White matter
Multiple realities
(covers information from several alternate timelines)
White matter was a type of tissue present in the Human brain.
In 2256, medical scans showed that the white matter tracts in Paul Stamets' medial temporal lobe had been restructured as a result of his navigating the spore drive. Shortly thereafter, when the USS Discovery jumped to the mirror universe, Stamets suffered from white matter hyperactivity. (DIS: "Into the Forest I Go")