The 27-year-old who allegedly shot and killed four people at a Midtown Manhattan office building yesterday carried a note in his pocket saying he had CTE, a brain disease linked to repeated hits to the head. That's according to a police source who spoke to ABC News. There's no evidence thus far that the suspect had CTE, but it has sparked renewed interest in brain injuries and how they can affect a person's mental state.

Maria Shilaos spoke to Dr. Benjamin Christiansen, a clinical neuropsychologist at Ogden Clinic, to get more information on CTE and brain injuries overall.

Dr. Christiansen also talks about how we in Utah are doing when it comes to protecting our kids' developing brains.