Glucose-specific signaling effects on delay discounting in intertemporal choice.

We propose that decisions related to resource management (e.g., intertemporal choice between a smaller-and-sooner reward and a larger-and-later reward) are sensitive to and regulated by fluctuating blood glucose levels. Circulating glucose affects intertemporal choice by means of signaling body energy condition instead of serving as a replenishing resource for effortful cognitive processing. We intend to dissociate calorie-supplying functions from glucose-unique anticipatory effects on behavioral resource management, measured by delay discounting in making intertemporal choices. Regarding the anticipatory functions of the glucose-insulin system in regulating the degree of delay discounting, we tested three predictions: First, we predict that the signaling effects of circulating glucose on delay discounting do not need to be dose-dependent as long as glucose fluctuation indicates a directional trend in body energy budget. Second, such effects of glucose fluctuation on delay discounting are phagic (appetite related) instead of dipsian (thirst related). Third, this glucose-insulin signaling system requires glucose as the specific input, thus is insensitive to other forms of sugar that are not insulin regulated. In Study 1, fasting participants were randomly assigned to one of five groups: water consumption, zero-consumption, and three glucose consumption (18g, 36g, and 72g cane sugar/250ml water) groups. The participants competed two sets of intertemporal choice questions with varying delay discounting rates before and after a beverage intervention. The results showed that the rate of delay discounting was negatively correlated to blood glucose levels. The effects of circulating glucose on delay discounting closely followed the changes in blood glucose levels showing a plateau on both dose-response curves (i.e., the sugar dose-blood glucose level curve and the sugar does-delay discounting curve). Secondly, the effects of circulating glucose on delay discounting were significant only in the glucose ingestion group, but not in the zero consumption and the water consumption groups, suggesting that the behavioral effects were in fact related to hunger-reduction instead of thirst-reduction. Study 2 revealed that glucose ingestion, but not water or another form of sugar (xylitol matched to glucose either for sweetness or for calories), reduced delay discounting, making future options more attractive. This result suggests that signaling of body energy budget is indeed glucose-unique. Our results suggest a forecasting mechanism of the glucose-insulin system for both metabolic and behavioral regulations of resource acquisition and allocation.

Psychological traces of China's socio-economic reforms in the ultimatum and dictator games.

Can traces of rapid socio-economic changes within a society be reflected in experimental games? The post-Mao reforms in China provide a unique natural quasi-experiment to study people from the same society who were raised with radically different values about distribution of wealth and altruistic behavior. We tested whether the size of offers in the ultimatum and dictator games are an increasing function of the number of years Chinese citizens experienced of the Mao era ("planned economy"). For the cohort that lived throughout the entire Mao era, we found that mean offers in the two games were substantially higher than what is typically offered in laboratory studies. These offers were also higher than those of two younger Chinese cohorts. In general, the amount offered decreased with less time spent under Mao, while in the oldest group in which every member spent the same amount of time under Mao, the younger members tended to offer more, suggesting an additional effect of early education under Mao and contradicting the alternative hypothesis that generosity increases with age. These results suggest that some of the observed individual differences in the offers made in experimental games can be traced back to the values of the socio-economic era in which individuals grew up.