What would happen if you slowly crushed a live brain?
It seems there's way too many variables here.  Crushing can occur in a number of ways, leading to different primary damage in different regions first and different people have a different level of system failure thresholds.  

Technically, there are no pain sensors on the brain, so you wouldn't feel any pain in the classical sense.  However, it's hard to determine how you would affect the pain interpretation circuits (again, "crushing" can occur a number of different ways); you could inadvertently cause pain signals.  

Losing consciousness would also depend on when what region of brian is crushed.  And how it's crushed.  Most of our higher processing regions associated with consciousness are on the very outer surface of our brain.  In one scenario, if it just gets compressed, and damage tend to accumulate in the center of the brain first, it would be a different outcome than if it was some kind of shear crushing force that damaged outer brian first.