Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

That whole paragraph would be an embarrassment to a reputable publication, but it's Cycling Weakly so no harm done.

"Concussion is caused by force, usually sudden deceleration acceleration, which may or may not be the result of a direct impact to the head. Therefore, a bike helmet cannot prevent mitigate concussion by reducing the acceleration...However, the primary role of a helmet is not to prevent concussion but to protect from structural skull injury to reduce acceleration"