Psychic States.—There are a number of human states representing extremes of sensory and intellectual conditions in man, that have always attracted attention, and in recent years have been special objects of investigation by physiologists. Natural sleep is one of these; the unconsciousness of narcotism or anesthesia is another. Hypnotism is allied to both of these, and would seem to lie on a plane between them. Then there are various states of exaltation in which sensations fail to produce their usual effect. Those {112} escaping from a fire, or passing through a severe panic of any kind may sustain all manner of injuries without being aware of them. Martyrs, for all manner of causes, are able to withstand suffering with such equanimity, and sometimes even joy, that it is evident that they cannot feel, as would people under ordinary conditions, the pain that is being inflicted on them.
Fig. 5.—FIRST, SECOND AND THIRD LAYER OF THE ANTERIOR CENTRAL CONVOLUTION (THAT IS, OF THE ASCENDING FRONTAL CONVOLUTION) OF THE BRAIN OF A CHILD ONE MONTH OLD. A, B, and C, little pyramids; D and E, medium-sized pyramids; F, cells with two sets of tufts; their axis cylinders resolved into end tufts; G, protoplasmic layer that comes from one of the large pyramids of the fourth layer; H and I, fine dentrites of the cells of the sixth and seventh layer; J, small cells with two end tufts; K, spindle cells with long axis cylinder. (Raymon y Cajal.)
FIG. 6.—LAYERS OF THE POSTERIOR CENTRAL OR ASCENDING PARIETAL CONVOLUTION OF A NEWBORN CHILD. 1. plexiform layer; 2. small pyramids; 3. medium-sized pyramids; 4. external large pyramids; 5. small pyramids and star shaped cells; 6, deep layer of large pyramids; 7, spindle and triangular shaped cells. (Raymon y Cajal.)
In the midst of intense mental preoccupation one may hold so cramped a position as would be quite impossible for the same length of time with the faculties normally engaged. There are pathological conditions, like hysteria, in which the pain and fatigue sense may, for a time at least, be quite in abeyance.
FIG. 7.—DIAGRAM OF CELLS OF CEREBRAL CORTEX (after Starr, Strong and Leaming). I, superficial layer; a, fusiform; b, triangular; c, polygonal cells of Ramon y Cajal; II, layer of small pyramids; d, smallest; e, small; f, medium-sized pyramidal cells with axones descending to the white matter and giving off collaterals in their course; III, layer of large pyramidal cells; g, largest (giant) pyramidal cells; k, large pyramidal cells with very numerous dendrites; all pyramidal cells are seen to send long apical dendrites up to I; m, Martinotti cell with descending dendrites and ascending axone; n, polygonal cells; IV, deep layer; p, fusiform cell; q, polygonal cell; V, the white matter containing the axones from the pyramidal cells, d, e, f, g, and from a cell of the deep layer q; r, neuroglia fibers. (Barker.)
FIG. 8.—SCHEME OF LOWER MOTOR NEURON. The motor-cell body, with protoplasmic processes, axis cylinder, side fibrils or collaterals, and end ramifications, represents parts of a neuron. a. h., axon hillock devoid of Nissl bodies, showing fibrillation; ax., axon. This process near the cell body becomes surrounded by myelin, m., and a cellular sheath, the neurilemma (not an integral part of the neuron); c, cytoplasm showing Nissl bodies and lighter ground substance; d, protoplasmic processes (dendrites) containing Nissl bodies; n., nucleus; n., nucleolus: n. r., node of Ranvier; s. f., side fibril; n. of n., nucleus of neurilemma; tel., motor end plate or telodendrion; m., striped muscle fiber; s. l., segmentation of Lautermann. (Barker.)
Neurons.—With the advance in our knowledge of brain anatomy, various explanations for these curious conditions have been suggested. The discovery that the central nervous system is composed of a large number of separate units, and not of a feltwork of continuous fibers with cells here and there, revolutionized all previous attempts at explanation of these conditions. We know now that it is not fibers but cells that are the most important components of the brain and spinal-cord substance, and that, indeed, the fibers are only prolongations of cells. The central nervous system is made up of nerve cells with various appendages, and each one of these cells and its appendages is called a neuron. These appendages are of two kinds, one the axon, the long conducting fiber which transmits the nerve force of the cell, the other the dendrons or connecting elements by which the cell is linked with the axon of another cell. The contact of the axon of one neuron with the dendrons of another is called a synapse. Each neuron does not extend to and from the brain and the periphery, but series of neurons connect the surface of the body with the brain. There is usually a group of neurons in the path from the surface to the brain cortex. The peripheral neuron for sensation runs from the surface of the body to the spinal cord, while for motion it runs in the opposite direction. There is a secondary neuron in each chain that runs up or down the spinal cord to and from the base of the brain. A third—sometimes, perhaps, a fourth—neuron connects in the two directions, afferent and efferent, the cortex and the base of the brain.
Neuronic Movement.—Duval, the French anatomist and histologist, suggested the possibility of voluntary and involuntary movement in the neurons or nerve cells themselves, thus making and breaking connections.
FIG. 9.—SCHEME OF THE VISUAL CONDUCTION PATHS (after C. von Monakow). a, rods and cones; b, rods; c, nuclei of rods; d, bipolar cells for the cones; e, bipolar cells for the rods; f, large multipolar ganglion cells giving rise to the axons of the N. opticus; g, centrifugal axon of a neuron, the cell body of which is situated in the collieulus superior, its telodendron being situated in the retina; h, Golgi cell of Type II, or dendraxon in the corpus geniculatum laterale; i, neuron connecting the corpus geniculatum laterale with the lobus occipitalis, its axon running in the radiato occipito-thalamica (Gratioleti). The visual impulses are indicated by the arrow. (Barker)
FIG. 10.—SCHEMATIC FRONTAL SECTION THROUGH THE OCCIPITAL LOBE ILLUSTRATING MANIFOLD CONNECTIONS IN A SINGLE LOBE (after H. Sachs), v, cornu posterius ventriculi lateralis; f. c, fissura calcarina; b, upper division: i, lower division; coll, sulcus collateralis; s. o. I, sulcus occipitalis superior (fissura interparietalis); s. o. II, sulcus occipitalis medius; s. o. III, sulcus occipitalis inferior; c. a., calcar avis; g. l., gyrus lingualis; g. f., gyrus fusiformis; g. o. s., gyrus occipitalis superior; g. o. m., gyrus occipitalis medius; g. o. i.. gyrus occipitalis inferior; c, cuneus; 1-10, forceps; 11-14, stratum sagittale internum: 15, stratum sagittale externum; 16, stratum calcarinum; 17, stratum cunei transversum; 18, stratum proprium cunei; 19, stratum proprium s. o. I; 20, stratum proprium s. o. II; 21, stratum proprium. s. o. III; 22, stratum proprium, s. coll.; 23, stratum profundum convexitatis. (Barker.)
According to his suggestion, sleep would be due to a separation of the neurons that run from the surface of the body to the brain cortex, because the various neurons had become too tired for further function. As a consequence of fatigue, their terminal filaments would fall away from one another, external sensations would no longer be communicated to the brain, because the peripheral neuron was not connected with the next in the chain. As a further result, the brain, undisturbed by sensations, would be left at rest so far as the body was concerned. Within the brain certain connections through which flow thoughts that would keep us awake, are also supposed on this theory to be broken, and consequently all the nerve cells have a chance to rest, except, of course, those concerned with such very vital functions as heart movement, respiration and peristalsis.
FIG. 11.—ISOLATED CELL FROM HUMAN SPINAL CORD (Obersteiner).
Somehow, these vital neurons obtain their rest in the intervals between the impulses which they send down, just as cardiac cells do between heart beats.
Neurons in Psychic States.—This same explanation would serve for narcosis, that is, for anesthesia, due to chloroform or ether, or any other drug. As a consequence of the effect of the narcotic upon the central neuron, they are brought into a condition resembling fatigue, at least to the extent of breaking their connections with other neurons so long as they are under the influence of the drug. While sensory nerves at the periphery, then, are being stimulated by the cutting of tissues to which they are attached, the message from them does not reach the brain because of a disturbance of the connections in the chain of neurons. Drunkenness illustrates the same phenomenon in a less degree. The effect of the intoxicant upon the central neurons disturbs sensation because it makes the connection much less complete than before, and so it is easy to understand the familiar occurrence of even severe injuries to drunken men without their being aware of them, or at least without their suffering nearly so much as would be the case if they were not intoxicated.
Hypnotism.—The same theory would also hold for the phenomena observed in hypnotism. After all, the best explanation of hypnotism that we have is that there is a turning inward of the patient's attention, so that only those sensations are allowed to reach the brain to which mental attention has already been called by suggestion. Hypnotism usually begins with a certain fatigue of peripheral neurons until these do not act normally, and then the cerebral neurons become, as it were, short-circuited on themselves with a consequent internal concentration of attention. The anesthesia so often noted in hypnotic or hysterical states is explained by the same theory. For the time being, at least, the connection between the peripheral neurons and the central neurons is broken or but imperfectly made, and conduction does not take place, or is hampered. There may be loss of motion as well as of sensation, or of motion without sensation. In all these cases, the discontinuity of the nervous system enables us to understand more readily the mechanism by which these curious phenomena occur. Exaltation or intense interest or profound preoccupation may so concentrate nervous energy within the nerve centers themselves as to inhibit the flow of sensory impulses from without and thus enable {118} people to stand pain and fatigue that would otherwise seem quite unbearable.
Unconsciousness.—The unconsciousness due to apoplexy, or to a blow on the head, would be comparatively easy of explanation on the same theory. The hemorrhage would actually push certain neurons apart within the skull, or the intracranial pressure produced by it would keep them from making proper connections. A blow on the head may readily be supposed to jar neuronic terminal filaments so severely that it would be some time before connections could be made, and the injury might be serious enough to prevent certain cells from ever again coming in contact in such a way as to allow the passage of nerve impulses from one to the other. Concussion of the brain would, on this theory, mean that neurons were so shaken apart as to produce some confusion in their terminal filaments and consequent serious disturbances of consciousness, if not its complete loss, and corresponding disturbance of the power to move. In a word, this theory would seem to afford a reasonably satisfactory explanation for most of the extraordinary phenomena of mental life and, therefore, might also be expected to be applicable to the ordinary phenomena, though these are so elusive that it is difficult to satisfactorily apply theories to them.
FIG. 12.—NEURON FROM THE OPTIC LOBE OF THE EMBRYO CHICK (after Kölliker). The axon n runs toward the center, giving off in its course several collaterals. One of these, c, is much branched. (Barker.)
Tired States.—When fatigued, it becomes extremely difficult for us to follow a train of thought, especially if it is somewhat intricate. It becomes easy to forget things, even such as under ordinary circumstances would be readily remembered. Names are much more likely to be forgotten. Facts and, above all, dates, refuse to come as they do under normal conditions. Efforts in the direction of recalling details are eminently unsatisfactory. The command goes forth, but there is {119} evidently hesitation about obedience. Other thoughts intrude themselves. Ideas come unbidden. The connection of thought is readily broken, and is hard to get at again. There may have been very little mental work, but somehow the fatigue of the general physical system is reflected through our central nervous system on the mind as well as the body. The early morning hours are the best for mental work, not, it seems, because the mind is fresher after its rest, but rather because the physical factors that are important for mental action are in good condition. Later they become disturbed by the fatigues of the day. The delicate cells of the brain become fatigued by sympathy with the somatic cells and it is harder to secure those nervous connections necessary for thought.
FIG. 13.—DEEP LAYER OF GIANT PYRAMIDAL CELLS OF THE POSTERIOR CENTRAL OR ASCENDING PARIETAL, CONVOLUTION OF A CHILD THIRTY DAYS OLD. a, axis-cylinder; c, collateral branch; d, long basilar dendrites; e, end tuft. (Ramon y Cajal.)
[Illustration: FIG. 14—PYRAMIDAL CELL OF CEREBRAL CORTEX OF MOUSE (after Ramon y Cajal).]
Voluntary Neuron Motion.—This theory of Duval's supposes that to some extent the neurons or nerve cells are possessed of voluntary movement. At least during certain states of the mind, they are moved and seem to have an inherent, if not quite voluntary, power {120} of motion. There are many objections urged against the theory because of this neuronic motion. It has been said that the movement of neurons has been observed in certain of the Medusae. The observation has been doubted and it lacks confirmation. In higher animals, of course, the observation is impossible because an investigation of the nervous system for this purpose would necessarily bring about the death of the animal and the cessation of spontaneous mobility. Whether it occurs or not, therefore, is a theoretic problem. So many objections tell against Duval's theory that it is now only discussed because of its subjective value.
Neuroglia Theory.—Ramon y Cajal elaborated a second theory of explanation for the mechanism of the nervous system that has seemed to many authorities in brain physiology much more satisfactory than Duval's theory of the actual motion of the neurons themselves. The Spanish nervous histologist had made a special study of the neuroglia or connective tissue cells in the central nervous system. These are very small in size but very numerous. Ramon y Cajal suggested that it was because the terminal filaments of these neuroglia cells inserted themselves between the neuronic filaments, thus insulating one from another, somewhat as if an insulating plug were inserted between two portions of an electric circuit, that the interruption of nervous currents took place. This explanation is free from many of the objections urged against Duval's theory.
The small size of the neuroglia cells makes it easy to understand how movement may take place in them sufficient to bring about separation of neurons. It would not be surprising if they should be more or less actively contractile. Whenever they contract, neuronic filaments which they have been holding apart, come together so as to permit the passage of nervous impulses, if any are flowing at the time. When the neuroglia cells become fatigued or seriously disturbed, they refuse any longer to obey the will in any way, or at least gradually get beyond control, and in their relaxation becoming prolonged, push neurons apart. When a man is very tired it gradually becomes impossible for him to keep awake. This is partly because poisons, produced in the course of fatigue, exhaust the vitality of the neuroglia cells and also of the neurons, so that less energy is required to push these latter apart.
It is easy to understand that the neuroglia cells might well become affected by the various narcotics and intoxicants in such a way as to produce the phenomena of anesthesia and drunkenness. The rapid recovery from anesthetics seems to indicate that it is not neurons, or essential nerve cells, that are so deeply affected, but some extraneous, and less important, mechanism within the brain. The neuroglia theory explains this very well and does away with the difficulty. Certain curious phenomena of hysteria are easily explained on this theory. When there is anesthesia in a member because of hysteria, this anesthesia does not follow the distribution of certain nerves, but is limited by a line in the shape of a cuff drawn round the limb. This indicates that the trouble is not peripheral but central, and that owing to psychic disturbance, all the neurons that receive sensory impulses from a particular portion of the body are so affected by a psychic condition that they are no longer capable of receiving impulses from the periphery. The neuroglia cells in a particular area have passed from the control of the will and, relaxing themselves, have {121} inserted their processes between the terminal filaments of neurons, thus preventing conduction.
FIG. 15.—NEUROGLIA CELLS OR THE FASCIA DENTATA; IN THE NEW-BORN RABBIT (method of Golgi). A, molecular layer; B, granular layer; C, layer of polymorphis cells; D. horn of ammon; a. neuroglia cell furnished with a descending appendage; b, another neuroglia cell; piroform; c. a cell more deeply situated; d, spider cell; e, fusiform neuroglia cell. (Ramon y Cajal.)
Varieties of Neuroglia.—The connective tissue cells are of many kinds, each probably exercising a special function. Ramon y Cajal has described and pictured a special kind of neuroglia cells for the gray and another for the white matter. In his description of these cells he has pointed out many interesting diversities of form, and probably also of function. He has also described particularly a special form of neuroglia cells which lie close to the blood vessels. These he calls perivascular cells, and they seem to have an important function in regulating the amount of blood that goes to a particular part of the brain. He has written so clearly and yet so concisely with regard to these that it seems better to cite his own words: [Footnote 15]
[Footnote 15: This article is a translation made by the author shortly after a visit to Ramon y Cajal in Madrid, in 1900. See International Clinics, Phila., Vol. II Series Eleventh.]
Under the term neuroglia are included at least three kinds of
cells,—those of the white brain substance, those of the gray
substance, and the perivascular cells, which have been described by
Golgi. The neuroglia cells of the white brain material are easily
recognizable, being large and with rather prominent, smooth, and
sharply outlined processes. As my brother seems to have shown, their
object appears to be to furnish an insulating, or, at least, a badly
conducting, substance to serve as an interrupter of nerve-currents.
They certainly do not represent interstices of true nerve substance
through which lymphatic fluid can conveniently find its way.
The neuroglia cells of the gray matter present a very special and
highly characteristic appearance. They are of manifold form,—at
times star-shaped, at times {122} like a comet
drawn out in length. These are the tall cells of von Retzius. They
have very numerous prolongations, with a large number of short
branched collaterals which give the whole cell the appearance of
having feathers projecting from its periphery. These cells have been
observed in two different conditions. One is that of relaxation, and
the picture is that given above. The other is that of contraction,
during which the cell body has more protoplasm in it, and the
processes become shorter and thicker, and some of the secondary
branches disappear entirely. These cells resemble, in certain ways
at least, the pigment cells which occur in the skin of some animals.
By means of their contractility, these pigment cells can stretch out
their processes while in a state of contraction. It must be
remembered that this form of neuroglia cells is most abundantly
present in those parts of the brain in which it might be expected
that a number of nerve currents would frequently come together. They
occur, for example, with special frequency in the molecular layer of
the cerebral cortex, where the bundle of pyramidal fibers, with
their immense number of terminal nerve-endings, come in contact with
one another.
FIG. 16.—NEUROGLIA CELL FROM THE SUBCORTICAL LAYER OF THE CEREBRUM FROM WHICH TWO PROCESSES GO TO A BLOOD VESSEL (Obersteiner).
FIG. 17.—NEUROGLIA CELLS FROM THE SPINAL CORD. Longitudinal section (Obersteiner).
The third form of neuroglia cells consists of those known as the
perivascular cells. They are found only in the neighborhood of the
capillaries of the gray matter and they send one or more firm
prolongations to the outer surface of the endothelium of the blood
vessels.
These processes are inserted in the walls of the blood vessels.
Every capillary has thousands of these little pseudopod
prolongations, and from the vessel the cell reaches out in a number
of directions. The object of these cells undoubtedly is by
contraction of the prolongations to bring about local dilatation of
the blood vessels. This dilatation of the blood vessels causes
greater or less intensity of the psychical processes in certain
parts of the brain, because of the greater or less congestion of the
circulation in a part which it produces.
With the exception of these last cells the object of the neuroglia
cells is to insulate nerve fibrils and cells from one another. When
the cells are relaxed, the passage of a nerve current is either
entirely prevented or rendered much less easy than before. It is in
this way that the true nature of intellectual rest is explained.
Sleep—not only natural sleep, but also artificial narcosis, such as
is produced by narcotics, hypnotics or hypnotization—is evidently
the result of the same conditions.
During the state of contraction the pseudopod of the neuroglia cells
are drawn in; that is to say, the protoplasm of the cells absorbs
the processes, and so the true nerve cells and nerve fibrils which
were separated from each other by the interposition of neuroglia
come into contact. By this mechanism the brain passes from the
condition of rest into one of activity. These neuroglia contractions
may, particularly in certain parts of the brain, occur
automatically. Often, however, they are produced by the action of
the will, which, in this manner is able to influence
{123} the definite groups of neuroglia cells. As
the result of this influence of the will the association of
intellectual operations can be guided in various directions. The
unusual course that the association of ideas sometimes takes, the
flow of words and of thoughts at certain moments, the passing
difficulty of speech, the recurrence of tormenting thoughts, the
disappearance of expressions or ideas from the memory, even the
increase of mental activity and of every kind of motor reaction as
well as many other phenomena of intellection, can be satisfactorily
explained on this hypothesis. It is only necessary to suppose that
in certain parts of the brain the neuroglia cells are at rest, while
at other parts they are in a condition of active contraction.
To put it all in a few words, the neuroglia cells of the gray
substance of the brain represent an insulating and switching
apparatus for nerve currents. They are an insulation apparatus when
in a state of contraction, a switching and insulating apparatus when
in a state of rest. It is to be remarked, then, that according to
this theory the contraction of brain cells does not take place, as
in Duval's theory, during intellectual rest, but, on the contrary,
during the state of activity of the cerebral cortex. It is much more
probable that the action of cells coincides with the active stage of
intellection than that brain cellular activity—that is,
contraction—should correspond with psychic rest.
The application of some of these theories enables us to understand just how short-circuiting may come about, how many of the curious phenomena of memory happen, and what are the effects, as well as the causes, of attention and distraction of attention and of diversion of mind. It is particularly the latter portion of Ramon y Cajal's theory, with regard to attention and the more or less voluntary though unconscious and usually indeliberate control of blood supply to various portions of the brain, that is of special interest. If the neuroglia cells, whose end plates are attached to blood-vessel walls, become over-contracted or lose their power of relaxation or of contraction, many of the curious phenomena of over-tiredness in neurotic conditions, and the lack of the power of concentration, and sufficient attention to things, can be readily understood. In a word, the theory enables us to translate many expressions that are vague and indefinite, from terms of mind into terms of the physical basis of mind—the anatomy and physiology of the brain.
While I have dwelt on Ramon y Cajal's theory, because for years it has been familiar, of course I must reëcho his own warning that it is, after all, only a theory. It presupposes an active interposition of the glia cells between the axon of one neuron and the dendrons of another. This cannot be demonstrated. A third theory of mental operations, then, has been suggested, and the English school, so ably led by Sherrington ("Integrative Action of the Nervous System," London, 1903) and McDougal ("Synapse Theory of Fatigue," Brain, 1910) has deservedly attracted wide attention. They contend that all the phenomena can be more simply explained without postulating the movement required for the Duval Theory or the glial activity of Ramon y Cajal's hypothesis. They consider that each nerve cell has, as it were, a certain potential energy which it sends forth in nerve impulses. These are transferred from neuron to neuron through the synapse. If what we might call, to borrow a figure from electricity, the voltage of the cell impulse be sufficient to overcome the resistance at the synapse, the impulse passes from neuron to neuron. In fatigue the potential energy of the cell is gradually dissipated. The impulses become feebler till they cease to pass. This occurs in the state we usually experience as tiredness and in analogous states such as sleep, unconsciousness, narcosis and the like. Obviously this {124} theory can be elaborated and applied parallel with the neuroglia theory except that here we are substituting synapse resistance for the hypothetical, undemonstrated action of the glial cells. But, as the latter seems a simpler process upon which to explain the various phenomena, especially to those not familiar with very recent developments in nervous histology and studies in nervous mechanism, and as it merely involves a question of the nature of the resistance and not of its site, I have used it for explanatory purposes without advocating either theory in the present state of our knowledge.
CHAPTER V
BRAIN CELLS AND MENTAL OPERATIONS
While the theories of neuronic action we have discussed do not represent absolute knowledge, they are at least suggestive and helpful in psychotherapy. Whenever there are disturbances of mental operations, patients are likely to become very solicitous, lest these represent organic and incurable changes. The application of Ramon y Cajal's neuroglia theory serves to bring out the fact that most of them can be very well explained as merely functional, due to passing disturbances of activity, and not necessarily to tissue changes. When patients become possessed of the fear that certain nervous symptoms portend definite injuries to the nervous system, this unfavorable suggestion keeps them from using, to its proper and full extent for repair and convalescence, the nervous energy which they possess. This disturbing influence can be counteracted by a straightforward exposition of Ramon y Cajal's or the newer English theory of brain mechanism.
Patients become very much disturbed if they observe a failure of certain faculties in themselves, and are prone to think that such a failure means serious exhaustion or enduring change. The power of attention is one of the faculties often disturbed in neurotic cases and causes patients needless solicitude. Disturbances of memory are the next most alarming elements in these cases. There are then many forms of mental distraction, absorption and preoccupation that sometimes frighten neurotic individuals who have become solicitous about themselves. Though only passing incidents, due to overattention to themselves and their ills, real or fancied, and the consequent lack of concentration of mind on a particular subject, the patients fear serious deterioration of their mental condition, or at least of mental control. The neuroglia theory of mental action throws a light on all these phases of mentality that serves to lessen the solicitude of patients and enable them to understand that, in spite of their fears, there is nothing but functional disturbance. The condition can be readily explained and it admits of complete restoration to health.
ATTENTION
Even more important, perhaps, than any other of the functions attributed to the neuroglia cells, is the rôle they may play in enabling the individual to concentrate attention on a particular subject, or at least to use a particular {125} portion of his brain, by bringing about a more active circulation in that portion than in any other, Ramon y Cajal attributes this power to the perivascular neuroglia cells. Every capillary in the brain has thousands of these little pseudopod prolongations. When the cells in a particular region contract, the blood vessels of the part are pulled wide open and a larger supply of blood flows more freely, stimulating the nerve cells by which it passes and supplying them with nutrition for the expenditure of energy that they may have to make. This is the physical process that underlies attention. When too much, that is, too long-continued attention is paid to any subject, without diversion of mind, the capillaries may easily acquire the habit of being open, and cells the custom of contraction, so that relaxation does not readily take place. Something of this kind is the most important element in the etiology of many functional nervous disorders.
FIG. 18.—AN ARTERY FROM THE CEREBRAL CORTEX.—One can see numerous fine fibers passing over to the brain substance (Obersteiner).
Ease and Pleasure in Mental Operations.—On the other hand this same set of ideas explains many things otherwise difficult of understanding. For instance, we all know that habit enables us to apply ourselves to a particular subject with ever growing ease. What was extremely difficult for us at the beginning, may after a time become comparatively easy, and later even positively pleasant. Study, that is application of mind, is, at the beginning, for most people, not agreeable. If persisted in, it almost inevitably becomes a pleasure. Hard exercise of any kind is, at the beginning, sure to require great energy of purpose, and requires some subsidiary motive of approbation or reward to make us persist in it. But what was a distinct labor at the beginning becomes pleasant after a while. This may be applied to the neuroglia cells apparently as well as to the muscle fibers. On this theory, the reason for the gradual acquirement of an intense pleasure in the intellectual life becomes easy to understand.
Dangers of Over-attention.—The danger of concentration of mind on one's self, quite as much as on any other subject, becomes clearer when this theory is accepted as explaining the physical basis of the mental operations involved in attention. If people allow thoughts of themselves and of their physical processes constantly to occupy their minds, gradually that portion of the brain ruling over these becomes over-fatigued and fails to respond to the calls for relaxation. Insomnia may develop readily as a consequence of continued solicitude and prove to be, as the worst forms of insomnia so often are, quite unamenable to direct drug treatment, because, even during the enforced sleep that comes from drugs, dreams with regard to self and the supposed ills may still occupy the overworked portion of the brain. Nervous people are, most occupied with those parts of the brain which have something to do with the omission and transmission of trophic influence to particular parts of the body. As a consequence of the persistent hyperemia, too many trophic impulses are sent down. These cause an exaggeration of physiological function, in the stomach, the heart, or some other important organ. Hence these organs may become oversensitive.
For all these reasons, this theory of attention, of the great Spanish {126} investigator, deserves to be well known by those who hope to treat neurotic affections, especially functional diseases of the brain, and therefore I prefer once more to give it in his own words. [Footnote 16]
[Footnote 16: International Clinics, Vol II, Series 11.]
Ramon y Cajal's Theory of Attention.—Under usual conditions, the motor apparatus of the gray matter suffices for the explanation or the varied course of association of ideas and of the reaction produced by voluntary motion. But as soon as attention is concentrated upon an idea, or a small number of associated ideas, there enters into the problem, besides the active retraction of the neuroglia of the corresponding part of the brain, a new factor—the active congestion of the capillaries of the over-excited region. As a consequence of this, the energy of emotion reaches a maximum. The heat and metabolism of the hyperemic parts is increased, which, of course, makes these parts capable of more work.
FIG. 19.—NEUROGLIA CELLS OF THE SUPERFICIAL LAYERS OF THE BRAIN FROM AN INFANT AGED TWO MONTHS (method of Golgi). A, B, C, D, neuroglia cells of the plexiform layer; E, F, G, H, K, R, neuroglia cells of the second and third layers; I, J, neuroglia cells with vascular pedicles; V, blood-vessel. (Ramon j Cajal.)
This congestion of various parts of the brain has been experimentally observed {127} by a number of physiologists. It can be best explained by considering that the will has an influence upon the nerves which produce a dilatation of the blood-vessels in different parts of the cerebral cortex. The process of attention, however, by which intellectual activity is concentrated upon a limited number of ideas, seems to be but very little under the control of the sympathetic nerve endings.
As a matter of fact, the capillaries of the brain are wanting in nerves and smooth muscle fibers. Hence they are not under the control of the sympathetic system. Only the relatively large arteries of the pia mater, which possesses a tunica muscularis are under a certain limited control of the sympathetic, which is able to produce in them an incomplete and not very well limited congestion. One of the difficulties of the problem of the activity of the sympathetic is best realized when we recall that vasomotor activity is usually involuntary. The process of attention, however, is entirely conscious and voluntary.
In the hypothesis that we have given, most of the difficulties disappear. Under the influence of the will, the pseudopod branches of the neuroglia cells, which end in the walls of the capillaries, contract. As the result of this, the bloodvessels, all of which are surrounded by lymph spaces, dilate, and this dilatation may proceed to such an extent that the vessels occupy the whole of the lymph spaces. Thus we can easily understand how the very limited congestions which are necessary for the concentration of thought upon a single idea may be brought about.
The perivascular lymph spaces which exist in the brain seem to be for the purpose of making these limited hyperemias easier. At the same time they serve a very useful purpose in preventing pressure or concussion, such as might be caused upon the neighboring nerve cells by too great dilatation of the blood vessels of a part.
It is needless to add that we do not consider the hypothesis that we have advanced to be absolutely without objection. On the contrary we believe that, owing to the difficulty of the problem and our, as yet, extremely slight knowledge of the anatomy and physiology of the nerve protoplasm, any theory as to the special mechanism of psychic processes is sure to be faulty. Rational hypotheses, however, which are supported by well-known facts, are not only justified, but are often fruitful of suggestive ideas. A scientific hypothesis often gives a new direction, suggests an untried method of observation, or hints at new ways of experiment, and, though it may not lead directly to truth, always brings us closer to methods of investigation and of criticism that are invaluable. Even though our further investigations should not confirm our hypothesis, the result will not be less positive. Negative conclusions lessen the number of possible hypotheses and therefore diminish the possibility of error in future investigations.
MEMORY
It is evident that some of the physical mechanisms that are employed for the lower grade mental processes at least can be explained on the neuroglia theory. Memory we share to a great extent with the animals, and for this the physical processes can be rather interestingly studied. We have all had the experience of being unable to recall a word when we wanted it. Commonly the word is a proper name with which there are not many direct connecting ideas, so that, somehow, we seem unable to trace the word to its depository in the brain. Occasionally we are sure that we know the first letter of the word. Sometimes we are able to name this letter, and, if we do so, the rest of the word will usually turn up a moment later. At times, however, the word fails to come and we grope for it. Then if we stop deliberately seeking it, the word will often after a longer or shorter time, come up spontaneously.
This experience is familiar to everyone. It is especially frequent with public speakers. Certain words have a habit of slipping away just when we {128} want them. At times by beginning a sentence confidently, even though there is a feeling that there is a missing word ahead, the word will turn up in time. Often it will not, and then a weak circumlocution must be indulged in. If it is a proper name, a description may have to be substituted, sometimes a confession may have to be made that the name will not come and the audience, unless it is very young, will sympathize with the speaker.
If we accept the idea that the memory has a definite location in the brain, the process is easily understood. Just how we cannot say, but somehow brain cells serve as the media by which our memory processes revert to knowledge that has been previously stored up. If now we assume that the repetition of things known is accomplished by bringing brain cells into connection with one another, and with the organs of speech, it is easy to understand that somehow the connection with a particular cell or set of cells cannot be secured at a given moment. This delay prevents us from being able to repeat things that we know, and know that we know, though we cannot somehow get at them. The will fails to reach the proper insulating plug of a neuroglia cell, which, if acted upon, would put a cell or group of cells in communication with others. As a result the message from it cannot flow down. We feel that we have it on the tip of our tongue, as we say, that a little effort may bring it to us and sometimes that effort succeeds. If there is any disturbance of consciousness by secondary motives, however, as by the excitement of public speaking or the flustering that comes to some people when they try to introduce even old-time friends and forget their names, then we cannot control the brain processes and memory fails. We do not for a moment think of attributing this failure of memory to the faculty of memory itself. We have the feeling that there is some mechanical obstacle. Ramon y Cajal's theory enables us to understand this obstacle better, perhaps, than any other.
An interesting phase of this lapse in memory helping us to a revelation of something of the physical process which underlies the faculty, is the fact that it implies a very intricate machine. Recalling has become such an obvious incident that we do not think of the complexity of action involved. Many things are brought together, and relations of all kinds serve to recall various facts and names and dates. Some of these relations are most bizarre. Particular names recall a definite series of facts. A color will bring up a scene or the memory of an individual. An odor will recall scenes long since apparently forgotten and will set trains of thought at work that are quite unexpected. Sometimes we wake in the morning with a name or a fact on our lips that we have been looking for for several days.
UNCONSCIOUS CEREBRATION
Some people actually learn to depend on unconscious cerebration. A man, for instance, who has to make an address on a particular subject or to write an article, will record that fact on a tablet and after gathering a few basic thoughts in connection with the subject proposed, will put it aside for the time being. He is confident that various illustrations and thoughts in connection with the subject will occur to him at intervals during the next few days, and that he will thus without direct labor accumulate an amount of {129} material for use. In the early morning hours he may find that thoughts on it come to him unbidden. Sometimes he will find these thoughts precious germs, that will develop during the course of the following days, and will be of great help to him. If he is worried and preoccupied with other things very much, this may not happen, but under ordinary circumstances he can continue routine occupations which demand practically all of his time, yet continue to develop the subject selected for his paper or address. The more he has occupied his mind with the subject at the beginning, the more will this unconscious cerebration continue.
ABSTRACTION OF MIND
Features of the mechanism of mental operations are brought out in certain phenomena of abstraction of mind, which show how the attention can be so short-circuited that sensations from the periphery utterly fail to penetrate to the consciousness. Most men have had the experience of taking out their watches, looking at them, and then putting them back. Presently somebody asks what time it is. Unable to recollect what it was that they saw, they have to look again. There is no doubt that they meant to observe the time.
The same thing is true for practically all the senses. A pickpocket takes advantage of our being occupied with many other feelings in the midst of the jostling in a crowd on a car, or before a show window, or he has a confederate add to the sensations already streaming up to us, calling attention particularly to the other side of the body, and then inserts his hand into our pocket and extracts what he finds. Sometimes we have a faint memory of something having happened to that pocket, but our attention was occupied elsewhere.
In hearing we have the same experience. When thoroughly occupied with a book, a person may talk to us or ask us a question and we have no idea of what was said, sometimes utterly failing to hear the voice; sometimes we hear the sound of the voice, but do not comprehend the meaning of the words.
When we are unprepared for a question we nearly always have to have it repeated to us. Sitting in a railroad train, if the person behind us, whom we did not expect to talk to us, asks a question, it is very probable that on the first asking we shall not notice it at all, considering that it is addressed to someone else. On its repetition, it may appeal to us as addressed to ourselves, but even then we readily lose its significance because our attention has not been called to the wording of it soon enough to enable us to comprehend it thoroughly. These experiences, so familiar that we have probably all had them at some time or other, indicate how universal is the power of the mind to concentrate itself upon itself to the extent of neglecting sensations from the outer world, even though they may pass the periphery of the organism and manifestly affect the first neuron of the chain that leads up to our brain and consequently to consciousness. They do not reach the center with sufficient intensity to be understood, and a conscious act of attention must be made before we comprehend their meaning.