Behabioral and neural evidence of state-like variance in intertemporal decisions

2012-08-21Humans are distinct from other species in their capacity to pursue temporally distant goals. One paradigm (""delay discounting"") used to investigate this capacity in lab settings requires people to make trade-offs between the magnitude and immediacy of outcomes. In my dissertation, first I review discounting studies from a two-stage (valuation and choice) model perspective, and provided four different hypotheses regarding the connection between valuation and choice, as well as a summary of brain structures relevant to facilitation of preferences for temporally distal rewards. Second, I examined an important yet underexplored area in intertemporal decision-making: state-like variance in discounting behavior as opposed to traditionally emphasized trait-like variance (study 1), as well as state-like variance in consistency of intertemporal preference (study 2). ❧ In study 1, twenty-two participants completed a dual task in which they were required to make intertemporal choices while simultaneously holding an expressive face in memory. From trial-to-trial, the facial expression of the priming stimulus varied between three alternatives: 1) fearful, 2) happy, and 3) neutral. Brain activity was recorded using functional Magnetic Resonance Imaging for sixteen participants. Across participants, the fearful prime was associated with greater preference for delayed rewards (vs. happy prime), and was also associated with greater signal change in the right dorsolateral prefrontal cortex (BA 9). In addition, fearful faces recruited greater brain activation in the posterior sector of anterior cingulate cortex (ACC) (BA 24) during decision-making. Furthermore, individual brain signal change in this activity predicted the behavioral difference in preference for delayed options during fear prime vs. happy prime. ❧ Given study 1's findings suggesting some effect of approach-/withdrawal-related motivation on intertemporal preference, in study 2, anticipatory gains and losses-related approach/withdrawal motivation primes were introduced while participants were performing an individualized intertemporal choice task. Primes varied on a trial-by-trial basis from anticipation of gain, anticipation of loss, anticipation of either gain or loss, and a neutral condition without anticipation of gain or loss. Participants' choice data were modeled using probit regression, and variability of choice was measured by the steepness of the probit function. In order to measure stochasticity with minimal influence of functional form of discounting, choices during study 2 were always between an immediate option and four-month delayed option. Across participants, there was a trend of higher consistency in intertemporal choice in the loss-related motivation prime condition (relative to gain prime). ❧ Taken together, these findings suggest that situational affect influences intertemporal behavior. Fear (relative to happiness) increased farsightedness, possibly through ""inhibition spillover"", and the posterior ACC is a potential neural correlate of this hypothesized biasing signal. Anticipatory loss-related motivation reduced stochasticity in preference possibly through increased emotional responses or value signaling