As key neural circuits weaken with age, our brains call upon alternate pathways to pick up the slack, study says

October 24, 1999

WALTHAM, Mass.--New research being published this week indicates that when the human brain's important neural circuits no longer work as well as they should-- a normal side effect of aging--the brain can compensate by calling upon substitute circuits to pitch in. The finding suggests that our brains may constantly reorganize themselves throughout our lives in an effort to ensure peak mental performance.

The study, conducted by researchers at Brandeis University, the University of Toronto, and the Baycrest Centre for Geriatric Care in North York, Ont., is detailed in the Oct. 25 issue of the journal Current Biology.

The new research helps explain why some kinds of memory--most notably visual memory--appear relatively immune to aging's harmful effects on higher-order brain functions. The apparent reason: Older adults compensate for neural slowing by using different areas of the brain to recall what they've seen.

Robert Sekuler, a Brandeis neuroscientist and vision expert involved in the study, likens the brain's adaptation to weakened neural pathways to the reshuffling undertaken by a football team whose star quarterback is out of com-mission. "When the quarterback is hurt and the backup comes in, his skills may mean that the team must change its game plan, running the football more and throwing it less," says Sekuler, the Louis and Frances Salvage Professor of Psychology in Brandeis's Volen National Center for Complex Systems. "But the team's aim remains to play as well as possible--exactly the same goal the brain works toward when it calls upon these surrogate circuits to process visual information."

Sekuler and his Canadian colleagues made their surprising finding by devising a simple test of short-term visual memory, wherein a small number of older and younger volunteers compared patterns shown to them in rapid succession. While the volunteers scrutinized the patterns of vertical stripes, the scientists used positron emission tomography (PET) scanners, a technology that measures instantaneous blood flow in the brain, to determine which areas of their brains were active.

"These brain images showed that older and younger people depend upon very different brain circuits to remember what they've just seen," Sekuler says.

The younger study participants (ages 20 to 30 years) and the older subjects (ages 60 to 79) watched a computer monitor as patterns of vertical lines flashed briefly before their eyes; they were then asked to identify which of the pair of patterns featured more closely-spaced lines. The use of PET scans--which exploit the fact that when one area of the brain becomes highly active, blood rushes to that area within seconds to satisfy its increased metabolic demands-- made it possible for the research team to pinpoint areas of the brain whose nerve cells were used in recalling visual patterns.

Sekuler and his collaborators--Randy McIntosh of the University of Toronto and the Baycrest Centre for Geriatric Care; Allison Sekuler, Patrick Bennett, Cigdem Penpeci, and Natasha Rajah of the University of Toronto; and Cheryl Grady of the Baycrest Centre--now plan to probe the brain's normal limits of reorganization, and search for ways to push those limits through training. They'll also look at other important cognitive tasks to determine whether the brain might be encouraged to compensate in other functions beside visual memory.

The Alzheimer's Association of America, the Natural Sciences and Engineering Research Council of Canada, and the Medical Research Council of Canada sponsored the research.

Brandeis University

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