Reduced White Matter Integrity Is Related to Cognitive Instability

Abstract

Increased performance variability has been demonstrated in several groups and conditions, including aging and cognitive decline. Structural brain characteristics underlying this phenomenon have so far been elusive. However, there is reason to expect that disconnectivity in associative pathways, whether caused by immature or degraded white matter (WM) tracts, will increase performance variability by neural noise. The aim of this study was to test whether the quality of WM, measured by diffusion tensor imaging, is related to performance variability in healthy adults. Intraindividual standard deviation of the reaction time (sdRT) across trials and median reaction time (mRT) from 270 participants were obtained from a speeded continuous performance task (Eriksen flanker task) with two conditions (congruent, incongruent). Tract-based spatial statistics was used to test the relationship with diffusion characteristics [fractional anisotropy (FA), mean diffusion (MD), radial diffusion (RD), axial diffusion (AD)]. Robust relationships between sdRT and all diffusion measures were found in most WM areas, independently of mRT, age, and sex. The effects were anatomically more widespread in the congruent than the incongruent condition, covering almost 50% of the voxels for RD and MD, and Ͼ25% of the voxels for FA and AD. Partial betas were in the range 0.45-0.55, and the strength of the relationships increased significantly with age. For mRT, the effects were smaller and unstable across condition. We concluded that performance variability is a likely consequence of individual differences in WM integrity, and that it is a promising behavioral correlate of individual differences in WM microstructure.

Associations between reaction time measures and white matter hyperintensities in very old age

“…Previous work suggests a dissociation exists between these RT metrics, with white matter integrity being associated with variability but not mean-RT (Bunce et al, 2010;Bunce et al, 2007;Fjell et al, 2011;Mella et al, 2013;Walhovd & Fjell, 2007) and in older samples with neuropathology, variability is a stronger predictor of group membership than mean-RT (e.g., Dixon et al, 2007). In contrast to this work, we found comparable results when using measures of IIV and mean-RT, and neither measure was uniquely predictive of WMH.…”

“…In healthy ageing, associations have been shown between IIV and white matter hyperintensities (WMH: Bunce et al, 2010;Bunce et al, 2007), white matter volume (Jackson, Balota, Duchek, & Head, 2012;Lovden et al, 2013;Ullen, Forsman, Blom, Karabanov, & Madison, 2008;Walhovd & Fjell, 2007) and diffusion tensor imaging metrics (e.g., FA -fractional anisotropy) (Deary et al, 2006;Fjell, Westlye, Amlien, & Walhovd, 2011;Mella, de Ribaupierre, Eagleson, & de Ribaupierre, 2013; Moy et al, 2011). Generally, RT variability and WMH in old age 4 these investigations show that greater behavioural variability is associated with poorer neuroanatomical integrity (i.e., increased WMH burden, reduced volume, and lower FA).…”

Becoming Consistent: Developmental Reductions in Intraindividual Variability in Reaction Time Are Related to White Matter Integrity

“…Only FA showed an age-independent relationship with IIV, with negative relationships in the splenium of the CC and in the left inferior fronto-occipital fasciculus. Fjell et al (2011) reported robust age-independent relationships between IIV and all tested DTI indices in 270 subjects aged 20 -83 years. Importantly, the two latter studies indicate that the associations between IIV and WM characteristics in adults are not restricted to the frontal lobes.…”

“…We administered a speeded version of the flanker task (Eriksen and Eriksen, 1974), similar to the task used by Debener et al (2005), Westlye et al (2009), andFjell et al (2011). An illustration of the task is shown in Figure 1.…”

“…Importantly, two recent diffusion tensor imaging (DTI) studies (Fjell et al, 2011;Moy et al, 2011) found relationships between performance variability and the quality of WM and that the strength of these associations increased in older adults. DTI is a neuroimaging technique that is sensitive to the self-diffusion of water molecules and provides quantitative measures of WM microstructural integrity and connectivity (Basser and Jones, 2002;Beaulieu, 2002;Le Bihan, 2003).…”