Biological Model of Addictive Behaviour

The biological model emphasises the influence of biochemical and genetic factors on addictive behaviours.
The Biological Model suggests people are addicted due to the physical dependence: the chemicals and biological reactions.
SMOKING
Initiation of a Smoking Addiction
The Biological Model states that initiation is due to the role of genetics.
Family and Twin Studies estimate the heritability of tobacco smoking to be between 39% and 80%.
Vink et al studied 1572 Dutch twin pairs and found that for both sexes there were individual differences in smoking initiation. This was explained by genetic (44%) and environmental (56%) influences.
Lerman et al (1999) have shown that people with a particular gene are less likely to take up smoking than those without it. The gene, called SLC6A3-9, works in the dopamine system.
Maintenance of a Smoking Addiction
Vink et al found that nicotine dependence is influenced primarily (75%) by genetics. Initiation may be more influenced by the environment however; regular tobacco use is linked more strongly to individual differences in nicotine metabolism.
Nicotine affects the brain chemistry by activating nAchRs in the brain, leading to the release of dopamine. This creates short-lived feelings of pleasure which when nicotine levels drop will create experiences of negative moods and reduced concentration.
These displeasurable feelings can be removed by another cigarette meaning that the cycle is repeated again and again to avoid withdrawal symptoms.
Relapse of a Smoking Addiction
Twin studies suggest that the ability to quit could also be attributed to genetic influences.
Xian et al (2003) carried out a twin study to test whether genetic factors influenced the failed attempt to stop smoking. They found a 54% heritability rate.
Uhl et al (2008) and other research has attempted to identify the specific gene clusters associated with quit success and nicotine dependence with the aim of matching specific antismoking treatments with the smokers which are most likely to benefit from them.
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A problem with biological explanations of addiction is that they neglect other possible determining factors, it is reductionist.
It reduces a complex phenomenon, such as smoking, down to a relatively simple level of explanation- an imbalance of brain chemicals. There are potential advantages to this approach such as allowing researchers to study the family history to develop an effective treatment. However, there are also limitations as the approach ignores all other potential influences such as irrational thought processes, social context, etc.
There is supporting evidence for the effect of individual differences (genetic influences). Thorgeisson et al (2008) identified a specific gene variant, a chromosome 15 that influenced the number of cigarettes smoked per day, the level of nicotine dependence and the risk of developing related diseases. Smokers who smoked less than 10 a day were less likely to have this variant of the gene. This suggests that genetic factors may not determine smoking initiation but make it more likely that some will become nicotine dependent once they begin.
Genomic medicine involves screening people to identify those who carry genes that increase their susceptibility to specific diseases or addiction. Individuals who are found to have a higher genetic risk of a smoking addiction could then be advised to change their behaviour or seek medical treatment to reduce their chance in developing related diseases. Smoking is a good candidate for this approach given the large public heath burden caused by smoking, as well as the increasing evidence of a genetic contribution. Alternatively, Gartner et al (2009) suggest that, at present, screening for genetic susceptibility is unlikely to be successful due to the small association between specific genes and smoking addiction.
GAMBLING
Initiation of a Gambling Addiction
Studies have shown that pathological gambling runs in families. Although many attribute this to social modelling influences, its possible that it could be due to genetic as well as environmental factors. A twin study by Shah et al (2005) found evidence of genetic transmission of gambling in men.
Black et al (2006) found that the 1^st degree relatives of gamblers were more likely to suffer from gambling than more distant relatives. This demonstrates a strong genetic link.
Maintenance of a Gambling Addiction
The Biological Model can explain the maintenance of a gambling addiction as being due to the pituitary adrenal response.
Recent research suggests that pathological gambling is associated with an under active pituitary- adrenal response to gambling stimuli.
Paris et al (2010) measured gamblers cortisol levels before and after watching a video of their favourite gambling method and a video of a neutral stimuli. Recreational gamblers had significantly increased salivary cortisol levels after both videos, whereas pathological demonstrated no change to either video.
Relapse of a Gambling Addiction
Intense stimulation and excitement for a pathological gambler. Blaszczynski et al (1990) found that poor tolerance for boredom may contribute to repetitive gambling behaviour. Pathological gamblers had significantly higher boredom proneness scores than a control group of non-gamblers. There were no significant differences between the different types of gambling.

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Genetic explanations can explain why some people develop pathological gambling yet others who have the same environmental experiences and life pressures do not. Some people are more vulnerable to develop an addiction because of their genetic predisposition. I.e. the diathesis stress model.
This idea of genetic vulnerability may also explain why some people are more resistant to treatment for their addictive behaviours and are more likely to relapse.
The biological model ignores the importance of external factors on the development of gambling behaviour. External factors include accessibility, peer pressure, etc. Therefore it is more likely that addictive gambling is a product of biological factors that predisposes them to an addiction plus external factors.
A limitation of the biological model is that explanations based on genetics or sensation seeking cannot explain why some types of gambling are more addictive than others. For example, Breen and Zimmerman (2001) found that men and women who got hooked on video gambling became compulsive gamblers within a year. Whereas other forms of gambling tend to take longer, around 3 ½ years before they were at risk of developing a compulsive gambling addiction.