Emotional inhibitor

An emotional inhibitor was a device fitted in all suits of Cybermen originating in Pete's World. It allowed a human brain to be installed into a suit and exist without the brain suffering a "meltdown" of overwhelming emotions at what they had become.

Mickey Smith hacked into Cybus Industries' mainframe and located the code on which all of the Cybermen's emotional inhibitors operated (6879760), then texted it to Rose Tyler's mobile phone, which the Tenth Doctor used to interface with the computer system. The code was shut down and the inhibitors turned off, resulting in all the Cybermen realising what they had become and dying from the emotions they felt. (DW: The Age of Steel)

Soon after, a zepplin was sent to the Cybus factory in Paris where it transmitted the same code, which disabled that factories emotional inhibitor. (VG: Save Paris) In other cases, a Preacher would be sent into the factory and destroy the inhibitor with their firearm. (VG: Cyber Assault)

The Cybermen of the Cyber Legions, who placed people into suits, also contained 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 that attempted to convert him, resulting in their destruction. (DW: Closing Time)