It's generally accepted that information sharing between distant cortical regions is a hallmark, if not the mechanism of consciousness. From there, there are many takes on that idea.
Really, though, it helps to understand what led to the idea if you want to understand the scope of the theory. The first models of consciousness actually weren't; they were instead models of attention and executive control, but researchers began to tease out both the function and hallmarks of conscious processing in these theories.
In the late 50's, Broadbent published on the famous "cocktail party effect", which basically states that bottom-up (extrinsic) attention can cause interrupts. In other words, you can be engrossed in a conversation, but still immediately notice your name being called out from across the room. He proposed a simple model that involves two steps:
1. a set of parallel sensory buffers that store information temporarily (later became sensory memory, e.g. iconic memory)
2. a unique, limited-capacity "perceptual system"
The big idea is that certain operations can take place in parallel, while others are strictly serial in nature. Things like speaking are serial, but extrinsic attention is parallel and can quite literally interrupt a conversation. From there the model was refined in several ways:
Baddeley and Hitch (1975) propose that between each processing step is a "loop" (the most famous of which is the phonological loop) that maintains information by rehearsing. The "central executive" then coordinates, selects, and triggers the maintenance and activity of the peripheral systems that implement the buffers. We now have a basic theory of multitasking by context-switch.
Norman and Shallice (1986) further clarify the distinction between automatic, non-conscious processes and voluntary, consciousness-dependent processes. This distinction is what sets the stage for modern, neurocomputational theories and models of consciousness.
To review, each of these models has the following in common:
1. A central (albeit ill-defined) component that is associated (albeit incidentally) with conscious perception and deliberate behavior.
2. The notion of an "observer" entity that issues command & control operations. (Note: the philosophical criticisms on this particular point are largely responsible for the ensuing paradigm shift, see Daniel Dennett)
3. Some independent, parallel functions. I like to think of them as goroutines.
The modern take is that there is indeed a distinction between automatic-and-parallel processes and their voluntary-and-serial counterparts. The shift is in understanding the nature of this serial controller. We no longer see it as a volitional homunculus, but essentially as a router.
The idea was first formally proposed by Bernard Baars (1989) and is called the "global neuronal workspace" theory. The idea is that there are hundreds (if not thousands) of independent local cortical processors that perform specialized tasks, in parallel. Consciousness, then, is the act of allowing these processors to communicate with each other through long-distance cortico-cortical connections (in particular, a fronto-parietal network of pyramidal neuron axons... but I digress), and this routing/broadcast structure is called the Global Neuronal Workspace (GNW).
From there, there are many schools of thought about how local information is granted access to the machinery of consciousness. My Ph.D explores the theory that attention may be the gatekeeper of mechanism, the implication being that attention must intervene in order for consciousness to occur. Here's our latest publication, which shows that retroactively orienting attention towards an unseen stimulus can render it conscious after the disappearance of the physical source: http://goo.gl/dYdRcl The implication is that we have a "pre-conscious" (see: http://goo.gl/xQXjGe for an explanation of the term pre-conscious) stimulus encoded into the visual system, that is not consciously perceived, and that will never be consciously perceived unless acted upon by an outside force. We show that attention can serve as this outside force, thus arguing in favor of the GNW by virtue of the fact that no other theory posits such a level of access control on the machinery of consciousness.
>I find it interesting to consider but have a hard time understanding how the brainstem fits into this.
I suspect much of the confusion is related to terminology: you have to distinguish between consciousness and consciousness ;) It's well-understood that the brainstem (or rather, not the brainstem per se but the thalamus) regulates consciousness in the sense of sleep/wake/arousal. It also plays a critical role in cortical oscillation, and oscillation implies communication, which is necessary (but not sufficient) for consciousness.
>-- psych. & computer science student with a strong interest in cognitive science & neuroscience
Keep it up! Cogsci is increasingly computational, so we need hackers. We also need better software engineering... badly!