Lewiston Maine Police Department/AP
Robert Card is thought to have been exposed to thousands of low-level blasts in his time at an Army hand grenade training range, according to the Concussion Legacy Foundation.
CNN  — 

Tissue samples from the brain of the man who killed 18 people during a shooting rampage at a bowling alley and a restaurant in Lewiston, Maine, in October showed evidence of traumatic brain injury but not the neurological disorder CTE, according to the Concussion Legacy Foundation.

Robert Card, 40, was a US Army reservist and certified firearms instructor who’d been hospitalized and ordered to undergo a psychiatric evaluation about three months before the shootings. He had no combat deployments, according to records provided by the Army. Card died of a self-inflicted gunshot, and his body was found two days after the October 25 shootings.

The Concussion Legacy Foundation said in a statement Wednesday that Card is thought to have been exposed to “thousands of low-level blasts” in his time at an Army hand grenade training range.

Low-level blast exposure has been associated with symptoms that can include concentration and memory problems, irritability and slowed reaction times. Research has found that some people who have had low-level blast exposure, such as in the military or in law enforcement, have elevated levels of proteins in their blood that are associated with traumatic brain injury.

The Maine Chief Medical Examiner’s Office requested a postmortem study of Card’s brain from the Boston University CTE Center “due to the combined history of military experience and actions,” Lindsey Chasteen, the office’s administrator, said in a statement in December. However, she noted that the findings wouldn’t change the results of his autopsy.

The study found that “Robert Card had evidence of traumatic brain injury. … There was no evidence of chronic traumatic encephalopathy (CTE),” Dr. Ann McKee, director of BU’s CTE Center – which frequently collaborates with the Concussion Legacy Foundation – said in Wednesday’s statement. “These findings align with our previous studies on the effects of blast injury in humans and experimental models. While I cannot say with certainty that these pathological findings underlie Mr. Card’s behavioral changes in the last 10 months of life, based on our previous work, brain injury likely played a role in his symptoms.”

A traumatic brain injury usually results from a blow to the head or severe shaking forceful enough to shake the brain inside the skull. It can range from mild – also known as a concussion – to severe and cause symptoms including headache, dizziness, loss of balance, depression, anxiety, mood swings and behavioral changes.

Repeated brain trauma or shaking can lead to CTE, or chronic traumatic encephalopathy, a debilitating neurological disorder. It’s a form of dementia that can include symptoms of depression, anger and forgetfulness and is formally diagnosed only after death, through brain samples taken from an autopsy.

A federal law enforcement source told CNN that the Army gave Card a “Command Referral” to seek treatment after he said he was “hearing voices” and for having thoughts about “hurting other soldiers.” A National Guard spokesperson confirmed to CNN that Card was transported to the Keller Army Community Hospital at the US Military Academy for “medical evaluation” after Army Reserve officials reported Card for “behaving erratically.”

The US Army said in a statement Thursday that the CTE Center’s findings “are concerning and underscore the Army’s need to do all it can to protect Soldiers against blast-induced injury.”

The Army and the Office of the Secretary of Defense “are updating guidance on how to mitigate risks from blast overpressure,” the statement says. “In the near future, the Army will begin an Army-wide blast overpressure safety campaign to increase understanding of potential risks, direct risk mitigation actions, require documentation of training environments that exceed 4 PSI, and require tracking of exposed personnel.”

The Concussion Legacy Foundation said Card’s family is allowing study of his brain tissue to continue.

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“We want to begin by saying how deeply sorry and heartbroken we are for all the victims, survivors, and their loved ones, and to everyone in Maine and beyond who was affected and traumatized by this tragedy. We are hurting for you and with you, and it is hard to put into words how badly we wish we could undo what happened. While we cannot go back, we are releasing the findings of Robert’s brain study with the goal of supporting ongoing efforts to learn from this tragedy to ensure it never happens again,” the family said in the statement.

“We thank the Maine Chief Medical Examiner’s office for requesting the brain analysis. We know it does not fully explain Robert’s actions, nor is it an excuse for the horrific suffering he caused, but we thank Dr. McKee for helping us understand his brain damage and how it may have impacted his mental health and behavior. By releasing these findings, we hope to raise awareness of traumatic brain injury among military service members, and we encourage more research and support for military service members with traumatic brain injuries.”

CNN’s Carma Hassan, Haley Britzky and Nadia Kounang contributed to this report.