Take a glass of water and float something on the surface of the water. Turn the glass slowly and the object will turn with the glass. Now try turning the glass sharply and see how the object fails to turn with the glass.
Your brain (the object) and skull (the glass) behave in the same way. Hence the significant brain damage from high-torque rotation of a helmet with your skull strapped to it whilst your brain is not.
Myself, I stuck the camara mount on the bike fairing, not my helmet