Volunteers (311 total: 180 women, 131 men) were recruited from a Plains Indian tribe living in rural Oklahoma. The mean (S.D.) ages of participants were; women: 44.0 (14.9) yrs; men: 41.7 (12.9) yrs. The study was approved by the Plains Indian Tribal Council. Probands were initially ascertained at random from the tribal register and the families of alcoholic probands were extended. Exclusion criteria included a history of brain trauma and neurological diseases, together with current use of psychotropic medications and evidence of alcohol intoxication or withdrawal at the time of testing. The study was carefully explained to participants and written informed consent was obtained according to a human research protocol approved by the human research committee of the National Institute on Alcohol Abuse and Alcoholism (NIAAA), National Institutes of Health (NIH). The protocol and consent forms were also formally approved by the Plains Indian Tribal Council.
