Please explain, then, how the consciousness of coma patients continues to exist without any of those inputs. And before you break out the tired "ah, yes, this is the brain synthesizing consciousness in the absence of said inputs, much like the way one hallucinates under sensory deprivation" please explain how the consciousness of briefly brain dead patients continues through their brain death. I've read into most of the modern theories of consciousness and they don't hold water when compared to our anecdotal, experiencial understanding of consciousness. We'll get there, but not until the scientific community experiences a massive paradigm shift.So each instant of consciousness integrates the smells, sounds and sights of that moment of experience. And consciousness is simply the feeling of this integrated information experience.
Many specific parts of the brain, and many non-specific parts of the brain, as well as parts that have nothing to do with the brain. The problem is that we see consciousness as a function of the brain, when it is not. It's a function of the organism, and perhaps, by extension, of the universe. No one can explain all of the anecdotal anomalies of consciousness (certainly there are many others besides just the ones you mention), because there's no working, accurate model of consciousness to begin with.But ask a neuroscientist to do the same for your own experience of the smell of chocolate—to somehow delete this—and he or she would be faced with an impossible task since the experience is correlated with many different parts of the brain.
What parts outside the brain are you referencing? The only way we can sense anything going on outside our brain is if we have a sensory apparatus transducing information from it and sending information up to our brain, and our experience of the smell of chocolate is no different - we have our olfactory nerve taking in the smell, our pyriform cortex processing it, and supplemental areas such as the hippocampus, amygdala, and association areas integrating it with our memories and emotions. If you're talking about memory, the current consensus is that it's distributed over the entire brain and is manifested in synapse changes, last I heard (motor learning especially, as it goes from requiring a lot of motor cortical involvement to being controlled by the spinal cord in many instances - cats can walk with support even after you transect their brain just above the brainstem). But it is a brain thing. From Wikipedia: In general, the more emotionally charged an event or experience is, the better it is remembered; this phenomenon is known as the memory enhancement effect. Patients with amygdala damage, however, do not show a memory enhancement effect.[33][34] Hebb distinguished between short-term and long-term memory. He postulated that any memory that stayed in short-term storage for a long enough time would be consolidated into a long-term memory. Later research showed this to be false. Research has shown that direct injections of cortisol or epinephrine help the storage of recent experiences. This is also true for stimulation of the amygdala. This proves that excitement enhances memory by the stimulation of hormones that affect the amygdala. Excessive or prolonged stress (with prolonged cortisol) may hurt memory storage. Patients with amygdalar damage are no more likely to remember emotionally charged words than nonemotionally charged ones. The hippocampus is important for explicit memory. The hippocampus is also important for memory consolidation. The hippocampus receives input from different parts of the cortex and sends its output out to different parts of the brain also. The input comes from secondary and tertiary sensory areas that have processed the information a lot already. Hippocampal damage may also cause memory loss and problems with memory storage.Brain areas involved in the neuroanatomy of memory such as the hippocampus, the amygdala, the striatum, or the mammillary bodies are thought to be involved in specific types of memory. For example, the hippocampus is believed to be involved in spatial learning and declarative learning, while the amygdala is thought to be involved in emotional memory.[32] Damage to certain areas in patients and animal models and subsequent memory deficits is a primary source of information. However, rather than implicating a specific area, it could be that damage to adjacent areas, or to a pathway traveling through the area is actually responsible for the observed deficit. Further, it is not sufficient to describe memory, and its counterpart, learning, as solely dependent on specific brain regions. Learning and memory are attributed to changes in neuronal synapses, thought to be mediated by long-term potentiation and long-term depression.
The consciousness of coma patients doesn't continue to exist because coma patients are, basically, unconscious. You may be thinking of individuals in a vegetative state, who exhibit varying degrees of it, but for various well-defined reasons cannot translate inner experience into outer expression. There is no such thing as a briefly brain dead patient, either. There is a specific definition of brain death that has to be observed using specific clinical symptoms, and brain death is permanent by virtue of the signs used in its diagnosis. You may be thinking of people who meet the clinical definition of death temporarily and who are revived. In that case, their brains are often doing some very interesting things with their lack of oxygen. (I have experienced a smaller version of this; I am prone to hypotensive states if I overexert myself or get blood drawn and I experience some really bizarre symptoms because blood is not getting to the parts of my brain that it needs to get to.) I think the issue with dealing with our anecdotal, experiential understanding of consciousness - c.f. why do we see the low end of the electromagnetic spectrum that we can see as red - is that we put too much emphasis on 'oh, we see it as red and not purple' and neglect the fact that this is how our brain is making sense of the difference between two wavelengths (and how about people who have different kinds of colorblindness? Surely the qualia people have considered that there are people who can't distinguish red and green). I mean, fundamentally our brains are electrical meat and there should be nothing mystical about it. EDIT: RationalWiki on qualia - http://rationalwiki.org/wiki/Qualia