A study to be published today in the journal "Neuropsychopharmacology" has found that amphetamines, specifically speed, cause workers to slack off and slackers to work harder.

Caffeine, on the other hand, causes workers to slack off but doesn't seem to have any effect on slackers.

The findings have implications for people like long-distance truck drivers who use stimulants to remain vigilant for hours on end, said Jay Hosking, a PhD candidate and one of four people who worked on the project.

"What's working for some people may not be working for others," said Hosking.

The research took place at the university over nine months, starting in 2009, and involved 40 male rats.

Hosking said members of the team wanted to learn how people make decisions and why some people make different decisions than others.

"Every day at work and anywhere we're confronted with this thing where we can either work towards something or be satisfied with the status quo," he said.

At the office, the difference can be seen in people who are willing to work hard for a promotion and people who are just "happy to laugh and hang out in the office and check their Facebook every 15 minutes and get their wage."

Hosking said members of the team had to first determine what rats were workers and what rats were slackers.

They did that by devising an experiment that rewarded the rats for poking their noses into one of five holes when a light flashed for different lengths of time.

In the easy version of the experiment, the light stayed on for a longer period of time, but in the harder version, the light only flashed briefly.

Hosking said the researchers found a spectrum of behaviour, notably that some animals were willing to work harder than others.

He said they called the animals that didn't work hard "slackers" and the animals that worked hard "workers."

After identifying the different groups, the researchers injected the animals with amphetamines and caffeine.

"I think the most important thing to take away from this is that we don't all make decisions in the same way," he said. "Some of us are willing to put in that extra effort and some aren't. There's a whole spectrum of behaviour."

The findings also suggest specialists should be thinking about more personalized treatments for people battling psychiatric illnesses, said Hosking.

"One cure won't fit all is what it suggests," he said.

Hosking said he now wants to take a look at different areas of the brain and how they are involved in the "circuit of decision making."

Copyright The Canadian Press