White matter microstructure is associated with the precision of visual working memory

Visual working memory is critical for goal-directed behaviour as it maintains continuity between previous and current visual input. Functional neuroimaging studies have shown that visual working memory relies on communication between distributed brain regions, which implies an important role for long-range white matter connections in visual working memory performance. Here, we characterised the relationship between the microstructure of white matter association tracts and the precision of visual working memory representations. To that purpose, we devised a delayed estimation task which required participants to reproduce visual features along a continuous scale. A sample of 80 healthy adults performed the task and underwent diffusion-weighted MRI. We applied mixture distribution modelling to quantify the precision of working memory representations and guess rates, both of which contribute to observed responses. Latent components of tract-specific microstructural indices were identified by principal component analysis. Higher working memory precision was associated with lower bulk diffusion across ten tracts of interest and higher directionality of diffusion in a group of frontoparietal-occipital tracts. Importantly, there was no association between guess rates and any of the structural components. Our findings suggest that microstructural properties of white matter tracts connecting posterior and frontal brain regions mediate, in a functionally specific manner, the precision of visual working memory.