Degraded white matter causes slower brain function as people age
About half of a brain's volume is white matter, which connects different regions of the brain through networks to perform mental tasks. Using magnetic resonance imaging (MRI), researchers are now able to study changes in white matter and how they affect brain functioning. To determine the effects of age on white matter, researchers had 52 adults, aged 19 to 81, receive MRIs and participate in tests that involved multiple cognitive processes. Compared with younger adults, older adults were slower on tasks that tested processing speed, working memory, and cognitive flexibility, but not on tests that measured their episodic memory and ability to switch tasks.
The researchers found that white matter in specific brain regions was related to a participant's success with a task. For example, processing speed was slower when prefrontal and parietal white matter was degraded. Additionally, episodic memory was associated with temporal and medial temporal regions, working memory was linked to middle cerebral white matter, and executive function was mapped to the posterior brain. White matter is a densely packed collection of neurons that moves information between sections of the brain's gray matter. When white matter is degraded, it hampers transmission between the regions that support cognition. Older adults' brains may be forced to reroute information to compensate for poorly performing white matter, the researchers suggest. This study was funded in part by the Agency for Healthcare Research and Quality (HS13819).
See "Aging white matter and cognition: Differential effects of regional variations in diffusion properties on memory, executive function, and speed," by Kristen M. Kennedy, Ph.D., and Naftali Raz, Ph.D., in the February 2009 Neuropsychologia 47(3), pp. 916-927.
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