MRI Identifies Source of Cognitive Decline in Aging Brains

As people age, memory and the ability to perform tasks frequently decline. Scientists looking for ways to lessen that decline often have focused on the gray matter--the cortical regions where high-level functions such as memory are located. However, there is new evidence that the search may need to be expanded.

A new study by neuroscientists from the Massachusetts Institute of Technology (MIT; Cambridge, MA, USA) has found that memory and cognitive impairments have a closer association with the loss of brain white matter, which forms connections within and between brain regions

The researchers used a new magnetic resonance imaging (MRI) brain scanning technique, known as diffusion tensor imaging, to examine the white and gray matter of two groups of healthy adults--one group aged 18 to 30, and the other aged 60 to 85. They also measured participants' performances in three categories: memory for specific events, memory for vocabulary, and ability to plan and carry out everyday tasks.

"Historically, a lot of people have put their eggs in the gray matter basket. This study suggests that what might really be important are the connections and the integrity of the connections,” said Dr. David Ziegler, a graduate student in the department of brain and cognitive sciences and lead author of an article on the research that appeared in the online edition of the journal Neurobiology of Aging in December 2008.

Enhancing white matter in older individuals through drug intervention or changes in diet or cardiovascular fitness could offer a new approach to counteracting some of the cognitive declines that are typical of advanced age, reported Dr. Ziegler, who works in the laboratory of Dr. Suzanne Corkin, professor of behavioral neuroscience.

The study is the first to examine changes in both white and gray matter and correlate those changes with declines in memory and cognition, according to Dr. Ziegler. White matter is comprised of bundles of neuronal axons that form connections between neurons, allowing brain regions to communicate with each other. Gray matter, or cortex, is where the bodies of neurons are located.

In the older subjects, the researchers found a correlation between decline in cognitive performance and deterioration in the white matter of the frontal brain regions, where planning and executive functions are located. Correspondingly, deterioration of white matter in the parietal and temporal lobes, which are involved in memory, was associated with memory impairment.

"Thus, age-related impairments in specific cognitive capacities may arise from degenerative processes that affect the underlying connections of their respective neural networks,” the researchers wrote in their article.

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