New study: Why the ability to multitask wanes with age

A new university study shows that as we age, it gets tougher to successfully “multitask,” or remembering to complete one task while distracted by another.

Using brain scans, a team of UC San Francisco researchers have discovered that people over age 60 are less agile in switching from one neural network to another — which means that brief attention-grabbing interruptions can undermine their ability to recall the original task.

“A lot of us feel the need to respond really rapidly to an email or text message,” said Dr. Adam Gazzaley, director of the UCSF Neuroscience Imaging Center and senior author of the study, which was published in Monday’s issue of the Proceedings of the National Academy of Sciences.

If we stop what we’re doing to send a reply, Gazzaley says, “there may be a price to be paid.”

While others have observed that aging adults experience difficulty completing a task after a distraction, no one had explored neurological science to learn why.

The problem is central to daily life as increasing numbers of digital distractions — such as electronic messages, alerts and feeds — demand our attention, interrupting the process of retaining information from deep learning.

The topic has growing relevance “especially as older adults stay in the workplace later “… and the societal expectations increase about how quickly we should respond” to interruptions, Gazzaley said.

In the study, the UCSF team compared two groups of healthy people, one averaging 24.5 years in age and the other averaging 69 years. Using “functional magnetic resonance imaging,” which reveals the activity of different neural networks, the team tracked and compared the blood flow in the participants’ brains.

Both groups were asked to view a natural scene, and hold it in mind for 14 seconds. But in the middle, an interruption occurred: a face popped onto the screen, and participants were asked to identify its sex and age. Then they were asked to recall the original scene.

Older people had more difficulty than younger people in maintaining the memory of the original image.

The brain scans showed why: Younger subjects could quickly disengage from the original image, respond to the interruption and then refocus their memory back onto the original scene. But older adults failed both to disengage from the interruption and re-establish the memory of the original scene. They continued to process the interrupted — and irrelevant — information, rather than suppress or forget it.

What’s to blame is not merely the memory, a problem familiar to many older adults, said Gazzaley.

Rather, it’s an impairment of the ability to shift between two neural networks: one for attention, and the other for memory.

“The impact of distractions and interruptions reveals the fragility of ‘working memory,’ ” he said.

Scientists speculate that the prefrontal cortex, which shrinks in volume as we age, may hinder the ability of the brain to “switch tracks” with agility.

It’s known that the brain retains a certain amount of plasticity in life — that is, it can be trained to respond to a faster pace. So there may be generational differences in our ability to multitask simply because younger people have more practice in handling interruptions, Gazzaley said. If so, perhaps older adults could be trained to better handle distractions, he said.

“We think that multitasking is a good thing, because it makes us more efficient,” he said.

“But this data suggests that performance declines when engaging in more than one thing at a time.”

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