Deal Or No Deal? Need For Immediate Reward Linked To More Active Brain Region

University of Pittsburgh investigators didn't study any of the game's players nor did they offer stakes nearly as high, but their research in 45 normal adult volunteers, who were taunted with the prospect of getting between 10 cents and $105 at that very moment or waiting one week to five years for a sure $100, provides new insight about reward-based decision making and may have implications for understanding and treating addiction disorders.

Not only do people differ in their preferences for immediate over delayed rewards of larger value, say the researchers in the Journal of Neuroscience, but these individual traits are mirrored by the level of activity in the ventral striatum, a key part of the brain's circuitry involved in mediating behavioral responses and physiological states associated with reward and pleasure. Research volunteers classified as more impulsive decision makers, who tend to seek rewards in the here and now, had significantly more activity in the ventral striatum.

The preference for immediate over delayed rewards of larger value, which researchers term "delay discounting," has already been linked to impulse-control problems, such as substance abuse, addiction and pathological gambling. And separate studies have shown that people with addiction disorders have a more active ventral striatum. The current study is the first to look at the relationship between individual differences in discounting behavior and individual ventral striatum activity, which in finding a strong connection between brain and behavior in normal subjects suggests the same neurocognitive mechanism could contribute to increased risk for addiction as well.

"The ventral striatum appears to be a nexus where we balance acting impulsively to achieve instant gratification and making prudent choices that may delay rewards. Understanding what drives individual differences in ventral striatal sensitivity could aid efforts to treat people who have difficulty controlling impulsive behavior, by adjusting the circuitry," explained lead author, Ahmad R. Hariri, Ph.D., assistant professor of psychiatry and director of the Developmental Imaging Genetics Program at the University of Pittsburgh School of Medicine and Western Psychiatric Institute and Clinic.

Based on their findings, Dr. Hariri and his colleagues are now looking at whether ventral striatum activity can help predict substance abuse disorders in those at risk. Since the activity of the ventral striatum is modulated by dopamine, a brain chemical also associated with reward, they plan to explore the role that variations in dopamine-related genes may play in determining differences in ventral striatum reactivity.

"Addiction and problem gambling represent behaviors on the extreme end of the continuum. But even in the most common, day-to-day situations, reward-based decisions dictate how we behave. For example, individual preferences for immediate versus delayed rewards could explain why some can't resist the temptation of dessert, an immediate gratification, while others will opt for a five-mile run knowing it will help shed pounds, a delayed gratification," added Dr. Hariri. "Food, sex and money are all sources of pleasure, yet individuals differ greatly in the rewarding aspects they derive from these pleasures."

In the study, subjects completed a computer-based task of delay discounting that required choices between immediate and postponed rewards -- a laboratory version of Deal or No Deal that gives investigators a reliable index of each volunteer's impulsive tendencies. Subjects had to choose between hypothetical amounts of money available to them that day, ranging from 10 cents to $105, and $100 that would be given after seven days, one month, three months, six months, one year or five years. Based on their cumulative choices, a switch-point value was calculated for each volunteer -- the specific dollar amount that caused indifference about receiving the money now or later.

After several months, fMRI brain imaging studies were performed to determine each subject's ventral striatum activity during a task that measures positive and negative feedback in anticipation of a monetary reward. Each volunteer was told that the amount they would receive depended on how well they performed in a card guessing game, yet the researchers fixed the odds and all subjects were paid $10.

The researchers found that individual differences in discounting behavior, as determined by the first test, corresponded with the magnitude of ventral striatum activity. Positive feedback produced the greatest activity, especially in those with a preference for immediate rewards.

The study's volunteers comprised participants in the Adult Health and Behavior project, in which researchers being led by Stephen Manuck, Ph.D., professor of psychology at the University of Pittsburgh's School of Arts and Sciences and a co-author of the Journal of Neuroscience paper, are assessing a wide range of behavioral and biological traits among non-patient, middle-aged, community volunteers.

In addition to Drs. Hariri and Manuck, other authors were Sarah M. Brown, and Douglas E. Williamson, Ph.D., department of psychiatry, University of Pittsburgh School of Medicine; Janine D. Flory, Ph.D., formerly of Mount Sinai School of Medicine and now at Queens College, New York City; and Harriet de Wit, Ph.D., department of psychiatry, University of Chicago.

The research was supported by the National Institute of Mental Health and the National Heart, Lung, and Blood Institute, both of the National Institutes of Health, and by a NARSAD Young Investigators Award given to Dr. Hariri.