  The internal deformation of the brain is far more complex than the rigid
motion of the skull. An ultrasound imaging technique that we have developed has
a combination of penetration, frame-rate, and motion detection accuracy
required to directly observe, for the first time, the formation and evolution
of shear shock waves in the brain. Experiments at low impacts on the traumatic
brain injury scale demonstrate that they are spontaneously generated and
propagate within the porcine brain. Compared to the initially smooth impact,
the acceleration at the shock front is amplified up to a factor of 8.5. This
highly localized increase in acceleration suggests that shear shock waves are a
fundamental mechanism for traumatic injuries in soft tissue.
