Popular Science Monthly/Volume 28/November 1885/The Motor Centers and the Will
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The Motor Centers and the Will
By Victor Horsley
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By VICTOR HORSLEY, F.R.C.S.
MY subject being the mechanism of the will, it might be asked, "What has a surgeon to do with psychology?" To which I would answer, "Everything." For, without sheltering myself behind Mr. Jonathan Hutchinson's trite saying that "a surgeon should be a physician who knows how to use his hands," I would remind you that pure science has proved so good a foster-mother to surgery, that diseases of the brain which were formerly considered to be hopeless, are now brought within a measurable distance of the knife, and therefore a step nearer toward cure. Again, I would remind you that surgeons rather than physicians see the experiments which so-called Nature is always providing for us—experiments which, though horribly clumsy, do on rare occasions, as I shall presently show you to-night, lend us powerful aid in attempting to solve the most obscure problems ever presented to the scientist.
The title I have chosen may possibly be objected to as too comprehensive; but until we are ready to admit a new terminology, we must employ the old in order to convey our meaning intelligibly, although there may be coupled therewith the risk of expressing more than we desire. Thus, when I speak of the mechanism of the will and the motor centers of the brain, I do not intend (as indeed must be obvious) to discuss the existence of the so-called freedom of the will, or the source of our consciousness of voluntary power.
I shall rather describe to you first the general plan of the mechanism which conveys information to our brain, the thinking organ; next the arrangement of those parts in it which are concerned with voluntary phenomena; and, finally, I shall seek to show by means of experiment that the consciousness of our existing as single beings, the consciousness of our possessing but one will, as people say, while at the same time we know that we possess a double nervous system, is due to the fact that pure volition is dependent entirely on the exercise of the attention which connotes the idea of singleness; consequently, that it is impossible to carry out two totally distinct ideas at one and the same moment of time, when the attention must, of course, be fully engaged upon each.
I fear that, in making my argument consecutive, I shall have to pass over very well-beaten paths, and so I must ask your patience for a few moments while I make good my premises. The nervous system, which in man is composed of brain, spinal cord, nerves, and nerve-endings, is arranged upon the simplest plan, although the details of THE MOTOR CENTERS AND THE WILL. loi
the same become hij^lily complex when we arrive at the top of the brain.
At the saiue time, while we have this t^imple plan of structure, we find that there is also a fundamental mode of action of the same — a mode which is a simple cx))osition of the priiioijdt', no effect willxnit a cause — a mode of action which is known as the phenomenon of simple reflex action.
The general plan of the whole nervous system is illuslrated by this model. Imbedded in the tissues all over the body, or highly special- ized and grouped together in separate organs, such as the eye or ear, we find large numbers of nerve-endings — that is, small lumps of proto- plasm from which a nerve-fiber leads away to the 8j)iual cord and so up to the brain. These nerve-endings are designed for the reception of the different kinds of vibration by which energy presents itself to us. As the largest example of these nerve-endings, let me here show you one of the so-called Pacinian bodies, or, more correctly, Marshall's corpuscles, for Mr. John Marshall discovered these bodies in England before Pacini published bis observations in Italy. Here you see one of these small oval bodies arranged on the ends of one of the nerves of the fingers, and here you see the nerve-fiber ending in the little protoplasmic bulb which is protected by a number of concentric sheaths. Pressure or any form of irritation of this body at the end of the nerve-fiber causes a stream of nerve-energy to travel through the spinal cord to the brain, and so we become conscious that some- thing is happening to the finger.
Here in this section of the sensitive membrane of the back of the eye, the retina, you see a similar arrangement, only more complicated — namely, nerve-fibers leading away from small protoplasmic masses which possess the property of absorbing light and transforming it into nerve-energy. It is this transformation of nerve-energy into heat, light, pressure, etc., which it seems to me should alone be called a sen- sation, irrespective of consciousness. And, in fact, we habitually say we fed a sensation. The terms " feeling " and " sensation," however, are frequently used as interchangeable expressions, although, as I shall show you directly, " feeling " is the conscious disturbance of a sensory center in the surface of the brain, and in fact feeling is the conscious perception of sensations. This distinction between feeling and sensa- tion, if dogmatic, will save us from disjiute as to the meaning of the word "sensation" ; and, further, the distinction is one, as I have just shown, which is justified by custom.
Now, the nerve-fiber which conveys the energy of the sensation is a round thread of protoplasm which in all probability connects the nerve-ending with a sensory corpuscle in the spinal cord. These nerve- fibers running in nerves are white, whereas, as you know, protoplasm is gray. They are white because each is instdated from its fellow by a white sheath of fatty substance, just as we protect telegra})h-wires
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with coatings. It is not stretching analogy too far to say tliat nerve- force may probably escape unless properly insulated.
In consequence of the fibers being covered with these white sheaths, they form what is called the white matter of the brain ; while the nerve-centers are grayish, and therefore form what is called the gray matter of the brain, so that the gray matter receives and records the messages conveyed to it by the white insulated fibers.
From the sensory corpuscle, which is a small mass of protoplasm provided with branches connecting it to neighboring corpuscles, the nerve-energy, if adequate, passes along a junction thread of protoplasm to a much larger corpuscle, which is called a motor corpuscle, and the energy of which, Avhen liberated by the nerve impulse from the sen- sory corpuscle, is capable of exciting muscles into active contraction. These two corpuscles form what is called a nerve-center.
Not only are the motor corpuscles fewer as well as much larger than the sensory ones, but also the nerve-fibers which go out from them are larger too. In fact, it would seem as if we had another close analogy to electrical phenomena ; for here, where we want a sudden discharge of a considerable intensity of nerve-force, we find to hand a large accumulator mechanism and a large conductor, the resistance of which may justly be supposed to be low. Finally, the motor nerve- fiber terminates in a protoplasmic mass which is firmly united to a muscle-fiber, and which enables the muscle-fiber to contract and so cause movement of one or more muscles. Now, with this idea of the general plan on which the whole nervous system is constructed, you will understand that muscular action — i. e., movement — will occur in proportion to (1) the intensity of the stimulation of the sensory cor- puscle ; and (2) the resistance in the different channels. When a sim- ple flow through the whole apparatus occurs, it is called a simple reflex action, and this was discovered in England by Dr. Marshall Hall.
To recapitulate : A nerve-center, theoretically speaking, we find to consist of a sensory corpuscle on the one hand and a motor corpuscle on the other, both these being united by junction threads or commis- sures. To such a center come sensations or impressions from the nerve-endings, and from such a center go out impulses which set the muscles in action.
I have dwelt thus at length on this most elementary point, because it appears to me that, in consequence of the rapidity with which func- tion is being demonstrated to be definitely localized in various portions of the cerebral hemispheres, we are in danger of losing sight of Dr. Hughlings-Jackson's grand generalizations on nerve-function, and that we are gradually inclining to the belief that the function of each part is very distinct, and therefore can most readily act without disturbing another part. In fact, we are perhaps drifting toward the quicksands of spontaneity, and disregarding entirely the facts of every-day life
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which show that every cyde of nerve-action includes a disturbance of the sensory side as well as the active motor agency. Did we, in fact, admit the possibility of the motor corpuscle acting per se, and in the absence of any sensory stimulation, we should again be placed in the position of believing that an effect could be produced in the absence of a cause.
For these reasons such a center has been termed kinssthetic or sensori motor, and such centers exist in large numbers in the spi- nal cord, and they perform for us the lower functions of our lives without arousing our consciousness or only the substrata of the same.
But now, turning to the brain, although I am extremely anxious to maintain the idea just enunciated that, when discussing the abstract side of its functions we should remember the sensori-motor arrange- ment of the ideal center, I shall have to show you directly that the two sides — namely, the sensory and motor — in the brain are separated by a wide interval, and that in consequence we have fallen into the habit of referring to the groups of sensory and motor corpuscles in the brain as distinct centers. I trust you will not confuse these expressions, this unfortunately feeble terminology, and that you will understand, although parts may be anatomically separated and only connected by commissural threads, that functionally they are closely correlated. In consequence of the bilateral symmetry of our bodies we possess a double brain — a practically symmetrical arrangement of two intimate- ly connected halves or hemispheres which, as you know, are concerned with opposite sides of the body, for the right hemisphere moves the left limbs, and vice versa.
For my purpose it will be sufficient if we regard the brain as com- posed of two great collections of gray matter or nerve-corpuscles which are connected with sensory nerve-endings, with muscles, and intimately with one another.
In this transverse section of a monkey's brain, which is stained dark-blue to show up its component parts, you will see all over the surface a quantity of dark -gray matter, which is simply the richly convoluted surface of the brain cut across. Observe, it is about a quarter of an inch deep, and from it lead downward numerous white fibers toward the spinal cord. The surface of the brain, the highest and most complicated part of the thinking organ, is called the cortex, bark, or rind, and in it are arranged the motor centers I am about to describe. These white fibers coming away from it to the cord, not only are channels conveying messages down to the muscles, but also carrying messages from the innumerable sense-corpuscles all over the body.
So much for one gray mass of centers. Now, down here at the base of the brain you see two lumps or masses of the same nature, and these are called, therefore, the basal ganglia or gray masses. Since they are placed at the side of the paths from the cortex, and undoubt-
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edly do not interfere with the passage of impulses along those paths, we may put them aside, remembering that they probably are con- cerned with low actions of the nervous system, such as eating, etc., which are popularly termed automatic functions.
In this photograph of a model made by Professor Aeby, of Berne, you see represented from the front the two cerebral hemispheres with the centers in the cortex as little masses on the surface, and the basal ganglia as darker ones at the bottom, while leading from them down into the spinal cord are wires to indicate the channels of communica- tion.
Note, in passing, that both hemispheres are connected by a thick band of fibers called the " corpus callosum." It is, I believe, the close union thus produced between the two halves that leads in a great measure (though not wholly) to consonance of ideas.
The arrangement of the fibers will be rendered still clearer by this scheme, in which the cortex is represented by this concave mass, and the fibers issuing from the same by these threads. The basal ganglia would occupy this position, and they have their own system of fibers.
I will now leave these generalizations, and explain at once the great advance in our knowledge of the brain that has been made during the last decade. The remarkable discovery that the cortex or surface of the brain contained centers which governed definite groups of muscles, was first made by the German observers Hitzig and Fritsch ; their results were, however, very incomplete, and it was reserved for Pro- fessor Ferrier to produce a masterly demonstration of the existence and exact position of these centers, and to found an entirely new scheme of cerebral physiology.
The cortex of the brain, although it is convoluted in this exceed- ingly complex manner, fortunately shows great constancy in the ar- rangement of its convolutions, and we may therefore readily grasp the main features of the same without much trouble. From this photo- graph of the left side of an adult human brain you will see that its outer surface or cortex is deeply fissured by a groove running back- ward just below its middle, which groove is called the "fissure of Syl- vius," after a distinguished mediaeval anatomist. This fissure, if car- ried upward, would almost divide the brain into a motor half in front and a sensory half behind.
Of equal practical importance is another deep fissure which runs at an open angle to the last, and which is called the " fissure of Rolando," Rolando being another pioneer of cerebral topography. Now, it is around this fissure of Rolando that the motor side of the centers for voluntary movement is situated ; and when this portion of the cortex is irritated by gentle electric currents, a constant movement follows according to the part stimulated.
Because of their upward direction, the convolutions bounding the fissure of Rolando are called respectively the " ascending frontal " and
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- ascending parietal " convolutions. Now here, at the lowest end of
the fissure of Rolando, wc find motor areas for the movement of both sides of the face : that is to say that, as regards this particular piece of the cortex, it has the power of moving not only its regular side of the face, the right, but also the left — that, in fact, both sides of the face move by impulse from it.
Higher up we find an area for movement of the opposite side of the face only. I reserve for a moment the description of this portion of tho brain, and pass on to say that above these centers for the face we find the next is for the upper limb, and most especially the com- mon movement of the upper limb — viz., grasping, indeed the only for- ward movement which the elbow is capable of, namely, flexion. The grasping and bringing of an object near to us is the commonest move- ment by far, and we find here that this cenrter is mainly concerned in it. Behind the fissure of Rolando, Dr. Ferrier placed the centers for the fingers. Next above the arm area is a portion of the cortex which moves the lower limb only, and in front of this again is an area for consonant action of the opposite arm and leg. Let me here remind you that this being the left hemisphere, these are the centers for move- ment of the opposite, that is, the right limbs, and that in the other hemisphere there are corresponding areas for the left limbs.
Thus here we have mapped out those portions of the cortex which regulate the voluntary movement of the limbs. So far I have omitted mention of the muscles of the trunk, namely, those which move the shoulders, the hips, and bend and straighten the back. Dr. Ferrier had shown that there existed on the outer surface of the cortex, here, a small area for the movement of the head from side to side.
Professor Schiifer and myself have found that the large trunk- muscles have special areas for their movement, ranged along the margin of the hemisphere, and dipping over into the longitudinal fissure. Thus all the muscles of the body are now accounted for, and I will first draw special attention to the fact that they are arranged in the order, from below upward, of face, arm, leg, and trunk.
The consideration of this very definite arrangement led Dr. Lauder Brunton to make the ingenious suggestion that it followed as a neces- sary result of the progressive evolution of our faculties. For, premis- ing, in the first place, from well-ascertained broad generalizations, that the highest center, physically speaking, is also the highest functionally and most recent in acquirement, we find that the lowest is the face, and then we remember that the lowest animals simply grasp their food with their mouth. I imagine it is scarcely necessary for me to repeat the notorious confession that our faculties are arranged for the pur- pose of obtaining food as the primary object of what is called bare existence.
Proceeding upward in the scale of evolution, we next find animals which can grasp their prey and convey it to the mouth, and so we find
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next to the face area evolved that for the arm. And so on, the next step would be the development of the legs to run after the prey, and here is the leg-center ; while, finally, the trunk-muscles are dragged in to help the limbs more effectually. To my mind this idea receives overwhelming support from the consideration of the fact that, the higher our centers are, the more they require education ; the infant, for instance, in a few days shapes its face quite correctly to produce the food-inspiring yell, yet takes months or years to educate its upper limbs to aid it in the same laudable enterprise. Finally, what terrible probation some people pass through at the hands of dancing-masters before their trunk-muscles will bend into the bow of politeness !
Now to return to the lower end of the fissure of Rolando, to the areas for movements of the face : it was long ago pointed out by the two Daxes and Professor Broca that when this portion of the brain immediately in front of the face area was destroyed, the person lost the power of articulate speech, or was only capable of uttering injec- tions and customary " strange oaths." In fact, this small portion of the left side of our brains (about one and a half square inch) is the only apparatus for expressing our thoughts by articulating sounds, and note particularly that it is on the left side. The corresponding piece on the right side can not talk, as it were. This remarkable state of things is reversed in left-banded people. In these the right hemi- sphere predominates ; and so we find that, when this portion was dis- eased, there followed aphasia, as it is called. While, however, the right side customarily says nothing, it can be taught to do so in young people, though not in the aged.
Before leaving these motor areas, let me repeat, by way of recapit- ulation, that the only truly bilaterally acting areas are those for the lower facial and throat muscles. This is a most important fact, for the idea has recently been propounded that both sides of the body are represented in each motor region of each hemisphere. That is to say, each motor area has to do with the movements of both upper limbs, for example. In support of my contention that this is not in accord- ance with clinical facts, let me here show you photographs of the brain of a man who was unfortunate enough to suffer destruction of the fibers leading from one motor area. Here you see a puncture in the brain which has caused haemorrhage beneath the fissure of Ro- lando and the motor convolutions in front and behind it.
In this transverse section of the same spot you see that the haemor- rhage has plowed up the interior of the brain. Here is the cortical gray matter, but its fibers leading down to the muscles are all de- stroyed. Kow, in examining this patient I asked him to move his left arm or leg ; he was perfectly conscious, and, understanding the ques- tion, made the effort, as we say, but no movement occurred. Now, if both sides of the body are represented in each hemisphere, it seems to me that such a case would be impossible, or at least that a little prac-
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tice would enable the other hemisphere to do the work ; but all clini- cal facts say that, once destroyed, the loss is never recovered.
If we examine this motor region of the cortex with the microscope, we of course find these large corpuscles, which we have learned are those which alone give energy to the muscles. But you must not imagine that the motor region consists solely of these corpuscles. On the contrary, as you see in this diagram, we have several layers of cor- puscles. I shall return to this arrangement of the corpuscles directly.
Looking back at the surface of the brain, you notice that I have only accounted for but a small portion of the cortex. Dr. Ferrier was the first to show that the portion of cortex which perceived (and I use the word in its strictest sense) the sensation of light was this part, and it is therefore called the " visual center or area." From recent re- searches it would appear that we must give it the limits drawn on this diagram ; below it Ave find the center for hearing. Thus we know where two sense perceptive centers are situated.
Microscopical investigation shows that this sensorial portion of the cortex is very deficient in large corpuscles, and is correspondingly rich in small cells. Here in this diagram you see these two kinds of struct- ure in the cortex cerebri. Xote the greater number and complication of the small corpuscles in the sensory part of the cortex, and the com- paratively fewer though much larger corpuscles in the motor region.
It seems to me that several beliefs are justified by these facts : In the first place, the movements produced by the action of these motor centers are always the same for the same center ; consequently, it has only one thing to do, one idea, as it were. Thus, for instance, bend- ing of the arm : this action can only vary in degree, for the elbow will not permit of other movements. Hence we may look upon it as one idea. Now, observe that where one idea is involved we have but few corpuscles. Next, consider the multitude of ideas that crowd into our mind when we receive a sensation. One idea, then, rapidly calls up another, and so we find anatomically that there are a corresponding much greater number and complication of nerve-corpuscles. To sum up, I believe we are justified in asserting that where in the nervous system a considerable intensity of nerve-energy is required — e. g., for the contraction of muscles — you find a few large corpuscles and fibers provided ; and that where numerous ideas have to be functionalized, there numerous small corpuscles are arranged for the purpose.
But, now, the special interest attaching to the sensory perceptive areas is that they, unlike the motor areas, tend to be related to both sides of the body. With our habit of constantly focusing the two eyes on one object, it will strike you at once that habitually we can only be attentively conscious of one object at a time, since both eyes are engaged in looking at it, and, as you know, we can not as a mat- ter of fact look at two things at once.
Hence, I take it, both sensory perceptive centers are always fully
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occupied with the same object at the same moment, and that therefore we have complete bilateral representation of both sides of the body in each hemisphere. As a further consequence, each sensory perceptive area will register the idea that engaged it ; in other words, both cen- ters will remember the same thing. Thus it happens that each sensory area can perform the duty of the other, and therefore it is a matter of comparative indifference whether one is destroyed or not, and as a mat- ter of fact when this happens we find that the person or animal recog- nizes objects as they actually are, and in fact has no doubt as to their nature. Here you see anatomically the reason of this peculiarity is found to be that the optic or seeing nerves cross one another incom- pletely in going to each hemisphere, and thus each sensory center rep- resents half of each eyeball.
I must pass rapidly to the description of the rest of the surface of the brain — the hinder and front ends. At the outset I must admit that all our knowledge concerning them is very hypothetical in the absence of positive experimental results.
This much we can say, that they are probably the seats of intel- lectual thought, for many reasons which I have not time to detail. Further, we know that these intellectual areas are dependent for their activity entirely on the sensory perceptive centers, for the dictum that there is no consciousness in the absence of sensory stimulation is very well established, as I shall now show you, however astounding it may appear. In the first place, you will remember that when we wish to encourage that natural loss of consciousness which we call sleep, we do all we can to deprive our sense-organs and areas of stimulation. Thus we keep ourselves at a constant temperature, we shut off the light, and abolish all noises if we can. But a most valuable observa- tion was made a few years ago by Dr. Striirapell, of Leipsic, who had under his care a youth, the subject of a disease of the brain, etc., which, while destroying the function of one eye and ear, besides the sensibility to touch over the whole body, still left him when awake quite conscious and able to understand, etc., using his remaining eye and ear for social intercourse. Now, when these were carefully closed he became unconscious immediately, in fact slept, and slept until he was aroused again, or awoke naturally, as we say, after some hours. Hence the higher functions of the brain exercised when that organ is energizing the reasoning of the mind are absolutely dependent upon the reception of energy from the sense perceptive areas.
But my only point with reference to this part of the brain is to attempt to determine how far they are connected with the motor cen- ters in the performance of a voluntary act. With the mechanism of choice and deliberate action I have nothing to do ; but there can be no doubt that the part of the brain concerned in that process of the mind is directly connected with the motor region, as indicated on this diagram, to which I would now return. From what I have here writ-
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ten you read, arranged schematically, the psychical processes, which, for the sake of argument, we may assume are carried on by the mind in these portions of the cortex.
I wish to point out that we have structurally and physiologically demonstrated with great probability the paths and centers of these psychical actions. There is no break : the mere sight of an object causes a stream of energy to travel through our sense areas, expand- ing as it goes by following the widening sensory paths here repre- sented, and at the same time we feel our intellect learns that new ideas are rising up and finally expand into the process of deliberate thought, concerning which all we know is from that treacherous support, name- ly, introspection.
Then come impulses to action, and these follow a converse path to the receptive one just described ; the nerve-energy is concentrated more and more until it culminates in the discharge of the motor cor- puscles. We might represent the whole process of the voluntary act by two fans side by side, and the illimitable space above their arcs would serve very well to signify the darkness in which we sit con- cerning the process of intellectual thought,
"What I have hastily sketched is the outline of the process of an attentive or voluntary act. I say attentive advisedly, for I wish now to put forward the view that the proper criterion of the voluntary nature of an act is not the mere effort that is required to perform it, but is the degree to ichich the atteyition is involved. The popular view of the volitional character of an act being decided by the effort to keep the action sustained is surely incomplete, for in the first place we are not seeking to explain our consciousness of an effort ; we endeavor to discover the causation of the effort. Our sense of effort only comes when the will has acted, and that same sense is no doubt largely due to the information which the struggling muscle sends to the brain, and possibly is a conscious appreciation of how much energy this motor corpuscle is giving out.
Now, to give you an example. I see this tambour, and decide to squeeze it, and do so. Now, this was a distinctly voluntary act ; but the volitionary part of it was not the effort made, it was the deliber- ate decision to cause the movement. I may now point out that in this whole process we say, and say rightly, that our attention is in- volved so long as we are deliberating over the object ; that as soon as another object is brought to us our attention is distracted, that is to say, turned aside.
All writers are agreed that the attention can not be divided, that we really only attend to one thing at once. It seems to me that this is so obvious as not to require experimental demonstration ; but I have led up to this ])oint because I now wish to refer to the third part of my subject, namely, the question as to whether we have a really double nervous system or not. But, by way of preface, let me re-
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peat that, although we may have a sub-consciousness of objects and acts, that sub-conscious state is true automatism, and that such auto- matic acts are in no sense vohintary until the attention has been con- centrated upon them. For example, again I press this tambour, be- cause I desire to raise the flag, and I keep that raised while I attend to what I am saying to you. My action of keeping the flag raised is only present to my consciousness in a slight or subordinate degree, and does not require my attention, deliberate thought, or choice, and therefore, I repeat, is not a voluntary action ; in fact, it could be carried on perfectly well by this lower sensori-motor center, which only now and then sends up a message to say it is doing its duty, in the same way as a sentry calls out " All is well " at intervals.
But to return. In consequence of the obvious fact that we have two nerve-organs, each more or less complete, some writers have im- agined that we have two minds ; and to the Rev. Mr. Barlow, a former secretary of this Institution, is due the credit of recognizing the circumstances which seem to favor that view. It was keenly taken up, and the furore culminated in a German writer (whose name, I am ashamed to say, has escaped me) postulating that we pos- sess two souls.
Now, the evidence upon which this notion rests, that the two halves of the brain might occasionally work independently of one another at the same moment, was of two kinds. In the first place it was asserted that we could do two different things at once, and in the second place evidence was produced of people acting and thinking as if they had two minds.
Now, while of course admitting that habitually one motor center usually acts at one moment by itself, I am prepared to deny in toto that two voluntary acts can be performed at the same time, and I have already shown what is necessary for the fulfillment of all the condi- tions of volition, and that these conditions are summed up in the word attention.
Further, I have already shown that, when an idea comes into the mind owing to some object catching the eye, both sensory areas are engaged in considering it. It seems to me I might stop here, and say that here was an a priori reason why two simultaneous voluntary acts are impossible ; but as my statements have met with some oppo- sition, I prefer to demonstrate the fact by some experiments.
The problem, stated in physiological terms, is as follows : Can this right motor region act in the process of volition, while at the same time this other motor area is also engaged in a different act of voli- tion ? Some say this is possible ; but in all cases quoted I have found that sub-conscious or automatic actions are confused with truly volun- tary acts. I mean that such automatic acts as playing bass and treble are not instances of pure volition, as the attention is not engaged on both notes at once.
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Consider for a moment the passage of the nerve impulses through the brain that would liave to occur. At the outset we find that the sensory perceptive centers would have to he engaged with two differ- ent ideas at once ; but Lewes showed long ago that introspection tells us this is impossible, that '* consciousness is a seriated change of feel- ings " : he might equally well have said ideas. And, again, we know that when two streams of energy of like character meet, tliey mutually arrest each other's progress by reason of interfering with the vibration- waves.
I will show directly that this is actually the case in the action of the cortex when the above-mentioned dilemma is presented to it. The experiment I have devised for this purpose is extremely simple. A person who is more or less ambidextrous, and who has been accus- tomed for a long time to draw with both hands, attempts to describe on a flat surface a triangle and circle at the same moment. I chose these figures, after numerous trials, as being the most opposite, seeing that in a triangle there are only three changes of movement, while in a circle the movement is changing direction every moment. To insure the attempt to draw these figures simultaneously succeeding, it is ab- solutely necessary that the experimenter should be started by a signal.
"When the effort is made, there is a very definite sensation in the mind of the conflict that is going on in the cortex of the brain. The idea of the circle alternates with that of the triangle, and the result of this confusion in the intellectual and sensorial portions of the brain is that both motor areas, though remembering, as it were, the determi- nation of the experimenter to draw distinct figures, produce a like confused effect, namely, a circular triangle and a triangular circle. If the drawing is commenced immediately at the sound of the signal, it will be found that the triangle predominates ; thus, if I determine to draw a triangle with my left hand and a circle with my right, the tri- angle (though with all its angles rounded off) will be fairly drawn, while the circle will be relatively more altered, of course made trian- gular. On the other hand, if the two figures are not commenced simultaneously, it will be found that usually the one begun last will appear most distinct in the fused result, in fact, will very markedly predominate.
Now, the course of events in such an experiment appears to be clear. The idea of a triangle and circle having been presented to the intellect by the sensory centers, the voluntary effort to reproduce these is determined upon. Now, if we had a dual mind, and if each hemi- sphere was capable of acting per se, then we should have each intel- lectual area sending a message to its own motor area, with the result that the two figures would be distinct and correct, not fused.
The other evidence that I referred to above, which is adduced in favor of the synchronously independent action of the two hemispheres is from the account of such cases as the following : Professor Ball, of
�� � Paris, records the instance of a young man who one morning heard himself addressed by name, and yet he could not see his interlocutor. He replied, however, and a conversation followed, in the course of which his ghostly visitant informed him that his name was M. Gabbage.
After this occurrence he frequently heard M. Gabbage speaking to him. Unfortunately, M. Gabbage was always recommending him to perform very outrageous acts, such as to give an overdose of chlorodyne to a friend's child, and to jump out of a second-floor window. This led to the patient being kept under observation, and it was found that he was suffering from a one-sided hallucination. Similar cases have been recorded in which disease of one sensory perceptive area has produced unilateral hallucination.
I can not see that these cases in any way support the notion of the duality of the mind. On the contrary, they go to show that while as a rule the sensory perceptive areas are simultaneously engaged upon one object, it is still possible for one only to be stimulated, and for the mind to conclude that the information it receives in this unusual way must be supernatural, and at any rate proceeding from one side of the body.
To conclude, I have endeavored to show that as a rule both cerebral hemispheres are engaged at once in the receiving and considering one idea; that under no circumstances can two ideas either be considered or acted upon attentively at the same moment; that therefore the brain is a single instrument.
It now appears to me that one is justified in suggesting that our idea of our being single individuals is due entirely to this single action of the brain,
Laycock showed that the Ego was the sum of our experience, and every writer since confirms him. But our experience means (1) our perception of ideas transmitted and elaborated by the sensory paths of the brain; and (2) our consciousness of the acts we perform. If, now, these things are always single, the idea of the Ego surely must also be single.—Nature.
- Lecture delivered at the Royal Institution of Great Britain.