Bridging cognition and action: executive functioning mediates the relationship between white matter fiber density and complex motor abilities in older adults

Abstract

Aging may be associated with motor decline that is attributed to deteriorating white matter microstructure of the corpus callosum (CC), among other brain-related factors. Similar to motor functioning, executive functioning (EF) typically declines during aging, with age-associated changes in EF likewise being linked to altered white matter connectivity in the CC. Given that both motor and executive functions rely on white matter connectivity via the CC, and that bimanual control is thought to rely on EF, the question arises whether EF can at least party account for the proposed link between CC-connectivity and motor control in older adults. To address this, diffusion magnetic resonance imaging data were obtained from 84 older adults. A fiber-specific approach was used to obtain fiber density (FD), fiber cross-section (FC), and a combination of both metrics in eight transcallosal white matter tracts. Motor control was assessed using a bimanual coordination task. EF was determined by a domain-general latent EF-factor extracted from multiple EF tasks, based on a comprehensive test battery. FD of transcallosal prefrontal fibers was associated with cognitive and motor performance. EF partly accounted for the relationship between FD of prefrontal transcallosal pathways and motor control. Our results underscore the multidimensional interrelations between callosal white matter connectivity (especially in prefrontal brain regions), EF across multiple domains, and motor control in the older population. They also highlight the importance of considering EF when investigating brain-motor behavior associations in older adults.

Keywords: aging; executive functions; fixel-based analysis; motor control; white matter connectivity.

Figure 1

3D-view of the cortical regions of interest (ROIs) used for the targeted CC tractography (center) and the assigned fixels of interest (surround). OF = orbitofrontal cortex, PF = prefrontal cortex, Pre/Supl = premotor and supplementary cortex, M1 = primary motor cortex, S1 = primary sensory cortex, Par = parietal cortex, Occ = occipital cortex, Temp = temporal cortex, A = anterior, P = posterior, S = superior, I = inferior.

Figure 2

Relationships between prefrontal fiber density, executive functioning performance, and motor performance in older adults. Scatter plot and the best least square line for (A) executive functioning and (B) motor performance association with prefrontal fiber density, after accounting for the estimated total intracranial volume (TIV), are shown. Partial Pearson’s coefficients and the Bonferroni-corrected p-values are indicated. (C) Executive functioning performance mediates the relationship between prefrontal fiber density and complex motor performance in older adults. * p < 0.01.