Biological Explanations of Phobic Disorders

- Phobias are among the most common mental disorders.

- Statistics suggest that around 4% of the adlt population suffer from phobias, however this rate varies from 2% to 13%. 

- Anxiety and fear are natural and adaptive responses, and therefore have a biological basis.

- This may lead us to expect that abnormal fears and anxieties are biologically based. 

Experiencing anxiety after an event has happened would not be an adaptive response, therefore animals have evolved to potential threats. Those ancestors who respond to appropriate threats were more likely to survive and pass on their genes.

Natural selection therefore has shaped our nervous system so that we attend to more cues than others. Prepotent fears are likely to develop into phobias.

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Ohman and Soares provided supporting evidence for prepotency effects. Masked pictures of feared objects were shown to participants, and those fearful of snakes or spiders showed greater GSR (indicates arousal) compared to viewing the neutral masked photos when compared to non-phobic participants.

This shows that important components of phobic disorders were set in motion before the phobic stimulus is presented in awareness, this could be prepotent signals.

This is the innate readiness to learn about dangerous situations rather than inheriting rigid behavioural responses to specific situations. 

Mineka et al

Found that Rhesus monkeys develop a fear of snakes if they see another Rhesus monkey demonstrating a fear of snakes, however, the same rapid associaton is not made if another rhesus monkey shows fear towards a flower.

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Ohman found it was easier to condition a feared response to snakes rather than neutral objects such as houses.

This indicates a biological preparedness to develop phobias of certain objects.

There are significant differences in the kind of phobias reported by different cultural groups.

Brown et al found that phobic disorders were more common among African American than white American participants even when socioeconomic factors were controlled. 

This shows that environmental/social factors are important in determining aspects of phobias. 

Ancient fears and modern minds

Some stimuli are more likely to be feared than others, such as snakes, heights, storms, darkness and strangers.

These may be referred to as ancient fears, and reflect real danger to ancestors.

Things that are dangered today such as motor cars, electricity or guns rarely develop into phobias because they haven't been around as long to be influenced by adaptive selection. 

It is clear that phobic disorders are not solely genetic, therefore a more credible explanation may be the diathesis-stress model.

The diathesis-stress model suggests genetic factors predispose an individual to develop phobias but life experiences play an important role in triggering such responses. 

- Phobias are among the most common mental disorders.

- Statistics suggest that around 4% of the adlt population suffer from phobias, however this rate varies from 2% to 13%. 

- Anxiety and fear are natural and adaptive responses, and therefore have a biological basis.

- This may lead us to expect that abnormal fears and anxieties are biologically based. 

Comparisons can be made between identical twins and non-identical twins.

As MZ twins have a closer concordance rate, this can act as evidence for a genetic basis of phobic disorders.

Torgerson - compared MZ and DZ twin pairs where one twin had an anxiety disorder.

Such disorders were five times more frequent in MZ pairs.

Family and twin studies provide modest support for the genetic basis, however, there has been considerable variation between disorders. Kendler et al estimated a 67% heritability rate for agoraphobia, 59% blood/injury, 51% social and 47% animal phobias. 

An issue of family and twin studies is that they fail to control the role of shared environment. MZ twins are likely to share the same environmental experiences than DZ due to similar interests. 

To resolve this, twins reared apart should be used but such studies have not been conducted. 

It may be that people inherit an oversensiive fear response. 

This can be explained in terms of the autonomic nervous system. In some individuals there may be abnormally high levels of arousal in the ANS which leads to increased amounts of adrenaline, this is the adrenergic theory. 

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Successful drug therapies block activity of the adrenergic system and ths reduce the symptoms of the anxiety. 

However, this is not evidence hat the differences cause the disorder, drugs may treat the symptoms that arise from phobias.