Brain stem
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  of this quality when attempting to acquire the frequencies that would lower Earth's defenses. ()

The psi-wave device used by the Prytt was connected directly to the brain stem. ()

In 2366, the Zalkonian known as "John Doe" suffered damage to his brain stem when his ship crash landed on an unidentified planet. ()

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. ()

In 2373, The Doctor's 'daughter' Belle's brain stem and motor cortex were compromised after she sustained a severe head injury. ()

External links

de:Hirnstamm
Brain anatomy