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Aging

Staying in touch

Nature Reviews Neuroscience volume 2, page 676 (2001)Cite this article

In cerebral white matter, axonal membranes and myelin restrict the motion of water, such that it tends to move in the direction of fibre tracts. In diffusion tensor imaging, this directionality can be quantified by fractional anisotropy (FA), which varies from zero (isotropic; equal diffusion in all directions) to 1 (unidirectional diffusion). A directionally averaged measure of diffusion — mean diffusivity — can also be obtained. If the integrity of a white matter tract is disrupted — for example, if the tract becomes demyelinated or less tightly packed — FA will decrease, whereas diffusivity will increase.

O'Sullivan et al. used these measures to examine the status of white matter in the brains of healthy volunteers. They showed that white matter FA declines with age, whereas mean diffusivity increases, consistent with an age-related deterioration of white matter tracts. When the sampled volume was divided into anterior, middle and posterior regions, they found that anterior white matter was disrupted most, whereas posterior areas were affected least; moreover, the integrity of anterior white matter seemed to decline more rapidly with age than that of more posterior regions. These data point to a selective disruption of frontal connections with advancing age, consistent with a progressive loss of executive skills, which are served by frontal cortical areas.

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References

ORIGINAL RESEARCH PAPER

  1. O'Sullivan, M. et al. Evidence for cortical “disconnection” as a mechanism of age-related cognitive decline. Neurology 57, 632–638 (2001)

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FURTHER READING

  1. Makris, N. et al. Morphometry of in vivo human white matter association pathways with diffusion-weighted magnetic resonance imaging. Ann. Neurol. 42, 951–962 (1997)

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  2. Tang, Y. et al. Age-induced white matter changes in the human brain: a stereological investigation. Neurobiol. Aging 18, 609–615 (1997)

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Authors
  1. Rebecca Craven
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Craven, R. Staying in touch. Nat Rev Neurosci 2, 676 (2001). https://doi.org/10.1038/35094527

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