Certain mental tasks become more challenging as people age. But one researcher wondered if maybe there’s more to the story than simply a decline in cognition.

What about motivation? It's known to play a role in our ability to complete a task at any age, couldn't it also play a big role in people’s ability to complete tasks as they age?

“My research team and I wanted to explain the difference we see in cognitive performance in different settings,” said study author Tom Hess in a news release.

“For example, laboratory tests almost universally show that cognitive ability declines with age, so you would expect older adults to perform worse in situations that rely on such abilities, such as job performance — but they don't. Why is that? ”

Older people in particular need to feel personally involved with a given task in order to commit their full cognitive reserves to it.

It takes more mental energy for older people to perform a given task as well as a younger person, studies have found. It also takes more time for them to “recover” from this type of mental effort afterward. This being the case, Hess and his team thought that older people’s brains might be making “decisions” about what tasks deserve and don’t deserve attention.

The team had also noticed that people performed better on certain types of cognitive tasks — for instance, on those with which they had some personal connection. “Tasks that people found personally relevant garnered higher levels of cognitive performance than more abstract tasks,” said Hess.

That's why seniors who may struggle with a test question asking them to recall as many digits or letters they can are still able to remember a recipe, fix a radio or give accurate directions.

Hess has developed a theory of “selective engagement” to explain this effect. It suggests that older people in particular need to feel personally involved with a given task in order to commit their full cognitive reserves to it. The more relevant it is, the more likely they are to give it their full brain-power. And this explains why they might not perform so well on lab tests, even though they’re doing fine at work.

If you’re no longer motivated in the right ways, the theory goes, you might not perform so well on tasks that require extra brain-power.

The theory may suggest one way to help when people show the first signs of cognitive decline. If motivation is as important as (or more important than) actual mental ability, then using tools to enhance motivation might be effective in helping people stay mentally active for longer.

The study was carried out by a team at North Carolina State University and published in Perspectives on Psychological Science.