NEW YORK — Exploring the anatomy of attention, researchers have discovered that middle-aged people are more readily driven to distraction by interruptions because of age-related changes in how their brains work.
In research made public today, scientists at the University of Toronto and the Rotman Research Institute documented for the first time how age altered the brain's ability to ignore irrelevant intrusions.
"I have certainly found that as I have gotten older it is harder to deal with distractions," said lead author Cheryl L. Grady, 52, who studies the cognitive effects of aging. "This experiment tells me why that is. This is happening in my brain."
By scanning the brains of healthy young, middle-aged and elderly people, Grady and her colleagues detected a gradual breakdown in the brain circuits that maintain the normal balance of the attention span.
Two key regions of the brain that allow the mind to focus on a single task and tune out unwanted thoughts get out of kilter much earlier in life than previously suspected.
Normally, special neural circuits in the prefrontal cortex become more active when the mind pays strict attention.
At the same time, related brain areas in the medial frontal lobe -- thought to monitor more general background activity -- simultaneously slack off.
When the mind is at rest, the level of brain activity in those regions is then supposed to reverse.
The researchers discovered, however, that starting at about age 40, this seesaw pattern began to break down during memory tasks.
"It's known that older adults are more easily distracted. We think we've found a mechanism in the brain to explain this," Grady said. "The functional changes are detectable by middle age."
The study, funded by the Canadian Institutes of Health Research, is published in the Journal of Cognitive Neuroscience.
As a practical matter, many researchers are trying to learn whether multi-tasking techniques meant to improve communication and productivity could instead make people scatterbrained, leaving them lethargic and forgetful.
By one published estimate, the typical office worker is interrupted every three minutes.
Scientists from King's College at the University of London, for example, recently determined that people trying to juggle phone calls, e-mail and other routine office distractions suffered a greater loss of IQ than someone smoking marijuana.
Grady, however, suggested that people in their 20s today -- their brains molded by instant messaging and all of the other high-technology of the short attention span -- may be better able to manage unwarranted interruptions when they reach old age.
"If you are a 20-year-old today," Grady said, "you may find it easier to deal with distraction when you are 60 because you have had so much practice."