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. Author manuscript; available in PMC: 2010 Jun 1.
Published in final edited form as: Addict Biol. 2008 Oct 9;14(1):108–118. doi: 10.1111/j.1369-1600.2008.00136.x

FIGURE 2.

FIGURE 2

Reward-associated error signalling by short-term (“phasic”) dopamine release (cf. Schulz et al., 1997). Top: An unexpected reward (banana pallets for rhesus monkeys), which was not predicted by previous stimuli, generates an error in reward prediction (unexpected reward) that is reflected in a short term increase in dopamine firing. Middle: After learning that a previously neutral (now conditioned) stimulus (light) regularly predicts a reward, the surprising appearance of the conditioned stimulus reflects an error in reward prediction and generates a short-term increase in phasic dopamine firing rate. The reward itself is now completely predicted by the conditioned stimulus and does not elicit dopamine firing. Bottom: If a conditioned stimulus is not followed by the expected reward, an error in reward prediction occurs (unexpected lack of reward), which is reflected in a phasic decrease in dopamine firing.