Incentive Salience – Synaptic Plasticity in the Mesocorticolimbic System, Nucleus Accumbens, and Dorsal Striatum
Much work in the nondrug state has shown that the firing rate of midbrain dopamine neurons changes in response to reward as an animal learns. A novel reward produces the transient firing of dopamine neurons and phasic release of dopamine in the nucleus accumbens (ventral striatum). As the animal learns to recognize the cues that predict a reward, the response of dopamine neurons changes. The response to the reward itself decreases or habituates, and dopamine neurons begin to fire in response to the cues that predict the reward. These data support the hypothesis that one function of dopamine release in the nucleus accumbens is to serve as an error-detection signal or learning signal. Such a change in firing pattern requires that midbrain dopamine neurons (or the postsynaptic medium spiny neurons that the dopamine neurons innervate) receive important information from the prefrontal cortex and other regions, such as the hippocampus (external context), insula (internal states), and basolateral amygdala, presumably from glutamate neurons. One term that has become synonymous with this process is “incentive salience,” which has been defined as a mechanism that explains the motivational value of specific learned stimuli (Pavlovian conditioned stimuli) and associated natural rewards (unconditioned stimuli) in humans and animals. One formulation defines incentive salience as a motivational magnet quality that makes the conditioned or unconditioned stimulus a desirable and attractive goal (for further reading, see Zhang et al., 2009).