In 2153, Captain Jonathan Archer's hippocampus became infected with a series of interspatial parasites which existed in a state of interspatial flux. The parasites inhibited Archer's ability to form new long-term memories, and proved impossible to eliminate with any traditional medical procedure. After twelve years, the parasites were finally eliminated through the initiation of a subspace implosion. Due to the parasites existing outside normal time, destroying the parasites in the present also had the effect of neutralizing them in the past, changing history in such a way as the infection never occurred. (ENT: "Twilight")