The cerebral cortex is part of the brain.
This neurological location was where Ceti eels would wrap themselves around, in a humanoid host. This left said-host vulnerable to suggestion. As the eels grew, putting pressure on the cortex, the victim would experience maddening pain to the point of death. (TOS movie: The Wrath of Khan)
In 2273, Commander Spock's cerebral cortex was traumatized after a staggeringly powerful mind-meld with V'Ger; through the stored data pattern of what was once Lieutenant Ilia. (TOS movie: The Motion Picture)