Assessing the effects of age on long white matter tracts using diffusion tensor tractography

Abstract

Aging is associated with significant white matter deterioration and this deterioration is assumed to be at least partly a consequence of myelin degeneration. The present study investigated specific predictions of the myelodegeneration hypothesis using diffusion tensor tractography. This technique has several advantages over other methods of assessing white matter architecture, including the possibility of isolating individual white matter tracts and measuring effects along the whole extent of each tract. The study yielded three main findings. First, age-related white matter deficits increased gradually from posterior to anterior segments within specific fiber tracts traversing frontal and parietal, but not temporal cortex. This pattern inverts the sequence of myelination during childhood and early development observed in previous studies and lends support to a "last-in-first-out" theory of the white matter health across the lifespan. Second, both the effects aging on white matter and their impact on cognitive performance were stronger for radial diffusivity (RD) than for axial diffusivity (AD). Given that RD has previously been shown to be more sensitive to myelin integrity than AD, this second finding is also consistent with the myelodegeneration hypothesis. Finally, the effects of aging on select white matter tracts were associated with age difference in specific cognitive functions. Specifically, FA in anterior tracts was shown to be primarily associated with executive tasks and FA in posterior tracts mainly associated with visual memory tasks. Furthermore, these correlations were mirrored in RD, but not AD, suggesting that RD is more sensitive to age-related changes in cognition. Taken together, the results help to clarify how age-related white matter decline impairs cognitive performance.

Lifelong Bilingualism Maintains White Matter Integrity in Older Adults

“…1b). Note that the FA values in the genu of CC for both groups (bilinguals: M ϭ 0.47, SD ϭ 0.04; monolinguals: M ϭ 0.44, SD ϭ 0.03) were lower than those usually reported for younger adults (M ϭ 0.55, SD ϭ 0.04 from Davis et al, 2009), as would be expected.…”

The cognitive neuroscience of ageing

“…Some studies 49,55 have found that age differences in activation within PFC were mediated by white matter integrity, such that more intact white matter was related to more activation, but others have failed to find this effect 94,136 . Despite this inconsistency in results, the use of DTI to assess white matter integrity holds considerable promise for the study of cognitive aging, particularly as the integrity of specific tracts has been shown to be related to speed of performance in older adults 137 or to accuracy of performance [138][139][140] . Of particular interest will be studies examining the relations among white matter integrity underlying specific functional networks, functional connectivity in those networks, and how these measures are related to behaviour in older adults.…”

Age-related changes in human and non-human primate white matter: from myelination disturbances to cognitive decline

“…But, in a study with a larger subject pool, FA declined with age in the frontal, parietal, and temporal cortices and correlated with deficits in executive function (Grieve et al 2007). WM deficits were also found to occur to a greater extent in the anterior segments of fiber tracts in the frontal and parietal cortices and increased RD in the anterior tracts corresponded with worse executive performance (Davis et al 2009). Impairments in working memory, problem solving, and motor function were also correlated with an agerelated decrease of FA in anterior and superior fiber tracts, which was interpreted to reflect myelin damage and fluid accumulation in regions around the axon (Zahr et al 2009).…”