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Unique risk taking in different disorders of natural and drug reward.

last modified May 06, 2015 05:00 PM

Unique risk taking in different disorders of natural and drug reward.

Scientists at the BCNI recently published the results of a large study looking at risk taking in disorders of natural and drug reward. Published in the Journal of Neuropsychopharmacology, the paper describes similarities and differences of risk taking behaviour in subjects with substance abuse disorders, obesity and binge eating disorder.

With a total of 339 participants (30 abstinent with alcohol dependence, 23 abstinent with methamphetamine dependence, 30 obese subjects with binge eating disorder, 30 obese subjects without binge eating disorder and 226 age- and gender- matched control subjects), the scope of the study allowed the researchers to characterise risk taking behaviour in various contexts.

In the experiment, participants played for a virtual monetary reward. On each trial, they had a choice between a sure and a risky option. The risky option was the chance to win a certain amount – i.e. £1,000 – with a probability indicated by a jar full of balls. If they lost, they received £0. The sure option yielded less money, but there was no chance of getting £0. The same game was also played for losses, where participants could choose to lose a sure amount, or gamble for losing £0 – but risk losing more than the sure amount. The amount won or lost in the sure option was always dependant on the amount and probability in the risky option.

The task participants faced in the reward (left) and loss condition.

The task participants faced in the reward (left) and loss condition.

Behaviour on this task is influenced by three components: whether the context is reward or loss, whether the probabilities of wins or losses are small or large, and whether the value of the sure and risky choice is small or large. Participants take more risks when the probability of a win is large or the probability of a loss is small; participants also take more risks when the value of the sure win is large or the value of the sure loss is small. The researchers found that each group studied showed a unique pattern of risk taking.

The researchers found that in the reward condition, substance abusers took more risks than control subjects. This pattern was also found in obese binge-eaters, but not in obese non-binge eaters. There was also a slight difference in methamphetamine subjects: these participants took more risks in the low-probability, high-reward trials, akin to playing in the lottery.

In the loss condition, substance abusers took more risk than controls when the probability of losing was small, and fewer risks when the probability of losing was large. In this condition, the substance abuse pattern was found also in the obese non-binge eaters, but not the binge-eaters.

The researchers suggest that developing a substance abuse disorder or a food disorder is influenced by an individual’s risk-taking behaviour. The patterns of risk taking in each disorder indicate different routes via which people develop these disorders.

Dr Valerie Voon, lead author of the study commented: “Risk taking is not just risk taking.  You can be risk taking in one context and less so in another.  How you respond to risk in different contexts may play a role in what types of substances/natural rewards one might misuse.”

The researchers also looked at non-linearity of probability weighting, a common experience in which judging the effect of an outcome becomes more difficult as the probability of its occurence becomes very small. As Dr Voon explains: “This effect has a physiological basis of being less likely to subjectively tell when a light is brighter with increasing brightness of the light. This non-linearity of probability weighting also accounts for the reasons we buy lottery tickets or insurance (as we have more difficulty with subjectively appreciating probability or likelihood as it approaches zero).

This leads (for example) the methamphetamine users to take more risks when there is a very small probability of winning a large sum. In a group of 40 healthy control subjects, a reduced ability to judge probabilities accurately was associated with lower volumes of the lateral, ventromedial and orbitofrontal prefrontal cortex.

The study opens up the possibility of studying the effects of pharmacological and behavioural interventions on risk-taking behaviour. Behavioural interventions could focus on attitudes towards risks and rewards.

The study was funded by a Wellcome Trust Fellowship awarded to Valerie Voon.

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