Linkingvalues to actionsandevaluating expectations relative tooutcomesarebothcentral to reinforcement learningandarethoughtto underlie financial decision-making. However, neurophysiology studies of these processes in humans remain limited. Here, we recorded the activity of singlehumannucleus accumbens neurons while subjects performed a gambling task.Weshowthat the nucleus accumbens encodes two signals related to subject behavior. First,wefind that under relatively predictable conditions, single neuronal activity predicts future financial decisions on a trial-by-trial basis. Interestingly, we show that this activity continues to predict decisions even under conditions of uncertainty (e.g., when the probability of winning or losing is 50/50 and no particular financial choice predicts a rewarding outcome). Furthermore, we find that this activity occurs, on average, 2 s before the subjects physically manifest their decision. Second, we find that the nucleus accumbens encodes the difference between expectedandrealized outcomes, consistent with a prediction error signal.Weshowthis activity occurs immediately after the subject has realized the outcome of the trial and is present on both the individual and population neuron levels. These results provide human single neuronal evidence that the nucleus accumbens is integral in making financial decisions.
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