Consciousness is information laden. Not only does it supply information about the external world, it also informs us about itself and our own body. In being conscious we find out about the world outside us and about our own subjective state and bodily condition. The faculties used to acquire these sorts of information are usually labeled perception, introspection, and proprioception. Consciousness is thus highly informative, a source of knowledge (do we have any other source?). It seems geared to disclosing facts about the world, providing us with a torrent of data; it is information rich. But there is one area in which it is conspicuously silent: information about our brain states. Nothing in consciousness reveals what is going on in the brain when consciousness itself is operative. True, we can look at the brain from the outside by opening up the head, but we receive no information about the brain simply by being conscious: no amount of concentrating and training can enable you to discover what is going on in your brain just by surveying your current state of consciousness. So far as consciousness is concerned, you don’t even have a brain—though assuredly consciousness affirms the existence of the external world, itself, and the body. This is a strange state of affairs, because the brain is surely, to put it mildly, closely involved in the activities of consciousness. Nothing is closer: everything that happens in consciousness depends on the brain (on neural activity), minutely and inescapably. Consciousness is basically a function of the brain—an aspect of the brain. You would think, then, that this alliance would show up in consciousness: consciousness would make it evident where its foundations begin and end. But no, nothing: it is as if consciousness refuses to acknowledge its origins in the brain. It won’t admit to its cerebral roots, keeping them discreetly out of the field of awareness. Nor are there any pathological conditions in which the activities of neurons force themselves into consciousness—no abnormalities in which the facts of neural life intrude upon the conscious state. No one ever suffers from “brain suffusion”—a sudden sense of cerebral susurration. It may be wondered why this is—why the deafening silence about the brain’s role in generating consciousness? Is it because it would be distracting and pointless? But consciousness is always distracting us from the main focus of the moment, and it might sometimes be useful to know what is going on inside your brain (injuries, diseases, etc.). This looks like a puzzle of nature: why the selective blindness? Consciousness is generally generous with information, but here it is stingy to the point of absolute silence. It is as if it has been designed to be selectively blind—as if the brain is a taboo subject. One would think it was ashamed of the brain, like a mad relative in the attic.  Nor is this selective blindness a necessary truth: we can imagine that it was not so—a species of sentient beings might well enjoy consciousness of its own brain, treating this is as completely routine, like our awareness of our limbs or lungs. Knowledge of the brain might be part of folk psychology.
What are the implications of this selective blindness? And what is its general character? You might think it provides an argument against materialism: for if materialism were true, wouldn’t its truth be evident to consciousness? Is it that consciousness supplies no information about the brain because it isn’t the brain—because it isn’t a material thing? Maybe so, but note that consciousness tells us nothing about a supposed immaterial substance either: it is equally blind about that. It is blind about whatever constitutes its underlying basis; it turns a blind eye towards its underpinnings. In any case, consciousness certainly has neural correlates, and it systematically ignores these correlates. The point concerns the epistemic capacities of consciousness not its metaphysics: it has a blind spot. It systematically conceals from itself its origins in the brain. Perhaps there is an inhibitory mechanism in the brain that prevents the brain from knowing about itself via consciousness: switch off that mechanism and knowledge of the brain will come flooding in. More likely, there are just no receptors capable of processing information about the brain in the brain—no “cerebroreceptors” analogous to photoreceptors. Whatever the mechanics of the matter may be consciousness evidently declines to dabble in its cerebral origins. Is it because consciousness itself has a nature that precludes such awareness? Does it form a kind of barrier to knowledge of the brain? People have felt that perceptual consciousness works as a barrier in relation to the external world (hence the sense datum theory); perhaps it also acts as a barrier to the world of the brain. We can picture consciousness in one of two ways: it is either like a thin translucent film clinging to the brain, or it is like a think opaque fabric cloaking the brain. If the former, then it should provide glimpses of what lies beneath—fissures, furrows, axon-nucleus-dendrite structures. If the latter, then it is simply too thick to afford any such glimpses: more like a brick wall than a wispy veil. I think there is something to this thickness intuition, though it is hard to articulate it clearly: one has the image of layers of consciousness forming a dense membrane that shrouds the brain in darkness. But then why is it that the barrier only exists where the brain is concerned and not in relation to the external world or the body? The question quickly becomes hopelessly obscure. Yet it seems true that consciousness is not like a diaphanous veil in relation to the brain but more like a dense and opaque shield or mask. This is the ontological counterpart to the epistemic point that consciousness doesn’t reveal the brain even slightly. Perhaps we should be struck anew by the miraculous ability of consciousness to reveal the external world, it being in here and the external world being out there: how does this preternatural reaching-out work?  It does feel somehow natural to suppose that consciousness is a self-enclosed reality (which is why Brentano’s thesis of intentionality is so striking): it has often been supposed that it can only ever contain information about itself as a self-enclosed reality. In any case, the matter is obscure and difficult, though worth thinking about. At present, I conclude, the explanation of brain-blindness must remain mysterious: it is evidently a fact, and a deep fact, but it is hard to see what accounts for it. It seems like an inexplicable contingency, yet deeply rooted—one of many mysteries of nature.
What I think I can do is provide an account of what this selective blindness consists in—what kind of phenomenon it is. And this will lead us to a property of consciousness that has not heretofore been recorded. I spoke earlier of a blind spot: the literal meaning of this phrase concerns the physical eye and its physiology. Each eye has a spot on the retina that contains no photoreceptors, where the optic nerve joins the retina: nothing can be seen at this spot, though we don’t normally notice it. The eye is thus selectively blind for hard anatomical reasons. It is easy to see that if the retina suffered damage to any region a similar blind spot would result, and indeed this occurs in certain circumstances. In cases of macular degeneration (and in other conditions) just such a blind spot results—it is called a scotoma by neurologists. From a phenomenological point of view this localized blindness does not appear as a gap in the visual field—a blank space with perceived boundaries—but rather simply as an absence of vision. It is as if a certain part of the visual field disappears, but without any awareness of an empty patch. The blind spot itself is thus conceived as a kind of natural scotoma, though one that is harmless enough. This concept has proved sufficiently useful that it has been extended to refer to other sorts of selective blindness–in particular, personality scotomas, in which a person is unaware of facets of his or her personality that are evident to others. It is a form of ignorance (“neglect”) that stems from a perceptual lack—a type of blindness. The word “scotoma” comes from a Greek word for darkness, and the concept is apt: the neglected aspect of reality lies in darkness for the would-be perceiver. We are familiar with the phenomenon of degraded vision at the periphery of the visual field (“semi-scotoma”, as we might call it); in full scotoma we have a complete absence of vision at a specific locus of the visual field, more or less extensive. Scotomas are generally acquired, but they could be genetic: we can imagine someone born with a rather large scotoma at a particular place in the visual field. Unlike total blindness, the person with a scotoma experiences undiminished awareness surrounding the affected area—so they can have normal visual acuity except in a certain location.
You can see where I am headed with this: brain blindness is a type of scotoma. That is, our inability to know about the brain via consciousness is an example of a scotoma at a higher level of cognitive function (it doesn’t concern the anatomy of the eye). It is a natural scotoma that we are born with not the result of injury or disease, but it functions just like other sorts of scotoma. We can imagine someone born with awareness of his own brain that then suffers an injury that removes this area of awareness: that would be the analogue of macular degeneration. As it is our brain blindness is like our genetically determined blind spot—just the way we are hooked up and hardwired. We are born with a kind of partial blindness. In both cases the blindness is surrounded by normal vision, indeed by excellent information reception, but it just so happens that there is a confined area of total blankness. We suffer from a scotoma with respect to the brain, which we take for granted. Beings naturally equipped with brain awareness might pity us for our selective blindness, but we have known nothing else so we take it in stride (compare a land of the exclusively color blind). Presumably this is true of all terrestrial animals, so we can say that all life on earth suffers from brain blindness: terrestrial sentience is scotoma-prone sentience. Consciousness contains a big gap where the brain ought to be.  And ironically this gap is precisely where the very origins of consciousness lie: consciousness thus has a blind spot for what makes it possible. We have no awareness of what makes awareness exist in the first place. The relative in the attic is actually our own nature as sentient physical beings. We are systematically blind to what enables us to see. A fine conceit, to be sure: our maker must be tickled pink. Consciousness is constitutionally blind to its conditions of possibility. 
It is inviting to postulate that consciousness has a characteristic not usually remarked upon: it is scotoma-prone. It is certainly rich in information content, acutely receptive to large sections of reality, but it is also selectively blind to certain parts of reality, for reasons not easy to fathom. Consciousness has intentionality, subjectivity, privacy, unity, a subject, and blind spots. It is, we might say, scotomic: gappy, holey, dark in places. In particular, it is blind to its own enabling conditions in the brain. The brain exists in close proximity to the conscious mind, closer than any other bodily organ, but for some reason consciousness refuses to disclose any information about the brain: it is studiedly vacant on the question. Its epistemic field contains a gaping hole where the brain ought to be. We can try to direct our consciousness to this area of neglect, or even attempt to train ourselves to be more receptive, but we come up empty handed. It really is as if we have an area of unalterable blindness where the brain is concerned. The only way we can know anything about the brain is by observing it from a third-person point of view. Of course, if the mind is really just an aspect of the brain, then we know about this aspect of the brain by introspection; but what we don’t know are the other aspects—those that involve neurons and their electrochemical processes. We don’t even know these aspects partially from the first-person point of view, as is the case for other bodily organs; our ignorance of the brain is far more principled. And this is particularly puzzling given that the brain is the closest thing to the mind in the entire universe. Shouldn’t we be aware of it at every moment? Why isn’t it constantly on our mind? It is as if the mind were intentionally keeping the brain a secret from us. 
 It might be thought that the brain just happens to be one of those organs of the body that keeps itself to itself, like the spleen or kidneys, so that there is nothing remarkable about its invisibility to consciousness. But (a) even those organs sometimes reveal themselves in abnormal circumstances (often in the form of pain) and (b) the brain is in its nature right next to consciousness, so that its doings could hardly be missed—yet it remains unrevealed.
 Another possible scotoma might be the unconscious: we have no inner eye capable of revealing the unconscious, even under special conditions. We have to infer the unconscious not know it by direct introspection. If we think of conscious awareness as a scanning device, then we can say that it is unable to scan the unconscious or the brain—though it can scan the external world, itself, and the body. It suffers from scanning gaps.
 Could it be that the conscious mind also keeps the self a secret? That is, do we have a scotoma with respect to the self? Hume famously found nothing when he searched within himself for himself, concluding (on one interpretation anyway) that there is no such self to find. But an alternative view would be that we have a blind spot with respect to the self: the self exists all right, but it doesn’t disclose itself to our spotty introspective powers. Selective blindness is thus wrongly interpreted as non-existence. One can imagine the same conclusion being drawn about the brain if we lacked the ability to observe the brain perceptually: we simply don’t encounter it in introspection. That is true enough, but it is false that the brain doesn’t exist. Likewise the self exists but at an introspective blind spot. So that makes three scotomas of consciousness: the brain, the unconscious, and the self. Any more?