The telencephalon (also known as cerebrum) was a part of the brain that encompassed the cerebral cortex.
In 2367, Nilrem was concerned that 'Rivas Jakara' – acutally Will Riker – might have suffered trauma to his telencephalon following a blow to the head. (TNG: "First Contact")
In 2368, Captain Jean-Luc Picard's cerebral functions were negatively affected by the Kataan probe but later were stabilized by Doctor Beverly Crusher and her medical team. (TNG: "The Inner Light")