Why it's harder to multitask as you get older

There you are with a phone in one hand and a drawer handle in the other, and after reading a few incoming texts you've completely forgotten why you went to open the drawer in the first place. These kinds of moments that happen to all of us, even 20-somethings. They're related to natural brain aging.

A new study sheds light on why older adults have more trouble with multitasking than younger people. Research published in Proceedings of the National Academy of Sciences shows that the brains of older people, when interrupted, tend to have greater difficulty switching back to their original task than younger folks.

Interruptions are bad for everyone's working memory, or the ability to remember things over brief periods of time, study authors say. Through functional magnetic resonance imaging (fMRI), researchers got a clearer picture of why this is worse for older adults. The study compared brain activity in 20 healthy adults, with an average age of 69, to 22 healthy younger people aged 18 to 32. Participants were given a memory task, which was interrupted with another task, and then asked to return to the original activity.

It seems that both older and younger people direct about the same amount of attention to the interrupting task, but older adults run into more trouble when they need to let go of the interruption and reestablish the neural network associated with the original memory.

"We find that [in] older and younger adults both, their working memory performance is diminished by being interrupted, but older adults are impacted more," said Dr. Adam Gazzaley, study co-author and neurologist at the University of California at San Francisco.

There are still a lot of open questions about how this decline takes place. Unpublished data from Gazzaley's group suggest that a lot of the brain changes involved in multitasking may begin as early as the 20s and 30s. It may be even earlier - in general, depending on how you measure particular abilities, everything is downhill after age 18, says Dr. Barry Gordon, neurologist at Johns Hopkins School of Medicine.

Some mental abilities do improve with age, such as vocabulary and wisdom that comes from life experience, Gordon says.

"How you use your brain overall can get better, but the individual components of it are suffering a gradual decline," Gordon says.

Gordon likened an 18-year-old's brain to a brand new computer with nicely polished pieces, but which has not been trained to do anything. People, like computers, need a lot of different abilities, as well as training and experiences in them.

"It’s not a matter of raw power. It’s a matter of putting it all together," he said.

What can be done to preserve your mind as it ages? Scientists are working on a variety of therapies, both behavioral and pharmaceutical, that could help cognitive decline. Gazzaley's group's study could help those efforts, as it gives a better understanding of how multitasking difficulties work in the brain, said Dr. Scott Small of Columbia University Medical Center.

It’s turning out to be much more difficult than researchers thought to identify cognitive exercises that would help the aging brain stay sharp, Small said. There is no specific regimen of activity that has been proved to work so far.

Gazzaley's group is currently working on video games with the potential to improve these mental abilities in older adults. Small and colleagues, meanwhile, look to identify potential drugs, including food products already known to be healthy that could turn out to help the brain, he said.

All of this does bring up an ethical question: Should we be developing drugs for "normal aging," which is not a disease per se? The general feeling in the field is that it's OK, Small said. But the bar is even higher than usual to show that such a drug intervention would be safe, he said.

The bottom line: Avoid interruption if you need to get something done, says Gordon. Do one task at a time rather than trying to juggle them. And if you're trying to study for an exam, spread out the learning over a long period of time.