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1.  Dissociable neural representations of future reward magnitude and delay during temporal discounting 
NeuroImage  2008;45(1):143-150.
In temporal discounting, individuals often prefer smaller immediate rewards to larger delayed rewards, implying a trade off between the magnitude and delay of future rewards. While recent functional magnetic resonance imaging (fMRI) investigations of temporal discounting have generated conflicting findings, no studies have focused on whether distinct neural substrates respond to the magnitude and delay of future rewards. Combining a novel, temporally distributed discounting task with event-related fMRI, we found that while nucleus accumbens (NAcc), mesial prefrontal cortical (MPFC), and posterior cingulate cortical (PCC) activation positively correlated with future reward magnitude, dorsolateral prefrontal cortical (DLPFC) and posterior parietal cortical (PPC) activation negatively correlated with future reward delay. Further, more impulsive individuals showed diminished NAcc activation to the magnitude of future rewards and greater deactivations to delays of future rewards in the MPFC, DLPFC, and PPC. These findings suggest that while mesolimbic dopamine projection regions show greater sensitivity to the magnitude of future rewards, lateral cortical regions show greater (negative) sensitivity to the delay of future rewards, potentially reconciling different neural accounts of temporal discounting.
doi:10.1016/j.neuroimage.2008.11.004
PMCID: PMC2685201  PMID: 19071223
temporal discounting; reward; accumbens; prefrontal; individual differences; FMRI; decision; human
2.  Neural and Behavioral Mechanisms of Impulsive Choice in Alcohol Use Disorder 
Background
Alcohol dependence has repeatedly been associated with impulsive choice, or the inability to choose large delayed rewards over smaller, but more immediate rewards. However, the neural basis of impulsive choice in alcohol use disorders is not well understood.
Methods
One hundred fifty one individuals with a range of alcohol use from social drinking to severe alcohol dependence completed a delay discounting task while undergoing functional magnetic resonance imaging (fMRI). Participants received customized trials designed to ensure an approximately equivalent number of immediate responses.
Results
Delaying gratification recruited regions involved in cognitive control, conflict monitoring, and the interpretation of somatic states. Individuals with more severe alcohol use problems showed increased discounting of delayed rewards and greater activation in several regions including supplementary motor area, insula/orbitofrontal cortex, inferior frontal gyrus, and the precuneus.
Conclusions
These results suggest that impulsive choice in alcohol dependence is the result of functional anomolies in widely distributed, but interconnected brain regions involved in cognitive and emotional control. Further, our results suggest that the neural mechanisms of impulsive choice in alcohol use disorders both overlaps with that observed in previous studies, and shows that individuals with alcohol use disorders recruit additional mechanisms when making intertemporal choices.
doi:10.1111/j.1530-0277.2011.01455.x
PMCID: PMC3117198  PMID: 21676001
Delay discounting; intertemporal choice; impulsivity; delayed gratification
3.  The neuroeconomics of nicotine dependence: A preliminary study of delay discounting of monetary and cigarette rewards in smokers using fMRI 
Psychiatry research  2012;202(1):20-29.
Neuroeconomics integrates behavioral economics and cognitive neuroscience to understand the neurobiological basis for normative and maladaptive decision making. Delay discounting is a behavioral economic index of impulsivity that reflects capacity to delay gratification and has been consistently associated with nicotine dependence. This preliminary study used functional magnetic resonance imaging to examine delay discounting for money and cigarette rewards in 13 nicotine dependent adults. Significant differences between preferences for smaller immediate rewards and larger delayed rewards were evident in a number of regions of interest (ROIs), including the medial prefrontal cortex, anterior insular cortex, middle temporal gyrus, middle frontal gyrus, and cingulate gyrus. Significant differences between money and cigarette rewards were generally lateralized, with cigarette choices associated with left hemisphere activation and money choices associated with right hemisphere activation. Specific ROI differences included the posterior parietal cortex, medial and middle frontal gyrus, ventral striatum, temporoparietal cortex, and angular gyrus. Impulsivity as measured by behavioral choices was significantly associated with both individual ROIs and a combined ROI model. These findings provide initial evidence in support of applying a neuroeconomic approach to understanding nicotine dependence.
doi:10.1016/j.pscychresns.2011.10.003
PMCID: PMC3530421  PMID: 22633679
Nicotine dependence; smoking; tobacco; behavioral economics; neuroeconomics; delay discounting; impulsivity
4.  Delay Discounting and Frontostriatal Fiber Tracts: A Combined DTI and MTR Study on Impulsive Choices in Healthy Young Adults 
Cerebral Cortex (New York, NY)  2012;23(7):1695-1702.
Delay discounting, a measure of impulsive choice, has been associated with decreased control of the prefrontal cortex over striatum responses. The anatomical connectivity between both brain regions in delaying gratification remains unknown. Here, we investigate whether the quality of frontostriatal (FS) white matter tracts can predict individual differences in delay-discounting behavior. We use tract-based diffusion tensor imaging and magnetization transfer imaging to measure the microstructural properties of FS fiber tracts in 40 healthy young adults (from 18 to 25 years). We additionally explored whether internal sex hormone levels affect the integrity of FS tracts, based on the hypothesis that sex hormones modulate axonal density within prefrontal dopaminergic circuits. We calculated fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusivity, radial diffusivity (RD), and magnetization transfer ratio (MTR), a putative measure of myelination, for the FS tract. Results showed that lower integrity within the FS tract (higher MD and RD and lower FA), predicts faster discounting in both sexes. MTR was unrelated to delay-discounting performance. In addition, testosterone levels in males were associated with a lower integrity (higher RD) within the FS tract. Our study provides support for the hypothesis that enhanced structural integrity of white matter fiber bundles between prefrontal and striatal brain areas is associated with better impulse control.
doi:10.1093/cercor/bhs163
PMCID: PMC3673180  PMID: 22693341
delay discounting; DTI; frontostriatal tracts; impulsivity; testosterone
5.  Frontal Hyperconnectivity Related to Discounting and Reversal Learning in Cocaine Subjects 
Biological psychiatry  2011;69(11):1117-1123.
BACKGROUND
Functional neuroimaging studies suggest that chronic cocaine use is associated with frontal lobe abnormalities. Functional connectivity (FC) alterations of cocaine dependent individuals (CD), however, are not yet clear. This is the first study to our knowledge that examines resting FC of anterior cingulate cortex (ACC) in CD. Because ACC is known to integrate inputs from different brain regions to regulate behavior, we hypothesize that CD will have connectivity abnormalities in ACC networks. In addition, we hypothesized that abnormalities would be associated with poor performance in delayed discounting and reversal learning tasks.
METHODS
Resting functional magnetic resonance imaging data were collected to look for FC differences between twenty-seven cocaine dependent individuals (CD) (5 females, age: M=39.73, SD=6.14) and twenty-four controls (5 females, age: M=39.76, SD = 7.09). Participants were assessed with delayed discounting and reversal learning tasks. Using seed-based FC measures, we examined FC in CD and controls within five ACC connectivity networks with seeds in subgenual, caudal, dorsal, rostral, and perigenual ACC.
RESULTS
CD showed increased FC within the perigenual ACC network in left middle frontal gyrus, ACC and middle temporal gyrus when compared to controls. FC abnormalities were significantly positively correlated with task performance in delayed discounting and reversal learning tasks in CD.
CONCLUSIONS
The present study shows that participants with chronic cocaine-dependency have hyperconnectivity within an ACC network known to be involved in social processing and mentalizing. In addition, FC abnormalities found in CD were associated with difficulties with delay rewards and slower adaptive learning.
doi:10.1016/j.biopsych.2011.01.008
PMCID: PMC3090521  PMID: 21371689
cocaine; functional connectivity; anterior cingulate; delayed discount; reversal learning; frontal
6.  How Many Impulsivities? A Discounting Perspective 
People discount the value of delayed and uncertain outcomes, and how steeply individuals discount is thought to reflect how impulsive they are. From this perspective, steep discounting of delayed outcomes (which fails to maximize long-term welfare) and shallow discounting of probabilistic outcomes (which fails to adequately take risk into account) reflect the same trait of impulsivity. Despite the fact that a hyperboloid function describes the discounting of both delayed and probabilistic outcomes, there is considerable evidence that the two kinds of discounting involve different processes as well as separate impulsivity traits. Several manipulations differentially affect delay and probability discounting, and correlational studies show that how steeply one discounts delayed rewards is relatively independent of how steeply one discounts probabilistic rewards. Moreover, people’s discounting of delayed money and health outcomes are uncorrelated as are discounting of real, consumable rewards and hypothetical money. These results suggest that even within delay discounting, there may be multiple ‘impulsivities,’ each of which may be important for understanding a different aspect of decision making. Taken together, the pattern of findings reviewed here argues for a more nuanced view of impulsivity than that which is usually assumed in discounting research.
doi:10.1002/jeab.1
PMCID: PMC3893105  PMID: 23344985
discounting; impulsivity; traits; delay; probability
7.  Cortical activation during delay discounting in abstinent methamphetamine dependent individuals 
Psychopharmacology  2008;201(2):183-193.
Background
Methamphetamine (MA)-dependent individuals prefer smaller immediate over larger delayed rewards in delay discounting (DD) tasks. Human and animal data implicate ventral (amygdala, ventral striatum, ventrolateral prefrontal cortex insula) and dorsal (dorsolateral prefrontal cortex, dorsal anterior cingulate cortex and posterior parietal cortex) systems in DD decisions. The ventral system is hypothesized to respond to the salience and immediacy of rewards while the dorsal system is implicated in the process of comparison and choice.
Methods
We used functional Magnetic Resonance Imaging to probe the neural correlates of DD in 19 recently abstinent MA-dependent patients and 17 age- and gender-matched controls.
Results
Hard DD choices were associated with greatest activation in bilateral middle cingulate, posterior parietal cortex (PPC), and the right rostral insula. Control subjects showed more activation than MA patients bilaterally in the precuneus and in the right caudate nucleus, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC). Magnitude of discounting was correlated with activity in the amygdala, DLPFC, posterior cingulate cortex and PPC.
Conclusions
Our findings were consistent with a model wherein dorsal cognitive systems modulate the neural response of ventral regions. Patients addicted to MA, who strongly prefer smaller immediate over larger delayed rewards, activate the dorsal cognitive control system in order to overcome their preference. Activation of the amygdala during choice of delayed rewards was associated with a greater degree of discounting, suggesting that heavily discounting MA-dependent individuals may be more responsive to the negative salience of delayed rewards than controls.
doi:10.1007/s00213-008-1261-1
PMCID: PMC2835463  PMID: 18685833
Methamphetamine; Delay discounting; Brain imaging
8.  ALTERING THE MAGNITUDE OF DELAY DISCOUNTING BY PATHOLOGICAL GAMBLERS 
The present study explored the delay discounting of future and past monetary rewards by pathological gamblers. Using a multiple baseline design, following repeated exposure to choices between smaller immediate and larger delayed consequences, participants completed a relational responding task that attempted to alter the psychological functions of irrelevant stimuli and to affect subsequent delay discounting. Results support previous literature on the discounting of delayed consequences by pathological gamblers, illustrate that the discounting of past rewards occurs in a similar fashion to the well-documented literature on the discounting of future rewards, and that magnitude of discounting can be altered.
doi:10.1901/jaba.2009.42-269
PMCID: PMC2695330  PMID: 19949514
addiction; choice; delay discounting; pathological gambling; self-control
9.  An Efficient Operant Choice Procedure for Assessing Delay Discounting in Humans: Initial Validation in Cocaine-Dependent and Control Individuals 
Delay discounting is the decline in a consequence's control of behavior as a function of its delay, and may be a fundamental behavioral process in drug dependence. Human delay-discounting studies have usually relied on choices between hypothetical rewards. Some human tasks have assessed delay discounting using operant procedures with consequences provided during the task, as in nonhuman animal studies. However, these tasks have limitations such as long duration, potentially indeterminate data, or confounding the effect of delay with probability. A study in 20 cocaine-dependent volunteers and 20 demographically matched non-cocaine-dependent volunteers was designed to investigate a novel operant delay-discounting task providing monetary reinforcement by coin delivery throughout the task (Quick Discounting Operant Task; QDOT). Participants completed a hypothetical delay-discounting procedure, a potentially real reward delay-discounting procedure, and an existing operant delay-discounting task: the Experiential Discounting Task (EDT). The QDOT resulted in complete data for all participants, showed systematic effects of delay that were well described by a hyperbolic function, had a maximum duration of 17 min, and resulted in relatively little variability in session earnings. QDOT performance was significantly, positively correlated with performance on the EDT but not the other tasks. The QDOT resulted in an effect size between the groups that was similar to most other delay discounting tasks examined, and showed the cocaine-dependent participants to delay discount significantly more than the control participants. The QDOT is an efficient operant human delay-discounting task that may be useful in a variety of experimental settings.
doi:10.1037/a0027088
PMCID: PMC3535463  PMID: 22329554
delay discounting; cocaine; real; hypothetical; human
10.  Regional White Matter Volumes Correlate with Delay Discounting 
PLoS ONE  2012;7(2):e32595.
A preference for immediate gratification is a central feature in addictive processes. However, the neural structures underlying reward delay tolerance are still unclear. Healthy participants (n = 121) completed a delay discounting questionnaire assessing the extent to which they prefer smaller immediate rewards to larger delayed reward after undergoing magnetic resonance imaging (MRI) scanning. Whole brain voxel-based morphometric analysis shows that delay discounting severity was negatively correlated with right prefrontal subgyral white matter volume and positively correlated with white matter volume in parahippocampus/hippocampus, after whole brain correction. This study might better our understanding of the neural basis of impulsivity and addiction.
doi:10.1371/journal.pone.0032595
PMCID: PMC3290657  PMID: 22393420
11.  Continuous theta burst stimulation of right dorsolateral prefrontal cortex induces changes in impulsivity level 
Brain stimulation  2009;3(3):170-176.
There is evidence that the right dorsolateral prefrontal cortex (DLPFC) may play a certain role in decision making related to reward value and time perception and, in particular, in the inhibitory control of impulsive decision making. Using the theta burst stimulation (TBS) and a delay discounting (DD) task, we investigated the potential role of right DLPFC in impulsive decision making defined by the rate of discounting delayed reward. Healthy right-handed volunteers underwent three stimulation sessions, intermittent TBS (iTBS), continuous TBS (cTBS), and sham. The steepness of the discount function (k-value), reaction time for choice and consistency were measured for each subjects. cTBS of the DLPFC reduced by 36.88 % the k-value of the DD task compared to sham condition. In contrast, iTBS did not affect impulsivity level. There were no changes neither in reaction time for choice nor consistency after either the iTBS or cTBS compared with the sham stimulation. These results demonstrate that cTBS-induced modulation of cortical excitability of the right DLPFC may affect and reduce impulsive decision making. These observations may provide some insights into the role of the right DLPFC in modulating impulsivity level and calculating reward value at different time scales under less ambiguous circumstances.
doi:10.1016/j.brs.2009.10.002
PMCID: PMC3707839  PMID: 20633446 CAMSID: cams3169
rTMS; theta burst stimulation; dorsolateral prefrontal cortex; decision making; impulsivity; delay discounting task
12.  Effect of continuous theta burst stimulation of the right dorsolateral prefrontal cortex on cerebral blood flow changes during decision making 
Brain stimulation  2012;5(2):116-123.
Decision making is a cognitive function relaying on a complex neural network. In particular, the right dorsolateral prefrontal cortex (DLPFC) plays a key role within this network. We used positron emission tomography (PET) combined with continuous theta burst transcranial magnetic stimulation (cTBS) to investigate neuronal and behavioral changes in normal volunteers while performing a delay discounting (DD) task. We aimed to test whether stimulation of right DLPFC would modify the activation pattern of the neural circuit underlying decision making during the DD task and influence discounting behavior.
We found that cTBS of the right DLPFC influenced decision making by reducing impulsivity and inducing participants to favor large but delayed rewards instead of immediate but small rewards. Stimulation also affected activation in several prefrontal areas associated with DD. In particular, we observed a reduced regional cerebral blood flow (rCBF) in the ipsilateral DLPFC (BA 46) extending into the rostral part of the prefrontal cortex (BA 10) as well as a disrupted relationship between impulsivity (k-value) and rCBF in these and other prefrontal areas.
These findings suggest that transcranial magnetic stimulation of the DLPFC influences the neural network underlying impulsive decision making behavior.
doi:10.1016/j.brs.2012.03.007
PMCID: PMC3707841  PMID: 22494829 CAMSID: cams3170
rTMS; Theta burst stimulation; Dorsolateral prefrontal cortex; Decision making; Impulsivity; Delay discounting task
13.  Decisions for Others Become Less Impulsive the Further Away They Are on the Family Tree 
PLoS ONE  2012;7(11):e49479.
Background
People tend to prefer a smaller immediate reward to a larger but delayed reward. Although this discounting of future rewards is often associated with impulsivity, it is not necessarily irrational. Instead it has been suggested that it reflects the decision maker’s greater interest in the ‘me now’ than the ‘me in 10 years’, such that the concern for our future self is about the same as for someone else who is close to us.
Methodology/Principal Findings
To investigate this we used a delay-discounting task to compare discount functions for choices that people would make for themselves against decisions that they think that other people should make, e.g. to accept $500 now or $1000 next week. The psychological distance of the hypothetical beneficiaries was manipulated in terms of the genetic coefficient of relatedness ranging from zero (e.g. a stranger, or unrelated close friend), .125 (e.g. a cousin), .25 (e.g. a nephew or niece), to .5 (parent or sibling).
Conclusions/Significance
The observed discount functions were steeper (i.e. more impulsive) for choices in which the decision-maker was the beneficiary than for all other beneficiaries. Impulsiveness of decisions declined systematically with the distance of the beneficiary from the decision-maker. The data are discussed with reference to the implusivity and interpersonal empathy gaps in decision-making.
doi:10.1371/journal.pone.0049479
PMCID: PMC3509068  PMID: 23209580
14.  Now or later? Striatum and insula activation to immediate versus delayed rewards 
Neuroimaging studies on delay discounting tasks that use reward delays ranging from minutes to days have implicated the insula and striatum in the processing of inter-temporal decisions. This study aimed at assessing whether these brain regions would also be involved in decision-making when subjects have to wait through the delays within the range of seconds. Employing functional magnetic resonance imaging (fMRI) in thirteen healthy volunteers, we repeatedly presented monetaryoptions with delays that differed within the range of multiple seconds. Using a region of interest approach, we found significant activation in the bilateral anterior insula and striatum when subjects chose either the immediate (smaller) or delayed (larger) option. In particular, insular activation was observed after the response and the delay, when the outcome of the immediate or the delayed choice was shown. Significantly greater activation was observed in the ventroanterior striatum while subjects chose the immediate, as opposed to the delayed, options, and also after receiving the outcome of waiting through the longer delay option. The evidence presented here indicates that both the ventral striatum and the insula are involved in the processing of choosing delay options as well as the consequences of choices with delays in the seconds’ range.
doi:10.1037/a0017252
PMCID: PMC2907916  PMID: 20657814
delay discounting; decision making; time perception; reward; fMRI
15.  Impulsiveness as a timing disturbance: neurocognitive abnormalities in attention-deficit hyperactivity disorder during temporal processes and normalization with methylphenidate 
We argue that impulsiveness is characterized by compromised timing functions such as premature motor timing, decreased tolerance to delays, poor temporal foresight and steeper temporal discounting. A model illustration for the association between impulsiveness and timing deficits is the impulsiveness disorder of attention-deficit hyperactivity disorder (ADHD). Children with ADHD have deficits in timing processes of several temporal domains and the neural substrates of these compromised timing functions are strikingly similar to the neuropathology of ADHD. We review our published and present novel functional magnetic resonance imaging data to demonstrate that ADHD children show dysfunctions in key timing regions of prefrontal, cingulate, striatal and cerebellar location during temporal processes of several time domains including time discrimination of milliseconds, motor timing to seconds and temporal discounting of longer time intervals. Given that impulsiveness, timing abnormalities and more specifically ADHD have been related to dopamine dysregulation, we tested for and demonstrated a normalization effect of all brain dysfunctions in ADHD children during time discrimination with the dopamine agonist and treatment of choice, methylphenidate. This review together with the new empirical findings demonstrates that neurocognitive dysfunctions in temporal processes are crucial to the impulsiveness disorder of ADHD and provides first evidence for normalization with a dopamine reuptake inhibitor.
doi:10.1098/rstb.2009.0014
PMCID: PMC2685816  PMID: 19487194
impulsiveness; timing; time perception; temporal discounting; attention-deficit hyperactivity disorder; methylphenidate
16.  Isolating the delay component of impulsive choice in adolescent rats 
Impulsive choice—the preference for small immediate rewards over larger delayed rewards—has been linked to various psychological conditions ranging from behavioral disorders to addiction. These links highlight the critical need to dissect the various components of this multifaceted behavioral trait. Delay discounting tasks allow researchers to study an important factor of this behavior: how the subjective value of a rewards changes over a delay period. However, existing methods of delay discounting include a confound of different reward sizes within the procedure. Here we present a new approach of using a single constant reward size to assess delay discounting. A complementary approach could hold delay constant and assess the utility of changing quantities of a reward. Isolating these behavioral components can advance our ability to explore the behavioral complexity of impulsive choice. We present in detail the methods for isolating delay, and further capitalize on this method by pairing it with a standard peak interval task to test whether individual variation in delay discounting can be explained by differences in perception of time in male and female adolescent rats. We find that rats that were more precise in discriminating time intervals were also less impulsive in their choice. Our data suggest that differences in timing and delay discounting are not causally related, but instead are more likely influenced by a common factor. Further, the mean-level change in our measure between post-natal day 28 and 42 suggests this test may be capturing a developmental change in this factor. In summary, this new method of isolating individual components of impulsive choice (delay or quantity) can be efficiently applied in either adolescent or adult animal models and may help elucidate the mechanisms underlying impulsivity and its links to psychological disorders.
doi:10.3389/fnint.2014.00003
PMCID: PMC3902300  PMID: 24478644
impulsive choice; delay discounting; peak interval; adolescence; sex differences
17.  Notes on Discounting 
In general, if a variable can be expressed as a function of its own maximum value, that function may be called a discount function. Delay discounting and probability discounting are commonly studied in psychology, but memory, matching, and economic utility also may be viewed as discounting processes. When they are so viewed, the discount function obtained is hyperbolic in form. In some cases the effective discounting variable is proportional to the physical variable on which it is based. For example, in delay discounting, the physical variable, delay (D), may enter into the hyperbolic equation as kD. In many cases, however, the discounting data are not well described with a single-parameter discount function. A much better fit is obtained when the effective variable is a power function of the physical variable (kDs in the case of delay discounting). This power-function form fits the data of delay, probability, and memory discounting as well as other two-parameter discount functions and is consistent with both the generalized matching law and maximization of a constant-elasticity-of-substitution utility function.
doi:10.1901/jeab.2006.85-05
PMCID: PMC1459845  PMID: 16776060
discounting; delay discounting; memory discounting; social discounting; probability discounting; matching; rational behavior; utility maximization
18.  Effort discounting in human nucleus accumbens 
A great deal of behavioral and economic research suggests that the value attached to a reward stands in inverse relation to the amount of effort required to obtain it, a principle known as effort discounting. In the current report, we present the first direct evidence for a neural analogue of effort discounting. Functional magnetic resonance imaging was used to measure neural responses to monetary rewards in the human nucleus accumbens, a structure previously demonstrated to encode reference-dependent reward information. The magnitude of accumbens activation was found to vary with reward outcome, but also with the degree of mental effort demanded to obtain individual rewards. For a fixed level of reward, accumbens was less strongly activated following a high demand for effort than following a lower demand. The magnitude of this effect was noted to correlate with preceding activation in the dorsal anterior cingulate cortex, a region that has been proposed to monitor information-processing demands and to mediate in the subjective experience of effort.
doi:10.3758/CABN.9.1.16
PMCID: PMC2744387  PMID: 19246324
19.  Delay Discounting and Future-directed Thinking in Anhedonic Individuals 
Anhedonia (lack of reactivity to pleasurable stimuli) and a negatively skewed view of the future are important components of depression that could affect economic decisions in depressed individuals. Delay discounting paradigms might be useful for probing putative affective and cognitive underpinnings of such decisions. As a first step to evaluate whether difficulties experiencing pleasure might affect delay discounting, 36 undergraduate students with varying levels of anhedonia performed a delay discounting task in which they made choices between a small immediate and larger future monetary reward. Increasing levels of anhedonia (Snaith-Hamilton Pleasure Scale) were negatively associated with delay discounting rate, indicating that anhedonic individuals tended to choose the larger, albeit delayed reward. These correlations remained after controlling for variables previously linked to delay discounting (working memory capacity and impulsivity) and pessimistic future-directed thinking. The current findings provide preliminary evidence indicating that anhedonic individuals make less myopic decisions about their future, possibly due to their decreased responsiveness to immediate rewards.
doi:10.1016/j.jbtep.2010.02.003
PMCID: PMC2862767  PMID: 20219184
Delay discounting; Anhedonia; Impulsivity; Working memory; Depression; Future-directed thinking
20.  Does delay discounting play an etiological role in smoking or is it a consequence of smoking? 
Drug and alcohol dependence  2009;103(3):99-106.
Although higher delay discounting rates have been linked to cigarette smoking, little is known about the stability of delay discounting, whether delay discounting promotes smoking acquisition, whether smoking contributes to impulsive choices, or if different relationships exist in distinct subgroups. This study sought to fill these gaps within a prospective longitudinal cohort study (N=947) spanning mid adolescence to young adulthood (age 15 to 21 years old). Smoking and delay discounting were measured across time. Covariates included peer and household smoking, academic performance, depression, novelty seeking, inattention and hyperactivity/impulsivity symptoms, and alcohol and marijuana use. The associated processes Latent Growth Curve Modeling (LGCM) with paths from the delay discounting level factor (baseline measure) and the trend factor (slope) to the smoking trend factor (slope) fit the data well, X2(19, n=947) = 15.37, p=.70, CFI=1.00, RMSEA=0, WRMR=.36. The results revealed that delay discounting did not change significantly across time. Baseline delay discounting had a significant positive effect on smoking trend (β=.08, z=2.16, p=.03). A standard deviation (SD=1.41) increase in baseline delay discounting resulted in an 11% increase (OR=1.11, 95% CI= 1.03, 1.23) in the odds of smoking uptake. The alternative path LCGM revealed that smoking did not significantly impact delay discounting (p’s > .05). Growth Mixture Modeling identified three smoking trajectories: nonsmokers, early/fast smoking adopters, and slow smoking progressors. Delay discounting was higher in the smoking versus nonsmoking trajectories, but did not discriminate between the smoking trajectories, despite different acquisition patterns. Delay discounting may provide a variable by which to screen for smoking vulnerability and help identify subgroups to target for more intensive smoking prevention efforts that include novel behavioral components directed toward aspects of impulsivity.
doi:10.1016/j.drugalcdep.2008.12.019
PMCID: PMC2743449  PMID: 19443136
Delay discounting; smoking acquisition
21.  Individual Differences in Delay Discounting Under Acute Stress: The Role of Trait Perceived Stress 
Delay discounting refers to the reduction of the value of a future reward as the delay to that reward increases. The rate at which individuals discount future rewards varies as a function of both individual and contextual differences, and high delay discounting rates have been linked with problematic behaviors, including drug abuse and gambling. The current study investigated the effects of acute anticipatory stress on delay discounting, while considering two important factors: individual perceptions of stress and whether the stressful situation is future-focused or present-focused. Half of the participants experienced acute stress by anticipating giving a videotaped speech. This stress was either future-oriented (speech about future job) or present-oriented (speech about physical appearance). They then performed a delay discounting task, in which they chose between smaller, immediate rewards, and larger, delayed rewards. Their scores on the Perceived Stress Scale were also collected. The way in which one appraises stressful situations interacts with acute stress to influence choices; under stressful conditions, delay discounting rate was highest in individuals with low trait perceived stress and lowest for individuals with high trait perceived stress. This result might be related to individual variation in reward responsiveness under stress. Furthermore, the time orientation of the task interacted with its stressfulness to affect the individual’s propensity to choose immediate rewards. These findings add to our understanding of the intermediary factors between stress and decision-making.
doi:10.3389/fpsyg.2012.00251
PMCID: PMC3400439  PMID: 22833731
delay discounting; stress; decision-making; future orientation; perceived stress
22.  Influence of Reward Delays on Responses of Dopamine Neurons 
The Journal of Neuroscience  2008;28(31):7837-7846.
Psychological and microeconomic studies have shown that outcome values are discounted by imposed delays. The effect, called temporal discounting, is demonstrated typically by choice preferences for sooner smaller rewards over later larger rewards. However, it is unclear whether temporal discounting occurs during the decision process when differently delayed reward outcomes are compared or during predictions of reward delays by pavlovian conditioned stimuli without choice. To address this issue, we investigated the temporal discounting behavior in a choice situation and studied the effects of reward delay on the value signals of dopamine neurons. The choice behavior confirmed hyperbolic discounting of reward value by delays on the order of seconds. Reward delay reduced the responses of dopamine neurons to pavlovian conditioned stimuli according to a hyperbolic decay function similar to that observed in choice behavior. Moreover, the stimulus responses increased with larger reward magnitudes, suggesting that both delay and magnitude constituted viable components of dopamine value signals. In contrast, dopamine responses to the reward itself increased with longer delays, possibly reflecting temporal uncertainty and partial learning. These dopamine reward value signals might serve as useful inputs for brain mechanisms involved in economic choices between delayed rewards.
doi:10.1523/JNEUROSCI.1600-08.2008
PMCID: PMC3844811  PMID: 18667616
single-unit recording; dopamine; neuroeconomics; temporal discounting; preference reversal; impulsivity
23.  Humans Can Adopt Optimal Discounting Strategy under Real-Time Constraints 
PLoS Computational Biology  2006;2(11):e152.
Critical to our many daily choices between larger delayed rewards, and smaller more immediate rewards, are the shape and the steepness of the function that discounts rewards with time. Although research in artificial intelligence favors exponential discounting in uncertain environments, studies with humans and animals have consistently shown hyperbolic discounting. We investigated how humans perform in a reward decision task with temporal constraints, in which each choice affects the time remaining for later trials, and in which the delays vary at each trial. We demonstrated that most of our subjects adopted exponential discounting in this experiment. Further, we confirmed analytically that exponential discounting, with a decay rate comparable to that used by our subjects, maximized the total reward gain in our task. Our results suggest that the particular shape and steepness of temporal discounting is determined by the task that the subject is facing, and question the notion of hyperbolic reward discounting as a universal principle.
Synopsis
When we make a choice between two options, we compare the values of their outcomes and select the option with a larger value. However, what if one option leads to a larger delayed reward and the other leads to a smaller more immediate reward? Naturally, we assign a larger value for a larger reward, but it is “discounted” if the reward is to be delivered later. Thus, the value is a monotonically decreasing function of the delays. Previous behavioral studies have repeatedly demonstrated that humans and animals discount delayed rewards hyperbolically. This has practical importance, as hyperbolic discounting can sometimes lead to “irrational” preference reversal: for instance, an individual may prefer two apples in 51 days to one apple in 50 days, but if the days come closer, he prefers one apple today to two apples tomorrow. On the contrary, exponential discounting is always “rational,” as it predicts constant preference. Here, in a new task that mimics animal foraging, and that uses delayed monetary rewards, Schweighofer and colleagues showed that humans can also discount reward exponentially. Furthermore, it is remarkable that by adopting exponential discounting, their subjects maximized their total gain. Thus, depending on the task at hand, the authors' study suggests that humans can flexibly choose the type of reward discounting, and can exhibit rational behavior that maximizes long-term gains.
doi:10.1371/journal.pcbi.0020152
PMCID: PMC1635539  PMID: 17096592
24.  Humans Can Adopt Optimal Discounting Strategy under Real-Time Constraints 
PLoS Computational Biology  2006;2(11):e152.
Critical to our many daily choices between larger delayed rewards, and smaller more immediate rewards, are the shape and the steepness of the function that discounts rewards with time. Although research in artificial intelligence favors exponential discounting in uncertain environments, studies with humans and animals have consistently shown hyperbolic discounting. We investigated how humans perform in a reward decision task with temporal constraints, in which each choice affects the time remaining for later trials, and in which the delays vary at each trial. We demonstrated that most of our subjects adopted exponential discounting in this experiment. Further, we confirmed analytically that exponential discounting, with a decay rate comparable to that used by our subjects, maximized the total reward gain in our task. Our results suggest that the particular shape and steepness of temporal discounting is determined by the task that the subject is facing, and question the notion of hyperbolic reward discounting as a universal principle.
Synopsis
When we make a choice between two options, we compare the values of their outcomes and select the option with a larger value. However, what if one option leads to a larger delayed reward and the other leads to a smaller more immediate reward? Naturally, we assign a larger value for a larger reward, but it is “discounted” if the reward is to be delivered later. Thus, the value is a monotonically decreasing function of the delays. Previous behavioral studies have repeatedly demonstrated that humans and animals discount delayed rewards hyperbolically. This has practical importance, as hyperbolic discounting can sometimes lead to “irrational” preference reversal: for instance, an individual may prefer two apples in 51 days to one apple in 50 days, but if the days come closer, he prefers one apple today to two apples tomorrow. On the contrary, exponential discounting is always “rational,” as it predicts constant preference. Here, in a new task that mimics animal foraging, and that uses delayed monetary rewards, Schweighofer and colleagues showed that humans can also discount reward exponentially. Furthermore, it is remarkable that by adopting exponential discounting, their subjects maximized their total gain. Thus, depending on the task at hand, the authors' study suggests that humans can flexibly choose the type of reward discounting, and can exhibit rational behavior that maximizes long-term gains.
doi:10.1371/journal.pcbi.0020152
PMCID: PMC1635539  PMID: 17096592
25.  Short-Term Temporal Discounting of Reward Value in Human Ventral Striatum 
Journal of Neurophysiology  2009;101(3):1507-1523.
Delayed rewards lose their value for economic decisions and constitute weaker reinforcers for learning. Temporal discounting of reward value already occurs within a few seconds in animals, which allows investigations of the underlying neurophysiological mechanisms. However, it is difficult to relate these mechanisms to human discounting behavior, which is usually studied over days and months and may engage different brain processes. Our study aimed to bridge the gap by using very short delays and measuring human functional magnetic resonance responses in one of the key reward centers of the brain, the ventral striatum. We used psychometric methods to assess subjective timing and valuation of monetary rewards with delays of 4.0–13.5 s. We demonstrated hyperbolic and exponential decreases of striatal responses to reward predicting stimuli within this time range, irrespective of changes in reward rate. Lower reward magnitudes induced steeper behavioral and striatal discounting. By contrast, striatal responses following the delivery of reward reflected the uncertainty in subjective timing associated with delayed rewards rather than value discounting. These data suggest that delays of a few seconds affect the neural processing of predicted reward value in the ventral striatum and engage the temporal sensitivity of reward responses. Comparisons with electrophysiological animal data suggest that ventral striatal reward discounting may involve dopaminergic and orbitofrontal inputs.
doi:10.1152/jn.90730.2008
PMCID: PMC2666398  PMID: 19164109

Results 1-25 (710352)