Department Sigma was a secretive and often independent department within Psi Corps established by Director Kevin Vacit to investigate means to increase telepathic abilities. Bureau 13 was either a subdivision of Department Sigma or another name for it. Though a full account of the department's activities are unknown, Sigma is known to have been heavily involved with elements of IPX, was present at the excavation of the Shadow Vessel found under Syria Planum in 2253 and was responsible for the experiments performed on Jason Ironheart and his friend. Until 2253, Department Sigma was headed by Natasha Alexander, formerly one of Vacit's most senior aids, until she was quietly assassinated by Director Johnston's faction within the Corps.
The Psi Corps sourcebook produced by Mongoose Publishing details the various experiments conducted by Department Sigma as well as mentions its sister agency, Shadow Science.