Brain activations during task are commonly investigated by gradient-echo functional MRI (GE-fMRI), which is sensitive to blood volume changes and blood deoxygenation. Recent studies have shown that diffusion MRI, which is regarded as static in the time-scale of minutes, might be sensitive to changes in activated areas. We investigated changes in signals acquired during a motor cortex paradigm using GE-fMRI and diffusion fMRI (dfMRI). We observed causality between the task and the dfMRI acquired at different diffusion weightings. These preliminary results suggest that the observed changes in the dfMRI signal might not be a pure result of blood volume alterations.