dopamine

• the key brain area linked to addiction is the mesolimbic pathway, often referred to as the reward pathway.
• mesolimbic pathway

  it is suggested that addictive behaviours and substances trigger the release of dopamine in the ventral tegmental area (VTA) of the brain, which leads to a sense of pleasure in the nucleus accumbens (NAc.)
• mesolimbic pathway

  the reward pathway has evolved in humans to be the usual response to natural behaviours, such as eating or sex.

  however, addictive drugs and behaviours also create this pleasure, flooding the brain with dopamine and other neurotransmitters, meaning the system becomes more maladaptive.
• mesolimbic pathway

  addictive drugs can release 2-10 times the amount of dopamine that natural rewards do, and they do it more quickly, overwhelming brain receptors.

  the brain responds by producing less dopamine or eliminating dopamine receptors.
• mesolimbic pathway

  as a result of these adaptations, dopamine has less impact on the brain's reward centre.

  addicts have to take more of their desired substance to obtain the same dopamine "high" because their brains have adapted - Griffiths described this characteristic as "tolerance."
• mesolimbic pathway

  Volkow et al. (1997) found that in cocaine users, there was a reduction in both the number of D2 receptors in the brain and a reduction in the release of dopamine, proving that dopamine must be linked to addiction.
• a simple pleasure response from the mesolimbic pathway is not enough to explain all the characteristics of addiction.

  it has been proposed that the frontal cortex is implicated in the maintenance of addiction.
• frontal cortex

  the frontal lobe is involved in higher order tasks, such as reasoning, planning of behaviour and memory.

  high levels of dopamine, caused by addiction, alter the functioning of parts of the frontal cortex - changes that persist even when the drug is no longer being taken, or the behaviour no longer engaged in.
• frontal cortex

  this causes addicts to pay more attention to stimuli associated with their addiction.

  Robinson and Berridge (2003) argue that this causes the addict to want to engage in the addictive behaviour, rather than just like it.