View full lesson: https://ed.ted.com/lessons/what-happens-when-you-have-a-concussion-clifford-robbins Each year in the United States, players of sports and recreational activities receive between 2.5 and 4 million concussions. How dangerous are all those concussions? The answer is complicated and lies in how the brain responds when something strikes it. Clifford Robbins explains the science behind concussions. Lesson by Clifford Robbins, directed by Boniato Studio.