Comparison of diffusion-weighted fMRI and BOLD fMRI responses in a verbal working memory task

Diffusion-weighted functional MRI (DfMRI) has been reported to have a different response pattern in the visual cortex than that of BOLD-fMRI. Especially, the DfMRI signal shows a constantly faster response at both onset and offset of the stimulus, suggesting that the DfMRI signal might be more directly linked to neuronal events than the hemodynamic response. However, because the DfMRI response also contains a residual sensitivity to BOLD this hypothesis has been challenged. Using a verbal working memory task we show that the DfMRI time-course features are preserved outside visual cortices, but also less liable to between-subject/between-regional variation than the BOLD response. The overall findings not only support the feasibility of DfMRI as an approach for functional brain imaging, but also strengthen the uniqueness of the DfMRI signal origin.

► We conducted diffusion-weighted fMRI (DfMRI) using a working memory task in human. ► DfMRI signal responded earlier than BOLD fMRI in all the core activated regions. ► Inter-individual magnitude variation failed to show correlation with BOLD. ► Spatial variation in response was prominent only in BOLD fMRI. ► These results have implications for unique origin of DfMRI signal change.