A treatment chamber built by the Doctor in a possible future to extend the dying Kes's lifespan, which instead sent her consciousness travelling backwards through her own life.
The biotemporal chamber appears in the Voyager episode Before and After. In a future in which Kes has reached the end of the short Ocampa lifespan, the Doctor places her in a field intended to push her cells back to an earlier state and win her another year or so.
The procedure awakens chroniton radiation that has lain dormant in her body since a Krenim attack years before. Kes begins to slip backwards in time, living through moments of her life in reverse order: her grandson's youth, her daughter's birth, her marriage to Tom Paris and the Krenim assault itself.
In each period she must persuade the crew of what is happening, until the Doctor of an earlier year purges the radiation and she returns to her proper present.