Reward and neurocomputational processes

Abstract

The neurobiology of eating disorders (EDs) is largely unknown. However, brain imaging studies over the past decade have identified neurotransmitter alterations that could be part of dysfunctional behavior characteristics of EDs. In this chapter we focus on a specific behavioral construct, the brain reward system, and demonstrate a functional brain imaging approach toward identifying dopamine function in anorexia nervosa (AN). We demonstrate how human brain reward activation can be used in a translational approach to test whether computer models, based on basic science research, can predict expected in vivo reward system activation, and how such an approach can identify specific biologic alterations in a psychiatric population.

Figure 1

Schematic tasks application, modeled after O’Doherty et al 2003. Subjects learned to associate a specific fractal with a particular taste. In 20% of cases there was a mismatch of fractal and expected taste (“Sucrose fractal” but no taste delivery; “Nothing fractal” but Sucrose delivery. A total of 280 trials is applied; every 2.1 seconds a brain scan is acquired.

Figure 2

Principals of the Neurocomputational Modeling Approach. A study participant in the functional magnetic resonance brain imaging (fMRI) scanner performs the taste task. The blood oxygen level dependent (BOLD) brain response is measured. The fist brain activation analysis tests in the whole brain activations that relate to the schedule of reward application and omission, reward expectation, etc. In the second analysis pathway, we use the individual reward task schedule data for each participant and import those data into a computer algorithm that computes the expected brain response based on the animal literature. Those outcomes are then regressed with the human in vivo data in order to 1. test whether significant regression results indeed occur in the expected brain regions, and 2. make group comparisons whether controls have a stronger or weaker activation pattern to a particular learning rate than the anorexia nervosa group.

Figure 3

Preliminary results from a whole brain analysis. The unexpected receipt or omission of the sweet taste stimulus resulted in exaggerated response in the anorexia nervosa (AN) group compared to control women (CW), more positive for the unexpected receipt, and more negative for the unexpected omission.