Mesiofrontal cortex

From Memory Alpha, the free Star Trek reference

The mesiofrontal cortex is an area of the Vulcan brain, responsible for the suppression of emotions.

In 2372, the Doctor detected a neurochemical imbalance in Lieutenant Tuvok's mesiofrontal cortex, after a mind meld with Lon Suder. This imbalance affected Tuvok's ability to suppress his violent impulses. (VOY: "Meld")