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Distraction blamed for memory loss

1st December 2008

Researchers in Canada have found that the slowing down of cognitive functioning in older people is partly the result of less ability to screen out distraction.

In a study published in the Journal of Neuroscience, the team asked groups of young and old people to take a memory test.

During the test, they were inside an MRI scanner, so scientists could see which parts of their brain were working.

The brains of the older people were more responsive to knocking and buzzing sounds made by the scanner as part of its normal mode of operation.

They were more easily distracted by these extraneous stimuli, and performed worse on the tests than the younger participants.

Lead author Dale Stevens of the University of Toronto said the older brains showed increased activation in certain regions that should normally be quieter or turned down when concentrating on a task.

The findings echo other research, which has suggested that mental decline may be due to a decreasing ability to "tune out" irrelevant information from their senses.

Older subjects have been shown to be more likely focused on the background landscape of a picture than on a figure which is its focal point.

In the Toronto study, 12 old and 12 young volunteers were put into a MRI scanner while they were asked to perform a face recognition tests.

During the test, scientists were able to see which parts of the brain were activated during a particular activity.

Activity in the hippocampus, which is known to be involved in the laying down of memories, was one area of focus.

Failure to remember a face coincided with less hippocampal activity in both the old and young volunteers.

But failure in older subjects also coincided with increased activity in sensory processing areas of the brain which deal with stimuli coming in from outside.

In these cases, the auditory cortex and the pre-frontal cortex, showed more activity than in the younger group.

The brains of the older people were assumed to be processing too much unnecessary information - in this case the normal knocking and rattling sounds produced by the MRI machine.

The poorer performance of the older people might be due to an inability to "tune out" this noise while their brains were trying to form new memories of the faces, Stevens suggested.

Psychologist Jan de Fockert of the Institute of Cognitive Neuroscience at University College London, said it was possible that the brain lost the ability to inhibit processing of distracting stimuli with age.

"Selective attention", or the ability to focus on something in spite of distraction, might also be affected by an age-related decline in "working memory", needed to perform everyday tasks.

Such an ageing process might make it harder for individuals to pay close attention to one thing, Fockert said.

However, he said the Toronto paper did not prove that the problems with selective attention were contributing to poor performance in the memory tasks.

 

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