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

Jason is a patient at a rehabilitation center in San Diego. He has been in a semicomatose state called akinetic mutism for several months before he is seen by my colleague Dr. Subramaniam Sriram. Jason is bedridden, unable to walk, recognize, or interact with people—not even his parents—even though he is fully alert and often follows people around with his eyes. Yet if his father goes next door and phones him, Jason instantly becomes fully conscious, recognizes his dad, and converses with him. When his father returns to the room, Jason reverts at once to a zombie-like state. It is as if there are two Jasons trapped inside one body: the one connected to vision, who is alert but not conscious, and the one connected to hearing who is alert and conscious. What might these eerie comings and goings of conscious personhood reveal about how the brain generates self-awareness?

These may sound like phantasmagorical short stories by the likes of Edgar Allan Poe or Philip K. Dick. Yet they are all true, and these are only a few of the cases you will encounter in this book. An intensive study of these people can not only help us figure out why their bizarre symptoms occur, but also help us understand the functions of the normal brain—yours and mine. Maybe someday we will even answer the most difficult question of all: How does the human brain give rise to consciousness? What or who is this “I” within me that illuminates one tiny corner of the universe, while the rest of the cosmos rolls on indifferent to every human concern? A question that comes perilously close to theology.

WHEN PONDERING OUR uniqueness, it is natural to wonder how close other species before us might have come to achieving our cognitive state of grace. Anthropologists have found that the hominin family tree branched many times in the past several million years. At various times numerous protohuman and human-like ape species thrived and roamed the earth, but for some reason our line is the only one that “made it.” What were the brains of those other hominins like? Did they perish because they didn’t stumble on the right combination of neural adaptations? All we have to go on now is the mute testimony of their fossils and their scattered stone tools. Sadly, we may never learn much about how they behaved or what their minds were like.

We stand a much better chance of solving the mystery of the relatively recently extinct Neanderthals, a cousin-species of ours, who were almost certainly within a proverbial stone’s throw of achieving full-blown humanhood. Though traditionally depicted as the archetypical brutish, slow-witted cave dweller, Homo neanderthalensis has been receiving a serious image makeover in recent years. Just like us they made art and jewelry, ate a rich and varied diet, and buried their dead. And evidence is mounting that their language was more complex than the stereotypical “cave man talk” gives them credit for. Nevertheless, around thirty thousand years ago they vanished from the earth. The reigning assumption has always been that the Neanderthals died and humans thrived on because humans were somehow superior: better language, better tools, better social organization, or something like that. But the matter is far from settled. Did we outcompete them? Did we murder them all? Did we—to borrow a phrase from the movie Braveheart—breed them out? Were we just plain lucky, and they unlucky? Could it as easily have been them instead of us who planted a flag on the moon? The Neanderthals’ extinction is recent enough that we have been able to recover actual bones (not just fossils), and along with them some samples of Neanderthal DNA. As genetic studies continue, we will assuredly learn more about the fine line that divided us.

And then of course there were the hobbits.

Far away on a remote island near Java there lived, not so long ago, a race of diminutive creatures—or should I say, people—who were just three feet tall. They were very close to human and yet, to the astonishment of the world, turn out to have been a different species who coexisted alongside us almost up until historical times. On the Connecticut-sized island of Flores they eked out a living hunting twenty-foot dragon-lizards, giant rats, and pigmy elephants. They manufactured miniature tools to wield with their tiny hands and apparently had enough planning skills and foresight to navigate the open seas. And yet incredibly, their brains were about one-third the size of a human’s brain, smaller than that of a chimp.²