Primary Aims: 1. To perform a 5-year study in which three consecutive days of DAR-0100A at a dose of 15 mg or placebo are administered intravenously over 30 minutes to 60 patients with SPD (12/yr) in a between-groups, randomized, double-blind design. Cognitive testing will be performed at baseline (Day 1) and on the third day of drug/placebo administration (Day 4). Subjects will return at Day 15 to receive drug (if randomized initially to placebo) or placebo (if randomized to drug) in a double blind fashion in an identical protocol. This allows all patients to receive drug for Secondary Aim 1 while maintaining the blind. Baseline (Day 1) and repeat cognitive testing (Day 4) is also administered to 60 healthy controls per year (12/yr). The cognitive tests of working memory serving as primary outcome measures will include the modified AX-CPT (d'), the N-back (% correct at the 2-back condition), the DOT Task (distance error at 30 second delay - no delay), and the Paced Auditory Serial Addition Task (PASAT)( correct responses). The investigators will also include other tests of memory, executive function, and verbal learning for secondary outcome measures (see Methods) as well as comparison tests not hypothesized to change with drug: the Benton line orientation test (JLOT) and the Trail Making Test A. 2. To compare changes on the primary outcome measures from baseline to Day 4 testing between drug and placebo administration in SPD subjects. 3. To compare primary outcome variables at baseline and change from baseline to Day 4 testing between patients groups and healthy controls. 4. To obtain plasma DHX concentrations on Day 4 to evaluate plasma concentrations in relation to cognitive changes as a potential covariate.