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A Natural Reward

By Jessica Tabak

Photo: Jessica Tabak

Photo: Jessica Tabak

As an undergraduate at Utah State University, Chesley Christensen, CAS '09, was intrigued by the question his Introduction to Psychology professor wrote on the board at the beginning of each class: Why do we do the things we do?

"That question is what really got me interested in psychology," he reflects. "It's pushed me ever since."

Christensen's graduate career has been characterized by this drive. In his five years at AU, he earned a psychology Master's degree and PhD and a Master's degree in statistics, coauthored six papers in peer-reviewed journals, presented at multiple national and international conferences, and won a $75,000 research grant from the National Institute on Drug Abuse. And this May, he added a 2010 University Student Award for Outstanding Scholarship on the Graduate Level—one of only two presented university-wide—to his already considerable achievements.

Christensen's psychology research compares the effects of drug rewards and "natural" rewards—like food, sex, and sleep—on rats, with the goal of determining whether drugs could reasonably be classified as addictive. "If drug rewards were shown to be more enticing than natural rewards, they could be considered distinct and thereby classified as addictive," Christensen explains.

He designed the experiments in two phases. For the first, he used a behavioral economic model to determine both a food and cocaine demand curve for each rat. "Basically, a rat would work in its cage and there was a certain 'price' we would require it to pay to earn either the food or the cocaine," Christensen says. These prices—measured by the number of times the animal needed to hit a lever in order to receive a dose of the food or drug—started low and increased over time in an effort to determine which substance it would pay more to receive.

The results? Food rewards were four times more powerful than the drug rewards. While these findings were in accord with previous research conducted on monkeys and humans, the degree of discrepancy was a surprise. "Food dominated cocaine," Christensen says. "It wasn't even close."

But Christensen was not ready to equate drug rewards with natural ones. He designed a follow-up experiment to determine whether increasing the animals' experience with cocaine would in turn increase the drug's power.

As it turned out, after the rats were given extended experience with the drug, the drug's power increased—but when the same experiment was done with food, the power of the food remained the same. As such, Christensen explains, "it becomes more and more difficult for the subject to choose natural rewards over drug rewards," thus indicating that, when framed in terms of increased experience, drug rewards were indeed addictive. Results from both phases of Christensen's experiment were published in Pharmacology, Biochemistry, & Behavior; Behavioral Neuroscience; and Psychopharmacology.

Since completing his degrees at the end of the fall semester, Christensen has worked as an industrial organizational psychologist—a job that entails going into an organization, determining its weaknesses and areas for improvement by measuring employee job performance, attitudes, and opinions and devising quantifiable action steps for the organization based on these data. With this marriage of his psychology and statistics training, "I get to apply everything that I've learned," he says. "And I really enjoy what I do."