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. (DW: 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. (VG: Save Paris) In other cases, a Preacher was sent into the factory to destroy the inhibitor with his firearm. (VG: 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. (DW: Closing Time)