Figure 3. Dopamine/opioid amplification of neural signals for incentive salience.
Neural signals of nucleus accumbens outputs were recorded in ventral pallidum. Two serial CSs had been previously learned by rats to predict sucrose UCS. Amphetamine (dopamine stimulation) or DAMGO (opioid stimulation) microinjections did not enhance prediction signal of upcoming reward elicited by first CS1 (which predicted CS2 and reward UCS with 100% certainty) (Smith et al., 2011). Drug stimulation did amplify >50% neural signals for incentive salience triggered by CS2 (associated with maximal motivation, though merely redundant predictor) microinjections. In a similar experiment (right), after Pavlovian training in a normal state, mesolimbic sensitization added incrementally to the acute effects of amphetamine on board in amplifying intensity of incentive salience triggered by sucrose CS (Tindell et al., 2005). Reprinted by permission.