[1] VAMC, PADRECC, Houston, TX 77030 USA
[2] Baylor Coll Med, Dept Neurol, Houston, TX 77030 USA
[3] Indiana Univ, Sch Med, Dept Med, Indianapolis, IN 46204 USA
[4] Indiana Univ, Ctr Aging Res, Regenstrief Inst, Indianapolis, IN 46204 USA
[5] Richard L Roudebush Vet Adm Med Ctr, Hlth Serv Res Program, Indianapolis, IN 46204 USA