Part 12

Naturally, after the two brain halves have been living together for a few years, growing up together in the same house, they learn to work almost like one. Still this signaling back and forth does take time. So long as we are merely eating, or walking, or shoveling snow, the process goes on fast enough. But talking is a different matter. When you are talking thirteen to the dozen, just as fast as you can chatter, every several letter of every single word you utter demands at least one change of position of tongue or lips or throat, and generally of them all.

What would happen if the two halves of the brain had to stop to call one another up and say, “Now I am on the point of starting to say ‘t’ with my half of the mouth. Are you ready with yours?” “Now I am going to tuck on an ‘h.’ Are you ready with your side?” “Now go ahead with the ‘e.’ Start.” It wouldn’t do at all. It’s altogether too slow a way to get talking done. So by way of saving time, one side of the brain has taken entire charge of the talking; for this, one side only of the brain runs both sides of the mouth.

When we eat, then, both sides of the brain are in action. But when we use the very same muscles for speaking, then we use one side of the brain only. When we lift a weight with both hands, we signal to the muscles from both halves of the brain. But when we play the piano with both hands, the same side of the brain takes charge of both. I am, for example, using a type-writer, and writing with both hands. Only one half of my brain, however, has charge of the writing. The other half simply side-tracks itself, stands aside, and doesn’t meddle. But the minute I stop writing and start to put my machine in its case, then the other half-brain switches on again, and takes care of its side. If I should hurt my right hand, so that I had to do all my writing with the left, the writing side of my brain would still do all the writing, while the other side that commonly manages my left hand would stand and look on. All these very special, complex, rapid and difficult tasks, like talking, writing, playing the piano, or running the type-writer, are done by one side of the brain. The slow and easy things are done by both.

But the animals, who do not either talk or write or play musical instruments, they use the two sides of their brains alike.

XIX

Why Most Of Us Are Right-Handed

We do our talking with one side of the brain only. But talking is somewhat intimately connected with thinking. We ought to always, we generally do, think before we speak; while much of our thinking, and on the whole the most important part, consists in saying over words to ourselves.

Speech and thinking, then, go so often together, that it becomes a great convenience to get the thinking done also on one side of the head only, and on the same side with the speech. It might have been either side; it did happen to be the left. One cannot say why, any more than why the heart should be on the left side and the liver on the right, or why some snail shells curl one way and some the other. But at any rate it is the left side.

Now I don’t know whether you have yet been taught in your school physiology, if you have not yet you will be shortly, that the nerves which run from the brain to various parts of the body, cross over to the other side from the one on which they start. Thus the right side of the brain controls the left side of the body; while the left side of the brain controls the right side of the body.

But if the thinking is all done on the left side of the head, which hand will act more quickly on the thought? Evidently, the right hand; messages for that hand travel directly along the nerves, crossing sides once. Therefore we are right-handed.

Some people, however, are born with the “speech center,” as it is called, on the right side of the head instead of on the left. For such persons the most direct path is to the left hand. These persons, then, are naturally left-handed. The difference, therefore, between a right-handed and a left-handed person is not so much in the side of the body with which they have learned to act, as in the side of the brain with which they have learned to think. But the animals, who think on both sides alike, also use either forefoot equally well, and are neither right nor left-handed.

This talking on one side of the brain has another curious result. Did you ever stop to think why a right-handed batter stands with his left side to the ball? Or why a driver of a horse sits on the right hand end of the seat? Or why the engineer of a locomotive sits on the right side of the cab, altho this position forces him to use his left hand for the throttle valve? Or why you sight a gun or look thru a spy-glass with the right eye? Or why you draw a bow with the right hand on the string?

It is all on account of this same one-sided speech center. This has made us right-handed; it has also made us right-eyed. We think much in words; but we also think much about how things look. We think most quickly concerning messages which come in on the thinking side of the brain; and those are from the right eye, since the eye nerves, like those from the hand, cross sides on the way. So hand and eye and speech and thought all use the same side of the head; and sight and thought and action follow one another most easily. Being then right-eyed, we stand to bat, or sit to drive, or use gun or bow or telescope, in the way which gives the better sight to the better eye. But of course, naturally left-handed people are also naturally left-eyed.

Some people, however, are as we say, ambidextrous; that is, they use both hands about equally well, just as all animals do. Nobody, however, is ever naturally ambidextrous. Sometimes the ambidexters are people who have hurt the right hand, and had to learn to use the left. More often they are persons naturally left-handed who have been taught to use the right hand more than is natural in an effort to make them right-handed, tho of course they really are just as left-handed at ever, since no use of the other hand will change over the speech center. But some ambidexters, oddly enough, are made so by an injury to the sight of the right eye, if they were right-handed to begin with, or to the left eye if they were left-handed. Hand and eye have so often to work together and work quickly, that one tends to use the hand on the side of the better eye, even when that is the wrong side.

At any rate, tho it is an excellent plan to learn to do all heavy work equally well on either side of the body and with either hand, fine work and quick work and thinking work had better be done with the hand that does it most naturally. This keeps writing, thinking, speaking, memory, and the rest all close together, on one side of the head, handy to one another, instead of scattering them about, some on the wrong side of the body, some on the right.

Where We Do Our Thinking

We think only on the left side of our heads—that is easy to say if we are normal right-handed persons. If for any reason we have got to thinking on the right side, that will, as I have explained, usually result in making us left-handed.

Yet we do not use the whole of even one side of the brain. So far as is known, we do not think at all with the front part of the head. All our speaking and most of our thinking are done from a spot hardly larger than a cart-wheel dollar, which lies on the side of the head just above the left ear. At any rate, an injury to this particular part of our brain puts a sudden stop to our ability to think and speak.

When you put your left elbow on the table and lean your head on your hand, your hand just about covers the only portion of the brain with which you ever do any thinking at all; while only with the part that lies directly under the middle of the palm, and is as I have said, about the size of a silver dollar, do you ordinarily think very much or hard. This thinking part of the brain lies on the outside, and is just about as thick thru as the hand is.

But even this small thinking place in the brain is not all alike. Directly over the ear, a place that you can almost cover with your thumb, lies the most important part of all, the place where we remember and handle words. At the bottom of this word spot, we remember how words sound. An inch farther up and toward the back, we remember how words look in print. A little farther up and forward lies the “speech center,” from which, when we want to talk, we direct the tongue and lips what to say. Thus we get our word-hearing, our word-seeing, and our word-speaking centers close together, so that when we speak we have close by and handy our memory of what we have heard in words, and of what we have read.

Just below the place where we remember words, and a little forward of it, lies the place where we remember other sounds which are not words, such as the noises of bells and whistles, barking of dogs, mewing of cats, all buzzings and creakings and gratings and crashings, all laughing and crying. Every kind of sound which isn’t either words or music is recognized and remembered here. Beyond this spot, still farther forward and down, and just above the rear end of the cheek-bone, is the place where we remember music. If we don’t know anything about music, and can’t tell Yankee Doodle from Old Hundred, then we don’t use this part of our brains at all. But if we do know one tune from another, and know a good many to recognize them when we hear them, here is where we do the knowing.

Back of the word-seeing part of the thinking spot, and reaching pretty well round to the back of the head, lies the place where we remember everything we see, except words written or in print. Above the word-speaking part of the brain, or speech center, from which we control the mouth, throat, lips, and tongue, which we use in speaking, lie the various points from which we manage other parts of the body. As you might expect, next the speech center lies the center for the rest of the face and for the head and eyes. Above that comes the center for the hand and arm. Still higher up, right on the top of the head, comes the center for the legs. So whenever we do anything with any part of the body, we have to signal the proper muscles from the part of the brain that lies between the tip of the ear and the top of the head. Close behind this region is the spot where we feel everything that touches the skin; so that we can make the movement and feel the results most handily.

So as you see, the surface of the brain is a sort of map or chart of the entire body. Every muscle, every point on the skin, the eyes, the ears, the nose, the tongue, every several organ which we possess, has its own special spot on the surface of the brain, somewhere above or behind the ear. Each half of the body is charted on one side of the brain, a spot in one for each spot in the other. But we who have to use these brains to think and remember with, as well as to see and hear and feel with, and to control our muscles, have chosen to do this thinking and remembering with the spot on the left side of the head which corresponds to the muscles of the lips and mouth and tongue, and to the eyes and ears and the right hand. Thus we have everything convenient, all in one small spot on one side of our heads, where we can get at everything with the least trouble. But what the front part of the brain is for, is something that nobody knows much about.

Certain very strange results follow from this practice of ours of using only one side of the brain to think, remember, and speak with; and using different parts of that for thinking and remembering about different sorts of things. Once upon a time there was a workman who was hit hard enough to break his skull, on the left side of his head, pretty well round toward the back, and just over the spot where, as I have explained, are stored up all the memories of things seen. He seemed not seriously hurt; but when his wife came to see him at the hospital, he did not know her. Neither did he know his children nor his friends. In fact, he didn’t even know that they were human beings. He had absolutely lost the memory of everything that he had ever seen.

But the minute his wife spoke he knew her at once. Or if he could feel of any familiar thing he knew what it was. All the while, he could see perfectly well. His eyesight remained as good as ever, he simply couldn’t remember that he had ever seen things before. The plain seeing, he could do with either side of his head; and the left side being hurt, he did it with the other. But the remembering that he had seen the same thing before, he did with the left side only; and when he could no more do it with that, he could not do it at all. Yet his memory for sounds and the feeling of things was just as good as ever; because the places where he did these sorts of remembering were not under the place where he got hit. And the moment the doctors lifted out the splinter of bone that was pressing on his seeing-things spot, then he remembered wife, children, friends, everything as before.

Here is another case, much like the first, and yet curiously different: An educated woman, somewhat well along in years, went to bed at night in ordinary health. During the night, however, a small blood vessel burst and formed a tiny blood blister on the left side of her brain, about an inch in front of the spot where, as I have been telling, the workman was hit who couldn’t remember his wife when he saw her. She had, in short, a sort of internal black eye, just on the spot that she had been using for sixty years and more to remember written and printed words.

She woke up in the morning, therefore, totally unable to read a single word. She could see as well as ever, understand perfectly every word said to her, speak and write without the least difficulty—but she simply could not read. Give her a printed book, she could count the letters in every word, draw them on paper, tell which were tall, short, round, or square, see them in fact just as well as before—but she no longer knew what they meant. It was exactly as if she had never learned to read at all; and being much too old to learn again, she never read another word as long as she lived.

There is another accident which is so little uncommon that probably every one who reads this book will some time in his life see an example of it. This is a case where a blood vessel bursts on the left side of the brain and wrecks the speech center. The person to whom this happens, immediately forgets how to talk. If the blood clot is small, so it presses upon the speech center and nothing else, the victim of this sort of accident can read and write as before, and understand all that is said to him. Oddly enough, too, he can make any sound that he ever could, and repeat parrot-like any words that he hears. But he cannot remember the meaning of words. He is precisely like a man suddenly transported to a foreign country where they speak a language which he never heard. His own language has become to him like Chinese.