'Go pills' blunt anticipation of rewards


Researchers have now found that amphetamines diminish people's anticipation of rewards. Scans of subjects' brains when they were led to anticipate a cash reward--as well as psychological self-assessments--revealed them to be less positively aroused by such anticipation under the influence of dextroamphetamine.

Amphetamines are popularly known as "go pills" among fighter pilots, who take them to reduce fatigue on long flights.

What's more, the researchers also found that the subjects who took the amphetamine were not as negatively aroused when they anticipated losses, which led the scientist to theorize that such drugs might help "maintain motivation, even in the face of adversity."

Brian Knutson, assistant professor of psychology and neuroscience at Stanford University, and his colleagues reported experiments in which they asked eight volunteers to perform a task in which they had to respond to shapes on a screen in return for anticipated cash rewards. The researchers gave the subjects doses of either dextroamphetamine or a placebo.

"While researchers have separately examined how either pharmacological or psychological incentives alter brain activity, this is the first study to utilize an event-related design to examine their combined influence," wrote the researchers.

Functional MRI scans of the subjects' brains during the task revealed--under the drugs, compared to placebos--a selective damping of peak activity in a region of the cortex known as the ventral striatum. Previous studies have shown that this region is activated by anticipation of reward. The analyses also showed that, while peak activity was damped, the length of the activity was prolonged.

The subjects were also asked to rate their feelings of happiness, excitement, unhappiness, and fearfulness after each task, which gave the researchers a psychological measure of the level of arousal from anticipation of gain or loss.

Both the MRI studies and psychological measures suggested that treatment with the drug "equalized" levels of ventral striatum activity and positive arousal during anticipation of both gain and loss, concluded the researchers.

"These findings suggest that therapeutic effects of amphetamine on incentive processing may involve reducing the difference between anticipation of gains and losses," they wrote.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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