January 25, 2008
The memory lapses and 'senior moments' of normal advancing age may be due to communications breakdowns within the brain in otherwise healthy older adults, new research reveals. The cognitive decline and brain problems may occur even in the absence of Alzheimer's disease and other forms of dementia that ravage the brain more severely.
Comparing the brains of young and old, researchers at Harvard found that the cognitive "fog" that afflicts many otherwise healthy seniors, which may cause someone to forget where they put the car keys or the name of a familiar face, are linked to problems in the brain's white matter. The white matter in the brain is critical for transmitting information from one brain region to another, somewhat in the way the components of a computer might "talk" to one another to create a smooth flow of data. The study was presented in the medical journal Neuron.
The researchers found that in some older adults, there are communication disruptions in the flow of information from one part of the brain to another. Not everyone was equally affected, which may help to explain why some otherwise healthy people maintain sharper memories into old age than others.
"This research helps us to understand how and why our minds change as we get older, and why some individuals remain sharp into their 90s, while others' mental abilities decline as they age," said study leader Jessica Andrews-Hanna, in the department of psychology at Harvard. "One of the reasons for loss of mental ability may be that these systems in the brain are no longer in sync with one another."
The researchers assessed brain function in a sample of adults ranging in age from 18 to 93 using an advanced brain scan called functional magnetic resonance imaging, or fMRI. The technique uses radio waves and magnetic fields to measure blood flow in the living brain. When someone is concentrating to recite the name of an object or recall items on a list, for instance, blood flow to areas of the brain actively involved in thinking, memory, and recall increases. The scan responds by lighting up a video image of those areas of the brain using various colors.
The researchers reported an overall "dramatic reduction" in functional connections when they compared the performance on memory tests of the 38 men and women younger than 35 with the 55 adults aged 60 and up. Specifically, processing of information from areas at the front of the brain and the back of the brain was out-of-synch to various degrees in the seniors, compared with the young adults.
To rule out the chance that early, undetected Alzheimer's disease might be causing some of the memory problems in older adults, the scientists used PET scans, another advanced brain scan technique, to look for patterns of reduced blood flow consistent with Alzheimer's. They also did a separate imaging study on a small group of older patients for beta-amyloid plaque content in the brain. These patients did not have a build up of beta-amyloid or reduced blood flow in regions associated with Alzheimer's, thus making it unlikely that they suffered from Alzheimer's. They found that these otherwise healthy adults showed a loss of coordination between different areas of the brain, independent of the problems that occur with Alzheimer's disease. Individuals with the greatest degree of communication problems were, overall, most affected by 'senior moments' and other memory problems.
"Our present results, in particular the analysis of individuals without amyloid deposition, show that normal aging is associated with a form of system disruption that is distinct from that associated with Alzheimer's disease," the researchers wrote.
The research opens up new avenues of understanding into why we lose mental abilities as we age. Such basic research is critical for unraveling what goes wrong in Alzheimer's disease, and sets the stage for new treatments.
To learn more about Alzheimer's and the way basic research is helping to work for a cure, visit www.ALZinfo.org, The Alzheimer's Information Site.
Andrews-Hanna JR, Snyder AZ, Vincent JL, Lustig C, Head D, Raichle ME, Buckner RL: "Disruption of Large-Scale Brain Systems in Advanced Aging." Neuron, Volume 56, Number 5, December 6, 2007, pages 924-935.