocampal areas.

  • Treatment with drugs

+ Successful treatment with the drug Citalopram or with CBT

+ Furmark et al - have been shown to decrease blood flow in the amygdala region

  • Inconclusive evidence

- not all people show blood flow abnormalities

- It is not clear whether they are a casual factor or a result of the phobic disorder.

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