Title

Reward Comparison in the Striatum

Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Psychology/Experimental

First Advisor

Howard Cromwell, PhD

Second Advisor

Verner Bingman, PhD (Committee Member)

Third Advisor

Mike Geusz, PhD (Committee Member)

Fourth Advisor

William Ingle, PhD (Committee Member)

Abstract

Reward comparison is a key component of decision making. Prior research has found single cells in the primate striatum that are influenced by relative reward value. This work used an operant task that demonstrated reward comparison without changing outcome-expectancy relationships or using devaluation or delays. This allowed experimenters to examine how animals compare rewards simply by manipulating the context in which different rewards were presented, and represents a more basic comparison scenario. There are some gaps in the literature regarding the brain and reward comparison. The first major gap is the lack of an operant paradigm to examine basic reward comparison in the rat model and a lack of a detailed analysis of behavior during basic reward comparison. The second major gap is a lack of demonstration of these basic neural reward comparison processes in rats during appetitive behavior and a lack of examination of the relationships to behavior. The third major gap is the absence of a topographical examination regarding the participation of single cells in two major subregions of the striatum during reward comparison (dorsal versus ventral). There were three specific aims. First, a novel behavioral paradigm was developed to examine basic reward comparison behavior in the rat model. Second, changes in neural activity in the two major subregions of the striatum were measured during this reward comparison task and correlated with changes in behavior. Third, proportions of activity in the ventral and dorsal striatum were examined during reward comparison. Results showed that the behavioral reward comparison effects were found in individual animal behavior. Behavioral results also showed that one of the behavioral measures was specifically sensitive to the presence of variety. Single unit results showed neurons in the striatum that were sensitive to relative reward value. These were most numerous during the consummatory aspect of the task, and were overall more prevalent in the ventral versus the dorsal striatum. Single units sensitive to variety were also found in the striatum. Changes in single unit firing were not correlated with changes in behavior. Findings are discussed in an overall framework of animal behavioral paradigms and brain reward circuitry.