Advaita Vedanta and Neuroscience are two very different philosophical systems that developed in different contexts and traditions, but they both have an overwhelming interest in consciousness.
Advaita owes its philosophical construction to Adi Shankara (Shankarachaya) of the eighth century in what was at the time a predominantly Buddhist India. Neuroscience owes its development to the late 19th and early 20th century, the convergent result of two sources: “pure” experimental neuroscience interested in looking at the molecular basis of phenomena, and the medical discipline of neurology, primarily interested in deficits and how they related to normal functioning.
Nevertheless, some comparisons between the two systems can be made. Both are realistic philosophies; that is, they both affirm “this conscious experience that I am having is real, beyond mere opinion.”
However, neuroscience–insofar as it takes consciousness as real (and thinkers like Dennett consider consciousness to be somewhat illusory)–is dualistic: neuroscientists generally affirm “this conscious experience I am having is the result of orchestrated material processes.” Generally speaking, neuroscientists identify consciousness with the waking state; dreams are seen as an aberration of the waking state, in which we have a conscious experience similar to the one where we interact with the “real, material world” without actually interacting with it; and in deep sleep, we are unconscious.
The materialism of neuroscience is typified in the dominant philosophy of explanation in neuroscience, mechanism: to explain consciousness is to find the mechanism responsible for it. The “hard problem” of consciousness is the question over whether this explanatory enterprise–explaining the “conscious mind” in terms of the “body” (e.g. brain cells and circuits)–will come to fruition.
It follows from neuroscientists’ affirmation that if I were to take a hammer and smash myself over the head with it, “my” conscious experience would come to an end.
In Advaita Vedanta, conscious experience is made of the very knowing of it. It comes in four different forms: the waking state, the dream state, deep sleep, and “turiya,” a kind of non-state of consciousness that is not subject to change.
For Advaita, we are conscious throughout all of these states: this is obvious enough in waking, and even in dreaming. However, in deep sleep, we certainly don’t feel like we’re conscious of it. From the clock, we know that 8 or so hours pass from our head hitting the pillow to the alarm ringing. And yet, besides our dreams, we don’t feel like we’re waiting for the waking state to arrive, as we would wait for a bus.
In fact, in the absence of dreams, we experience sleep as two timeless moments: our memory of waiting for sleep, and that of waking up. Even this distinction between two “moments” is a conceptualisation: what we really experience is a kind of continuum. The mind knows no objects in deep sleep.
For Advaita, consciousness is incommensurable with phenomenal reality–taking a hammer to one’s head does not destroy consciousness. It is through false identification that we suppose that conscious “depends on” (or has some relationship with) processes inside our skull. Of course, the content of conscious experience changes in function of brain activity in certain regions, but the substrate–conscious knowing of experience–doesn’t.
In conclusion, what really separates Advaita from neuroscience is their position on the objective world: for neuroscience, the objective, material world and brain processes come first, and conscious comes after as something of an add-on; for Advaita, consciousness comes first–the objective world is nothing other than consciousness: that does not mean that it isn’t; but Advaitins claim that the objective world has no independent being other than our conscious experience of it. The objective world is thus “nothing” in the literal sense of it being no thing (and therefore is not real in the Latin sense of re meaning thing), for if the world is none other than consciousness, and the latter is known to be no object, then there is no thing for the world to be. But the world is, since we all have an experience of it, and for the Advaitins, once the experience of the world is stripped of its false identification, the mind experiences sat cit ananda–being, consciousness, bliss–the divine Image seen through the filter of the empirical mind.