In for a penny, in for a pound: methylphenidate reduces the inhibitory effect of high stakes on persistent risky choice

Abstract

Methylphenidate (MPH) is a stimulant that increases extracellular levels of dopamine and noradrenaline. It can diminish risky decision-making tendencies in certain clinical populations. MPH is also used, without license, by healthy adults, but the impact on their decision-making is not well established. Previous work has found that dopamine receptor activity of healthy adults can modulate the influence of stake magnitude on decisions to persistently gamble after incurring a loss. In this study, we tested for modulation of this effect by MPH in 40 healthy human adults. In a double-blind experiment, 20 subjects received 20 mg of MPH, while 20 matched controls received a placebo. All were provided with 30 rounds of opportunities to accept an incurred loss from their assets or opt for a "double-or-nothing" gamble that would either avoid or double it. Rounds began with a variable loss that would double with every failed gamble until it was accepted, recovered, or reached a specified maximum. Probability of recovery on any gamble was low and ambiguous. Subjects receiving placebo gambled less as the magnitude of the stake was raised and as the magnitude of accumulated loss escalated over the course of the task. In contrast, subjects treated with MPH gambled at a consistent rate, well above chance, across all stakes and trials. Trait reward responsiveness also reduced the impact of high stakes. The findings suggest that elevated catecholamine activity by MPH can disrupt inhibitory influences on persistent risky choice in healthy adults.

Figure 1.

The options for each choice—Play or Quit—appeared randomly on the left and right side of the computer display during the decision phase. Each round began with a loss (also the stake) displayed for 3 s. This was followed by a choice to accept that loss (Quit) and end the round or to risk the value of the loss (Play) to try and recover it. Subjects responded by pressing keys on a mouse corresponding to the side of their desired choice. Choices were randomly assigned to sides of the display from round to round. Outcome displays (2 s) indicated whether subjects had won a gamble and that no money was lost (Play & Win); whether they had lost a gamble and the amount lost (Play & Lose); or the amount lost from assets if subjects chose to give up (Quit). If the loss reached 6400 kr, the round automatically ended with no chance of recovery (Play & Lose Max). At the end of each round, subjects were informed of the amount that would be taken off their final total as a result of that round. There was no time limit for making a decision. The dotted line indicates the subject's choice but was not displayed to subjects. Words were translated to Danish. Displays were presented to subjects in color with losses, negative outcomes, and Quit displays indicated in red font. Positive outcomes were indicated in green.

Figure 2.

Interaction of drug and stake on risky persistence. Probability of decision to accept a double-or-nothing gamble across various magnitudes of stake. Gambling probability was reduced with increasing stakes in the placebo group but not the MPH group (see Table 2). This led to a significant difference of gambling probability at high stakes (1600 kr). Error bars are ±1 SE (between subjects). *p < 0.05.