The Parents' Review

A Monthly Magazine of Home-Training and Culture

Nervous Mechanisms and Their Bearings on Education

II.

As regards the functions of those higher nervous structures, which we are now about to consider, it is a great difficulty in conveying clear ideas about them, that although the general facts are certain, yet the details, especially as to the localities to which the different functions belong, are unsettled; and I do not like to state any one theory about dubious matter where my limits prohibit allusion to other theories, so I must confine myself to general statements, which are always less intelligible than particular ones and less easy of illustration.

Recurring to the case of a tickled foot; we traced the impulse from this irritation through various cells, whose activity, thus excited, performed various functions; the impulse further passes to certain other cells in the brain, whose excitement, when sufficient and attended to, causes the phenomenon of consciousness. For clearness sake, let us drop the consideration of the other cells and confine ourselves to these of consciousness. Suppose a needle-point is gently placed against the skin of the foot, an impulse is sent along a nerve-fibre (probably through various cells) which reaches a certain cell in the brain; this cell is excited to action, and that action causes consciousness; the individual is conscious of the touch on that part of his skin. The consciousness is acute in proportion to the degree of the cell action, and when this exceeds a certain amount the consciousness becomes unpleasant. The degree of the cell action depends partly on the degree of the skin irritation; if the skin is barely touched by the needle point, the resulting cell action may be so slight as not to cause any consciousness, then the touch will not be felt; a little more contact and the increased cell action causes consciousness, the point is just felt; a little more and the still increased cell action causes marked consciousness, the point is distinctly felt; further cell action causes an unpleasant degree of consciousness, the prick is now painful. The amount of the cell action also depends on the attention given to it; suppose the needle point pressed gently against the skin; if the attention is diverted elsewhere, as by some strong interest, the point will be quite unfelt; that is, the action of the nerve cell will be drawn to the point and it will be at once felt; let attention be fixed intently on the sensation and it will become more and more acute and may become painful, even unbearably so. Let some interest again divert attention, and the point is again unfelt. Here there is no change in the external conditions, and therefore the changes in the cell action must be due to internal influence; this may be partly from impulses through its connections with other nerve-cells, but is mainly the effect of the mere attention itself. Each little spot of skin over the body is connected with its own nerve-cell in the brain; and irritation of each spot causes action of its corresponding cell, and this causes consciousness of the irritation of the spot of skin. The collection of these nerve-cells we may call the "touch-centre;" the whole surface of the body is represented in it.*

* In actual fact it is the minute organs of touch in the skin that are connected with these nerve cells. The number of these organs varies greatly in different parts of the body; they are very numerous in the lips, tip of tongue, and finger tips, very few and scattered on the back, for instance, hence the acuteness of the sense of touch in the former parts, which are very much represented in the touch-centre.

Let us now turn to a really easier example, sight; for simplicity's sake consider only one eye. The images of all objects fall in miniature on the interior of the back of the eye, over which is spread a delicate membrane called the retina, which is the actual organ of sight; from every spot of the retina, nerve fibres pass to the back of the eye, and all these fibres, united, form a thick nerve called the optic nerve; this passes back into the brain, and there each fibre eventually passes into a nerve-cell, so that each spot of the retina is represented by a collection of nerve-cells; this collection of cells we will call the "sight-centre."* Suppose now an eye open in the dark; the retina is unaffected, and the sight-centre cells quiet; now let a feeble spark appear; its image falls on a spot of the retina, which sends an impulse to its cell in the sight-centre, causing action in that cell; and this causes consciousness, the consciousnes of that spark. Let the spark brighten, and the cell action is increased, and the consciousness is greater; with greatly increased irritation the cell action may be so violent as to cause an unpleasant degree of consciousness, or pain; but this never to the same degree as in the case of touch. Now, suppose, instead of a single spark, a line of light of definite shape, say a circle, then a definite set of nerve-cells will be thrown into action; the consciousness caused by this will be the idea of a circle. Thus we see how all our ideas of form arise, they are the consciousness caused by the action of definite groups of nerve cells in the sight-centre. Again, brightness and dulness are merely the degrees of consciousnes caused by the degrees of violence of the cell actions. A certain group of cells slightly acting causes the consciousness of a certain dull figure; violently acting, of the same figure bright; some of the cells acting slightly and some violently, will cause the consciousness of the same figure partly dull and partly bright.

* I adopt these terms quite arbitrarily, and without reference to their ordinary text-book significance.

A cell may vary not only in the degree but in the manner of its action; thus, if the spark be red, we have one manner of action of the cell, if blue, another. The former causes the consciousness of a red spark, the latter of a blue spark; thus we get our ideas of coulour.

We see now how all our ideas of outline, light and shade, and colour, which form the mass of knowledge derived from eyesight, are dependent on cell action; outline, definite group of cells; light and shade, degree of action; colour, manner of action.

We are dependent, then, for our idea of any object of sight first, on the eye; next, on the collection of cells constituting the sight-centre. If any of these cells are defective, so much of our field of vision is impaired; if all these cells are absent, or inactive, we can have no consciousness of any object of sight at all.

When a panorama is passing before the eye, there is a continued succession of varying actions in the nerve-cells of the sight-centre; such a succession of actions may take place without the panorama; one view might be presented, and the eye closed; there will then be a variety of cell actions caused by the view, and these will start a succession of cell actions, which will be maintained in virtue of the cell connections, just as in the case of the controlling cells; but, instead of causing a succession of movements as these did, the cells we are now considering will cause a succession of states of consciousness, or a train of thoughts; or, as we limit ourselves at present to the sight-centre, a mental panorama.

When cells are once excited to action there is a certain effect produced upon them, which is permanent in proportion to the degree of the action and the frequency of its repetition; in the cells of consciousness the effect of this change in their constitution is such that when another similar action of the cells takes place, it not only causes the consciousness appropriate to it, but also the additional consciousness that it occurred before; this constitutes Memory. For instance, a certain image is presented, and excites the definite combination of cell actions which causes the consciousness of that image; the next time this same combination of cell actions occurs, the same consciousness of that image will be again caused, and the additional consciousness that it was experience before; that is, the image will not only be seen but remembered. The vividness of this second consciousness (i.e., the consciousness of former experience) will depend on the amount of permanent change impressed on the nerve cells before; and this depends on the amount of the former cell action, and the frequency of its repetition; that is to say, the vividness of memory depends on the intensity of the first impression, and on its repetition, as we already know. Again, the impression on the nerve-cells may wear out, especially if slight; then, when the image reappears, it will excite its definite cell actions, and they will cause the consciousness of the image; but there will be no additional consciousness of its having been seen before; it will have been forgotten.

All that has been said about sight applies equally to hearing, smell, and all the other senses. Each sense has its collection of nerve-cells, whose action causes the consciousness of the ideas of that sense; and it is only through the action of the cells in each "sense-centre" that the consciousness of the ideas of that sense can arise; were such cells absent, the corresponding ideas would not exist. Thus, if the cells of the smelling centre were destroyed, the individual would never have another idea of smell, nor any consciousness of what smell was at all; similarly, for each other sense. If all the sense-centres were absent, he would have no consciousness whatever; he would be "unconscious." The same thing would happen temporarily if the sense-centres were rendered inactive, as in the following instance. All the organs of the body depend on a free supply of pure blood for their healthy action, and, when exhausted by vigorous action, need rest, that is, restoration by a free blood supply, before their functions can be resumed; this is most the case in the most active organs, such as nerve-cells; if a nerve-cell is deprived of blood its action at once ceases. When we receive any severe shock, such as a fright of severe pain, the action of the heart is lowered; and this may be to such a degree that the circulation of blood in the brain is insufficient for the nerve-cells to carry on their functions; then the individual faints, becomes unconscious. When a person faints, they usually first lose vision, everything becomes blank, that is, the sight-centre cells failing; then sounds pass away and they hear nothing, hearing-centre cells failing; then they lose all consciousness, all other sense-centre cells fail.

The cells in each sense-centre are connected freely with each other, and also with the cells in the other sense-centres, so that an impression from one sense may excite a succession of cell actions through all the sense-centres; the consciousness caused by this will be a train of general thoughts. To illustrate this, suppose a lump of sugar presented to the eye, then certain cells in the sight-centre will be excited and cause the consciousness of its whiteness and form. From these cells impulses will pass to certain cells in the touch-centre, whose excitement will cause the consciousness of its peculiar roughness. From these cells impulses will pass to certain cells in the taste-centre, causing the consciousness of its sweetness. From these, cells in the hearing-centre will be excited, causing the consciousness of the noise of its crunching. Why does the sight of the lump of sugar start this particular train of thought? Because of the cell connections. What has formed these cell connections so? Education. When the baby first looks at a lump of sugar no ideas beyond those of its colour, shade, and outline arise; the cells in the sight-centre on which these ideas depend act, and impulses tend to pass in various directions, but no cell connections are developed enough to excite other cells sufficiently to cause definite consciousness. Then the baby picks up the lump of sugar, and the cells in the touch-centre act, giving the consciousness of its roughness, and the flow of the impulse between the sight-centre cells and these touch-centre cells is facilitated and the development of the connecting fibres is encouraged. Then the baby puts the sugar in his mouth, and the same thing occurs in reference to its sweetness; he crushes it and the sound is connected. The next time the baby sees a lump of sugar the succession of cell actions takes place more readily, and after a few times the cell connections have developed, the succession is established. Then, when these cells in any one of the sense-centres are thrown into action by impulses from its own sense organ, all the others will be thrown into action too; that is, the sight, or feel, or taste, or sound of the sugar will, any one of them, suggest the ideas of all its other properties.

This example is a simple illustration of the "association of ideas," a most important element in education; and it shows that this association is merely due to the manner in which the nerve-cell connections are developed; all the ideas of the various qualities of the lump of sugar are associated with each other through the development of the cell connections mentioned above.

The same example also illustrates one of the most important faculties of the mind, the imagination, and shows its physical basis. Imagination is the power of having ideas without the actual external presence they represent; and it is seen to depend on the fact that the cells of consciousness may, through their connection with other cells, be thrown into action independently of their own sense organs. Now, the action of a cell, and therefore the resulting consciousness, is essentially the same, whether it is caused by an impulse from its connection with its organ of sense, or by an impulse from its connection with another cell; therefore an imagined idea is essentially the same as an idea from the senses. But the vividness of the idea depends on the degree of consciousness caused, and that on the degree of cell excitement; and usually the impulse from the senses is stronger than that from other cells; therefore, for this reason the sense idea is more vivid than the imagined idea. But again, attention will have very great influence; we have seen that by attention cell action is intensified, and by neglect weakened, so by attending to the sense excited by impulse from other cells, its action may be rendered just as vigorous as if it were excited by a sense impulse; and so the consciousness caused may be as great, and the idea as vivid; that is, by attention an imagined idea may be rendered as vivid as a sense idea. Usually, however, rather the reverse is the case; when some of the cells in a sense-centre are excited from other cells, and some of the cells in the same sense-centre are excited from its own sense, the latter will be usually attended to and intensified, that is, the sense idea will overpower the imagined idea.

For example, if, when gazing at the street we hear the word grass, then we may imagine grass, see it, but faintly, and divested of all reality by the street paving actually see; if we close the eyelids the image of the grass is much more vivid; and, in a slightly dreamy state, when the attention is taken off other things, the imagined grass may be very vivid indeed; as vivid as reality. The cell conditions which cause all this are as follows. The sounds of the word grass sends impulses to certain cells in the hearing-centre, which in their turn send impulses to certain cells in the sight-centre; these, being thus excited to action, cause the consciousness of seeing grass; but the action of these cells in the sight-centre is feeble, and the attention is diverted from them by the consciousness caused by the more vigorous action of cells in the same centre excited directly from the eyes, which consciousness (that of the paved street) is therefore more vivid than that of the grass. If by closure of the eyelids the impulses from the eyes are cut off, then the cell actions which cause the consciousness of the street paving cease, and the attention is more directed to those cells whose action causes the consciousness of grass, and their action is therefore intensified and the image of the grass more vivid.

In many instances it is impossible for us to tell whether the cell actions, which cause consciousness, are excited by impulses from the senses, or from other cells; then we do not know whether the idea is imagined, or caused by the actual presence it represents. This is the case in dreaming, and is the cause of hallucinations. A very common instance of how readily the consciousness caused by cell actions excited from within may be taken as caused from without (or in other words, how readily imagined things may be taken for actual things) is in the idea we get of the appearance of an object hastily seen. In such a case what happens is this: a certain number of cells in the sight-centre act from impulses received from the hasty glance; more cells in this centre act through their connections with these externally excited cells, or perhaps through their connections with cells in other centres; the action of all these cells in the sight-centre causes a consciousness of a complex image, some of which is due to actual sense impulses, but most of which is, evidently, purely imaginary, due to cells excited from within. Most of our ordinary views of things are of this type, having only a main feature or two drawn from actual sight, the details being filled in by imagination; for instance, a friend has a peculiar gait, you see someone approaching with this gait, and turn hastily round to say A.B. is coming; and you are prepared to affirm you saw his usual expression and coloured scarf; and you did see them, but it was in imagination. What actually happened was, the peculiar gait sent impulses to certain cells in the sight-centre, and they by connection caused others in the same centre to act, the united action caused a compound consciousness, which to you was exactly the same as if all the cells had been set in action by impulses direct from the eyes. Of course the effect would be greatly intensified by any suggestion through some other sense; for instance, had it just been mentioned that A.B. was coming, the sound-cells so excited would intensify the action of the connected sight-cells and strengthen the illusion. The illusion with regard to partially or hastily seen objects (and the same remarks apply, in a minor degree, to the other senses) is worth remembering, as such illusions are a very common cause of mistakes and disputes; "I saw it with my own eyes," or, "I must believe the evidence of my senses," are not at all so conclusive as is supposed. The error usually arises from culpable carelessness or lack of attention.

It has now been shown, how consciousness, the possibility of having any thoughts at all, depends on the action of nerve-cells; how the association of ideas and the faculties of imagination and memory depend on these cells and their connections. It is evident, then, that the brain is the bodily organ of thought, in just as full a degree as the eye is the bodily organ of sight. But up to this we have only considered the brain as a purely automatic machine, responding to impulses from without, but otherwise passive; and this by no means embraces all the mental and emotional phenomena that we experience.

When a number of cells act from any cause their action will start a complicated chain of actions in numerous other cells, which succession of actions would, apparently, go on continuously, and be only regulated by the already existing connections between the cells; such action would be what is known as automatic. This automatic train of cell actions may be affected in two ways; first, as has been already mentioned, by fresh impulses from the senses, which, by exciting new combinations of cells, alter the existing course of the train. Now we have, to a great degree, voluntary control over our senses; and, in this, we have one powerful agent at our command for controlling the course of our cell actions, and so regulating our trains of thought. By this means, also, we can direct the trains of thought of other persons, by presenting to their senses such appeals as will set in action the particular cells we desire. We have another powerful means of directing the successions of our own cell actions, in the remarkable effect that Attention has upon them. It has already been shown that by attention any cell action is intensified, by inattention enfeebled. Whenever a number of cells are thrown into action, there will, as a rule, be several different trains of cell actions set going from them, some more, and some less vigorously; when one of these trains is specially attended to, it becomes intensified and all the others enfeebled. This same process will take place at every successive step of the train; it is like a man starting from a point at which several roads diverge and selecting one, after going a few steps he finds another set of diverging roads, and again selects one; and so on. We see that the exact power Attention has over the successions of cell actions is a guiding one; the Will can neither itself start cell actions, nor can it stop them when once started; but, by its control over the Attention, it can direct them. That is, we can, by our own voluntary effort, neither originate, nor stop, any train of thought, but we can guide them by attention or inattention.

It will be remembered that our command over the action of the (motor) controlling cells, mentioned in the last paper, is, in many ways precisely the same as that explained above; as regards the way in which their action is carried on, there is no apparent difference between one set of cells and another, the essential difference being in their function. The relationship between the cells of consciousness and the controlling cells is a very intimate one, and will be referred to subsequently.

The degree of consciousness varies with the amount of the cell action; when the latter is very vigorous it compels attention and the resulting thought is very vivid; with a less degree of cell action, attention is slight, and the train of thought less vivid; with a still less degree, attention is hardly exerted, and thoughts pass by us in a dreamy reverie. It often appears to us, especially in the states of less intense thought, as if several trains of thought were going on simultaneously; but it is doubtful if this is ever quite a correct statement of what takes place. Several trains of cell actions are going on simultaneously, with nearly equal vigour, and the attention is glancing from one to another; each, as attended to, excites consciousness and becomes thought, and the to and fro action of the attention is so rapid that it appears as if there were simultaneous trains of thought.

From the foregoing, and from what we already know of cell actions, it appears that very many trains of these are started, which receive no attention, are too feeble to cause consciousness, and therefore do not cause thought; indeed, considering that of all the possible successions of cell actions, only one train causes consciousness, it is evident that the cell actions which cause thought are only a very small proportion of those going on in the brain. These unnoticed trains of cell actions are known as "unconscious cerebration," and it will be seen that we are indebted to them for a large amount of our mental work; and their importance is all the greater because they are quite independent of any Will control, being merely the result of the physical constitution of the brain. A very familiar instance of unconscious cerebration is that which takes place when, after having vainly tried to recall a forgotten name, we turn our thoughts away from it; in a brief time, when thinking of something else, the name is suddenly presented to the mind; the train of cell actions which we turned our attention away from when we gave up trying to recall the name, continued to act without consciousness, until, at length, that particular combination of cell actions which cause the consciousness of the name is excited; and the name is thus, as it were, abruptly thrust before us.

The more violent the action of a cell, the more quickly it is exhausted; hence, the exhaustion which is due to the extra cell action induced by voluntary attention is far greater than when the action is merely automatic; and, therefore, such acts cannot be long continued, for the cells will cease to act until they have a rest during which they are replenished by the blood. This is the explanation of the well-known fatigue caused by any operation (mental or bodily) each step of which needs attentive effort, and the comparative ease with which habitual operations are carried on. Unconscious cerebration is analogous to the action of the (motor) controlling cells in directing habitual movements, such as walking, writing, piano-playing; in each case the successions of cell actions are now merely due to the grown brain structure (nerve-cells and connections); and in each case this structure is due to education; the movements having been first either taught to us by sense impressions by others, or learned with conscious volitional effort; and the "cerebration" having been first "conscious," and caused either by impressions made on our senses by others, or by our own volitional attentive control of our trains of cell actions. The analogy goes further; the great majority of an adult's movements are habitual; the great majority of an adult's cerebration is unconscious; and therefore, for the accuracy of most of his movements, and the soundness of most of his cerebration, he is dependent on the grown structure of his brain, i.e., on education. It will be readily seen how much more important this fact is in connection with unconscious cerebration than with habitual movements; the latter are quickly detected and can be corrected, at any rate so long as we can keep our Attention fixed on them; in short can, for so long, be made non-habitual; but unconscious cerebration, because unconscious, is utterly beyond all control. The practical range of unconscious cerebration will be shown more fully in a later paper; for the present, its importance will be enough realised if we remember that all our so-called instinctive likes and dislikes, all those apparently unreasoning intuitions by which we arrive at so very many of our practical conclusions, are really the work of unconscious cerebration. And this work will be inaccurately done if education has not fostered the growth of the brain correctly.

Finally, inasmuch as habitual movements and "habitual cerebration" (I drop the word unconscious here, for conscious cerebration is also most of it "habitual," in the sense of being the result of brain structure and uninterfered with by sense impressions or volition) are performed with much less fatigue than "attentive" movements or cerebration, it follows that the possession of a correctly grown (or well educated) brain confers the power of performing accurate mental and bodily operations with the least possible amount of fatigue.

Typed August 2013; Proofread by LNL, June 2024