A systematic investigation into the reliability of inter-temporal choice model parameters

Decades of work have been dedicated to developing and testing models that characterize how people make inter-temporal choices. Although parameter estimates from these models are often interpreted as indices of latent components of the choice process, little work has been done to examine their reliability. This is problematic because estimation error can bias conclusions that are drawn from these parameter estimates. We examine the reliability of parameter estimates from 11 prominent models of inter-temporal choice by (a) fitting each model to data from three previous experiments with designs representative of those typically used to study inter-temporal choice, (b) examining the consistency of parameters estimated for the same person based on different choice sets, and (c) conducting a parameter recovery analysis. We find generally low correlations between parameters estimated for the same person from the different choice sets. Moreover, parameter recovery varies considerably between models and the experimental designs upon which parameter estimates are based. We conclude that many parameter estimates reported in previous research are likely unreliable and provide recommendations on how to enhance the reliability of inter-temporal choice models for measurement purposes.

Dissociable fronto-striatal functional networks predict choice impulsivity

Fronto-striatal structural connectivity is associated with choice impulsivity. Yet, to date, whether distinct fronto-striatal functional coupling associates with impulsive choices are largely unknown. Using seed-based resting-state functional MRI (rsfMRI) combined with multivariate pattern analysis (MVPA), the present study aimed to explore the predictions of dissociable frontal-striatal functional connectivity on choice impulsivity in a relatively large sample (N = 429). Adaptive delay-discounting task was utilized to assess choice impulsivity and the striatum was further divided into three subregions including the nucleus accumbens (NAcc), caudate, and putamen. Results revealed that both the functional coupling between the NAcc and the limbic/dorsolateral prefrontal cortex, and between the caudate and the dorsal prefrontal cortex, including the dorsomedial prefrontal cortex (DMPFC), successfully predicted the delay-discounting rate. However, such pattern was not observed in the putamen-prefrontal functional connectivity. These findings suggest fronto-striatal-dependent neural mechanisms of choice impulsivity and further provide a better understanding of the contributions of striatum subregions and their functional connectivities with different areas of prefrontal cortex upon inter-temporal choice.

Temporal discounting does not influence body mass index

The prevalence of obesity has driven searches for cognitive or behavioural economic factors related to Body Mass Index (BMI). One candidate is delay discounting: those who prefer smaller sooner rewards over larger but later rewards are hypothesised to have higher BMI. The findings in the literature are mixed however, with meta analyses suggesting only a very small correlation between discounting and BMI. Here we present novel empirical data (N=381) and Bayesian analyses which suggest no such relationship between discounting of either monetary or weight loss rewards and BMI. We also find evidence against our novel proposal that discounting moderates the rate of BMI gain over time. We also present our data in the context of a random effects Bayesian meta-analytical result which does suggest the presence of a small correlation overall. The strength of the correlation is so weak (2.25% shared variance) that its practical significance may be minor to non existent. However because we found decisive evidence for unaccounted for study-level variance, due to study heterogeneity, we argue that we should treat such meta-analytic correlations with extreme caution. While the relationship between discounting and health outcomes such as BMI remain theoretically appealing, our empirical and meta-analytic results suggest we should be cautious in inferring a correlational, let alone a causal, role for discounting processes in driving BMI or moderating BMI gain with age.

Hunger increases delay discounting of food and non-food rewards

How do our valuation systems change to homeostatically correct undesirable psychological or physiological states, such as those caused by hunger? There is evidence that hunger increases discounting for food rewards, biasing choices towards smaller but sooner food reward over larger but later reward. However, it is not understood how hunger modulates delay discounting for non-food items. We outline and quantitatively evaluate six possible models of how our valuation systems modulate discounting of various commodities in the face of the undesirable state of being hungry. With a repeated-measures design, an experimental hunger manipulation, and quantitative modeling, we find strong evidence that hunger causes large increases in delay discounting for food, with an approximately 25% spillover effect to non-food commodities. The results provide evidence that in the face of hunger, our valuation systems increase discounting for commodities, which cannot achieve a desired state change as well as for those commodities that can. Given that strong delay discounting can cause negative outcomes in many non-food (consumer, investment, medical, or inter-personal) domains, the present findings suggest caution may be necessary when making decisions involving non-food outcomes while hungry.

Sex difference in the relationship between salivary testosterone and inter-temporal choice

Humans often prefer a small immediate reward to large reward in the future. This myopic tendency in inter-temporal choice is termed delay discounting, and has been the focus of intensive research in the past decades. Recent studies indicate that the neural regions underlying delay discounting are influenced by the gonadal steroids. However, the specific relationship between the testosterone levels and delay discounting is unclear at this point, especially in females. The present study investigated the relationship between salivary testosterone concentrations and discounting rates in delay- and probability-discounting tasks with healthy males and females. The results revealed a positive correlation between testosterone concentrations and delay-discounting rates in females and a negative correlation in males. Testosterone concentrations were unrelated to probability-discounting rates. Although causal effects of testosterone cannot be certain in this correlational study, if testosterone directly influenced this behavior, observed sex differences in delay discounting may be evidence of a curvilinear effect of testosterone. Alternatively, the findings may reflect inverse pattern of responsiveness to testosterone between male and female neural systems, or basic sex-difference in the neural mechanism underlying delay-discounting independent of testosterone itself.

Impaired Decision Making is Associated with Poor Inhibition Control in Nonpathological Lottery Gamblers

Previous studies by questionnaires have demonstrated that lottery gamblers who have not meet the criteria of pathological gambler show greater gambling acceptability. However, few empirical evidence of whether such nonpathological lottery gamblers (NPLGs) display the same impairments of decision making with pathological gamblers has been found so far. In present study, NPLGs and matched controls (MCs) were asked to perform the Iowa Gambling Task (IGT) and inter-temporal choice task (ICT). We found that compared to MCs, NPLGs displayed much lower IGT scores, net gains and proportions of advantageous decks in the IGT task and much higher percentages of trials during which smaller-but-sooner rewards were chosen in the ICT. These findings indicate that NPLGs display much more risky and impulsive decision makings, just like pathological gamblers in the previous studies. Next, the Go/NoGo task was employed to explore the role of response inhibition in the impairment of decision making in NPLGs. We found that NPLGs did show much higher commission errors compared to MCs. Moreover, IGT scores, net gain and proportions of advantageous decks were significantly negatively correlated with commission errors, which indicates that poor response inhibition might be involved in the impairments of decision making in NPLGs. To our knowledge, we provided the first empirical evidence of impairment of decision making and its cognitive mechanisms in NPLGs.

Immediate return preference emerged from a synaptic learning rule for return maximization

Animals including human often prefer immediate returns to larger delayed returns. It holds true in the human communications. Standard interpretation of the immediate return preference is that an animal might subjectively discount the value of a delayed reward, and that might choose the larger valued one. The interpretation has been successfully applied to explain behavior of many species including human. However, the description is not necessarily sufficient to apply for interactions of individuals. This study adopts a different approach to seek a possibility that immediate return preference may be reproduced by learning rule to maximize objective outcomes. We show that a synaptic learning rule to achieve the temporal difference (TD) learning for outcome maximization fails the maximization and exhibits immediate return preference if the context is not properly represented as a internal state.

The biological effects of acute psychosocial stress on delay discounting

Organisms prefer to receive rewards sooner rather than later because they excessively discount the subjective value of future rewards, a phenomenon called delay discounting. Recent studies have reported an association between cortisol-which is secreted by the hypothalamic-pituitary-adrenal (HPA) axis-and delay discounting. However, no study has examined whether acutely induced psychosocial stress modulates delay discounting. Thus, the present study examined the effect of acute psychosocial stress and its hormonal and inflammatory correlates on the rate of delay discounting. To accomplish this purpose, we assessed the participants' discounting rates using the questionnaire version with inter-temporal choice before and after an acute psychosocial stress task (the Trier Social Stress Test; TSST). The results demonstrated that TSST increased rates of delay discounting in only cortisol responders (not in non-responders), indicating the possible influence of the pathway from the HPA axis to the dopaminergic systems under acute stress. Furthermore, the findings of correlation analysis indicated a U-shaped relationship between baseline level of C-reactive protein and delay discounting rate, suggesting a complex relationship between inflammatory markers and delay discounting rate.