The brain being necessary for whatever consciousness is does not imply that consciousness resides in the brain much less anywhere else. To prove your claim you would first need a working definition of consciousness.
Super old thread now, but I resurfaced onto this site (And am happy to see it is still alive so that discussions around topics like this are not insta-banned) .
Maybe this will sound like a diatribe, and it is formulated as an argument, I will preface by saying I'm not an expert in these topics, but I'm also going to say noone is an expert on the topic of intelligence or consciousness, and anyone who claims to have conscious experience, or has possessed any form of thinking through what felt like a 'stuck-point' in their lives, to move past it, can have whatever opinions they want about both of these topics.
I really wanted to point out terminology like ''resides in the brain" when referring to consciousness is misleading. As
@eternalmelancholy points out, according to Anesthesiologists , and I think very very likely according to the vast majority of Neuroscientists, the subjective experience of reality we (many as far as we know) claim and seem to possess called "consciousness" , or in less cryptic and probably also less pretentious speak this (Feynman inspired phrase) "seat of the pants feeling" that we are "driving" our "selves" along as life unfolds, can be "turned off" so to speak. I think this is where Anesthesiologists must have the most personal experience with, as their patients upon receiving treatment and after I suppose may as well have not existed for that period of time, from their perspective (the patient) and the Anesthesiologist.
Further to this point, there must be and I do not know the names of but there are as you say, regions of the brain which substances that Anesthesiologists use in their practice make significant interaction with, which maybe in layman terms (or at least in terms I would usually think in so that I can understand what claims they are making, I am nowhere near these fields) even "turn down" or " switch off", so in this sense, and therefore it seems and it would be to me too initially intuitive that such regions are where whatever conscious experience is "lives'' or ''resides''.
What I want to understand now , (if my argument (which is about to come , ignoring these parenthesis) is flawed, despite me being unable to believe it is), is why this implies consciousness , assuming so I don't sound like a pedant (although I think the definition point is important) has already been defined adequately, as adequately as the first whole number 1 is defined , exists as an object, or is a collection of phenomenon that certain regions of the brain produces.
The reason I don't see these as the immediate conclusions is because of the whole 'brain could be a receiever' thing that you see now and again on the internet, I think espoused by John Lilly and maybe Terrence Mckenna at some points too. But this is not the entire reason at all.
What I understand of my own brain, is that despite not having an inkling of understanding of how its doing what its doing, at some basic level it processes sensory input/data/information, organizes it to some extent (potentially discarding or deprioritizing extraneous input, extraneous for whatever you need to survive or the task you have committed to currently at hand or whatever) , and then respond to it. I feel personally, this is how I have feelings, they often do feel spontaneous, but on some level it feels like I know that they are still responses to stimuli, and the brain is responsible for producing feelings in response to observed or unobserved stimuli, therefore in as much as, if "consciousness" at its bare bones is something akin (but surely much greater than) a single feeling, why can the brain not produce whatever it is, in response to observed or unobserved stimuli? This is now drawing from really old memories but I thought that's what were evolved to do, respond to stimuli, be it physical pain or mental, observed or unobserved.
In that case, if this is what happens, why do we not say things like "sadness" lives in the brain. Or "happiness" lives in the brain. At least I've not heard this said before to my current memory, surely we seem to agree that our brains are capable of producing such feelings, but it would seem that these productions are in response to stimuli promoting these states. What if whatever "consciousness" is, if we want to call it an object, is the source of or is the main source of the stimuli our brain responds to (on average) when/ to produce what we refer to as a "conscious experience".
But if that is the case, why are we not thinking about whether "happiness" , or "sadness" exist as objects at all. Or what the definitions of these things are, and why are we not wondering if there is a main/central source of stimuli that on average when received by a brain produces a state of "happiness" or "sadness", and if so why is it not a possibility that these sources should be if we want to call feeling ""x" an object, the definition of "x"", and "feeling x" the sequence of events occurring on average by animals capable of receiving stimuli from the source stimuli "x" (through the brain I suppose as far as we know, at least for humans) as a response to the stimulus obtained through stimuli "x".
So in that case what about simpler questions (seemingly simpler), what is the nature of any emotion/feeling at all, before consciousness, first? What about even philosophizing more about these things first over consciousness? Doesn't that even fit Occam's razor?
Now this is granting we have a working definition of consciousness, I don't think experts have one, here I am lumping in philosophers and mathematicians ,physicists into the equation to, anyone who has wrestled with the notions of things like ''truth" or "existence" or "provability" to me seem to be entitled to think and perhaps have a fresh perspective to bring to the table about this topic. Penrose points this out but I think it also occurs to perhaps many students of mathematics when they learn about things like computability and Gödel's incompleteness theorems. It seems sort of natural to question whether we really know anything in such an absolute sense, because these results question and in some sense say that there is no such thing as ''absolute truth''' even in the abstract formal sense, so how can there be anything close to this in the approximate truth sense in which empiricists deal with?
Anyway I want to reiterate the pretentious speak isn't something I can avoid when I try and engage in overly pedantic and likely very likely fallible attempts at making logical counterarguments on the internet, and isn't intended to put anyone here in low spirits, put anyone down, or make me feel better about myself , although admittedly typing this stuff out is fun for me on an intellectual level and is a nice distraction to woes that I am confident many people here experience more than me 100 fold in life.
Good day.