Regenerative dissonance

Regenerative dissonance was a mental illness seen in Time Lords. It occurred when the personalities of a Time Lord's previous incarnations lived on inside the body of their current incarnation, exerting just as much influence on the body as the personality of the current incarnation. Time Lords known to suffer from this illness often committed suicide as they couldn't cope with the voices. (AUDIO: World of Damnation)

The Time Lord calling himself the Eleven by his eleventh incarnation suffered from this. (AUDIO: The Eleven) Other than him, the Time Lord who lasted the longest with this condition shot out both his hearts with a staser in his eighth body. (AUDIO: World of Damnation)

Neural inhibitors allowed users with regenerative dissonance to maintain control over the different personalities within their mind. The High Council gave the Twelve one as she went on a mission for them. (AUDIO: Planet of the Ogrons)