Journal of Neurology, Neurosurgery and Psychiatry 74: 835.
British Neuropsychiatry Association annual conference (13-14 February 2003; London, UK)

The anatomical basis of desire and addiction
Cardinal, R.N.
Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK.

Animals work for rewards, such as food and sex, for a variety of reasons. They learn that they like a reinforcer, and that their actions can cause the reinforcer to be delivered to them; integrating these two pieces of information causes them to work for the reinforcer. Animals may also work for reinforcement because it has become habitual to them to do so. Additionally, environmental cues that have in the past been paired with reinforcement (Pavlovian conditioned stimuli) gain motivational significance; animals will work for these cues themselves (termed conditioned reinforcement) and these cues can influence their tendency to work for primary rewards (termed Pavlovian-instrumental transfer). How are these aspects of motivation implemented in the brain, and how might they go wrong in pathological states such as addiction? The neural systems responsible for the motivation to work for rewards have been doubly dissociated from those required for so-called consummatory behaviour (such as eating and copulation). Natural reinforcers and artificial reinforcers such as drugs of abuse activate common motivational circuits within the brain. The nucleus accumbens and its mesolimbic dopamine innervation strongly influences the ability of environmental cues paired with reward to motivate behaviour, and this may be one aspect of motivation that goes awry in addiction. Structures including the amygdala are involved in the mechanism by which environmental cues gain motivational value in the first place. The same circuits are activated when stimuli induce craving in humans, giving insight into human pathological desires and possible therapeutic targets.