Sometimes as the fog of sleep lifts, the mind becomes aware of its traffic. Like commuters on an expressway, messages speed across the corpus callosum, a thick bridge of 200-250 million nerve fibers spanning the brain's two hemispheres. More will follow in a continuous stream of hubbub going in both directions. The brain is a duet of specialists which produces a single experience that's part enterprise, part communion, but all process, all motion.
The right brain is the strong silent one. It can see and act, but not report. Only the left brain talks, and it jabbers all day long, in a self-styled monologue and running commentary on the world, punctuated by conversations with other folk blessed (or cursed) with equally gabby left brains. What's more, the two sides specialize in different facets of mind, with the left excelling at speech and language and the right better at visual-motor skills. Heavy lifting is fine, but don't ask the right brain to solve knotty verbal problems. Which is not to say that the right side doesn't process language - it does, but weakly compared with the eloquent feats of the left. Damage the left hemisphere and language becomes a night- mare, especially for men (women generally recover better from left hemisphere injuries). But people vary greatly and the brain is resilient, so, fortunately, some victims with injured left brains do manage to regain speech. Mind you, that doesn't necessarily mean they can write. As it happens, writing isn't much related to speaking. A relatively recent invention, it's not part of our evolutionary heritage, but more like a sophisticated team sport with changing equipment and rules.
These days, it's fashionable to wear the psychic badge of being "a right-brain person" or "a left-brain person," usually to justify arty behavior, or the lack of it. The left-brain person is supposedly eloquent, analytic, introspective, attuned to details, logical, a problem solver, and good at stories, not to mention alibis. But she tends not to see the whole picture, or do math well, be inventive, or have a strong spatial sense. Jigsaw puzzles are out of the question. Like me, she's probably capable of pulling off a highway to get gas and, afterward, leaving in the wrong direction.
It's the right-brain person who supposedly is intuitive, artistic, musical, looks at the parts and sees the whole, is spatial, recognizes faces, is open to dreamwork and free association, does math, and excels at reading all the nuances of emotion. Though right-handed, I hold a telephone receiver to my left ear (which corresponds to the right brain), maybe because it's then easier to decipher the emotional landscape in a caller's voice.
Of course it's not as rigid as that stereotype. Visual details can often be better on the left, and the slower, more prosodic elements of language better on the right. Most people blend left and right brain use so fluently they're not aware of the divide, or that one side toils silently while the other questions nonstop. Some people use both sides equally, in others one side dominates, and then there are those who are grossly lopsided and make you wonder if they're not actually part android or reptile. But even for them, mind isn't a tug-of-war with the left brain on one side and the right brain on the other, but a collaboration, an open exchange.
More surprising, perhaps, the two hemispheres can differ in their outlook on life, how they feel about themselves, their future, and the treatment they expect from others. The right side manages negative feelings, the left positive. In studies conducted at the University of Wisconsin, people with very dominant left brains had a better self-image and tended to describe themselves as optimistic, happy, confident, enthused by life, not as stressed. They weren't immune to depression, but once afflicted could recover well. People with very dominant right brains felt worse about themselves, were more anxious and pessimistic, and they easily succumbed to depression. Small wonder antidepressants and psychotherapy stir up the left side of the brain. Our emotional lives walk a tightrope between the two, finding balance despite tipping a little one way or the other, or rather because of the tipping. Each side seems to play a critical role in diluting the other. This becomes especially poignant when someone damages only one hemisphere. Then the opposite side can run wild, and if it's the right side, the person may suddenly become uncharacteristically sad, violently anxious, or stewed in negative moods.
That we have brains whose left and right hemispheres specialize isn't unheard of in the animal kingdom, but it's odd. Not just because animals tend to be symmetrical, and even choose mates based on how symmetrical (apparently free from genetic mutations) they appear, but because backup systems aid in survival. Our hemispheres are complementary, more like fraternal twins than like clones. Why would some abilities be laid down in only one hemisphere?
For decades, Michael S. Gazzaniga, director of Dartmouth's Center for Cognitive Neuroscience, has been conducting ingenious experiments with "split brain" people, whose corpus callosum has been surgically severed to prevent the spread of epileptic seizures. Such studies offer insight into how the hemispheres divide their labor. For example, if a split-brain person looks at something only with the right eye (which corresponds to the left hemisphere of the brain), he can say what he sees. But show the same picture to his left eye (right hemisphere) and he'll "see" nothing. The Cheshire cat effect it's called, after the peek-a-boo cat in Lewis Carroll's Alice's Adventures in Wonderland. When the right brain is asked to point to the "invisible" object, the person has no trouble. Many clever experiments with long-suffering volunteers have revealed the left brain to be talkative, the right silent.
In another of Gazzaniga's experiments, a personal favorite of mine, he showed one large picture and four small pictures to each of a volunteer's hemispheres, and then the volunteer was asked to choose the small picture that seemed related to the large one. Neither side knew what the other side was viewing. For a snowstorm scene, the volunteer's right brain had to choose among a shovel, a lawn mower, a rake, and an ax. To go with a picture of a bird's foot, his left brain had to choose among a toaster, a chicken, an apple, and a hammer. Not surprisingly, the right brain correctly chose the shovel for the snowstorm, and the left brain correctly chose the chicken for the bird's foot.
Then things got really interesting. When Gazzaniga asked the subject why his right hemisphere had chosen the shovel, his talky left hemisphere answered, but since the split hemispheres couldn't exchange information, it didn't know about the snow scene and had no idea why the shovel was chosen. So it quickly made up a plausible explanation based on the only information it had, that a chicken was somehow involved. The subject reasoned: "The chicken claw goes with the chicken and you need a shovel to clean out the chicken shed." Good answer, if wrong. Gazzaniga calls the left brain the Interpreter, "a device that seeks explanations for events and emotional experiences." When something bad or advantageous happens, it's essential to know why so one can predict and prepare for future events. Mystery causes a mental itch, which the brain tries to soothe with the balm of reasonable talk. The left brain, that is; the right brain prefers to turn a mute eye.
Born fictioneers, all of us, we quest for causes and explanations, and if they don't come readily to hand, we make them up, because a wrong answer is better than no answer. Also, a fast good-enough answer is better than a slow perfect answer. We're devotees of the hunch, estimate, and best guess. I find it hard to watch, say, a David Lynch film like Mulholland Drive, which shards into free-associative imagery halfway through, and not try to figure it out.
Critics plague Lynch with "But what does it mean?" It's not enough to be startling, beautiful, artful, it has to mean, even if much of life simply is. Despite knowing that, my left hemisphere, not content to joyously perceive, insists on asking why. A word children use relentlessly and adults continue asking. And so we pass our lives, striving to make sense, even if it produces nonsense, which, of course, we never utter, only other people with less-exacting minds. Otherwise, we'd feel at sea, and painfully sure, as the philosopher William Gass says in an essay, that "life, though full of purposes, had none, and though everything in life was a sign, life managed, itself, to be meaningless."
Left brain, right brain, cleft brain. What does this have to do with the dime-size bed of geckos? It hints at our brain's evolution, and why the brain's hemispheres aren't the same. Maybe because of abilities we've lost, not gained. In an embarrassment of riches, our brain didn't have space for two of all the faculties available to it. Doling them out to separate hemispheres was its salvation. In further experiments with split-brain patients, Gazzaniga tested the brain's ability to group things visually and found that mice could make simple distinctions humans couldn't. As he says, "That a lowly mouse can perceive perceptual groupings, whereas a human's left hemisphere cannot, suggests that a capacity has been lost." Did the dawn of language, requiring an immense amount of brain space, force out that perceptual knack? If so, what other abilities did we sacrifice to make room for our own private storytellers?
As I move my left hand, the right hemisphere's wand, I notice how two parallel blue veins make a tuning fork at my wrist, and wonder if tops of hands are unique, like fingerprints. Then, picturing fingerprints in my mind's eye, I'm reminded of loopy weather systems, a simile that makes me smile. That reminds me of William Safire's clever book title, Let a Simile Be Your Umbrella. My hand rises and my eyes watch it. Anywhere my hand goes steals my attention. We've designed computer programs to be our mechanical shadows: move the arrow or cartoon hand to a spot on the screen, and it's like a toddler pointing to a jar out of reach, grasping it with her gaze.
Just point to something and all eyes follow; pointing and desiring go hand in hand. We are the animals who point and name. Moving my hand to the desktop, I check my calendar, where I'm reminded it's Saturday. A farmers' market down by the lakefront beckons with friends and familiar-looking strangers. Should I invite a girlfriend to meet me there? The last time we spoke, her voice sounded tense. Is she miffed with me for some reason? At the market, I'll find handcrafts from pottery to color-drenched yarn to painted T-shirt dresses (does the artist know that his niece just landed her first nursing job?), and whatever local flowers and produce may be in season, which no doubt will include tiny bouquets of fragrant miniature roses. Restaurant stalls will be offering Thai to macrobiotic cuisine. Fresh mushroom and barley soup, ladled by Robert at Your Daily Soup, would taste great for lunch: slippery mushrooms and chewy barley in broth. An inky scrawl on my calendar tells me it's also time to pay taxes in advance, which I dare not forget. My hand reaches for a cup on a saucer, and I feel the porcelain's sudden coolness as my pointer finger angles through the curved handle and I admire the design of Scotch broom with blue butterflies winding around the cup in a botanical frieze, also noting the residue of mocha foam inside, and hearing the tinkling rattle of the cup being lifted unevenly from the saucer.
Much of what happened in that last free-associative paragraph relied on the right side of my brain, from moving my left hand to picturing the layout of the farmers' market to reexamining the emotion in my friend's voice to the very act of free-associating. I can probably thank the left side of my brain for remembering so many details it can weave together into stories about my life and my environment. Sensory feedback informed both sides of the brain, and I used both to predict the outcome of not paying my taxes. But only we human apes can do what I just did. Because we evolved an extra layer of brain tissue, which we use in unique ways, providing more abilities, we have our own special mental world and the ramparts of thought. Our current neocortex has two hemispheres, each with four lobes. Physical sensations stalk the parietal lobe. The occipital lobe gives us sight. We hear using the temporal lobe. The frontal lobe moves our muscles. But none of that commands much gray matter. Most of each lobe is employed in the grand human saga of making associations among events, ideas, personal experiences, strategies, and people. It seems absurd to lump all that tempest together, but we do: thought. The word even sounds like a thick knot. Endlessly raveling and unraveling, thought combines colorful yarns to clothe each moment.
- Diane Ackerman (‘An Alchemy of Mind’)