Diffusion fMRI Can Detect Neural Activation When the BOLD fMRI Response Is Abolished by Nitroprussiate

Tomokazu Tsurugizawa¹, Boucif Djemai¹, Luisa Ciobanu¹, Denis Le Bihan¹

Diffusion-weighted functional MRI (DfMRI) has been shown to be sensitive to neural activation, however, its vascular or non-vascular origin has been a subject of controversy. We have compared the DfMRI and BOLD responses at 7T in the rat brain during forepaw electrical stimulation with and without nitroprussiate, a neurovascular coupling inhibitor, and compared these responses with recorded neural activity. Under the nitroprussiate infusion, while the BOLD signal was completely suppressed, the neuronal activation and DfMRI signal were conserved, demonstrating that DfMRI includes a genuine diffusion component which directly reflects neuronal activation.