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

by V.S. Ramachandran

neuron that becomes active whenever Smith’s hand is poked with a needle. But the surgeon is astonished by what he sees next. The same neuron fires just as vigorously when Smith merely watches another patient being poked. It is as if the neuron (or the functional circuit of which it is a part) is empathizing with another person. A stranger’s pain becomes Smith’s pain, almost literally. Indian and Buddhist mystics assert that there is no essential difference between self and other, and that true enlightenment comes from the compassion that dissolves this barrier.

Within some of these regions, there is a special class of nerve cells called mirror neurons. These neurons fire not only when you perform an action, but also when you watch someone else perform the same action. This sounds so simple that its huge implications are easy to miss. What these cells do is effectively allow you to empathize with the other person and “read” her intentions—figure out what she is really up to. You do this by running a simulation of her actions using your own body image.

These abilities (and the underlying mirror-neuron circuitry) are also seen in apes, but only in humans do they seem to have developed to the point of being able to model aspects of others’ minds rather than merely their actions. Inevitably this would have required the development of additional connections to allow a more sophisticated deployment of such circuits in complex social situations.

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.

The key difference is that in the first case, there is a true alarm requiring urgent attention. In the second case it’s a false alarm, and by laughing you inform your kin in the vicinity not to waste their resources rushing to his aid. It is nature’s “all’s okay” signal. What is left unexplained is the slight schadenfreude aspect to the whole thing.

When an ape is approached by another ape, the default assumption is that it is being approached by a potentially dangerous stranger, so it signals its readiness to fight by protruding its canines in a grimace. This evolved further and became ritualized into a mock threat expression, an aggressive gesture warning the intruder of potential retaliation. But if the approaching ape is recognized as

How we smile!

a friend, the threat expression (baring canines) is aborted halfway, and this halfway grimace (partly hiding the canines) becomes an expression of appeasement and friendliness.

How we smile.

The eyes of the octopus are eerily similar to our own, despite the fact that our last common ancestor was a blind aquatic slug-or snail-like creature that lived well over half a billion years ago.1 Eyes are not unique to us, but vision does not occur in the eye. It occurs in the brain.

Eyes and vision

Furthermore, the shift in diet from tiny nocturnal insects to red, yellow, and blue fruits, as well as to leaves whose nutritional value was color coded in various shades of green, brown, and yellow, propelled the emergence of a sophisticated system for color vision.

The question of how neurons encode meaning and evoke all the semantic associations of an object is the holy grail of neuroscience, whether you are studying memory, perception, art, or consciousness.

A drug can’t suddenly induce sprouting of new axon connections, and such connections would not magically vanish after the drug wore off. Thus it must be enhancing the activity of preexisting connections in some way—which is not inconsistent with the possibility that synesthetes have more of these connections than the rest of us.