Whether it is mechanical (trauma), chemical (anaesthesia) or electrical - which part of the brain is shut down to cause loss of consciousness?
There is no widely-accepted neurological structure that mediates 'consciousness.' Even if some structures have been shown to be necessary for consciousness, they have not been shown to be sufficient. This is true with anesthetic mechanisms as well -- their ability to paralyze and block pain signals is fairly well-understood, but the mechanism of loss-of-consciousness is still unknown.
Still, 'consciousness' has to be there, somewhere between being awake and being dead, states which anesthetics can readily bridge (review):
Later in the same review:
This is consistent with my own take. Consciousness itself is the subjective experience of 'brain,' so it can't be lost, just poorly integrated.
Two structures are required for consciousness: the brain stem reticular activating system (RAS) and one cerebral hemisphere. e.g. a lesion in the RAS or bicerebral injury will induce loss of consciousness.