Default Mode Network On Drugs
If we can say that the ego has a location in the brain, it would be the default mode network. Its very active when you are doing nothing - its where self talk takes place. Default Mode Network regulates a lot of other parts of the brain - when drugs dials it down the rest of the brain is "let off the leash". Networks in the brain that don't generally communicate directly starts communicating directly. This can have an effect of jolting the brain out of bad habits.
This area will have a lot to do with your Self Concept.