The understanding regarding concussions and how the brain reacts is still up in the air. For example, the idea that suffering a concussion increases your chances for having another one is or is not true depending upon your definition of 'healed.' One thought is that you are at increased risk because of the chemical changes that can leave your brain debilitated for up to a year---having a previous concussion can make you more susceptible for another.
http://scienceline.org/2008/04/ask-heger-concussion/
There's a difference between healing and accommodation. Even those with severe brain injury can function as the brain accommodates for the injury with alternate neural pathways and connections. If you look at the outward behavior and actions of the injured person it certainly appears that they have healed. We've got a lot of extra wiring up there that can be used. The problem is there is no way to know the 'normal' way the person would have aged had they not experienced a concussion earlier in life. We write off deterioration in memory as something that happens with age---or is it the expression of damage done many years before that is showing itself?
It is the repeated damage that football players go through that leads to severe issues. Repeat concussions cause cumulative effects on the brain. Successive concussions can have devastating consequences, including brain swelling, permanent brain damage, long-term disabilities, or even death.
https://www.forbes.com/sites/carlos...term-effects-of-concussions-on-nfl-players/2/
Pretty certain that our man Rosen has read up on all this research----I would not be surprised if he calls it quits after his next concussion for fear of his future quality of life.