This single-center, open label, randomized, 3-period cross-over study will compare 3 modified-release formulations of RO4917523 in healthy volunteers. Subjects will be randomized to one of six sequences to receive single oral doses of RO4917523 slow, target and fast release modified release (MR) capsules along with a reference intravenous microdose with the target capsule. A washout period of at least 21 days will occur between treatments.