Age-related changes in brain metabolites underlie slowing of speed-accuracy trade-off

Aging leads to response slowing but the underpinning cognitive and neural mechanisms remain elusive. We studied cognitive components of response speed with a diffusion drift model to estimate nondecision, boundary-separation, and drift-rate contributions to choice reaction times of older (62-80 years) and younger (18-29 years) adults (n=25 each). We characterised age-related differences in the metabolic and microstructural profile of cortical regions and white matter (WM) pathways of visuo-perceptual and attention networks with magnetic resonance spectroscopy and multi-shell diffusion-weighted imaging. Aging was associated with increased non-decision time and boundary-separation, reduced N-acetyl aspartate (NAA) concentrations in anterior cingulate (ACC) and posterior parietal cortices, and reduced WM microstructure in the optic radiation (OR), inferior and superior longitudinal fasciculus (ILF, SLF) and fornix. NAA in ACC and diffusivities in OR and SLF predicted non-decision time, while restricted diffusivity signal fraction in the ILF and fornix, and diffusivity in OR predicted boundary-separation. These results suggest that age-related deterioration of neuronal health and WM microstructure in visuo-perceptual and attention networks contribute to response slowing in aging.