you have your direct impact. you got to remember, the brain is floating in water. so there is the direct hit and then actually the brain will ricochet and be forced on the opposite side will hit the brain. so the brain is literally bouncing against the skull. elisabeth: you receive the hit, it ricochets. then depending on the strength of the hit, what happens then? a lot of things can happen. a concussion can be very mild. it can be quite severe where there is injury to the blood vessels and there is bleeding. more swelling could take place. you can have swelling that takes place. you have to remember the brain is in a limited space. so if there is swelling, there is very little room for that to be accommodated. direct injury and also the secondary effects of a concussion. elisabeth: so you also want to show us a normal brain versus a concussion brain so we can get an idea of what happens. in this particular study, which is done with special mri s, you can see the deep struct