[1] Johns Hopkins Univ, Sch Med, Dept Neurol, Baltimore, MD 21205 USA
[2] Johns Hopkins Univ, Sch Hyg & Publ Hlth, Dept Mol Microbiol & Immunol, Baltimore, MD 21205 USA
[3] Natl Neurosci Inst Singapore, Singapore, Singapore
[4] NIH, Cent Nervous Syst Studies Lab, Bethesda, MD 20892 USA