Picture this: a young, talented football player is just making his start in the NFL.

A 4th round draft pick by the New England Patriots, he signs a four year contract and quickly becomes one of the best in the league. He is a machine, an unstoppable force, critical in leading his team to a Super Bowl. He has a mansion, a fiancee and a new daughter, and a whole life ahead of him. But soon, that all comes crashing down around him.

This is the story of Aaron Hernandez. On June 26, 2013, at just 24 years old, Hernandez was arrested and charged for the murder of his friend, Odin Lloyd. Within two hours of his arrest and before he was even charged, his team had completely cut ties with him. On April 15, 2015, he was found guilty of first degree murder and sentenced to life without parole.

Four days after the 2-year anniversary of his conviction, Hernandez was found hanging by his bedsheets in his prison cell.

After his death, Hernandez’s family donated his brain to Boston University’s Chronic Traumatic Encephalopathy (CTE) center, in the hope that they might find some logical reason for why he may have committed the acts that led to his suicide.

Hernandez was found to have the worst case of CTE ever seen for someone his age.

He was diagnosed with stage three out of four of the disease, a diagnosis often given to someone aged 60 or older who has had the disease since their youth. Images of his brain provided by BU show large chunks of it seemingly missing, deteriorated by the disease.

New research has shown the prevalence of CTE in retired athletes who participated in contact sports. It is believed to be caused by repeated concussive and subconcussive hits to the brain. The action causes destruction of tissues in the brain, and the symptoms can include everything from mood and behavioral alterations to cognitive difficulties.

A football player may receive over a thousand of these hits in a season, said Dr. Robert Stern, a Boston University neurologist and researcher of traumatic brain injuries.

Unlike a full concussion, subconcussive hits have no symptoms and are therefore often not accounted for or treated. The repeated action of these hits takes a toll on the brain, causing CTE.

But CTE is a difficult disease. Though trial studies are in the works, there is currently no way to test for it in a living person, and symptoms appear differently in everyone. Because so little is known about it, scientists are still speculating about some of the potential risks the brain damage could cause.

A 2016 study by the Center for Disease Control (CDC) and National Institute for Occupational Safety and Health (NIOSH) found that players in the NFL were at a lower risk for suicide than the general population.

This study specifically looked at causes of death from suicide among 3439 retired NFL players who played at least five seasons from 1959-1988. NIOSH first conducted this study in 1994 based on a request from the NFL Players Association.

“NIOSH planned at that time to do a follow-up study, and reanalysed the data for these same players 16 years later,” said Douglas Trout, Deputy Director of the NIOSH Division of Surveillance, Hazard Evaluations, and Field Studies. “…Because, to date, few studies have examined suicide and suicide risk factors in sports cohorts, we decided to pursue this within the cohort we were already studying.”

It took into account no other factors, such as genetic history or the psychological state of any of the players. It also did not examine results in short term, high school, or college players, nor does not determine why any of these players took their lives.

An additional 2016 study published in the Canadian Medical Association Journal, however, found that someone who was diagnosed with a concussion on a weekday had three times the risk of suicide than the general population. Those who were diagnosed on a weekend had four times the risk.

It examined over 235,000 patients who were diagnosed with a concussion in Ontario between 1992 to 2012. This study took into account several factors, such as depression, income, and gender. It also looked at whether the concussion occurred on a weekend or weekday.

As most contact sports events, most notably the NFL, play on weekends, there is the potential that these athletes are at a greater risk, said Dr. Michael Fralick, a Harvard Researcher and contributor to the aforementioned study. In addition, the majority of football players have suffered many concussions in their career.

Most of those who suffered concussions on weekdays were involved in workplace accidents, versus the weekends when most incidents were recreational.

As the study explains, “The risk of a second concussion, use of protective safeguards, propensity to seek care, subsequent oversight, sense of responsibility and other nuances may also differ for concussions acquired from weekend recreation rather than weekday work.”

As the NFL is a professional organization with career athletes; however, concussions are monitored to a more severe degree, much like a workplace accident for a regular civilian. But this does not account for the sub-concussive hits that cause CTE, which are not monitored by the NFL.

Boston University’s Stern also said that in some cases of CTE,  there are damages to parts of the brain that control impulse and emotion.

“If you have someone who has increased emotional stuff going on and they lack impulse control, they lack the ability to stop an impulsive behavior, and perhaps another part of their brain that is responsible for judgement is impaired, that can be a really bad combination,” he said.

There is one general idea that these scientists can agree on, however. As said by Fralick, suicide is rare and complex, and whether or not there is a direct link is still not known.

“We showed an increased risk of suicide from concussions, but it was a relative risk,” Fralick said. “Most people who we studied did not commit suicide. But that doesn’t mean this is not an important issue.”

Trout also added that more research is needed before any solid conclusions can be made.  “Studies of the psychological health of living players occurring over long periods of time… are needed before reliable conclusions can be drawn on the relation among football play, concussion, CTE and suicide,” he said.

In order for more to be understood, however, scientists still need to develop a way to find the disease in living people. The DIAGNOSE CTE (Diagnostics, Imaging, And Genetics Network for the Objective Study and Evaluation of Chronic Traumatic Encephalopathy) project is devoted to doing this.

Funded by the National Institutes of Health, the study will take men between the ages of 45-74 who were in the NFL, played college football, and never played any contact sports, and run a series of tests to try to find any possible correlation between their athletic history and brain function.

According to Stern, scientists are currently developing a serum that will attach to the proteins that cause CTE, making them temporarily radioactive. The radioactive proteins will then be able to be picked up by a PET scan, where they will be compared to a normal image of the brain taken in a CAT scan.

So how can CTE and concussions be prevented? Stern simply replied, “Not hitting heads.”

“The brain is such an important organ,” he said. “It controls whether we move, whether our heart beats… It’s also responsible for our personality. [CTE] can hurt anything and everything about us.”