Here is some reading on that issue
http://www.fastcodesign.com/1671752/...ncussion-proof
How the best football helmets are designed, the challenges of protecting against concussion and also against major injury (fracture etc)
(BTW, the article says motorcycle helmets are designed for 18 mph impacts, which is misleading - 18 mph impact against a steel anvil is equivalent to an angled fall onto concrete at 60-70 mph or into an auto door or window at 30-40 mph.)
http://www.cycleworld.com/2013/01/04...et-technology/
A motorcycle helmet designed to protect against concussion, with an elaborate double-shell design
A similar football helmet was introduced a few years ago, Xenith X1, not sure if it has been successful
But these designs are impractical for bicycle use