Biological explanations of Addiction

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  • Biological Models of Addiction
    • Neurochemic-als
      • Initiation
        • In the centre of the brain sits the reward pathways which is responsible for driving our feelings of motivation, reward and behaviour. Memory tells us that a particular behaviour will make us feel good and so the brain tells the body to initiate the behaviour. When this behaviour is carried out, dopamine is released in the brain which gives a sense of reward. In addition, the reward pathway is responsible for making sure we repeat the behaviour. The reward pathway is vital for survival but it is when other substances activate the reward pathway that addictions could develop.
      • Maintenance
        • Chronic exposure to drugs or alcohol eventually result in the activity of these positive reward circuits in the brain. This causes stress for the addict, characterised by withdrawal symptoms when the drug is not taken. This stress state causes the dominant driving force that causes the addict to continue taking the drug. The user no longer uses the drug to obtain a pleasurable experience, but to avoid an unpleasant state. As a result of downregulation, the drug levels that are needed to trigger the brain's reward pathways.
      • Relapse
        • The reward pathways also link to other areas of the brain including the memory areas and help makes addicts highly sensitive to reminders of past highs; addicts learn to expect a rewarding experience from taking a drug. This makes them more vulnerable to relapse when stressed and unable to control the urge to repeat the behaviour
      • Gambling application
        • One of the factors that seem to motivate gamblers is the high they experience when they seem close to winning. It has been found that dopamine increases in the reward pathway of gamblers after a winning streak. Stopping gambling seems to result in withdrawal symptoms associated with stopping drugs. Over 60% of gamblers reported physical side effects during withdrawal.
      • Evaluation
        • Volkow (2001) gave ritulin to a group of normal adult volunteers. Some of them loved the feeling of the drug whereas others said they experienced no rush at all. Their brains were then scanned and it was found there were fewer dopamine receptors in the brains of those who enjoyed the rush. This explains why not everyone who experiments with drugs goes on to develop an addiction.
        • These explanations often neglect other possible contributing factors in the development of an addiction such as the social context of addictive behaviours. As a result, often treatments for addicts involve pharmacolog-ical methods rather than psychological methods that might be more effective in addressing why the addict began the behaviour in the first place.
        • Caine et al (2007) found that mice bred to lack a particular brain receptor do not develop a cocaine addiction.Mouse brain cells usually only have 5 dopamine cells, but mice modified to lack the D1 do not self-administer cocaine when given the chance to do so. Normal mice by contrast keep returning for more.
    • The role of genetics
      • Family studies
        • Merikangas et al (1998) found that 36% of the relatives of individuals with an alcohol addiction had also been diagnosed with an alcohol addiction
      • Twin studies
        • Hufford (1997) studied monozygotic twins and dizygotic twins and found that concordance rates for MZ twins were 76% for alcohol addiction, but for DZ twins it was only 38%.
          • However, there must be some enviornmental influence as the concordance rates should be 100% for MZ twins and 50% of DZ twins.
        • A study of over 300 MZ twins and 200 DZ twins estimated the contribution of genetic factors and enviornmental factors to substance abuse in adolscents. It concluded that the major influence on the decision to take substances was enviornmental not genetic
      • Specific genes
        • Researchers have linked the D2 dopamine receptor gene to severe alcholism.
          • Noble et al found that the A1 variant of this gene was present in more than two-thirds of deceased alcoholics, compared to only one-fifth of deceased non-alcoholics hadthe A1 variant of this gene. This led Noble to refer to the D2 dopamine receptor gene as the 'reward gene'. People who inherit this are more likely to become addicted to drugs.
          • Blum et al found a higher number of children born to alcoholics with the A1 variant of this gene. Individuals with the A1 variant of the D2 receptor gene appeared to have significantly fewer dopamine receptors in the pleasure centres of the brain
      • Smoking application
        • Thorgeirsson et al (2008) began the study with a smoking history questionnaire distributed to over 50,000 Icelanders, in which respondents were asked to say whether they had ever smoked, were still smokers, and if so, how many cigarettes they smoke a day. The research group then studid the DNA of over 10,000 current and former smokers who had responded to the original questionnaire.They found that a particular gene pattern was more common amongst people who developed lung cancer, than among those who stayed healthy.
      • Evaluation
        • A problem here is that not everyone who carries the D2 receptor gene will develop an addiction. There will always be individual differences; those who carry the gene are more vulnerable to developing an addiction but something in the environment is needed to trigger the addiction.
        • Research has found that the D2 receptor gene occured in people with several disorders, including autism and Tourette's syndrome as often as it appeared in alcoholics. This finding creates a problem for the idea of this gene being a rewarding gene.
        • In a meta-analysis by Noble (1998), it was found that 48% of severe alcoholics compared with only 16% of non-alcoholics carried the D2 receptor gene, thus supporting the role of this gene
          • Other research has failed to find such a relationship between alcohol addiction and the D2 gene


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