You could stare for years at The Creation of Adam, and never notice it. But once someone points out the metaphor in Michelangelo's masterpiece, it's hard to interpret it any other way.
Focus on the purple cloak swirling around the deity and his host of angels (as a medical student named F.L. Meshberger did in 1990, in an article published in the Journal of the American Medical Association). Notice, especially, how the fabric gathers and tucks. Doesn't it resemble a side view of the human brain, attached to its flexible column of spinal cord?
Now, consider what the "brain" encloses: the Supreme Being, maker of heaven and earth, day and night, winter and summer, seas and stars and spinning planets. And, consider what is happening in the painting: God is about to infuse humanity with a spark of his divine essence.
Could there possibly be a better expression of the awesome potential of human creativity?
"The brain is a metaphor-making machine," says Michael Salcman, a Baltimore neurosurgeon.
"It routinely expresses the concrete in terms of the figurative. Robert Frost once said, 'Poetry provides the one permissible way of saying one thing and meaning another.' That is what artists and scientists do all the time. The ability to compare one thing to the next is inherent in the way the brain is structured."
Humanity long has been fascinated by the sources and causes of the creative impulse, traditionally associating it with the supernatural. Michelangelo, for instance, was known as "Il Divino" -- "the Divine One."
But it has only been in the past half-century that a new discipline, neuroscience, was developed to study the brain. And it wasn't until the 1990s that technical advances made it possible to map brain functions while the subjects are awake and performing specific mental tasks -- an immense boon for researchers.
As a result, scientists are just beginning to probe fundamental questions about creativity, from what happens during a brainstorm, to the oft-debated link between genius and insanity.
Salcman isn't doing independent research. But by drawing on experiments conducted by others, and adding a few ideas of his own, he has come up with a plausible mathematical explanation as to what might be going on in our brains when we think creatively, whether we're devising a prize-winning recipe or diagnosing the source of a troubling rattle in a car motor.
Before proceeding further, it's important to state that Salcman's theories are just that -- a hypothesis, not fact. But it's not just anyone who's doing the guessing.
The 60-year-old Salcman is former chairman of neurosurgery at the University of Maryland Medical Center, and is past president of the prestigious Congress of Neurological Surgeons. He also is a poet and avid collector of modern art, and has been thinking for his entire career about brains and how they form ideas. Since 1979, Salcman has published his hypotheses on the creative process in such medical journals as Neurosurgery and the Journal of Neurophysiology.
For Salcman, when we say that we're thinking creatively, what we really mean is that we're solving a problem, whether the question is aesthetic, scientific, pragmatic or interpersonal.
The mechanism for the problem-solving process, he thinks, lies in the almost unfathomable number of neurons, or nerve cells, in our brains -- and the even greater number of connections between these cells.
Think of neurons as the building blocks of the brain. Their main job is to communicate critical data to one another: Look! Over there! What color is it? What shape? How fast is it moving? Etc.
Neurons "talk" to one another by sending electrical impulses across minute gaps between cells called synapses, and this incessant chatter among neurons, the constant give-and-take, is the basis of thought itself.
The argument for the superiority of the human brain to those of animals boils down to simple numbers: Human skulls are crammed with more neurons than are the craniums of other species, so we can process more information more quickly, and at a higher level of complexity.
The human brain contains roughly a trillion neurons, and each neuron has 10,000 synapses -- which means that each man, woman and child has roughly 10 quadrillion connections (or 10¹^6) in a 14-ounce organ roughly the size and color of a cauliflower. "The number of connections in the human brain approaches the numbers of stars in the universe," Salcman says. "Both systems are about equally complex."
In comparison, an ant's brain has roughly 10,000 neurons, while a frog's has about one million.
Every beginning biology student knows that the brain is divided into two hemispheres, and that specific areas in each hemisphere perform different functions.
So, for instance, the occipital lobes generally are used for vision; the temporal lobes for hearing; the parietal lobes for spatial perception, while the frontal lobes are allocated oversight functions, such as abstract thinking and some types of memory.
But the vast majority of each brain is comprised of something called the association cortices, and they are aptly named.
"Their function is to make comparisons between different types of information and data," Salcman says, "and they respond to more than one type of sensory input."
He thinks the ability to riffle between and coordinate cues from different senses is one of the things that makes us unique.
Norman Geschwind, a teacher of Salcman's, performed ground-breaking experiments in the 1960s that demonstrated that chimpanzees shown a long, yellow fruit could be trained to press a lighted button with the word "banana" on it. But, if the animals were blindfolded and a banana was placed into their paws, they were unable to identify it.
Humans, in contrast, had no such trouble. They would calculate: "Hmm. It's about the length of length a banana, and it's squishy like a banana, and if I dig in my fingernail, I can peel it like a banana, so perhaps it is a banana."
In her 2005 book, The Creating Brain: The Neuroscience of Genius, Nancy Andreasen, a professor of psychiatry at the University of Iowa and a winner of the National Medal of Science, writes:
"These association regions are the last to mature in human beings. They continue to develop new connections up to around the early twenties. They also are much larger in human beings than in other higher primates."
According to studies that Andreasen has conducted, when a human being engages in the random, undirected flow of thoughts called "free association," the part of the brain most actively involved is the association cortex. She concludes:
"Apparently, when the brain/mind thinks in a free and unencumbered fashion, it uses its most human and complex parts."
Semir Zeki, a professor of neurobiology at University College in London, suggested in 1998 that this coalescing and ordering of our perceptions is what we mean when we talk about "consciousness."
For instance, if we're walking through the jungle and we see something move ahead and to the left out of the corner of our eye, we perform a number of rapid assessments based on vision (large, furry and tawny) smell (the metallic stench of blood) and sound (the brittle snap of bones).
We don't analyze these sensations separately. We experience them simultaneously, and conclude: "A lion is almost through with his lunch. Run."
"This synthesizing enables us to have a unified vision of the world," Salcman says. "We can process it as a whole and react."
So, human beings are uniquely situated not only to process vast quantities of data, but to draw conclusions from what we find. And those conclusions are expressed in turns of metaphors.
It's worth noting that not all metaphors are visual, though Salcman makes the point that vision is our dominant sense; fully half of our cranial nerves are involved in seeing.
But a composer who uses a flute to mimic the sound of laughter in his new score is making a metaphor, as is the cook who imbues his recipes with the flavors of a particular region of Italy. And so, for that matter, are physicists who work in string theory and the mathematicians who deal with imaginary numbers.
"Marcel Proust was an excellent neuroscientist," Salcman says. "He found that a single taste of a madeleine could open an entire world."
(The pastry famously evoked the flood of recollections that resulted in Proust's Belle Epoque French masterpiece, The Remembrance of Things Past.)
But the capacity for making associations differs greatly between individuals. Some people, asked to say the first words that come to their minds upon hearing "moon" will respond "sun."
But W.B. Yeats saw in the moon the waxing and waning orbs of his pet feline, Minnalousche, and wrote a charming poem called The Cat and the Moon:
"Does Minnalousche know that his pupils / Will pass from change to change, / And that from round to crescent, / From crescent to round they range?"
The instant we read the words, the poet's observation makes sense. We can "see" the comparison that Yeats was drawing. More than that, it is a delightful surprise that invigorates us and reawakens our sense of wonder. But, who, other than a genius poet, would have thought to connect the two?
"Possessors of extraordinary creativity are apparently blessed with brains that are more facile at creating free associations," Andreasen writes. "Neurally, they may have more enriched connectivity between their various association cortices, or they may have different kinds of connection."
But the mere fact that an association requires an imaginative leap -- or is "wide," to use the scientific jargon -- doesn't necessarily mean that it is valid.
Someone who is mentally ill might see the moon and associate it with a living-room couch. The association is so strange and far-fetched that it doesn't awaken a corresponding recognition in others, and we reject it.
As Salcman sees it, the brain doesn't merely sift all the data and devise one metaphor; it presents us with several. When Yeats saw the moon, he probably had a great many other thoughts about that glowing, white sphere: some that were prosaic, some that were irrelevant, but one that was just right.
"The brain's operation is probabilistic in nature," Salcman says.
"We examine a number of possibilities, and play out a number of scenarios before making a decision. The difference between a genius like Einstein or Yeats and the rest of us is that they pick metaphors that are correct."
As Henri Poincare, the great French mathematician and theoretical physicist, famously said: "Invention is discernment."
Salcman thinks that the mechanism for choosing the best response from many possibilities might lie in a group of nerve cells in the frontal lobe called "mirror neurons."
In the 1990s, an Italian scientist named Giacomo Rizzolatti tracked the neurons that fired when monkeys performed a specific gesture, such as sticking out their tongues. He found that some neurons fired both when the monkey performed the activity himself and when he merely watched his cellmates do it. Human beings are thought to have these specialized cells as well.
Some researchers have hailed Rizzolatti's discovery as one of the most important scientific breakthroughs of the decade, as mirror neutrons seem to have potential implications for understanding such behaviors as imitation and language development.
Anecdotially, all parents know that their infants laugh with glee when they make a gesture, and Mom or Dad copies it.
Scientists think that mirror neurons may be key for developing empathy. Thus, when Jonas Salk discovered the polio vaccine, he not only learned something interesting -- how to develop a form of a virus that provides immunity without a corresponding infection -- he realized what his brilliant invention could be used for.
And, when Michelangelo climbed up on his scaffolding in the Sistine Chapel, he thought not just about hue, perspective and form, but about how the figures he was painting would be viewed by humans on the cathedral floor, craning their necks upward.
He knew we would be drawn to the jolt of color, to that miraculous purple cloak, and would trace its outline with our eyes. Perhaps, he knew as well, that he wasn't providing merely a scene from the Bible for his future visitors. He was providing us an image of the most secret and mysterious part of ourselves.