Using MR elastography, the shear modulus of a mouse brain was monitored during noxious stimulation. Localized changes in tissue elasticity of >10% were observed in previously identified regions associated with noxious stimuli. The observed mechanical response persists over two decades of stimulus frequencies from 0.1-10 Hz. This demonstrates the mechanism behind the change in stiffness is not of vascular origin, which has a much slower response than 10Hz. but rather is either directly related to, or tightly coupled to primary neuronal activity. This opens a new window to explore the spatio-temporal processing of signals in the brain.