Slacker rat, worker rat

When it comes to intellectual challenges, rats, like people, fall naturally into categories of slackers and workers. And a shot of stimulant sometimes gets slackers to work harder while prompting the workers to ease off, researchers report online March 28 in Neuropsychopharmacology.

Hard work can come in many forms. Animal studies that explore the costs and benefits of such tasks usually involve rodents physically working, such as pushing a lever or scaling a wall for a reward. But those kinds of experiments don’t account for mental effort, says Jay Hosking of the University of British Columbia in Vancouver.

“We were trying to find something that modeled a little more closely what you see in the human experience,” Hosking says. “In everyday life, it’s the cognitive side where people really have to make those decisions, like whether you work harder throughout the day in hopes of getting a promotion, or coast through and check Facebook every 15 minutes and earn your wages.”

In the study’s rodent analog of a work day, rats poked their nose into one of five holes to indicate the location of a flash of light. By pushing a lever before the trial began, the rats chose either an easy version or a hard one. In the easy task, the light shone for a full second, making its location easy to spot. In the hard version, the light briefly flashed for a fifth of a second, a time so brief that the rats had to really concentrate to choose the right hole. The harder task came with double the sugar-pellet reward. 

When compared to the average behavior, some individuals reliably went for the easy version and collected their small reward. Other animals overwhelmingly chose the intellectually harder route. Not only do these divisions between what the team termed slackers and workers exist, the researchers showed, but the differences persist across many trials.

“This article opens up a new area related to mental effort,” says behavioral neuroscientist John Salamone of the University of Connecticut in Storrs. For instance, scientists can now start to explore the relationship between physical and mental work.

Giving rats the stimulants amphetamine and caffeine produced varied effects depending on individual’s personality, the team found. For slacker rats, amphetamine sharpened the mental work ethic, making the animals more likely to choose the harder task. But for workers, amphetamine caused the animals to choose the easier option more. Meanwhile, caffeine turned worker rats into slackers, but didn’t make the slackers work any harder. 

The researchers can’t yet explain why stimulants would cause workers to choose the easier task. One possibility is that hard workers are already performing optimally, so anything that swings the system out of whack, such as stimulants, could cause a net decrease in productivity.

More generally, the results show that drugs aren’t necessarily one-size-fits-all, Salamone says.