The frontal lobe was a part of the brain located at the very front of the brain.
In 2367, Dr. Beverly Crusher detected increased neural activity localized in Jean-Luc Picard's prefrontal and parietal lobes. This was as a result of Picard's Humanity reasserting itself after his assimilation by the Borg. (TNG: "The Best of Both Worlds, Part II")
The Ktarian game initiated a serotonin cascade in the Human brain, explaining why people were so interested in the game. (TNG: "The Game")
In 2373, The Doctor discovered strong evidence of telepathic activity in B'Elanna Torres' frontal lobe, indicating that she was experiencing implanted memories. (VOY: "Remember")