Zom was a low-gravity planet and homeworld to a once violent criminal race with a population of 20 million. Beyond the city of Zombus the agricultural lands (used to grow Krakwheat) were mechanised and others were left as swamp. The Brains Trust were developed to find a solution to the problem and concluded the cause of all crime to be emotion. In the controlled enviroment of the City of Zombus emotion was removed. There was much resistance to the new ways that eventually meant that the people of Zom were fitted with cranial sockets at birth creating a direct link to the brain for the Harmoniser. In extreme cases a Ultra-Harmoniser was used for a full brain wipe. Emotion was later restored following the the Doctor's visit when the City was attacked by the Barabara. (DWM: City of the Damned)