Neuroeconomics of Reward Information and Motivation
Humans must integrate information to make decisions. This thesis is concerned with studying neural mechanisms of decision making, and combines tools from economics, psychology, and neuroscience. I employ a neuroeconomic approach to understand the processing of reward information and motivation in the brain, utilizing neural data from functional magnetic resonance imaging (fMRI) to make connections between cognitive neuroscience and economics.
Chapter 1 lays the groundwork for the thesis and provides background on neuroscience, fMRI, and neuroeconomics. Chapter 2 sketches the central challenges of using neuroscience to address economic questions. The first half of the chapter discusses familiar arguments against the integration of neuroscience and economics: behavioral sufficiency and emergent phenomenon. The second half constructs principles for interdisciplinary research linking mechanistic (neuroscience) data to behavioral (economic) phenomena: mechanistic convergence across experiments and biological plausibility in models.
Chapters 3 and 4 employ a nonstandard analysis technique, multivariate pattern analysis (MVPA), to identify brain regions that contain information associated with different types of economic valuation. Chapter 3 uses a combinatoric approach to evaluate how brain regions uniquely contribute to the ability to predict different types of valuation (probabilistic or intertemporal). MVPA shows that early valuation phases for these rewards differ in posterior parietal cortex and suggests computational topographies for different rewards. Chapter 4 employs within- and cross-participant MVPA, which rely on potentially different sources of neural variability, to identify brain regions that contain information about monetary rewards (cash) and social rewards (images of faces). Cross-participant analyses reveal systematic changes in predictive power across multiple brain regions, and individual differences in statistical discriminability in ventromedial prefrontal cortex relate to differences in reward preferences. MVPA thus facilitates mapping behavior to both individual-specific functional organization and general organization of the brain across individuals.
Chapter 5 employs a reward anticipation task to measure variation in relative motivation without observing choices between rewards (money and candy). A reaction-time index captures individual differences in motivation, and heterogeneity in this index maps onto variability in two brain regions: nucleus accumbens and anterior insula. Further, the nucleus accumbens activation mediates the predictive effects of anterior insula. These results show that idiosyncrasies in reward efficacy persist in the absence of a choice environment.
Chapters 6 and 7 conclude the thesis. Chapter 6 complements discussions of neuroeconomics with text analysis of an exhaustive corpus from top economics journals and references from a large set of review articles. The analysis shows a mismatch between topics of importance to economics and prominent concepts in neuroeconomics. I show how neuroeconomics can grow by employing cognitive neuroscience to identify biologically plausible and generalizable models of a broader class of behaviors.
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