Here's a video showing a helmet at work, I couldn't believe that he got up and finished the race and although he lost some time he didn't lose his current position. His head appears to take quite a shot into the pole. Also I never thought a helmet would help much in this type of impact as it's the side of the helmet that looks to take the impact.

https://www.youtube.com/watch?v=5q0eWT16IQY