As a neuroscientist, I know that the gunk (technical term) in your head is kinda important. Thus, when you're riding a bike, it's a damn good idea to wear a bike helmet.
Since I've been riding in Berlin, I've noticed a few things about bike helmets. First, just about every kid on a bike is wearing a helmet. This is true for little ones riding in a kindersitz or little bigger ones riding on their own bikes. I have only seen rare exceptions to this, including two very little kids (one couldn't have been much older than 8 months old!), but with so many people riding bikes, you're bound to find some knuckleheads.
The situation with adults, however, is a completely different story. The vast majority of adults do not wear a helmet. Younger and older alike, I would say only about 20% of the adults I see are wearing a helmet. This is nuts. Many of the bike lanes in Berlin are simply just dashed lines running along the side of the road. And with so many uncontrolled intersections and clueless pedestrians, serious accidents must abound. And a bike offers no protection what so ever, and you can really get going at a very fast pace. AND the most likely part of your body to hit the pavement during a head-on collision (the most likely kind) is your HEAD.
I'm glad that many of the kids here wear helmets. But it's depressing that many of the adults do not. I can't imagine anything worse than a serious brain injury. Really, I think I would rather lose a foot or a hand than lose a part of my cortex. But maybe this is a Berlin thing. Are people in other parts of Germany more likely to wear helmets?