Functional localization of the human color center by decreased water displacement using diffusion‐weighted fMRI

Decreased water displacement following increased neural activity has been observed using diffusion‐weighted functional MRI (Df MRI ) at high b ‐values. The physiological mechanisms underlying the diffusion signal change may be unique from the standard blood oxygenation level‐dependent ( BOLD ) contrast and closer to the source of neural activity. Whether Df MRI reflects neural activity more directly than BOLD outside the primary cerebral regions remains unclear. Methods Colored and achromatic Mondrian visual stimuli were statistically contrasted to functionally localize the human color center Area V4 in neurologically intact adults. Spatial and temporal properties of Df MRI and BOLD activation were examined across regions of the visual cortex. Results At the individual level, Df MRI activation patterns showed greater spatial specificity to V4 than BOLD . The BOLD activation patterns were more prominent in the primary visual cortex than Df MRI , where activation was localized to the ventral temporal lobe. Temporally, the diffusion signal change in V4 and V1 both preceded the corresponding hemodynamic response, however the early diffusion signal change was more evident in V1. Conclusions Df MRI may be of use in imaging applications implementing cognitive subtraction paradigms, and where highly precise individual functional localization is required.