March 29/Vancouver/University of British Columbia -- Workers who thrive on difficult tasks lose their motivation when given stimulants such as caffeine and amphetamine, according to a study by University of British Columbia researchers.

Researchers divided rats into two groups based on their preference for high-difficulty/high-reward tasks or low-difficulty/low-reward tasks to determine whether certain drugs would affect them differently based on that personality trait, according to psychologist Jay Hosking, who executed the study with co-author Catharine Winstanley.

Bosses take note: the "worker" rats tended to choose the challenging task less often when given either caffeine or amphetamine. By contrast, "slacker" rats chose the challenging task more often when given amphetamines but showed no change when given caffeine.

Alcohol had no effect on the choices made by either the slackers or the workers, according to the study published in the journal Neuropsychopharmacology.

"In everyday life, things we want require effort. You can either work hard for the promotion, or you can slack off and take it easy and sit around the water cooler all day," said Hosking. "We wanted to tap into how individuals make those decisions."

Even in the rat world, some are go-getters and others would rather coast.

"Some animals are willing to work really hard at this task, and others are really happy to slack off and they are very stable in their choices," said Hosking.

The experiment was designed so that the rats' choice of tasks closely resembles the choices humans make about work -- in particular, choosing or not choosing tasks that require more attention and concentration -- and to gauge the effects of drugs such as caffeine and amphetamine that are used by humans to overcome the fatigue that results from mental effort.

"Amphetamine and caffeine turned the workers into slackers and amphetamine turned slackers into workers," he said.

The study says the animals respond differently to certain drugs based on their personality type has implications for the treatment of human illnesses that affect the "recruitment of mental effort" -- such as depression, post-traumatic stress disorder and attention deficit hyperactivity disorder.

"We need to look at individual differences when we design therapies, rather than just looking at the main effect of a drug on an entire group," he said. "If these results extend to humans, then maybe a cure isn't a one-size-fits-all kind of thing."

 From the March 29, 2012, Prepared Foods’ Daily Update