Multiple realities(covers information from several alternate timelines)
The brain stem was the part of a humanoid brain that controlled all vital functions.
When employed as an interrogative aid, Centaurian slugs attached themselves to a victim's brain stem and released a toxin that would compel answers. In 2258 of the alternate reality, Nero informed Christopher Pike of this quality when attempting to acquire the frequencies that would lower Earth's defenses. (Star Trek)
The psi-wave device used by the Prytt was connected directly to the brain stem. (TNG: "Attached")
In late 2366, the Zalkonian known as "John Doe" damaged his brain stem when his ship crash landed on a planet. (TNG: "Transfigurations")
In 2369, while performing an autopsy on Hon-Tihl, Dr. Julian Bashir noted that Hon-Tihl's membrane permeability in the columnar cells in his brain stem were off. (DS9: "Dramatis Personae")
In 2373, The Doctor's 'daughter' Belle's brain stem and motor cortex were compromised after she suffered a severe head injury. (VOY: "Real Life")