Inclusion criteria | Exclusion criteria | |
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All participants (N = 240) | Male; age 45–74; no contraindications for MRI, LP, or PET procedures; English as primary language; agree to all procedures; willingness to have and availability of a study partner (i.e., informant who knows the participant well, speaks or visits with participant at least weekly for a minimum of 6 months, is > 18 years of age, has English as primary language) who agrees to participate in a telephone interview and respond to a series of online questionnaires. | History of clinical stroke or significant neurologic condition; vision or hearing impairment severe enough to compromise neuropsychological testing; impaired decisional capacity to provide informed consent to participate in study; currently clinically significant infectious disease, endocrine or metabolic disease, pulmonary, kidney or liver impairment, or cancer; body weight > 400 pounds |
Unexposed group (UE) (N = 60) | No history of participation in organized contact/collision sportsa or military combat service or training; asymptomatic, based on telephone screening questionsb (asked of both participant and informant) regarding current mood, behavior, or cognitive symptoms, as well as functional dependence; have at least 2 years of post-secondary education at a 4-year accredited college/university, or have an associate’s degree | History of TBI or concussion; history of formal diagnosis or treatment of psychiatric illness or cognitive impairment; body mass index (BMI) < 24 |
Former college football player group (COL) (N = 60) | Played > 6 years of organized American football, with > 3 years at the college varsity level; played one of the following positionsc while in college: offensive lineman, defensive lineman, linebacker, offensive back or receiver, or defensive back (individuals whose primary position was kicker or quarterback were not included); no organized football or other contact/collision sport following college | |
Former professional football player group (PRO) (N = 120) | Played ≥ 12 years of organized football, including > 3 in college and > 3 seasons in the NFL; played one of the following positionsc while in the NFL: offensive lineman, defensive lineman, linebacker, offensive back or receiver, or defensive back (individuals whose primary position was kicker or quarterback were not included) |