Mind control was any method of influencing the actions of another sentient being. It could range from absolute control, where the subject has no will of his or her own, to more subtle forms, such as suggestion. Some forms of mind control leave the victim aware that he behaved against his will, while others leave him believing that his actions were his own. Mind control can be performed psionically or mechanically. Some Federation species, notably Vulcans, are able to perform very limited forms of mind control, more akin to strong suggestions. Mechanical mind control is beyond the generally available technology of the 24th century (but see neural neutralizer for an example of a 23rd century approach).
Mind control was sometimes referred to by the historical term brainwashing, a term that had fallen out of use by the mid-23rd century and that was called inaccurate by Data in 2367. (DIS: "Despite Yourself"; TNG: "The Mind's Eye")
During the 23rd century, the Manchurian test might be used to detect the installation of commands or personality engrams underneath a functioning consciousness. It was deemed highly effective. (DIS: "Despite Yourself")
- The neural neutralizer was a mechanism briefly employed at the Tantalus Penal Colony. It inhibited selected neural activity in a way that made the subject extremely suggestible. (TOS: "Dagger of the Mind")
- The self-aware computer Landru exerted absolute control over the entire population of Beta III for about 6,000 years. Kirk and Spock destroyed the machine to save their ship, and this freed its enslaved population. (TOS: "The Return of the Archons")
- Spock successfully induced a guard on Eminiar VII to enter the cell where the landing party was imprisoned to facilitate an escape. (TOS: "A Taste of Armageddon") He repeated this feat on a Kelvan, and nearly injured himself in the process; the sophistication of the Kelvan mind temporarily incapacitated him. (TOS: "By Any Other Name")
- The aliens Sylvia and Korob, encountered in 2267 on Pyris VII, employed a device called the transmuter to amplify their own will. Among other feats, this permitted them to enthrall visitors telepathically. Subjects were aware of who they were and their surroundings, but were entirely unable to resist the aliens' will. (TOS: "Catspaw")
- While restrained, Spock caused a native of Omega IV to operate his communicator, summoning help for the landing party. (TOS: "The Omega Glory")
- In 2285, Khan used Ceti eels to gain the cooperation of Captain Clark Terrell and Commander Pavel Chekov of the USS Reliant. However, both men fought against the eels' control of them; Terrell even committed suicide (vaporizing himself with his own phaser), rather than execute Admiral James T. Kirk as Khan had ordered him to do. After Terrell's death, Chekov collapsed in agony, whereupon the eel that had infected him – possibly sensing the death of its "brother" – crawled out of Chekov's ear and fell to the ground, where it was quickly vaporized by Kirk. (Star Trek II: The Wrath of Khan)
- Etana Jol attempted to use the Ktarian game to covertly take control of the Federation, prolonged use of the game rendering the player vulnerable to external suggestion as they became essentially addicted to the manner in which it stimulated the brain's pleasure center. (TNG: "The Game")
- Romulans working with Sub-Commander Sela used a mechanism that interoperated with Geordi La Forge's VISOR interface to brainwash him, exploiting the VISOR's pre-existing link to his brain, so he would obey the commands of a Klingon traitor. (TNG: "The Mind's Eye")
- A Thought maker is a form of mind control and it is dangerous to use. Thought makers are illegal to own on all Federation, Vulcan, and Ferengi worlds. Daimon Bok used it on Picard so he could get revenge for the Battle of Maxia where his son was killed. (TNG: "The Battle").
- In 2374, Chakotay was subject to a mind control technique by the Vori that trapped him in a simulation where he would eventually be compelled to act against their enemies, the Kradin, the program and his conditioning convincing him that they were more malevolent and dangerous than they were. (VOY: "Nemesis")
- In 2377, Bajoran Vedek Teero Anaydis used mind control in an attempt to incite a Maquis mutiny on the USS Voyager. He had implanted suppressed memory commands into Tuvok at a colony near the Badlands in 2370. The commands were triggered by a chant that was subliminally hidden in a letter sent to Tuvok, with Tuvok subsequently programmed to implant similar commands in the former Maquis via forced mind melds. (VOY: "Repression")