A T'lokan schism was a term in Vulcan medicine, referring to a condition where a previously inhibited traumatic memory was resurfacing. This caused disruption in memory engrams in the dorsal hippocampus, which in turn damaged surrounding tissue. In its advanced stages, memories and thought processes became confused.

There was no medical treatment for a T'lokan schism in the 2370s. Vulcan psycho-cognitive research recommended a mind meld with a family member. That family member then served as a pyllora, a guide, to help the patient bring the repressed memory into the conscious mind.

In 2373, Tuvok experienced the symptoms of a T'lokan schism as a result of a memory virus, which had disguised itself as a repressed memory. (VOY: "Flashback")