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1 Cambridge University, UK, 2 MRC Cognition and Brain Sciences Unit, Cambridge, UK, 3 MRC Behavioural and Clinical Neurosciences Institute, Cambridge, UK, 4 Washington University
Reprint requests should be sent to James B. Rowe, Neurology Unit, Cambridge University, Box 83, Addenbrookes Hospital, Cambridge, CB2 2QQ, UK, or via e-mail: james.rowe{at}mrc-cbu.cam.ac.uk.
The prospect of reward changes how we think and behave. We investigated how this occurs in the brain using a novel continuous performance task in which fluctuating reward expectations biased cognitive processes between competing spatial and verbal tasks. Critically, effects of reward expectancy could be distinguished from induced changes in task-related networks. Behavioral data confirm specific bias toward a reward-relevant modality. Increased reward expectation improves reaction time and accuracy in the relevant dimension while reducing sensitivity to modulations of stimuli characteristics in the irrelevant dimension. Analysis of functional magnetic resonance imaging data shows that the proximity to reward over successive trials is associated with increased activity of the medial frontal cortex regardless of the modality. However, there are modality-specific changes in brain activity in the lateral frontal, parietal, and temporal cortex. Analysis of effective connectivity suggests that reward expectancy enhances coupling in both early visual pathways and within the prefrontal cortex. These distributed changes in task-related cortical networks arise from subjects' representations of future events and likelihood of reward.
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