Emotional inhibitor

An emotional inhibitor was a device fitted into all Cybermen from Pete's World. It allowed a human brain to exist without suffering a "meltdown" of overwhelming emotions at what it had become.

Mickey Smith hacked into Cybus Industries' mainframe and located the code which all of the Cybermen's emotional inhibitors used (6879760) and texted it to Rose Tyler's mobile phone. The Tenth Doctor loaded it to the computer system. The code was shut down and the inhibitors turned off. All the Cybermen realised what they had become and died from the emotions they felt. (TV: The Age of Steel)

Soon after, a zeppelin was sent to the Cybus factory in Paris where it transmitted the same code. It disabled that factory's emotional inhibitor. (GAME: Save Paris) In other cases, a Preacher was sent into the factory to destroy the inhibitor with his firearm. (GAME: Cyber Assault)

The Cybermen of the Cyber Legions, who placed people into suits, also used emotional inhibitors. When Craig Owens fought back an attempt to convert him using the love for his son, this overloaded the emotional inhibitors of the six Cybermen trying to convert him, resulting in their destruction. (TV: Closing Time)

When Danny Pink was converted into one of Missy's Cybermen, his emotional inhibitor was off as he chose not to delete his emotions in the Nethersphere. This allowed Danny to retain control of himself, but in order to access the Cyberiad, he needed it turned on. Clara Oswald used the Twelfth Doctor's sonic screwdriver to turn it on, but Danny still retained control as his love for Clara overrode the inhibitor. Later, the Brigadier appeared and like Danny, he still retained control even with the inhibitor due to his love for his daughter. (TV: Death in Heaven)