http://www.nature.co...l/1301117a.html
http://www.ncbi.nlm..../pubmed/8393485
Dopamine: Dopamine is related to recreational drugs including amphetamines, cocaine, and morphine, which increase extracellular levels of dopamine in both the NAc shell and the NAc core, but the effect of these increases is more pronounced in the shell. Only amphetamine at high levels increases extracellular levels of dopamine to similar levels in both the shell and the core. All of this points to a 'functional heterogeneity' in the nucleus accumbens between the shell region and the core region.[27]Similarly to drug rewards, non-drug rewards also increase levels of extracellular dopamine in the NAc shell, but drug induced DA increase is more resilient to habituation when exposed repeatedly to drug-stimuli, unlike non-drug rewarding stimuli induced dopamine increases, which do succumb to habituation. Recent[when?] studies have shown that the repeated influence of drug-inducing DA projection has an abnormal strengthening effect on stimulus-drug associations and increases the drug-reward stimuli’s resistance to extinction. This may be a contributing factor to addiction. This effect was more pronounced in the NAc shell than in the NAc core.[19][28]
