Altruism in time: social temporal discounting differentiates smokers from problem drinkers

Rationale

Recent studies on reinforcer valuation in social situations have informed research on mental illness. Social temporal discounting may be a way to examine effects of social context on the devaluation of delayed reinforcers. In prior research with non-drug-using groups, we demonstrated that individuals discount delayed rewards less rapidly (i.e., value the future more) for a group of which they are a member than they do for themselves alone.

Objectives

The current study examined how cigarette smoking and level of alcohol use relate to rates of delay and social temporal discounting.

Methods

In this study, we used crowd-sourcing technology to contact a large number of individuals (N?=?796). Some of these individuals were hazardous-to-harmful drinkers (n?=?269), whereas others were non-problem drinkers (n?=?523); some were smokers (n?=?182), whereas others were nonsmokers (n?=?614). Delay discounting questionnaires for individual rewards (me now, me later) and for group rewards (we now, we later; me now, we later) were used to measure individuals’ discounting rates across various social contexts.

Results

Our analyses found that smokers discounted delayed rewards more rapidly than controls under all conditions. However, hazardous-to-harmful drinkers discounted delayed rewards significantly more rapidly than the non-problem drinkers under the individual condition, but not under the social conditions.

Conclusions

This finding suggests that the use of different abused drugs may be associated with excessive discounting in the individual condition and has selective effects when discounting for a group in the social conditions.     

Delay Discounting of Oral Morphine and Sweetened Juice Rewards in Dependent and Non-Dependent Rats

Rationale

Opioid-dependent humans are reported to show accelerated delay discounting of opioid rewards when compared to monetary rewards. It has been suggested that this may reflect a difference in discounting of consumable and non-consumable goods not specific to dependent individuals. Here, we evaluate the discounting of similar morphine and non-morphine oral rewards in dependent and non-dependent rats

Methods

We first tested the analgesic and rewarding effects of our morphine solution. In a second experiment, we assigned rats randomly to either dependent or non-dependent groups that, 30 min after daily testing, received 30 mg/kg subcutaneous dose of morphine, or saline, respectively. Delay discounting of drug-free reward was examined prior to initiation of the dosing regimen. We tested discounting of the morphine reward in half the rats and retested the discounting of the drug-free reward in the other half. All tests were run 22.5 h after the daily maintenance dose.

Results

Rats preferred the morphine cocktail to the drug-free solution and consumed enough to induce significant analgesia. The control quinine solution did not produce these effects. Dependent rats discounted morphine rewards more rapidly than before dependence and when compared to discounting drug-free rewards. In non-dependent rats both reward types were discounted similarly.

Conclusions

These results show that morphine dependence increases impulsiveness specifically towards a drug reward while morphine experience without dependence does not.     

Relationship between education and delay discounting in smokers

Smokers are less educated and are more likely to discount future rewards than nonsmokers. We assessed the relationship between delay discounting and education level in 77 smokers entering smoking cessation treatment. There was an effect of education on computer task and the questionnaire measures of discounting, with participants having no college discounting delayed rewards significantly (P < .01) more than those attending college. Subjects discounted small rewards more than large rewards for both tasks (P < .001). Results show that education level is inversely associated with discounting in smokers.     

Effects of acute and sub-chronic nicotine on impulsive choice in rats in a probabilistic delay-discounting task

Rationale

Cigarette smokers typically display impulsivity by preferring immediate rewards over larger, delayed rewards at shorter delays than do non-smokers. Suggesting causality, nicotine injections in rats increase the choice for an immediate reward over a larger, delayed reward.

Objectives

To examine the generality of this latter effect, the present study employed a delay-discounting task to determine if acute and sub-chronic nicotine will also increase impulsive choice when subjective reward value is manipulated by changes in the probability, rather than magnitude, of reward.

Materials and methods

Rats were presented with two levers, one of which delivered an immediate water reward on half of the trials, while the other lever delivered the same reward on every trial, but only after one of five increasing delays.

Results

Acute injections of 1.2 mg/kg, but not 0.8 mg/kg, of nicotine increased the preference for the immediate (but less certain) reward lever at intermediate delays. Moreover, twice-daily injections of 0.8 mg/kg of nicotine for 6 days progressively increased the preference for the immediate reward. Latency to make the first response on each trial was not affected by nicotine.

Conclusions

The similar increases in impulsive choice produced by both acute and sub-chronic nicotine in delay-discounting paradigms whether subjective reward value is manipulated by changes in reward magnitude or probability suggests that nicotine may be increasing what is common to these paradigms, namely delay discounting. Whatever the mechanism, these data indicate that both acute and sub-chronic nicotine may help develop and maintain an addiction by increasing impulsivity.     

Cigarette smokers show steeper discounting of both food and cigarettes than money

People with drug addiction show steeper discounting of drugs of abuse than money. One suggestion is that this effect is related to withdrawal processes in drug dependence. We investigated whether it could be related to the fact that drugs are directly consumable, whereas money is not. We determined whether regular cigarette smokers discount food (another consumable outcome) less steeply than cigarettes, both of which were predicted to be discounted more steeply than money. Cigarette smokers (N=20) indicated preferences for immediate and delayed outcomes in a titration procedure that determined indifference points at various delays. In three separate conditions, the choices involved food, cigarettes, or money. The value of the delayed option was always US$ 10 or US$ 10 worth of the outcome. Cigarette smokers discounted both cigarettes and food more steeply than money. Most importantly, cigarettes and food were discounted to a similar degree. Cigarettes may be steeply discounted in part due to their consumable nature, rather than solely due to withdrawal-related processes.     

Alcohol-dependent individuals discount sex at higher rates than controls

Background

Research on delay discounting has expanded our understanding of substance dependence in many ways. Recently, orderly discounting of sexual rewards has been demonstrated in both substance-dependent individuals, and healthy controls. Less clear, however, is if rates of sexual discounting are higher than controls in alcohol-dependent-individuals.

Methods

20 alcohol-dependent individuals and 21 healthy control participants completed two delay-discounting tasks. One task involved monetary rewards, whereas the other involved the discounting of sexual rewards (i.e., number of sex acts).

Results

Alcohol dependent individuals discounted sexual rewards at significantly higher rates than did controls. There was a trend toward, but not a similarly significant relation for the discounting of monetary rewards.

Conclusions

Rates of sexual discounting are elevated in alcohol dependent individuals. If this relation is replicated in other at risk populations, the rapid devaluation of sexual rewards may be a laboratory marker of impulsive sexual choices.     

Genetic influences on delay discounting in smokers: examination of a priori candidates and exploration of dopamine-related haplotypes

Rationale

Delay discounting is a behavioral economic index of impulsivity that reflects a person’s relative preference for small immediate rewards versus larger delayed rewards. Elevated delay discounting is robustly linked to addictive disorders and has been increasingly investigated as a viable endophenotype for genetic influences on addiction.

Objective

The aim of this study is to examine associations between delay discounting and two a priori loci, rs4680 in COMT and rs1800497 in ANKK1, and three exploratory haplotypes proximal to rs1800497 in a sample of daily smokers.

Methods

Participants were 713 (60.2 % male) daily smokers of European ancestry who completed a delay discounting assessment and provided a DNA sample.

Results

Significant associations were detected between greater discounting of medium magnitude rewards (~$55) and the G allele of rs4680, as well as the T allele of rs1800497. Exploratory haplotype analyses identified two haplotypes (rs1160467/rs1800497; rs6277/rs1079597) significantly associated with delay discounting rates. However, the rs1160467/rs1800497 haplotype associations appeared to be entirely attributable to variation in rs1800497, suggesting that the association of rs1800497 with discounting is best understood at the individual SNP level. Similarly, the rs6277/rs1079597 haplotype findings suggested that the association was specific to rs1079597.

Conclusions

This study provides further evidence that rs4680 and rs1800497 genotypes are significantly associated with delay discounting preferences and does so among smokers for the first time. The study also provides evidence of specificity for the rs1800497 association and identifies a novel locus, rs1079597, as a genetic contributor to higher delay discounting rates.

     

Is all risk bad? Young adult cigarette smokers fail to take adaptive risk in a laboratory decision-making test

Rationale

Cigarette smoking has been linked to real-world risky behavior, but this association has been based largely on retrospective self-reports. Limitations of self-report data can be avoided by using laboratory, performance-based measures, such as the Balloon Analogue Risk Task (BART; Lejuez et al., J Exp Psychol Appl 8:75?C84, 2002). Initial studies have suggested that smokers display greater risk-taking on this task than nonsmokers, but these studies did not account for drug abuse and psychiatric comorbidities, which are commonplace among smokers.

Objectives

We sought to examine the performance of smokers and nonsmokers on the BART after excluding drug abuse and psychiatric comorbidities.

Methods

We conducted a study of late adolescent/young adult (age 18 to 21) smokers (n?=?26) and nonsmokers (n?=?38) performing the BART and excluded individuals with positive drug or alcohol toxicology screens, substance abuse or dependence diagnoses, and/or current psychiatric conditions.

Results

Contrary to previous findings, smokers did not display greater risk-taking on the BART than nonsmokers. In fact, when performance was examined trial-by-trial, the nonsmokers displayed progressively greater pumping relative to smokers over time (p?<?.001), earning them a nonsignificantly greater amount of money than the smokers. Controlling for smoking status, additional analyses revealed that pumping on the BART was positively associated with years of education, nonverbal IQ, and employment.

Conclusions

The results suggest that in young adults, smoking may be associated with a failure to take risks in situations where risk-taking is adaptive.     

The relationship between reward and punishment processing and the 5-HT1A receptor as shown by PET

Rationale

The serotonin (5-HT) system has been reported to be involved in decision-making. A key component of this neurotransmitter system is the 5-HT_1A receptor, and research is beginning to show how this receptor can influence decision-making. However, this relationship has rarely been studied in humans.

Objectives

This study assessed whether individual variability in 5-HT_1A availability correlates with decision-making in healthy volunteers.

Methods

We measured regional availability of the 5-HT_1A receptor in the hippocampal complex and striatum using positron emission tomography and correlated this with performance on two decision-making tasks measuring sensitivity to probability, rewards and punishments and temporal discounting, respectively.

Results

No relationship between decision-making behaviour and 5-HT_1A availability in the striatum was found. However, a positive correlation was detected between participants’ 5-HT_1A availability in the hippocampal complex and their sensitivity to the probability of winning. Furthermore, there was a negative correlation between the degree to which participants discounted future rewards and 5-HT_1A availability in the hippocampal complex.

Conclusions

These data support a role for the 5-HT_1A receptor in the aberrant decision-making that can occur in neuropsychiatric disorders such as depression.     

Effects of cigarette smoking status on delay discounting in schizophrenia and healthy controls

Background

Delay discounting is a measure of future-oriented decision-making and impulsivity. Cigarette smoking is associated with rapid discounting of the value of delayed outcomes. In schizophrenia, however, cigarette smoking improves certain neurocognitive impairments associated with the disorder which may explain the high smoking rates in this population. This study examined the relationship between cigarette smoking and delay discounting in schizophrenia and control participants.

Methods

A total of N = 130 participants, including those with schizophrenia (n = 68) and healthy controls (n = 62) were assessed on the Kirby Delay Discounting Task and compared across smoking status (smokers; non-smokers) and smoking history (current, former; never smokers).

Results

Smokers exhibited higher discounting rates (i.e., were more impulsive) than non-smokers of the same diagnostic group. Current and former smokers with schizophrenia exhibited similar and significantly higher discounting rates than never smokers, suggesting that in schizophrenia delay discounting is a trait-dependent phenomenon independent of current cigarette smoking. Consistent with previous studies, there was a trend for higher discounting rates in control current smokers compared to control former and never smokers.

Conclusions

Smokers with and without schizophrenia have higher rates of delay discounting than non-smokers. However, in schizophrenia, rapid delay discounting appears to be a trait associated with having ever been a smoker (i.e., current and former smoking).     

Impulsivity and cigarette smoking: delay discounting in current, never, and ex-smokers

Rationale: Impulsivity is implicated in drug dependence. Recent studies show problems with alcohol and opioid dependence are associated with rapid discounting of the value of delayed outcomes. Furthermore, discounting may be particularly steep for the drug of dependence. Objectives: We determined if these findings could be extended to the behavior of cigarette smokers. In particular, we compared the discounting of hypothetical monetary outcomes by current, never, and ex-smokers of cigarettes. We also examined discounting of delayed hypothetical cigarettes by current smokers. Methods: Current cigarette smokers (n=23), never-smokers (n=22) and ex-smokers (n=21) indicated preference for immediate versus delayed money in a titration procedure that determined indifference points at various delays. The titration procedure was repeated with cigarettes for smokers. The degree to which the delayed outcomes were discounted was estimated with two non-linear decay models: an exponential model and a hyperbolic model. Results: Current smokers discounted the value of delayed money more than did the comparison groups. Never- and ex-smokers did not differ in their discounting of money. For current smokers, delayed cigarettes lost subjective value more rapidly than delayed money. The hyperbolic equation provided better fits to the data than did the exponential equation for 74 out of 89 comparisons. Conclusions: Cigarette smoking, like other forms of drug dependence, is characterized by rapid loss of subjective value for delayed outcomes, particularly for the drug of dependence. Never- and ex-smokers could discount similarly because cigarette smoking is associated with a reversible increase in discounting or due to selection bias. Received: 3 March 1999 / Final version: 11 May 1999     

The Experiential Discounting Task is sensitive to cigarette-smoking status and correlates with a measure of delay discounting

This research compared three different measures of discounting in adult cigarette smokers (n=15; consumed >or=20 cigarettes per day) and nonsmokers (n=15; self-reported never smokers). Participants completed the Experiential Discounting Task (EDT) and question-based measures of delay and probability discounting. The Experiential Discounting Task is a new real-time choice procedure purported to assess delay discounting. The Experiential Discounting Task provides choice consequences (i.e. delays, probabilities, and monetary rewards delivered from a coin dispenser) during choice sessions, whereas the question-based measures are hypothetical (i.e. delays, probabilities, and rewards are not directly experienced). Smokers discounted more than nonsmokers on all three measures. Additionally, the Experiential Discounting Task was significantly correlated with the question-based measure of delay discounting but not probability discounting. These results suggest all three discounting procedures are sensitive to cigarette-smoking status among adult smokers and nonsmokers and that the Experiential Discounting Task may be more comparable to measures of delay discounting than probability discounting.     

Adolescent smokers rate delayed rewards as less certain than adolescent nonsmokers

This research compared adolescent smokers (n=45) and nonsmokers (n=35) on ratings of certainty about receiving delayed rewards during a delay discounting procedure. Consistent with a previous finding [Patak, M., Reynolds, B., 2007. Question-based assessments of delay discounting: do respondents spontaneously incorporate uncertainty into their valuations for delayed rewards? Addict. Behav. 32, 351-357] participants generally rated the delayed rewards as increasingly uncertain with longer delays, and ratings of certainty were correlated with delay discounting (r=.37). Also, the adolescent smokers rated the delayed rewards as significantly less certain than the nonsmokers. These findings indicate that adolescents who smoke cigarettes evaluate delayed outcomes as less certain than adolescents who do not smoke cigarettes.     

Moderate drug use and delay discounting: a comparison of heavy, light, and never smokers

Delay discounting was examined in light smokers (10 or fewer cigarettes per day) and compared with previously published delay discounting data for heavy and never smokers. Participants evaluated several hypothetical outcomes: money gains and loses ($10, $100, and $1,000), health gains and losses (durations of improved and impoverished health subjectively equivalent to $1,000), cigarette gains and losses (amounts subjectively equivalent to $1,000), and potentially real rewards ($10 and $100). Light smokers discounted money significantly more than never smokers, but light smokers did not differ from heavy smokers. The 3 groups did not statistically differ in discounting of health consequences. Similarly, the 2 smoking groups were not found to differ in discounting of cigarettes. Like heavy smokers, light smokers discounted cigarettes significantly more than money and health. Several significant, positive correlations were found between smoking rate and various discounting measures in the heavy smokers but not in the light smokers. Several previous findings were replicated, helping to validate the present results: the sign effect (greater discounting of gains than losses), the magnitude effect (greater discounting of smaller rewards), reliability of discounting measures over time, and the consistency of hypothetical and potentially real rewards. These data suggest that even moderate levels of drug use may be associated with high delay discounting levels.     

Mild opioid deprivation increases the degree that opioid-dependent outpatients discount delayed heroin and money

RATIONALE: A growing literature suggests that excessive temporal discounting of delayed rewards may be a contributing factor in the etiology of substance abuse problems. Little is known, however, about how drug deprivation may affect temporal discounting of delayed rewards by drug-dependent individuals. OBJECTIVE: To examine the extent to which opioid deprivation affects how opioid-dependent individuals discount small, medium and large quantities of delayed heroin and money. METHODS: Thirteen opioid-dependent individuals maintained on buprenorphine completed a hypothetical choice task in which they choose between a constant delayed reward amount and an immediate reward amount that was adjusted until they expressed indifference between both outcomes. The task was completed for three values of heroin and money rewards during eight sessions under conditions of opioid deprivation (four sessions) and satiation (four sessions). RESULTS: Across conditions, hyperbolic functions provided a good fit for the discounting data. Degree of discounting was significantly higher when subjects were opioid deprived. Consistent with previous findings, degree of discounting was higher for heroin than money and inversely related to the magnitude of the reward. CONCLUSION: Opioid deprivation increased the degree to which dependent individuals discounted delayed heroin and money. Understanding the conditions that affect how drug-dependent individuals discount delayed rewards might help us understand the myopic choices made by such individuals and help improve treatment outcomes.     

Needle sharing in opioid-dependent outpatients: psychological processes underlying risk

Needle sharing contributes to the spread of the human immunodeficiency virus and other health concerns and remains a persistent problem among injection drug users. We determined whether needle sharing may be related to the discounting of the value of delayed outcomes. Outpatients in treatment for heroin dependence indicated preference for immediate versus delayed hypothetical monetary and heroin outcomes in a titration procedure that determined indifference points at various delays. The degree to which the delayed outcomes lost value was estimated with a nonlinear decay model. Participants who agreed to share a needle in a scenario (N=15) discounted delayed money more steeply than did the nonsharing group (N=17). Both groups discounted delayed heroin more steeply than delayed money. Persistent needle sharing may be related to the relative inability of delayed outcomes to impact current behavior. Training to mitigate the effect of delay on outcome value may offer reductions in needle sharing and drug abuse.     

Histological changes of gingival epithelium in smokers and non-smokers

Background

Smoking patients show a reduction of inflammatory clinical signs that might be associated with local vasoconstriction and an increased gingival epithelial thickness. The purpose of this work was to evaluate the S-thickness of the marginal gingival oral epithelium in smokers and non-smokers.

Methods

Twelve biopsies were obtained from three different groups. Group I: non-smokers with gingivitis, group II smokers, and group III health persons without any periodontal disease. These biopsies were histologically processed, serially sectioned at 5 ??m, and underwent evaluation of the major epithelial thickness, the epithelial base thickness, and the external and internal epithelial perimeters. Differences between the groups were analyzed using ANOVA test. The criteria for statistical significance were at the probablity level p < 0.05.

Results

A greater epithelial thickness was observed in smokers.

Conclusion

The increased epithelium thickness can contribute to the reduction of inflammatory clinical signs in the gingival tissue.     

Reinforcement enhancing effects of nicotine via smoking

Rationale

In animals, nicotine enhances reinforcement from stimuli unrelated to nicotine intake. Human research is suggestive but has not clearly shown a similar influence of nicotine.

Objectives

We assessed acute effects of nicotine via smoking on enhancement of positive (money, music) or negative (termination of noise) reinforcers, or no “reward” (control). These different rewards determined the generalizability of nicotine effects.

Materials and methods

Dependent (n?=?25) and nondependent (n?=?27) smokers participated in three sessions, each after overnight abstinence. Using a within-subjects design, sessions involved no smoking or smoking denicotinized (0.05 mg) or nicotine (0.6 mg) Quest^R brand cigarettes. For comparison, a fourth session involved no abstinence prior to smoking one's own brand to gauge responses under typical nicotine satiation. Reinforcement was assessed by responses on a simple operant computer task for the rewards, each available singly on a progressive ratio schedule during separate trials.

Results

The reinforcing effect of music, but not other rewards, was greater due to the nicotine cigarette, compared to the denicotinized cigarette or no smoking. Reinforcement enhancing effects of nicotine did not differ between dependent and nondependent groups, indicating no influence of withdrawal relief. Responding due to acute nicotine after abstinence was very similar to responding to one's own brand after no abstinence.

Conclusions

Acute nicotine intake per se from smoking after abstinence enhances the reinforcing value of rewards unassociated with smoking, perhaps in a manner comparable to ad lib smoking after no abstinence. Nicotine's reinforcement enhancing effects may be specific to certain rewards, perhaps those sensory in nature.     

Discounting delayed and probabilistic monetary gains and losses by smokers of cigarettes

Rationale Nicotine dependence has been associated with impulsivity and discounting delayed/uncertain outcomes. Objectives This study had two main objectives: (1) to examine the relationship between the number of cigarettes consumed per day and the degree to which delayed and uncertain monetary gains and losses are discounted by smokers, and (2) to determine the relationship between the estimated dose of nicotine intake per day and the degree to which four types of discounting occur. Methods Twenty seven habitual smokers and 23 never smokers participated in this experiment. They were required to choose between immediate and delayed monetary rewards (or losses), or between guaranteed and probabilistic rewards (or losses). Results The degree to which delayed monetary gains were discounted was significantly and positively correlated with both the number of cigarettes smoked and the estimated dose of nicotine intake per day. Conversely, there was no relationship between smoking and the remaining three types of discounting. Also, mild smokers in our sample did not differ from never smokers in discounting monetary gains or losses. Conclusions In general, our results suggest that both the frequency of nicotine self-administration, as well as the dosage, are positively associated with greater delay discounting of gains. One neuropsychopharmacological explanation for this effect is that chronic nicotine intake may induce neuroadaptation of the neural circuitry involved in reward processing.     

Acute effects of THC on time perception in frequent and infrequent cannabis users

Rationale

Cannabinoids have been shown to alter time perception, but existing literature has several limitations. Few studies have included both time estimation and production tasks, few control for subvocal counting, most had small sample sizes, some did not record subjects’ cannabis use, many tested only one dose, and used either oral or inhaled administration of Δ⁹-tetrahydrocannabinol (THC), leading to variable pharmacokinetics, and some used whole-plant cannabis containing cannabinoids other than THC. Our study attempted to address these limitations.

Objectives

This study aims to characterize the acute effects of THC and frequent cannabis use on seconds-range time perception. THC was hypothesized to produce transient, dose-related time overestimation and underproduction. Frequent cannabis smokers were hypothesized to show blunted responses to these alterations.

Methods

IV THC was administered at doses from 0.015 to 0.05 mg/kg to 44 subjects who participated in several double-blind, randomized, counterbalanced, crossover, placebo-controlled studies. Visual time estimation and production tasks in the seconds range were presented to subjects three times on each test day.

Results

All doses induced time overestimation and underproduction. Chronic cannabis use had no effect on baseline time perception. While infrequent/nonsmokers showed temporal overestimation at medium and high doses and temporal underproduction at all doses, frequent cannabis users showed no differences. THC effects on time perception were not dose related.

Conclusions

A psychoactive dose of THC increases internal clock speed as indicated by time overestimation and underproduction. This effect is not dose related and is blunted in chronic cannabis smokers who did not otherwise have altered baseline time perception.