Motor imagery

“ How The Brain Produces Muscular Movements
The motor area is itself aroused to action by nerve currents entering it through axons coming from other parts of the cortex; and it is by way of the motor area that any other part of the cortex produces bodily movement. There are a few exceptions, as, for example, the movements of the eyes are produced generally by the "visual area" acting directly on the lower motor centers for the eye in the brain stem; but, in the main, any motor effect of brain action is exerted through the motor area. ”

“ A lower motor center is a group of motor and central neurones, lying anywhere in the cord or brain stem, and capable of directly arousing a certain coördinated muscular movement. One such unit gives flexion of the leg, another gives extension of the leg, a third gives the rapid alternation of flexion and extension that we see in the scratching movement of the dog. Such a motor center can be aroused to activity by a sensory stimulus, and the resulting movement is then called a reflex. ”

“ Moving objects exert, as is well known, a peculiar motor stimulation upon the eye, they draw our attention and our look after them. If the look really follows them ... we assume that they move. But if the eye, instead of following the moving objects, remains steadfastly at rest, it must be that the constant stimulus to motion which it receives is neutralized by an equally constant current of innervation flowing into its motor apparatus. ”

“ This mode of motor enjoyment is realized when standing in the middle of a building or an avenue of trees, and tracing an imaginary central receding line, and it is noticeable that we naturally place ourselves in the position and execute this kind of movement whenever we wish to appreciate the effect of perspective. It may be added that a union of gradation of velocity with that of duration, as in tracing the path of a projectile across the field of vision, affords the eye its richest form of motor delight. ”

“ To start a mechanism that will produce well-ordered movement, as when I lift this book from the table, impulses or messages, whatever you like to call them, must first be transmitted from the body itself to the brain. Such messages may come to the brain by nerve-fibres from some organ of sense, it may be from the skin, or from the eyes, or from the muscles themselves, but they must be sent to the brain before the brain will send out messages along motor nerves to groups of muscles which are called into action, so as to perform a definite movement. ”

“ First, the question is raised by some psychologists as to whether kinæsthetic or motor images really exist. An example of such an image would be to imagine yourself as dancing, or walking downstairs, or writing your name, or saying the word "bubble." Those who object to such an image type claim that when one tries to get such an image, the attempt initiates slight muscle movements and the result is a sense experience instead of an imaged one. They believe this always happens and that therefore a motor image is an impossibility. ”

“ Thus, a sensation is propagated along the sensory nerve to the sensory nerve-centre, whence it is transmitted to the motor-centre, which acts as an accumulator of stored-up energy, a large flow of which is sent through the large conductor of the motor-nerve to the muscle, which it causes to contract and thus produces motion. It is thus that the simpler involuntary actions are produced by a process which is purely mechanical. In the more complex cases, in which consciousness and will are involved, the process is essentially the same, though more complicated. ”

“ Many physiologists claim that these cells are only excitable by the will. For the theory of motor centers they substitute that of psycho-motors. Reserving this discussion for another time and place, we may say that, whether we excite the cells or the fibers that arise from them, the result is the same.
All stimulation, whatever its nature or origin, acts upon a nerve according to its functions. Excite a motor nerve at any point of its course, and you produce movement; excite a sensory nerve, and the subject will feel a sensation which will vary with the nature of the nerve. ”

“ The far-reaching effects of motor expressions are too infrequently emphasized, but psychology forces us to give them prime consideration. We are first apprised of their importance when we study the nervous system, and find that every incoming sensory message pushes on and on until it finds a motor pathway over which it may travel and produce movement. This is inevitable. The very structure and arrangement of the neurones is such that we are obliged to make some movement in response to objects affecting our sense organs. ”

“ To accomplish a true reflex movement, a whole mechanism is necessary, set up in the spinal cord or the medulla. To choose voluntarily between several definite courses of action, cerebral centres are necessary, that is, crossways from which paths start, leading to motor mechanisms of diverse form but equal precision. ”

“ We conclude, accordingly, that perception of an object is not absolutely the same thing as motor response to the object, nor even as motor readiness to respond, although the transition from perception to motor readiness may be so quick that the whole reaction seems a unit. In reality, perception of the object precedes the motor adjustment, and is one factor in determining that adjustment. ”

“ Everybody, too, must often have observed how the execution of any but mechanical movements arrests attention to thoughts or sensations, and how, vice versa, a striking impression or thought interrupts him in the performance of skilled movements. Let us suppose, then, that we have at any given moment a certain distribution of attention between sensory and motor presentations; a change in that distribution then will mean a change in the intensity of some of all of these. But, in the case of motor presentations, change of intensity means change of movement. ”

“ Its function is to receive stimulation, to provide motor apparatus, and to present the largest possible number of these apparatuses to a given stimulus. The more it develops, the more numerous and the more distant are the points of space which it brings into relation with ever more complex motor mechanisms. In this way the scope which it allows to our action enlarges: its growing perfection consists in nothing else. ”

“ On the other hand, as a great multitude of motor tracks can open simultaneously in this substance to one and the same excitation from the periphery, this disturbance may subdivide to any extent, and consequently dissipate itself in innumerable motor reactions which are merely nascent. Hence the office of the brain is sometimes to conduct the movement received to a chosen organ of reaction, and sometimes to open to this movement the totality of the motor tracks, so that it may manifest there all the potential reactions with which it is charged, and may divide and so disperse. ”

“ We have already shown how the nerve mechanism is so well adapted to the innumerable stimuli of environment that it can accurately transmit and distinguish between the infinite variations of speed in the ether waves producing light, and the air waves producing sound. Each rate of vibration energizes only the mechanism which has been attuned to it. With marvelous accuracy the light and sound waves gain access to the nerve tissue and are finally interpreted in terms of motor responses, each by the brain pattern attuned to that particular speed and intensity. ”

“ Moreover, the process of abstracting these common qualities is itself a motor process. It is, physiologically speaking, the same sort of activity as collecting postage stamps or beetles’ wings. Indeed, the simplest perception of any concrete object, any red object, for example, involves motor activity of a highly elaborate character. When we look at such an object, not only is the retina of the eye stimulated, but various muscles and glands are simultaneously activated to an elaborate transformation of energy. ”

“ The lower motor centers, called also reflex centers, are located in the cord or brain stem, and their nerve cells give rise to the axons that form the motor nerves and connect with the muscles and glands. A muscle is thrown into action by nerve currents from its lower motor center. ”

“ We note in the first place the motor manifestations: movements, gestures, and attitude of the body, a modification in the voice, blushing or pallor, tremors, changes in the secretions or excretions, and other bodily phenomena, varying in different cases. We may observe them in ourselves, in our fellows, and in animals. Although they may not always be motor in the strict sense, we may so call them, since they are all the result of a centrifugal action. ”

“ The discharge from the motor centre into the motor nerve is supposed to give a sensation sui generis, opposed to all our other sensations. These accompany incoming currents, whilst that, it is said, accompanies an outgoing current, and no movement is supposed to be totally defined in our mind, unless an anticipation of this feeling enter into our idea. The movement's degree of strength, and the effort required to perform it, are supposed to be specially revealed by the feeling of innervation. ”

“ It is the universal motor adapted in the most exquisite manner to every form and state of the lungs, which communicate their general motion to every part of the body, and set every wheel in its infinitely complex organism revolving upon its axis, and give to every muscle and nerve the power to expand and contract and vibrate in the performance of its use, and in this way to fill every organ in the whole universe of the body with the power of sensation. ”

“ Closely connected with these facts, perhaps only a somewhat different aspect of them, is the phenomenon of motor mechanization. Any movement repeated tends to become a circular reaction, as it is called; that is, the end of one repetition serves as a cue for the beginning of the next. ”

“ The motor attitude of the animal towards the excitations of the external environment constitutes the predominant part of its objective world. The reactions with their sensori-motor effects are part and parcel of the total percept. Sensori-motor life gives reality to the world of objects. The spatial, the resistant, the material character of objects depends on our motor reactions which give content and reality to the world of things. ”

“ The "weaker and purer" sensory currents furnish "ideas of the environment," while the "motor feelings" only furnish "ideas of the organism." What he means by motor feelings as distinguished from motor impulses following normally upon the discharges of the sensori-motor centers it is difficult to see. He seems to think there can be motor without sensory phenomena, and to forget that all sensory currents, whether peripheral or internal may produce motor effects. ”

“ The lowest condition of the motor system is the limbs, which represent no peculiar sense, but only the sense of feeling refined or set in motion. This motor system ascends into the head, and there no longer exercises its motive powers in prehension, progression, &c., but418 solely unto sensation. Now, a system, which converts its function into that of sensation, is a sense. ”

“ In lifting an object in the hand I can discover no sensation of volitional energy. I perceive in the first place a slight tension about the head, but that this results from a contraction in the head muscles, and not from a feeling of the brain-discharge, is shown by the simple fact that I get the tension on the right side of the head when I move the right arm, whereas the motor discharge takes place in the opposite side of the brain.... ”

“ The circuit which connects any one single perception with action, through sensory nerve, sensory centre, motor centre, motor nerve and muscle, is as purely mechanical as that of an electric circuit. Reflex motions such as breathing, and even more complex motions which by repetition have become reflex or instinctive, are also mechanical and involve no exercise of will. ”

“ But this assumption that sensory and motor ideas are associated before volition, and that volition begins where automatic or reflex action ends, is due to that inveterate habit of confounding the psychical and the physical which is the bane of modern psychology. How did these particular sensory and motor presentations ever come to be associated? The only psychological evidence we have of any very intimate connexion between sensory and motor representations is that furnished by our acquired dexterities, i.e. ”

“ Experiment and pathology, despite all the contradictions, seem to point to the existence of a motor zone on the surface of the hemispheres. This means that certain parts of the brain are directly concerned with the movements of particular muscles and groups of muscles; also, that these parts can not be shown to be connected with sensations. The natural, primary occasions of their activity may be the states of consciousness which we call volitions; they are not, so far as evidence goes, the states of consciousness we call sensations. ”

“ To say that motor-habits, with which when they are established consciousness may have little to do, can be registered in a flexible motor instrument and acted over and over again, is reasonable enough ”

“ Now there is in fact a portion of the cortex in mammals the functions of which are so pre-eminently motor, as judged by our present methods, that it is commonly designated the motor cortex (see fig. 24) . This region of the cortex occupies in the Primates, including Man, the pre-central gyrus. Among the items of evidence which reveal its motor capabilities are the following.
The Precentral or Motor Region of the Cortex.—The application to it of electric currents excites movements in the skeletal muscles. ”