Consider that your brain is an egg yolk floating in a shell. A concussion is the rapid loss of velocity slamming the yolk into the inside of the shell, scrambli

Consider that your brain is an egg yolk floating in a shell. A concussion is the rapid loss of velocity slamming the yolk into the inside of the shell, scrambling it up if you will. A helmet can't do much there except minimize the velocity a tad bit. The benefit of the helmet is prevent a crack in the shell, your skull, so your brains don't spill out onto the pavement in a crash. It's not perfect, but given your are traveling at high rates of speed on a hard surface, the insurance is your brain mostly intact inside the shell versus a scrambled mess on the ground. Preventing concussions - the yolk from slamming into the inside of the shell - is a hard problem. The brain is floating in liquid - the cerebrospinal fluid. To take another example, drop a ping pong ball into a glass of water. Now try to move fast without the ball hitting the side of the glass. The amount of padding on the outside of the glass won't do much to prevent the ball from hitting the inside of the glass. It's not just crashes you need to worry about. Even roller coasters cause concussions, albeit small ones, but still with cognitive decrements.