The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

SOMETIME IN THE twenty-first century, science will confront one of its last great mysteries: the nature of the self. That lump of flesh in your cranial vault not only generates an “objective” account of the outside world but also directly experiences an internal world—a rich mental life of sensations, meanings, and feelings. Most mysteriously, your brain also turns its view back on itself to generate your sense of self-awareness.

The search for the self—and the solutions to its many mysteries—is hardly a new pursuit. This area of study has traditionally been the preserve of philosophers, and it is fair to say that on the whole they haven’t made a lot of progress (though not for want of effort; they have been at it for two thousand years). Nonetheless, philosophy has been extremely useful in maintaining semantic hygiene and emphasizing the need for clarity in terminology.² For example, people often use the word “consciousness” loosely to refer to two different things. One is qualia—the immediate experiential qualities of sensation, such as the redness of red or the pungency of curry—and the second is the self who experiences these sensations. Qualia are vexing to philosophers and scientists alike because even though they are palpably real and seem to lie at the very core of mental experience, physical and computational theories about brain function are utterly silent on the question of how they might arise or why they might exist.

Let me illustrate the problem with a thought experiment. Imagine an intellectually highly advanced but color-blind Martian scientist who sets out to understand what humans mean when they talk about color. With his Star Trek–level technology he studies your brain and completely figures out down to every last detail what happens when you have mental experiences involving the color red. At the end of his study he can account for every physicochemical and neurocomputational event that occurs when you see red, think of red, or say “red.” Now ask yourself: Does this account encompass everything there is to the ability to see and think about redness? Can the color-blind Martian now rest assured that he understands your alien mode of visual experience even though his brain is not wired to respond to that particular wavelength of electromagnetic radiation? Most people would say no. Most would say that no matter how detailed and accurate this outside-objective description of color cognition might be, it has a gaping hole at its center because it leaves out the quale of redness. (“Quale,” pronounced “kwah-lee,” is the singular form of “qualia.”) Indeed, there is no way you can convey the ineffable quality of redness to someone else short of hooking up your brain directly to that person’s brain.

Perhaps science will eventually stumble on some unexpected method or framework for dealing with qualia empirically and rationally, but such advances could easily be as remote from our present-day grasp as molecular genetics was to those living in the Middle Ages. Unless there is a potential Einstein of neurology lurking around somewhere.

I suggested that qualia and self are different. Yet you can’t solve the former without the latter. The notion of qualia without a self experiencing/introspecting on them is an oxymoron. In similar vein Freud had argued that we cannot equate the self with consciousness. Our mental life, he said, is governed by the unconscious, a roiling cauldron of memories, associations, reflexes, motives, and drives. Your “conscious life” is an elaborate after-the-fact rationalization of things you really do for other reasons. Because technology had not yet advanced sufficiently to allow observation of the brain, Freud lacked the tools to take his ideas beyond the couch, and so his theories were caught in the doldrums between true science and untethered rhetoric.³

Might Freud have been right? Could most of what constitutes our “self” be unconscious, uncontrollable, and unknowable?⁴ Despite Freud’s current unpopularity (to put it mildly), modern neuroscience has in fact revealed that he was right in arguing that only a limited part of the brain is conscious. The conscious self is not some sort of “kernel” or concentrated essence that inhabits a special throne at the center the neural labyrinth, but neither is it a property of the whole brain. Instead, the self seems to emerge from a relatively small cluster of brain areas that are linked into an amazingly powerful network. Identifying these regions is important since it helps narrow the search. We know, after all, that the liver and the spleen are not conscious; only the brain is. We are simply taking a step further and saying that only some parts of the brain are conscious. Knowing which parts are and what they are doing is the first step toward understanding consciousness.