disrupted. the outside of the brain may look fine, but the way the brain talks to itself, the connections might be interrupted. >> elisabeth: would a normal checkup show this? >> no. you would never be able to see it on a normal mri. >> elisabeth: when we talk about young players getting hit versus an adult, we're hearing young players taking adult size hits on their brains, what's the difference there and how does it impact a kid? >> in one hand, younger patients do very well in terms of recovery from all kinds of injuries. myself as a stroke specialist, young patients always do well. however, kids are more fearless. i think they're more apt to jump in. there is also a push for kids to be tough. you got to get back in the game. there is a lot of pressure to keep performing even though the patient might be impaired in many different ways than what would be obvious. >> elisabeth: the nfl is sustaining hits over time. so we have the statistics coming in aren't great. we've got discussions going on between the league and players. is it the amount of hits that occur over a period of time or is it the impact? >> this is a very important