"A normal brain, that is, an individual that has had, does not have this injury or does not have any other condition, you shouldn't see any of this dark brown pigment," McKee explained.
"It would be completely white. None of this brown pigment would show up," she added.
But the darkened pattern on the brain is only seen in trauma, McKee explained.
Just this year, Dr. McKee has examined the brains of 16 former athletes, including 11 football players.
The results were shocking: they all had the brain disease, CTE. Her research was published in a leading medical journal in the field.
"I've looked at brains from people that have lived to be 110. And you just don't see anything like this, what we see in these athletes," she told Simon
Even more troubling, she says, CTE actually progresses undetected for years, silently eating away at brain cells, until it causes dementia and other cognitive problems.
"It seems to be triggered by trauma that occurs in a person's youth; their teens, their 20s, even their 30s. But it doesn't show up for decades later," she explained. "People think it's a psychological disease or maybe an adjustment reaction, maybe a mid-life sort of crisis type of thing. But actually, they have structural disease. They have brain disease."
Dr. McKee's research found that athletes in any contact sport are at risk of permanent brain damage.
The National Football League commissioned a telephone survey of 1,000 retired players that was released just two weeks ago. The study found the players under the age of 50 were 19 times more likely to have been diagnosed with dementia, Alzheimer's and other memory related diseases, compared to the general public.
But the NFL has taken issue with its own findings, saying in depth clinical research needs to be done to verify the survey.
60 Minutes asked the NFL for an interview. They referred us to Dr. Andrew Tucker, a member of the NFL's brain injury committee and the team doctor for the Baltimore Ravens.
"Do you not believe that multiple concussions can lead to later life dementia, depression, etcetera?" Simon asked.
"It's a risk factor, probably, for something that can happen later in life. I think the majority of athletes that play collision sports suffer a couple or a few concussions in their career and don't have any problems later in life. Some do. And I think one of the greatest challenges for the medical profession is to try to identify the people that might have problems down the road," Dr. Tucker said.