I'd like to point to and recommend the book;
"The Feeling of What Happens: Body and Emotion in the Making of Consciousness" by Antonio Damasio.
I read it a while ago, but my recollections are that his basic thrust was there are levels of structure (chiefly) in the brain which when damaged cause specific behavioural and reported conciousness alterations.
I remember that he mentioned a linguistic base for consciousness, but didn't believe it had much support, I don't remember why.
He describes three differentiable types of observed neural activity and offers an interpretation of each:
1) The proto-self which is largely status registers of the current state of the organism. A useful construct to maintain homeostasis but not conscious. The control structures of the body and brain maintain and update this construct via neural and humoral means.
2) Core consciousness which is a supervisor and observer of the overall state of the proto-self. It is created moment by moment by the proto-self state and is conscious, but not continuously.
3) Autobiographical consciousness wherein the self recognizes itself and forms interrelationships between self and environment. Lots easer to protect and maintain self if one recognizes there is a self to protect.
Personally, I believe there are observable structures of greater or lesser complexity than ourselves and that they may be considered alive, but I fail to see evidence that they exhibit a conscious self.
My operating definition of alive was stolen from my applied thermodynamics professor:
"Any system which focuses a stream of energy on itself to maintain or diminish its local entropy."
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