1. Cortical Physiology Section, NINDS, National Institutes of Health, Bethesda, MD 20892
2. Department of Neurology, Johns Hopkins University, Baltimore, MD 21287
3. Clinical Pharmacokinetics Research Laboratory, Clinical Center Pharmacy Department, National Institutes of Health, Bethesda, MD
4. Human Motor Control Section, NINDS, National Institutes of Health, Bethesda, MD 20892, USA