Poster F128, Tuesday, March 28, 8:00 – 10:00 am, Pacific Concourse
Neural Subjective Value Representations across Age and Discount Factors: Time Delay, Physical Effort, and Probability Discounting
Kendra Seaman1, Nicholas Brooks1, Teresa M. Karrer1,2, Linh Dang3, Ming Hsu4, David H. Zald3, Gregory R. Samanez-Larkin1; 1Yale University, 2TU Dresden, 3Vanderbilt, 4University of California Berkeley
Here we attempt to dissociate behavioral preferences for different discount factors to examine the convergence and divergence of neural representations of subjective value in an adult life span sample. We examined neural subjective value representations when monetary rewards must be integrated with one of three discount factors: time delays, physical effort, or probability. 77 healthy participants between the ages of 22 and 83 (N=33M/44F) completed fMRI studies at Vanderbilt University. Participants made choices between either (1) a smaller magnitude reward with a shorter time delay / higher probability / lower physical effort required and (2) a larger magnitude reward with a longer time delay / lower probability / higher physical effort required. For each task, participants were compensated with the payout from one trial. Subjective values were computed using individual subject discount rates estimated using a hyperbolic discount function. We found that discount rates – preferences for short time delays, lower physical effort, or high probability – were not correlated across tasks. In spite of the apparent behavioral dissociation between preferences, we found overlapping subjective value-related activity in the medial prefrontal cortex. These results suggest that while the tolerance of these decision features is behaviorally dissociable, they share a common neural representation. Interestingly, the regions that are critical for computing and/or representing subjective value have a high density of dopamine receptors. All participants also completed a PET scan; in the future we will examine whether individual differences in subjective value representation are related to individual differences in dopamine receptor availability.
Topic Area: THINKING: Decision making