Neural mechanisms underlying the in uence of associative learning on valuation and decision-making in humans

Reward is a powerful modulator of behavior. Animals and humans are endowed with the ability to learn to associate events and actions with reinforcing stimuli, and exibly adapt their behavior. The experiments described in this thesis use functional magnetic resonance imaging (fMRI) to study the neural mechanisms of reward learning in humans, the neural substrates by which reward associations in uence behavior, and the neural plasticity that can be induced by provision of reward. Attractive faces have been shown to be a form of visual reward, but their in uence on behavior has yet to be characterized. We show that reward prediction errors in the nucleus accumbens are engaged when subjects learn associations between neutral cues and attractive faces, as has been shown with other reinforcers such as juice and money. This learning increases the subjective value of cues associated with attractive faces. Animal studies have shown that Pavlovian cues can in uence response vigor and decision-making. We present the rst investigation into the neural mechanisms by which Pavlovian cues in uence human decision-making. We nd that activity in the ventral striatum di erentiates between decisions to act in a manner compatible or incompatible with a concurrently presented Pavlovian cue. In the next section we apply associative learning techniques to directly instrumentally condition neural activity, using reward feedback derived from fMRI images processed and analyzed in real time. This technique presents an alternative to standard bio/neurofeedback approaches and may prove useful in many clinical and research applications. We demonstrate that this method can be used to probe the causal in uence of regional brain activity; speci cally we test the impact of medial