Ann McKee takes thin slices from each brain and applies a brown stain that will indicate the presence of a protein called tau, found in high levels in patients with Alzheimer's disease.
It's part of the research the Boston University neurologist and her colleagues are spearheading, analyzing the brains of former athletes.
In healthy brains, it takes a microscope to detect the presence of tau, Dr. McKee says. But in the brains of the former football players she has looked at, there was no need for one.
"The buildup of tau is so severe, the changes can be detected on the slides with the naked eye," she says.
"I've examined thousands of brains from individuals from all walks of life and from all ages, including centenarians, and you never see this profound buildup of tau protein in this distinctive pattern unless there is a history of repetitive head trauma."
Those results indicate a condition called chronic traumatic encephalopathy, or CTE, which has many of the same symptoms as Alzheimer's disease, including personality changes and dementia - symptoms that were manifested in some of the men whose brains she examined after their deaths. Until relatively recently, CTE had mostly been seen in the brains of former boxers.
Was it the accumulation of blows to the head that eventually led to the buildup of tau? Are some players more vulnerable, perhaps those with genes that make them more susceptible to Alzheimer's or other neurological diseases?
To answer these questions, Dr. McKee says she needs to examine the brains of many more former athletes who played contact sports.