I have never heard this comparison between CE and AD. I know there is a direct comparison in that both will show up as reduced brain volume in an MRI or such. There are different progression lines between CE and AD.

My memory is failing me as to the specifics but it goes something like this. In one, AD I think, memory deteriorates first with executive functioning deteriorating later. In CE, the pattern of deterioration is the opposite, executive function goes first, memory later.

My father passed away from CE but was lazily diagnosed as AD. His progression of symptoms was CE related from a statistical basis. He had to take early retirement at fifty-eight because his executive functions were failing him. He was a rocket engineer and could no longer prepare the status reports to required standards. His memory was still sharp and remained that way for another 10 to 15 years. This delayed his diagnosis of 'AD' until the last two years.

His CE was most likely caused by thirty to forty years of undiagnosed central sleep apnea. He would frequently stop breathing for two to three minutes at a time with this cycle repeating every six minutes or so. He refused to be tested in a sleep lab. He was a very independent and self sufficient man. The brain damage due to sleep apnea is diffuse similar to a diffuse axonal injury.

We all envied how he could take naps during the day with ease. Now we understand why he could.

There needs to be caution when considering the long term effects of PCS and CE. History of multiple head traumas are leading indicators of minimal recovery. Boxers have a different form of brain injuries that football players. Boxer have more axial damage. That means they get their brain twisted inside their skulls. This is a result of a hook to the chin. This quick rotation of the skull creates a vast amount of shearing and bruising action within the skull as the brain is grated against the protuberances inside the skull.

Studies have been done that show this axial damage is far worse for the amount of energy released against the skull. A straight on jab is far less damaging that the hook of equal force. It is understandable if one watches a boxing match and observes the punishment that can be taken on from straight on jabs and even an upper cut. Then a lone hook to the jaw and the opponent goes down.

There is also a big difference between quarterback concussions and those suffered by linemen. The linemen get repeated smaller impacts over the time of a single game. The quarterback gets infrequent impacts with most concussions coming from an impact to the back of the head as it hits the ground. Studies show that the repeated lesser impact have a more devastating result than the infrequent (less than one per game) hard tackle of the quarterback.

Troy Aikman may have substantial neuro-psychological deficiencies that do not show up in his football commentary. This would likely be due to what is called "over-learned skills." Over-learned skills are the last skills to be lost to dementia. They have been learned so many times and accessed in memory so many times that the memory access routes in the brain or many fold. This is how a person with a severe concussion can still walk easily or do manual tasks but may have problems learning new physical skills.

Troy was a lifelong student of the game. This provides for a great ability to recall and understand the football discipline.

I understand this personally because I suffer from this problem. I have high levels and numbers of over-learned skills but can struggle to learn a new skill.

Reading comprehension will require that I read an article three or more times before I retain the information. I have excellent retention once this critical mass of repetitions is exceeded. I also have excellent use of over-learned disciplines learned over a lifetime. Just don't expect me to learn anything after just the first try. It aint gonna happen. Been there. Done that. It is very frustrating.

It is important to understand that different brain functions have different abilities to withstand impact and recover. Redundancy is very common in memory functions. It is not so common in processing functions. Learning new ways to process is of greater likelihood that establishing the redundant memories.

I can substitute auditory memory for weaknesses in visual memory. This is a common outcome of occupational, speech and other therapies. Some will try to call this 'rewiring' but it is more like using a Stillson wrench when you have lost you Crescent wrench. Both will get the job done. The Crescent wrench is just easier to use.