Berkeley -- The short-term memory problems that accompany normal agingare associated with an inability to filter out surroundingdistractions, not problems with focusing attention, according to astudy by researchers at the University of California, Berkeley.
Although older patients often report difficulty tuning outdistractions, this is the first hard evidence from functional magneticresonance imaging (fMRI) studies of the brain that memory failure owesmore to interference from irrelevant information than to an inabilityto focus on relevant information.
"Difficulty filtering out distractions impacts a wide range ofdaily life activities, such as driving, social interactions andreading, and can greatly affect quality of life," said study leader Dr.Adam Gazzaley, adjunct assistant professor of neuroscience at UCBerkeley and a newly appointed assistant professor of neurology andphysiology at UC San Francisco.
"These results reveal that efficiently focusing on relevantinformation is not enough to ensure successful memory," he said. "It isalso necessary to filter distractions. Otherwise, our capacity-limitedshort-term memory system will be overloaded."
The finding could mean that an inability to ignore distractinginformation is at the heart of many cognitive problems accompanyingaging, Gazzaley said, and suggests that drugs targeting that problemmay be more effective at improving memory than drugs that improvefocusing ability. He now is exploring the therapeutic role of differentmedications - including one of the main drugs to treat Alzheimer'sdisease - in older individuals with suppression deficits.
Because Gazzaley and his colleagues have identified areas ofthe brain that are markers for focusing and ignoring visualinformation, fMRI may be a good tool for assessing the value oftherapies designed to improve memory and for diagnosing attention andmemory problems in young and old, ranging from attention deficitdisorder to dementia.
"Is this a unifying mechanism that can account for broaderproblems regarding attention and memory?" asked coauthor Dr. MarkD'Esposito, UC Berkeley professor of neuroscience and psychology anddirector of the campus's Henry Wheeler Brain Imaging Center. "I thinkit explains a lot of it. If you are unable to block out distractinginformation, you can't really attend to what you are supposed to attendto, you can't get in what you are supposed to remember, and you have ahard time retrieving what you are supposed to remember. Rather thanthink of it as someone having an attention problem and a memoryproblem, you can just think of it as someone having one problem - theinability to filter out distracting information - that's affectingother domains such as attention and memory."
Gazzaley, D'Esposito, research assistant Jeffrey W. Cooney andgraduate student Jesse Rissman will report their findings in thejournal Nature Neuroscience, to be published online Sept. 11.
Gazzaley and his colleagues compared young adults aged 19 to 30with older adults aged 60 to 77 using a simple memory test thatintroduced irrelevant information. The tests were conducted whilesubjects' heads were inside a fMRI scanner so that activity in thebrain could be pinpointed.
While young subjects were easily able to suppress brainactivity in areas that process information irrelevant to the memorytask, older adults on average were unable to suppress such distractinginformation. Both groups were equally able to enhance brain activity inthe areas dealing with information relevant to the task.
Interestingly, six of the 16 older adults had well-preservedshort-term memory and no problems ignoring irrelevant information,suggesting that some people are able to avoid memory loss as they age.Gazzaley hopes to find out what makes these people different from theaverage aging adult.
"Encouragingly, a subgroup of the older population does notexperience this suppression deficit and accompanying memory impairment,opening the road for studies of successful aging," Gazzaley said.
Gazzaley, a neurologist who specializes in treating mildcognitive impairment common in older adults, set out to see howattention affects short term or "working" memory. He developed a testto distinguish two aspects of attention: the brain's ability to focuson a visual stimulus, and the ability to suppress or ignore othervisual information. He noted that both involve brain activity in thehigher level neocortex, acting on the visual cortex - a process herefers to as "top-down modulation."
The test involves presenting a sequence of four images, two ofthem faces and two natural scenes. Subjects were asked to remembereither faces, in which case the scenes were irrelevant information; orscenes, in which case faces were irrelevant. Subjects then were askedwhether a particular face or scene appeared among the four images. In aseparate test, subjects were asked only to observe the stimuli withoutattempting to remember them.
After first identifying with the fMRI the regions in the brainattentive to faces and scenes (they differ slightly in eachindividual), Gazzaley presented his subjects with the three tests andrecorded brain images in each case.
When asked to remember faces, young adults showed enhancedactivity in the brain area dealing with faces and decreased activity inthe area dealing with scenes (the parahippocampal/lingual gyrus).Similarly, when asked to remember scenes, they showed enhanced activityin the scene area of the brain and suppressed activity in the areadealing with faces.
Older adults, however, while showing comparable enhancement ofthe face area when asked to concentrate on faces, exhibited poor or nosuppression of the scene area, and vice versa.
"These data suggest that older individuals are able to focus onpertinent information, but are overwhelmed by interference from failingto ignore distracting information, resulting in memory impairment," theauthors wrote.
D'Esposito said that the technique Gazzaley developed to probefocusing and ignoring ability opens the door to numerous experimentsthat could shed light on a popular theory today - that problems ofaging have to do with a decline in the brain's frontal lobe.
"The frontal lobes are the highest level of cognition and thearea that integrates information from all over the brain," he said. "Ifyou look at the frontal lobes over time, that is the area where thereis more decline than any other part of the brain."
To shed light on this hypothesis, Gazzaley and D'Esposito planto look at patients with known or presumed frontal lobe damage, to seeif they also have problems with focusing or ignoring. Also, they planto look at people with attention deficit disorder, addiction problems,and mild cognitive impairment in search of evidence that these problemstoo are due to dysfunction of the frontal lobe.
"There may be unknown lesions in the frontal lobe that affectattention," Gazzaley said. "Aging is not a disease, but I think therelikely is a problem with top-down control that could be fixed withdrugs."
"If aging is a frontal lobe dysfunction, it is a mild form ofit," D'Esposito said. "And if we learn something about it, then we maybe able to help and know more about patient populations that have amore severe form of frontal lobe damage, like traumatic brain injuryand strokes and dementia."
The work was funded by grants to Gazzaley and D'Esposito from theNational Institute on Aging of the National Institutes of Health and bythe American Federation of Aging Research.
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