Individual Differences in Impulsive-like Behavior & Sensitivity to Money

1. Individual Differences in Impulsive-like Behavior & Sensitivity to Money • as a Function of Sensation Seeking Status • LaBedz, S., Babalonis, S., & Kelly, T.H. • University of Kentucky Abstract Previous research indicates that high sensation seekers are at increased vulnerability to drug abuse relative to low sensation seekers. This enhanced risk has been characterized by earlier initiation and greater frequency of drug use among high sensation-seeking adolescents, and increased sensitivity to the reinforcing and other behavioral effects of drugs in laboratory studies, such that high sensation seekers exhibit higher break-points on progressive ratio schedules maintained by drug delivery. The present study examined sensitivity to a generalized reinforcer (i.e., money) and impulsive-like behavior as a function of sensation-seeking status among healthy young adults. Twenty participants scoring in the top and bottom quartiles of gender-adjusted population norms on the impulsive-sensation seeking scale of the Zuckerman-Kuhlman Personality Questionnaire (10 high- and 10 low-impulsive sensation seekers) completed one session in which performance on several behavioral tasks was assessed. Participants completed a progressive ratio task in which they could earn up to $4.00 (in .50 increments) by completing progressively increasing response requirements. Other measures included performance on the Balloon Analog Risk Task, a hypothetical delay-discounting task, and a delay-discounting task with a lottery outcome. Breakpoints on the progressive ratio task did not vary as a function of sensation-seeking status. Likewise, performance on behavioral measures of impulsivity did not vary between high and low sensation seekers. These data suggest that group differences in drug-maintained behavior between low and high sensation seekers are not observed when behavior is maintained by money. Moreover, sensation-seeking status was not associated with performance on any laboratory measure of impulsivity (delay discounting, BART). Supported by DA-05312, DA-024127, University of Kentucky Department of Behavioural Science. Results Progressive Ratio • Progressive Ratio Task- This task has been used in a variety of experimental settings to examine behavioral sensitivity to the reinforcing effects of a stimulus. The breakpoint, i.e. the last ratio completed, generally serves as the dependent measure of reinforcing efficacy. The selected ratio value was based on previous research (Stoops et al., 2007). These contingencies engendered variability in responding; however, breakpoint did not vary as a function of sensation seeking status. Previous studies have shown that performance on this task maintained by d-amphetamine administration differs as a function on sensation seeking status. • Money served as a reinforcer in both high and low sensation seekers; however, there were no differences in breakpoints as a function of sensation seeking status. • Hypothetical Delay Discounting Task- This task has been used to characterize behavioral sensitivity to reinforcer delay, such that a value of a reinforcer decreases as the delay to its delivery increases. Performance on this task differs as a function of current drug or alcohol use, gambling habits, smoking status, and age of first use of alcohol or illicit substance (see Bickel & Marsch, 2001; Reynolds, 2006). • Prototypical discounting functions were generated in this task; however, there were no significant differences in indifference points as a function of sensation seeking status. • Real Delay Discounting Task- Similar to the hypothetical task, this task generates behavior that differs as a function of particular behavioral histories (i.e., drug use, gambling, etc.) This task differs from the hypothetical task by introducing contingencies, such that one choice is randomly selected and rewarded (e.g., $15 delivered in 10 days). • Prototypical discounting functions were generated in this task; however, there were no significant differences in indifference points as a function of sensation seeking status. • Balloon Analog Risk Task (BART)- This task has been used to examine sensitivity to reward and inhibitory control. Previous studies have shown that performance on this task differs as a function of drug abuse history, smoking status, and presence of behavioral problems (Lejuez et al., 2002, 2003, 2007). • Prototypical behavior was emitted on the BART; however behavior did not vary as a function of sensation-seeking status. Earnings ($) Number of Clicks Sensation Seeking Status Background The sensation seeking personality trait is described as an inclination towards intense emotional experiences and/or situations and the pursuit of risky or impulsive behavior in order to achieve the sensation (Zuckerman, 1994). Previous studies have shown that a high sensation seeking status may increase an individual’s susceptibility to drug abuse (Wills et al., 1994). Previous laboratory research has shown that the reinforcing and behavioral effects of drugs (d-amphetamine, alcohol, nicotine) are enhanced in high sensation seekers, relative to low sensation seekers (Stoops et al., 2007; unpublished data), indicating that high sensation-seekers may be more vulnerable to the reinforcing effects of drugs, and thereby might be at greater risk for developing repeated patterns of drug-seeking behavior. The purpose of the present study is to determine if the reinforcing effects of a generalized reinforcer (i.e. money) and performance on laboratory measures of impulsive-like behavior will differ between high and low sensation seekers. Methods Participants: Twenty, non-smoking healthy adults, ages 19 to 32, gave written consent prior to participating in a single session lasting approximately 2.5 hours. Ten participants were classified as High Sensation Seekers, and ten were classified as Low Sensation Seekers, with each group having equal numbers of male and female participants. All participants provided drug-free urine and alcohol-free breath samples prior to participation. All subjects received task training and practice prior to the experimental session and were paid for their participation upon completion of the session. Sensation-Seeking Status: Volunteers completed items from the impulsive sensation-seeking scale of the Zuckerman-Kuhlman Personality Questionnaire. Those who scored in the upper and lower 25% of the population, based on established norms, were classified as High and Low Sensation Seekers, respectively, and invited to participate. Assessment Tasks Progressive Ratio Task: This task consisted of eight consecutive opportunities to earn money in increments of $0.50 by responding on a computer mouse. Participants could earn none, some, or all of the available money ($4.00). To earn the first $0.50, participants were required to click the mouse 50 times. The requirement then doubled for each additional $0.50 (e.g., 100, 200, 400, 800, 1600, 3200, and 6400 clicks), such that 12,750 were required to earn all of the available money ($4.00). However, the participant could choose to stop responding at any time, either by selecting “no” when asked if they wished to continue after earning an increment of money or by stopping clicking at any time (e.g., an IRT ≥ 2 minutes ended the task). The dependent measures of interest during this task ware break-point (the last ratio completed) and concomitantly, the amount of money earned. Hypothetical Delay Discounting Task: A series of hypothetical choices were presented, positing a choice between two options: an immediate, smaller amount of money and a larger, delayed amount of money. The immediate amount was increased until preference between the two options reached indifference. The hypothetical delayed money option was fixed ($1000) and was presented at 7 delay values (1 week, 2 weeks, 1 mo, 6 mo, 1 yr, 5 yr and 25 yr). The dependent measure was indifference point for each delay value (I.e., the immediate amount of money that shifts preference from the larger, delayed option). Participants were instructed that each of their choices were hypothetical and they would not be paid for any of their selections. Real Delay Discounting Task: A series of choices were presented, positing a choice between two options: an immediate, smaller amount of money and a larger, delayed amount of money. The delayed money option was fixed ($20) and was presented at 10 delay values (1 day, 3 days, 5 days , 1 week, 10 days, 2 weeks, 3 weeks, 25 days, 1 month, and 2 months). The immediate amount ($20, $18, $15, $12, $10, $8, $6, $4, $2, and $1), was increased until preference between the immediate amount and the delayed amount ($20) reached indifference. This indifference point served as the dependent measure. Of the 200 choices the participants made, they were paid for one randomly selected choice (ex.: $15 in 2 weeks). Balloon Analog Task: This task simulated a balloon being inflated in small increments controlled by clicking on a computer mouse (e.g., Lejuez et al., 2003). On each trial a participant decided to inflate the balloon or move to another balloon. A successful inflation resulted in a monetary increment to a temporary bank and an increase in the probability of the balloon popping on the next inflation. If a participant choose to move to another balloon, the amount in the temporary bank was placed in a permanent bank; if a participant choose to inflate the balloon and it popped, money in the temporary bank was lost. Figure 1. The amount of money earned (left panel) and total number of clicks emitted (right panel) on the Progressive Ratio Task as a function of sensation-seeking status. No significant differences between groups were detected in either measure. Delay Discounting Tasks Subjective value ($20) Subjective Value ($1000) Time (days) Figure 2. Mean discounting curves generated under real (left panel) and hypothetical (right panel) conditions when indifference points are fit to the hyperbolic discounting function [A = V/(1+kD)]. Both graphs display prototypical discounting functions, with the subjective value of money decreasing as a function of delay to its delivery. No differences in discounting functions between groups were detected in either task. Balloon Analog Risk Task Conclusions There were no differences detected in behavioral sensitivity to a generalized reinforcer or delay to a reinforcer as a function of sensation seeking status. Behavioral effects were not significantly different with respect to other factors such as gender, age, and education. The lack of significant difference on performance task measures between the personality groups may be attributed to the heterogeneous nature of impulsivity and the reliability of quantitative measures of personality as a predictor of behavior. Previous studies have shown that the reinforcing effects of drugs differ between high and low sensation seekers. However, no differences were observed when a generalized reinforcer was available. These results suggest that differential sensitivity to reinforcers as a function of sensation seeking status may be specific to certain commodities (i.e., drugs). Responses per Balloon Number of Pops Earnings ($) Sensation-Seeking Status Figure 3. Mean number of responses per balloon on balloons that did not pop (left panel); mean number of popped balloons (middle panel) and mean earnings as a function of sensation-seeking status. Each bar represents the mean of three task presentations with error bars representing +- one standard error of the mean. No practice effects were detected across the three task presentations for either group and no significant differences between groups were detected on any measure.