I can't get past the 3rd life support system. The first one is easy, just blow it up. The 2nd one, just pull the switch. For the third one I figured you have to get out of the labrynth chambers before they collapse and crush you but the layout of the rooms seems to change and I can never get out. What's the secret????????
PS cheating for invincibility doesn't work here either. I suppose I could levelwarp but that's boring, I want to beat it.

the room that is on the main floor by the brain leads to a room filled with three snippers on the right side. Shoot them to get to the switch on the left, ( it is behind you if you step into the room with the snippers.) Then shoot them again because they reappeared and hit the second button on the right side. After that, shoot them again and you have to jump on this narrow platform in the middle of the room to the side to get to the third button and run back to the area where the second switch is and hit the fourth button in that small room. This will cut the power. The snippers are still there so once again, shoot them and try to get on their platform and blow up the electric generator and a room will open, the alien brain dies. After that, I'm not sure what to do to deactivate the life support.