Faculty Bibliography

Making appropriate choices often requires the ability to learn the value of available options from experience. Parkinson's disease is characterized by a loss of dopamine neurons in the substantia nigra, neurons hypothesized to play a role in reinforcement learning. Although previous studies have shown that Parkinson's patients are impaired in tasks involving learning from feedback, they have not directly tested the widely held hypothesis that dopamine neuron activity specifically encodes the reward prediction error signal used in reinforcement learning models. To test a key prediction of this hypothesis, we fit choice behavior from a dynamic foraging task with reinforcement learning models and show that treatment with dopaminergic drugs alters choice behavior in a manner consistent with the theory. More specifically, we found that dopaminergic drugs selectively modulate learning from positive outcomes. We observed no effect of dopaminergic drugs on learning from negative outcomes. We also found a novel dopamine-dependent effect on decision making that is not accounted for by reinforcement learning models: perseveration in choice, independent of reward history, increases with Parkinson's disease and decreases with dopamine therapy.

We present an overview of recent paradigms used for studying visual information and reward processing in the human and monkey oculomotor pathways. Current evidence indicates that eye movements made during visual search tasks rely on neural computations similar to those employed when eye movements are planned and executed to obtain explicit rewards. These data suggest that human eye movements originate from the processing of (predominantly visual) sensory information, feedback about previous errors, and expectations about factors, such as reward. We conclude that these properties make the saccadic system an ideal model for studying both the behavioral and neural mechanisms for human voluntary and involuntary choice behavior.

We review and synthesize recent neurophysiological studies of decision making in humans and nonhuman primates. From these studies, the basic outline of the neurobiological mechanism for primate choice is beginning to emerge. The identified mechanism is now known to include a multicomponent valuation stage, implemented in ventromedial prefrontal cortex and associated parts of striatum, and a choice stage, implemented in lateral prefrontal and parietal areas. Neurobiological studies of decision making are beginning to enhance our understanding of economic and social behavior as well as our understanding of significant health disorders where people's behavior plays a key role.