Juggling several mental activities at once can be a challenge for even the brainiest among us, but for older adults multitasking is even trickier.
Now neuroscientists have figured out why the capability to multitask wanes with age. The cause is a mental "glitch," and the research could lead to novel ways to get past these glitches.
The capacity to hold and manipulate information in the mind for a period of time, known as working memory, is the foundation of all mental operations, from following the train of a conversation to carrying out the complex tasks of comprehension, learning and reasoning.
Research has suggested that, on average, we can hold four items in working memory at once. Studies have also found that multitasking adversely affects working memory regardless of age. Still, the many anecdotes one hears over the years of "senior moments" — where older adults forget, say, what they want from the fridge after getting a phone call — and recent studies suggest this impact grows with age.
To learn more about the brain networks involved with multitasking, scientists compared the working memory of 40 healthy volunteers: half whose average age was 25, and half whose average age was 69.
The volunteers watched a picture of a natural landscape and were asked to keep it in mind as their brains were scanned using functional magnetic resonance imaging (fMRI). During this period, which lasted 14.4 seconds, the participants were subjected to an interruption — an image of a face popped up, and the volunteers were asked to determine its sex and age.
Afterward, they were shown a picture of a landscape and asked if it matched the one they had originally seen.
As expected, the older volunteers had more difficulty correctly remembering what the original image looked like.
At first, one might think the problem started with the interruption — perhaps older adults focus more on interruptions than younger people do, taking mental resources away from working memory. However, scans of the fusiform face area, the part of the brain that analyzes faces, suggested both young and old paid equal amounts of attention to the interruption.
Instead, the problem apparently came after the interruption. The scans revealed that the older people’s brains failed to switch off the part of the brain paying attention to the interruption, and they also failed to re-engage a memory maintenance brain network devoted to the original task.
"The glitch has to do with how brain networks switch between tasks," researcher Adam Gazzaley, a cognitive neuroscientist and director of the Neuroscience Imaging Center at the University of California, San Francisco, told LiveScience.
The team's preliminary findings from an upcoming study suggest that such problems with multitasking do not start at any particular age but accumulate over time.
"Multitasking is being fed by a dramatic increase in the accessibility and variety of electronic media and the devices that deliver them, many of which are portable," Gazzaley noted. [ Digital Overload: Is Your Computer Frying Your Brain? ]
Given that people are now staying longer in the work force, he predicted that the problems posed by multitasking will become more apparent and important.
The researchers are now exploring the potential of software brain-training programs to help older people improve their ability to multitask.
"Understanding what's happening in the head could help us devise strategies to resolve problems with interference better," Gazzaley said.
The scientists detailed their findings online today (April 11) in the journal Proceedings of the National Academy of Sciences.