Washington, November 26 : A Canadian study has provided further evidence that older adults are less capable than their younger counterparts in filtering out distracting information.
Scientists with the Rotman Research Institute at Baycrest have revealed that they made this discovery while scanning the brains of some research participants while they were inside the noisy functional magnetic resonance imaging (fMRI) scanner.
The researchers said that it was due to the annoying noise of the scanner that they could discover a unique brain activity underlying memory-encoding failure, which appeared to occur only in older brains.
During the study, 12 younger adults of average age 26 and 12 older adults of average age 70 participated in a face recognition task that involved having their brains scanned with fMRI, as they were shown pictures of faces and later again when trying to recall whether they'd seen each face before.
The study showed that when younger and older adults had difficulty encoding a new memory (certain face), which was marked by decreased activity in brain regions important for encoding, such as the hippocampus.
Though the researchers were not surprised by that finding because of an abundance of scientific evidence indicating the importance of hippocampus for making memories, they observed that the older brains showed additional increased activation in certain regions during memory encoding failure that was not found in younger brains.
"The older brains showed increased activation in certain regions that normally should be quieter or tuned down," said Dale Stevens, who led the study as a psychology graduate at Baycrest's Rotman Research Institute, with senior scientists Drs. Cheryl Grady and Lynn Hasher, both of whom are distinguished researchers in aging, memory, attention and distraction.
"The auditory cortex and prefrontal cortex, which are associated with external environmental monitoring, were idling too high. The older brains were processing too much irrelevant information from their external environment - basically the scanner noise," said Dr. Stevens, who is now a post-doctoral fellow in the Department of Psychology and Cognitive Neuroscience at Harvard University.
The researcher said that the younger brains did not show the abnormal high idling observed in older participants, during their failed memory encoding.
While older adults performed as well as their younger cohorts in the number of faces correctly recognized, the older adults forgot more faces overall than younger adults.
Dr. Stevens said that that was partially due to the inability of the older brains to tune out the distracting noise, when they were trying to form new memories of faces.
The researcher revealed that researcher participants are generally given ear plugs and cushions around the head and ears to block the "jack hammer" sort of noise the fMRI scanner makes, but older individuals complain more often than younger ones that the noise is irritating.
"Not only are we reporting new brain evidence of the well known problem of distraction in aging, but we show that the fMRI might inherently make older adults' cognitive performance worse than it would be in the real world, outside the scanner," noted Dr. Grady.
A research article was published by the Journal of Cognitive Neuroscience.