Closetbiker,

I think on DAI we are saying the same thing; the head moves violently, and the brain impacts the inside of the skull, causing one of several types of brain injury, DAI included. No, it doesn't have to be an external impact, but it does have to involve severe change of motion and high G-forces in order to cause these kinds of brain injury. The most common way of this happening to a cyclist is if the head hits something, and rebounds. But it can happen to a baby that is shaken violently, or through a car accident. What happened to JWC was an instantaneous change in motion (an acceleration) to 20 mph from the side. This is a change in direction and motion of the skull, just as described by JWC about the egg in the bowl. What Brian says still stands--there can be no injury unless there is skull movement.

John