The brain is neither a solid nor a liquid.
The mechanical response of the brain to external loads is strain-rate dependent. Thus, a viscoelastic constitutive model can be used to describe the brain.
The following video by The Bentil Group illustrates the response of a pig’s brain to impact by a .177 cal pellet. Images were acquired at a frame rate of 100,000 frames per second.
NOTE: The meninges were not removed from the brain and can be seen tearing.