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

by V.S. Ramachandran

“When the only tool you have is a hammer, everything

starts to look like a nail.”

“I know, my dear Watson, that you share my love of all that is bizarre and outside the conventions and humdrum routine of everyday life.”

Whenever Susan looks at numbers, she sees each digit tinged with its own inherent hue. For example, 5 is red, 3 is blue. This condition, called synesthesia, is eight times more common in artists, poets, and novelists than in the general population, suggesting that it may be linked to creativity in some mysterious way. Could synesthesia be a neuropsychological fossil of sorts—a clue to understanding the evolutionary origins and nature of human creativity in general?

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. I used to think this was just well-intentioned mumbo-jumbo, but here is a neuron that doesn’t know the difference between self and other. Are our brains uniquely hardwired for empathy and compassion?

example, a patient may attempt to touch her nose, feel her hand overshooting, and attempt to compensate with an opposing motion, which causes her hand to overshoot even more wildly in the opposite direction. This is called an intention tremor.

Surrounding the top portion of the brainstem are the thalamus and the basal ganglia. The thalamus receives its major inputs from the sense organs and relays them to the sensory cortex for more sophisticated processing.

Damage to cells in the basal ganglia results in disorders like Parkinson’s disease, in which the patient’s torso is stiff, his face is an expressionless mask, and he walks with a characteristic shuffling gait.

Broadly speaking, the occipital lobes are mainly concerned with visual processing. In fact, they are subdivided into as many as thirty distinct processing regions, each partially specialized for a different aspect of vision such as color, motion, and form.

The temporal lobes are specialized for higher perceptual functions, such as recognizing faces and other objects and linking them to appropriate emotions.

Damage to the right parietal lobe commonly results in a phenomenon called hemispatial neglect: The patient loses awareness of the left half of visual space.

Even more remarkable is somatoparaphrenia, the patient’s vehement denial of ownership of her own left arm and insistence that it belongs to someone else.

Yet he has lost many of the most quintessential attributes that define human nature: ambition, empathy, foresight, a complex personality, a sense of morality, and a sense of dignity as a human being. (Interestingly, a lack of empathy, moral standards, and self-restraint are also frequently seen in sociopaths, and the neurologist Antonio Damasio has pointed out they may have some clinically undetected frontal dysfunction.)

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.

Why do patients with temporal lobe seizures believe they experience God and exhibit hypergraphia (incessant, uncontrollable writing)?

The entire skin surface of the left side of the body is mapped onto a strip of cortex called the postcentral gyrus

running down the right side of the brain.

When your arm is intact, the sensory feedback from the skin, muscles, and joint sensors in your arm, as well as the visual feedback from your eyes, are all testifying in unison that your arm is not in fact moving. Even though your motor cortex is sending “move” signals to your parietal lobe, the countervailing testimony of the sensory feedback acts as a powerful veto. As a result, you don’t experience the imagined movement as though it were real.

If the arm is gone, however, your muscles, skin, joints, and eyes cannot provide this potent reality check. Without the feedback veto, the strongest signal entering your parietal lobe is the motor command to the hand. As a result, you experience actual movement sensations.

Sudek’s atrophy

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

our predilection for oral sex may also be an evolutionary throwback to our ancestors’ days as frugivores (fruit eaters).

canonical neurons. These neurons are similar in some respects to the mirror neurons I introduced in the last chapter. Like mirror neurons, each canonical neuron fires during the

performance of a specific action such as reaching for a vertical twig or an apple. But the same neuron will also fire at the mere sight of a twig or an apple. In other words, it is as though the abstract property of graspability were being encoded as an intrinsic aspect of the object’s visual shape.

homunculus fallacy. If the image on the retina is transmitted to the brain and “projected” on some internal mental screen, then you would need some sort of “little man”—a

homunculus—inside your head looking at the image and interpreting or understanding it for you.

The fact that your perception of an unchanging image can change and flip radically is proof that perception must involve more than simply displaying an image in the brain.

Perception is an

actively formed opinion of the world rather than a passive reaction to ...

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.

Let’s first consider the two pathways by which visual information enters the cortex. The so-called old pathway starts in the retinas, relays through an ancient midbrain structure called the superior colliculus,

and then

projects—via the pulvinar—to the p...

This disorder is called agnosia, a term coined by Sigmund Freud meaning that the patient sees but doesn’t know.

Would a patient with Capgras syndrome never get bored with his wife? Would she remain perpetually novel and attractive? If the syndrome could somehow be evoked temporarily with transcranial magnetic stimulation…one could make a fortune.

What’s the connection—if any—between synesthesia and creativity?

“Cross-modal” refers to sharing information between senses, as when your vision and hearing together tell you that you’re watching a badly dubbed foreign film.)

Even when we are alone, how often do we think with pain and pleasure of what others think of us, or their imagined

approbation or disapprobation; and this all follows from sympathy, a fundamental element of the social instincts. —CHARLES DARWIN

Culture consists of massive collections of complex skills and knowledge which are transferred from person to person through two core mediums, language and imitation.

It isn’t clear how exactly the mirror neuron is wired up to allow this predictive power. It is as if higher brain regions are reading the output from it and saying (in effect), “The same neuron is now firing in my brain as would be firing if I were reaching out for a banana; so the other monkey must be intending to reach for that banana now.” It is as if mirror neurons are nature’s own virtual-reality

simulations of the intentions of other beings.

Reduced olfactory-bulb activity would diminish oxytocin and prolactin, which in turn might reduce empathy and compassion.

“synesthetic bootstrapping theory.”

it provides a valuable clue to understanding the origins of not only

language, but also a host of other uniquely human traits such as metaphorical thinking and abstraction. In particular, I’ll argue that language and many aspects of abstract thought evolved through exaptations whose fortuitous combination yielded novel solutions. Notice that this is different from saying that language evolved from some general mechanism such as thinking, and it also diff...

An inherited disorder called phenylketonuria (PKU) is caused by a rarely occurring abnormal gene that results in a failure to metabolize the amino acid phenylalanine in the body. As the amino acid starts accumulating in the child’s brain, he becomes profoundly retarded. The cure is simple. If you diagnose it early enough, all you do is withhold phenylalanine-containing

foods from the diet and the child grows up with an entirely normal IQ.

Most people recognize that the purpose of art is not to create a realistic replica of something but the exact opposite: It is to deliberately distort, exaggerate—even transcend—realism in order to achieve certain pleasing (and sometimes disturbing) effects in the viewer.