Correlation of Brain White Matter Diffusion Anisotropy and Mean Diffusivity with Reaction Time in an Oddball Task

Background: Reaction time (RT) is a frequently used measure of information processing speed, but the underlying physiological and anatomical conditions are not yet fully understood. A correlation between measures of white matter (WM) ultrastructural properties and RT is expected-particularly for those WM tracts that are involved in the attentional system of the brain. Methods: Diffusion tensor imaging data were acquired in 43 unrelated healthy subjects (age: 22.7 +/- 1.8 years), and RT was measured during an attention-requiring visual oddball task in the same scanning session. Voxel-by-voxel and region of interest analyses were performed for the large association tracts. A linear regression model was used to correlate fractional anisotropy (FA) and mean diffusivity (MD) values with mean RT. Results: Our analyses revealed significant positive correlations between RT and MD in several WM association tracts, predominantly in the right hemisphere. To a lesser extent, significant negative correlations were found between RT and FA in right temporal WM. Conclusion: These findings suggest that subcortical ultrastructural properties of the dorsal and ventral visual stream are relevant with regard to information processing speed. Furthermore, MD appears to be more sensitive than FA in detecting functionally relevant ultrastructural variations in WM tracts. Copyright (C) 2009 S. Karger AG, Basel