The authors have declared no competing interest. This research was funded by the National Institute on Alcohol Abuse and Alcoholism (U10AA008401 to BP, and R01AA030010 to JM and AA) and a National Institute on Aging administrative supplement (3R01AA030010-02S1 to JM). I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.