How is the BOLD fMRI signal generated still remains unclear. By using a combination of simultaneous calcium imaging and fMRI, we studied the involvement of both astrocytes and neurons in blood flow regulation during electrical hindpaw stimulation in mice. The observed response duration varies based on the anesthesia used, however a strong correlation between astrocytic calcium and BOLD signal was present. Our method allows the study of neurovascular coupling mechanisms in the intact brain and points to the importance of astrocytes in this process, and can be further used to study BOLD signal alterations e.g. in models of neurodegeneration.