Age‐related mapping of intracortical myelin from late adolescence to middle adulthood using T₁‐weighted MRI

Abstract

Magnetic resonance imaging (MRI) studies in humans have reported that the T -weighted signal in the cerebral cortex follows an inverted "U" trajectory over the lifespan. Here, we investigated the T -weighted signal trajectory from late adolescence to middle adulthood in humans to characterize the age range when mental illnesses tend to present, and efficacy of treatments are evaluated. We compared linear to quadratic predictors of age on signal in 67 healthy individuals, 17-45 years old. We investigated ¼, ½, and ¾ depths in the cortex representing intracortical myelin (ICM), in the superficial white matter (SWM), and in a reference deep white matter tract. We found that the quadratic fit was superior in all regions of the cortex, while signal in the SWM and deep white matter showed no global dependence on age over this range. The signal trajectory in any region followed a similar shape regardless of cortical depth. The quadratic fit was analyzed in 70 cortical regions to obtain the age of maximum signal intensity. We found that visual, cingulate, and left ventromedial prefrontal cortices peak first around 34 years old, whereas motor and premotor areas peak latest at ∼38 years. Our analysis suggests that ICM trajectories over this range can be modeled well in small cohorts of subjects using quadratic functions, which are amenable to statistical analysis, thus suitable for investigating regional changes in ICM with disease. This study highlights a novel approach to map ICM trajectories using an age range that coincides with the onset of many mental illnesses. Hum Brain Mapp, 2017. © 2017 Wiley Periodicals, Inc.

Exercise and microstructural changes in the motor cortex of older adults

“…There was no significant change in VO 2 peak O 2 /kg within either group (passive control p = .17, exercise p = .6), nor with VT1 O 2 /kg (passive control p = .31, exercise p = .73), but there were increasing trends in the exercise group and a decrease in the passive control group in both measures. An average R 1 map for the control group is displayed in Figure , which resembles previously reported myelin maps (Dinse et al, ; Glasser & Van Essen, ; Marques, Khabipova, & Gruetter, ; Rowley et al, ; Shafee, Buckner, & Fischl, ).…”

“…In this study, we probed cortical microstructure using quantitative R 1 (1/T 1 ), as T 1 values have previously been shown to be spatially correlated with intracortical myelin levels in the common marmoset (Bock, Kocharyan, Liu, & Silva, ). Quantitative R 1 imaging and its related qualitative parameter T 1 ‐weighted imaging (T 1 W) have been previously used to study cortical microstructure, often in reference to intracortical myelin, in humans (Dinse et al, ; Ferguson et al, ; Fracasso et al, ; Lutti, Dick, Sereno, & Weiskopf, ; Rowley et al, ; Sehmbi et al, ; Sereno, Lutti, Weiskopf, & Dick, ). A benefit of R 1 over T 1 W imaging is that it provides a quantitative value that at a given MRI field strength is independent of the method of measurement and similar across studies (Trampel, Bazin, Pine, & Weiskopf, ).…”

Quantitative MRI provides markers of intra-, inter-regional, and age-related differences in young adult cortical microstructure

“…Previous MR studies have shown that myelination in humans begins in the subcortex (Partridge et al, 2004;Deoni et al, 2011;Barkovich et al, 1988;Nakagawa et al, 1998; for review, see Paus et al, 2001;Baumann & Pham-Dinh, 2001). Further, MR studies have found myelination of primary and association cortex progresses during childhood (Deoni et al, 2015;Dean et al, 2016) and adolescence (Grydeland et al, 2013), before age-related de-myelination begins during middle adulthood (Vidal-Piñeiro et al, 2016;Grydeland et al, 2013;Salat et al, 2009; see also Rowley et al, 2017). DTI investigations have also found that white matter structure within association cortex develops over extended periods, typically to beyond late adolescence (Klinberg et al, 1999;Barnea-Goraly, 2005).…”

Intra‐cortical myelin mediates personality differences

“…Recently, there has been a growing interest in assessing the content of intra‐cortical myelin via noninvasive but indirect neuroimaging techniques. While other quantifications of intra‐cortical myelin are under development (Alonso‐Ortiz, Levesque, & Pike, ; Does, ; Heath, Hurley, Johansen‐Berg, & Sampaio‐Baptista, ), previous magnetic resonance imaging (MRI) studies have shown that the ratio between the T1‐ and T2‐weighted MRI signal intensity can provide useful information regarding the neocortical myelo‐architecture (Grydeland et al, ; Rowley et al, ; Shafee, Buckner, & Fischl, ). The T1‐weighted and T2‐weighted signals are the two basic MRI signals which, respectively, relate to the spin–lattice and spin–spin relaxation time (the spin is the intrinsic rotation of protons while the lattice is their surrounding environment).…”

“…The MRI T1‐/T2‐weighted ratio also consistently estimates the relative changes in intra‐cortical myelin across the lifespan, that is, from childhood throughout adolescence to adulthood and old age (Grydeland et al, ; Rowley et al, ; Shafee et al, ). Variability in the T1‐/T2‐weighted contrast ratio has also been linked to individual differences in cognitive performances (Grydeland et al, ).…”