The Hypothalamus is a region of the brain that secretes hormones, located above the pituitary gland in the Human brain.
In the Denobulan language, the phrase for "The Hypothalamus" is "Ya-sah degata". Phlox mentioned this while testing Hoshi Sato's Denobulan while she was recovering after being injured by a Romulan mine in 2152. (ENT: "Minefield", deleted scene)