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

But starting in the 1990s, this static view of the brain was steadily supplanted by a much more dynamic picture. The brain’s so-called modules don’t do their jobs in isolation; there is a great deal of back-and-forth interaction between them, far more than previously suspected. Changes in the operation of one module—say, from damage, or from maturation, or from learning and life experience—can lead to significant changes in the operations of many other modules to which it is connected. To a surprising extent, one module can even take over the functions of another. Far from being wired up according to rigid, prenatal genetic blueprints, the brain’s wiring is highly malleable—and not just in infants and young children, but throughout every adult lifetime. As we have seen, even the basic “touch” map in the brain can be modified over relatively large distances, and a phantom can be “amputated” with a mirror. We can now say with confidence that the brain is an extraordinarily plastic biological system that is in a state of dynamic equilibrium with the external world. Even its basic connections are being constantly updated in response to changing sensory demands. And if you take mirror neurons into account, then we can infer that your brain is also in synch with other brains—analogous to a global Internet of Facebook pals constantly modifying and enriching each other.

As remarkable as this paradigm shift was, and leaving aside its vast clinical importance, you may be wondering at this point what these tales of phantom limbs and plastic brains have to do with human uniqueness. Is lifelong plasticity a distinctly human trait? In fact, it is not. Don’t lower primates get phantom limbs? Yes, they do. Don’t their cortical limb and face representations remap following amputation? Definitely. So what does plasticity tell us about our uniqueness?

The answer is that lifelong plasticity (not just genes) is one of the central players in the evolution of human uniqueness. Through natural selection our brains evolved the ability to exploit learning and culture to drive our mental phase transitions. We might as well call ourselves Homo plasticus. While other animal brains exhibit plasticity, we are the only species to use it as a central player in brain refinement and evolution. One of the major ways we managed to leverage neuroplasticity to such stratospheric heights is known as neoteny—our almost absurdly prolonged infancy and youth, which leaves us both hyperplastic and hyperdependent on older generations for well over a decade. Human childhood helps lay the groundwork of the adult mind, but plasticity remains a major force throughout life. Without neoteny and plasticity, we would still be naked savanna apes—without fire, without tools, without writing, lore, beliefs, or dreams. We really would be “nothing but” apes, instead of aspiring angels.

INCIDENTALLY, EVEN THOUGH I was never able to directly study Mikhey—the patient I met as a medical student who laughed when she should have yelped in pain—I never stopped pondering her case. Mikhey’s laughter raises an interesting question: Why does anybody laugh at anything? Laughter—and its cognitive companion, humor—is a universal trait present in all cultures. Some apes are known to “laugh” when tickled, but I doubt if they would laugh upon seeing a portly ape slip on a banana peel and fall on his arse. Jane Goodall certainly has never reported anything about chimpanzees performing pantomime skits for each other à la the Three Stooges or the Keystone Kops. Why and how humor evolved in us is a mystery, but Mikhey’s predicament gave me a clue.