This is part of IEEE Spectrum's SPECIAL REPORT: THE SINGULARITY
Would you sell your soul on eBay? Right now, of course, you can't. But in some quarters it is taken for granted that within a generation, human beings—including you, if you can hang on for another 30 years or so--will have an alternative to death: being a ghost in a machine. You'll be able to upload your mind--your thoughts, memories, and personality--to a computer. And once you've reduced your consciousness to patterns of electrons, others will be able to copy it, edit it, sell it, or pirate it. It might be bundled with other electronic minds. And, of course, it could be deleted.
That's quite a scenario, considering that at the moment, nobody really knows exactly what consciousness is. Pressed for a pithy definition, we might call it the ineffable and enigmatic inner life of the mind. But that hardly captures the whirl of thought and sensation that blossoms when you see a loved one after a long absence, hear an exquisite violin solo, or relish an incredible meal. Some of the most brilliant minds in human history have pondered consciousness, and after a few thousand years we still can't say for sure if it is an intangible phenomenon or maybe even a kind of substance different from matter. We know it arises in the brain, but we don't know how or where in the brain. We don't even know if it requires specialized brain cells (or neurons) or some sort of special circuit arrangement of them.
Nevertheless, some in the singularity crowd are confident that we are within a few decades of building a computer, a simulacrum, that can experience the color red, savor the smell of a rose, feel pain and pleasure, and fall in love. It might be a robot with a ”body.” Or it might just be software--a huge, ever-changing cloud of bits that inhabit an immensely complicated and elaborately constructed virtual domain.
We are among the few neuroscientists who have devoted a substantial part of their careers to studying consciousness. Our work has given us a unique perspective on what is arguably the most momentous issue in all of technology: whether consciousness will ever be artificially created.
We think it will--eventually. But perhaps not in the way that the most popular scenarios have envisioned it.
Consciousness is part of the natural world. It depends, we believe, only on mathematics and logic and on the imperfectly known laws of physics, chemistry, and biology; it does not arise from some magical or otherworldly quality. That's good news, because it means there's no reason why consciousness can't be reproduced in a machine--in theory, anyway.
In humans and animals, we know that the specific content of any conscious experience--the deep blue of an alpine sky, say, or the fragrance of jasmine redolent in the night air--is furnished by parts of the cerebral cortex, the outer layer of gray matter associated with thought, action, and other higher brain functions. If a sector of the cortex is destroyed by stroke or some other calamity, the person will no longer be conscious of whatever aspect of the world that part of the brain represents. For instance, a person whose visual cortex is partially damaged may be unable to recognize faces, even though he can still see eyes, mouths, ears, and other discrete facial features. Consciousness can be lost entirely if injuries permanently damage most of the cerebral cortex, as seen in patients like Terri Schiavo, who suffered from persistent vegetative state. Lesions of the cortical white matter, containing the fibers through which parts of the brain communicate, also cause unconsciousness. And small lesions deep within the brain along the midline of the thalamus and the midbrain can inactivate the cerebral cortex and indirectly lead to a coma--and a lack of consciousness.
To be conscious also requires the cortex and thalamus--the corticothalamic system--to be constantly suffused in a bath of substances known as neuromodulators, which aid or inhibit the transmission of nerve impulses. Finally, whatever the mechanisms necessary for consciousness, we know they must exist in both cortical hemispheres independently.
Much of what goes on in the brain has nothing to do with being conscious, however. Widespread damage to the cerebellum, the small structure at the base of the brain, has no effect on consciousness, despite the fact that more neurons reside there than in any other part of the brain. Neural activity obviously plays some essential role in consciousness but in itself is not enough to sustain a conscious state. We know that at the beginning of a deep sleep, consciousness fades, even though the neurons in the corticothalamic system continue to fire at a level of activity similar to that of quiet wakefulness.
Data from clinical studies and from basic research laboratories, made possible by the use of sophisticated instruments that detect and record neuronal activity, have given us a complex if still rudimentary understanding of the myriad processes that give rise to consciousness. We are still a very long way from being able to use this knowledge to build a conscious machine. Yet we can already take the first step in that long journey: we can list some aspects of consciousness that are not strictly necessary for building such an artifact.
Remarkably, consciousness does not seem to require many of the things we associate most deeply with being human: emotions, memory, self-reflection, language, sensing the world, and acting in it. Let's start with sensory input and motor output: being conscious requires neither . We humans are generally aware of what goes on around us and occasionally of what goes on within our own bodies. It's only natural to infer that consciousness is linked to our interaction with the world and with ourselves.
Yet when we dream, for instance, we are virtually disconnected from the environment--we acknowledge almost nothing of what happens around us, and our muscles are largely paralyzed. Nevertheless, we are conscious, sometimes vividly and grippingly so. This mental activity is reflected in electrical recordings of the dreaming brain showing that the corticothalamic system, intimately involved with sensory perception, continues to function more or less as it does in wakefulness.
Neurological evidence points to the same conclusion. People who have lost their eyesight can both imagine and dream in images, provided they had sight earlier in their lives. Patients with locked-in syndrome, which renders them almost completely paralyzed, are just as conscious as healthy subjects. Following a debilitating stroke, the French editor Jean-Dominique Bauby dictated his memoir, The Diving Bell and the Butterfly , by blinking his left eye. Stephen Hawking is a world-renowned physicist, best-selling author, and occasional guest star on ”The Simpsons,” despite being immobilized from a degenerative neurological disorder.
So although being conscious depends on brain activity, it does not require any interaction with the environment. Whether the development of consciousness requires such interactions in early childhood, though, is a different matter.
How about emotions? Does a conscious being need to feel and display them? No: being conscious does not require emotion . People who've suffered damage to the frontal area of the brain, for instance, may exhibit a flat, emotionless affect; they are as dispassionate about their own predicament as they are about the problems of people around them. But even though their behavior is impaired and their judgment may be unsound, they still experience the sights and sounds of the world much the way normal people do.