Imaging localized neuronal activity at fast timescales through biomechanics

Mapping neuronal activity noninvasively is a key requirement for in vivo human neuroscience. Traditional functional Magnetic Resonance Imaging has a temporal response of several seconds and therefore cannot measure high-level cognitive processes that evolve in tens of milliseconds. To advance neuroscience, imaging of fast neuronal processes is required. Here, we directly show in vivo imaging of fast neuronal processes at 100ms timescales by quantifying brain biomechanics noninvasively with MR-Elastography. We show brain stiffness changes of ~10% in response to repetitive electric stimulation of a mouse hind-paw over two orders of frequency from 0.1Hz-10Hz. We demonstrate in sedated mice that regional patterns of stiffness modulation are synchronous with stimulus switching and evolve with frequency. For very fast stimuli (100ms), mechanical changes are mainly located in the thalamus, which is the relay location of afferent input to the cortex. Our results demonstrate a new methodology for noninvasively tracking brain functional activity at high speed.