The limbic system was a set of brain structures which seemed to support a variety of cerebral functions including emotion.
In 2153, T'Pol was infected with a microbe which caused damage to her limbic system by triggering pon farr (ENT: "Bounty")
In 2372, the neuropeptide levels in Tuvok's limbic systems decreased by 15 per cent, after a mind meld with Lon Suder. (VOY: "Meld")
In 2375, Julian Bashir believed that a slight elevation in Sarina Douglas' norepinephrine levels was probably due to limbic overcompensation for the new thalamic connections. (DS9: "Chrysalis")