The brain and its functions

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Author's Preface

The present work, on the structure and functions of the brain, is an abstract of my personal experience as regards this subject, and of most of the ideas I have for many years been endeavouring to popularize in my public lectures at the asylum of La Salpetriere.

It is divided into two very distinct parts.

The first, anatomical, serves as the foundation of the work. It is followed by a second, purely physiological, which is its complement and necessary sequence.

In the first part I have explained all the technical processes employed in arriving at the results indicated ; insisting at the same time upon the value of the method which I have found it necessary to adopt, which consists in making regularly stratified sections of the cerebral tissue, in the faithful reproduction of these by means of photography, and in the employment of successively graduated powers for the representation of certain details.

I have been able, by means of these new methods of investigation, to penetrate further into the still unexplored regions of the nervous centres, and, like a traveller returned from distant lands, to bring back correct views and faithful representations of certain territories of which our predecessors caught scarcely a glimpse.

vi author's f-reface.

Thus, in fact, by making this photo-microscopic analysis of the nervous elements, I have been able to throw fresh light upon the intimate structure of the nerve-cell, and on the organization of its protoplasm, and to study it in situ, in its connections with the nerve-fibres and the surrounding network of neuroglia.

In my explanation of the grouping of the various portions of the cerebral mechanism, I have endeavoured as much as possible to simplify their description, and above all, to avoid employing that strange vocabulary now-a-days so improperly imported into the nomenclature of the different central regions of the brain.

I have therefore sketched synthetically the general economy of the structure of the brain, pointing out the intimate relations which exist between the cerebral cortex, the true sphere of psycho-intellectual activity, and the central ganglions (those of the optic thalami and corpora striata) which are in a manner the intermediate regions interposed between this and the excitations which proceed from the external world. I have insisted on the fact, which ten years ago I was the first in France to bring to light, namely, that the optic thalamus, with the isolated grey ganglions of which it is composed, represents a place of passage and reinforcement for excitations radiated from the sensorial periphery, while the corpus striatum, with its different compartments, and arches one within another, is on the contrary directly related to the passage of voluntarymotor excitations.

In this anatomical part I have particularly emphasized those details of the essential structure of the cerebral cortex, to the existence of which sufficient attention has

AUTHORS PREFACK vil

not as yet been paid, and have utilized them from the stand-point of physiological interpretation.

Thus, having established the presence in the cerebral cortex of special zones of small cells subjacent to the pia-mater, and quite different in configuration from the zones of large cells occupying the deeper regions, I was led to see in this anatomical arrangement a clear relationship to a similar disposition existing in the constitution of the grey axis of the spinal cord.

As a consequence, I was led to think that if, as is experimentally demonstrated, the small elements in the spinal cord be affected by the phenomena of sensibility, it was natural to admit physiological analogies where morphological analogies exist ; and consequently to consider the sub-meningeal regions of the cerebral cortex as being the histological territory specially reserved for the dissemination of sensible impressions ; while the deeper zones of large cells (analogous to the anterior motor columns of the cord) might be considered as the regions of emission (psycho-motor centres) for exciting voluntary motion. Thus, I arrived at the demonstration that, in the very structure of the cerebral cortex, among the thousands of elements of which it is composed, there is an entire series of special nerve cells, intimately connected one with another, constituting perfectly defined zones, anatomically appreciable, and serving as a common reservoir for all the diffuse sensibilities of the organism, which, as they are successively absorbed in these tissues, produce in this region of the sensorium commune that series of impressions which brings with it movement and life.

viil AUTHORS PREFACE.

In the second part, which comprises an explanation of the uses of the different cerebral apparatuses of which the anatomical details have been previously analyzed, I have in the first place given a physiological explanation of the different fundamental properties of the nervous elements, considered as living histological units.

I have in this manner shewn that these properties, which are the ultimate generating elements of all the forms of activity of cerebral life, may be finally reduced to three principal forms : — sensibility, by virtue of which the cerebral cell enters into relation with the surrounding medium ; organic phosphorescence, which confers upon it the property of storing up in itself and retaining the sensorial vibrations which have previously excited it (as we see in the inorganic world phosphorescent bodies preserve for a longer or shorter period traces of the luminous vibrations which have impinged upon them) ; automatism, which is merely the aptitude which the nerve-cell possesses, for reacting in presence of the surrounding medium, when once it has been impressed by this.

Having thus surveyed each of these elementary properties of the nervous elements in their origin, in their evolution throughout the organism, in their normal manifestation and pathological deviation, I arrive at the demonstration that it is by means of their combination, and by the harmonious co-ordination of all their truly specific energies, that the brain feels, remembers, and reacts ; and that, in fact, being the properties in which all the others originate, they are the only living forces that are always present, always underlying the infinite series

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of operations which it every moment accomplishes ; and that without them that admirable and complex apparatus, at once so delicate and so simple, would be as absolutely without life and without movement, as the earth would be without the sun.

Having thus examined the elementary properties of the nervous elements, I have shewn how their co-operation may be used to explain the principal phenomena of cerebral physiology.

I have in this manner made it clear that by grouping among themselves the foregoing data, we may perceive that all manifestations of cerebral activity — even though we have to deal with the phenomena of psychical life proper, or the operations of intellectual life, — like their fellows which have the spinal cord for a theatre (reflex phenomena) are always susceptible of being decomposed into three elementary phases ; that they are always originally determined by the arrival of an incident sensorial impression, recent or former (phase of incidence) ; accelerated by the particular reaction of the interposed medium, reacting by virtue of its specific energy (intermediate phase) ; and completed by the secondary reaction of the intermediate medium, reacting and carrying outwards the primordial vibration which has been communicated to it (phase of reflexion).

It results, then, from this manner of looking at the phenomena of cerebral activity, that it is always a fact of the vital order which is at the origin of every process in evolution. Sensibility is always the primary motor agent ; it originates all movement. Propagated through the sensori-motor machinery of the cortex, it becomes x author's preface.

insensibly transformed, like a force in evolution, and ends by disengaging itself from the organism in the form of a motor act.

In short, in these researches, in which my sole object has been to carry the data of contemporary physiology into the hitherto uninvaded domain of speculative psychology, I have endeavoured to show that the most complex acts of psycho-intellectual activity are all definitely resolvable, by the analysis of nervous activity, into regular processes ; that they obey regular laws of evolution ; that, like all their organic fellows, they are capable of being interrupted or disturbed in their manifestations by dislocations occurring in the essential structure of the organic substratum which supports them ; and that, in a word, there is from this time forth a true physiology of the brain, as legitimately established, as legitimately constituted, as that of the heart, lungs, or muscular system.

As a consequence of what has just been said, it necessarily follows that this range of studies, so new and so attractive, should properly belong to the physiological physician and to him alone. Henceforward he may claim as his peculiar patrimony that special domain of the nature of man concerning which speculative philosophy has for so many centuries so long and learnedly harangued. It will be his task to fertilize it by his incessant labour, and to make it yield what all labour intelligently directed should afford, legitimate fruits — practical consequences which may be utilized for the benefit of suffering humanity. The history of medical science is present with its daily lessons, to shew us that the useful acquisitions which it has made have always been inevitably subordinated to clearer and more

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precise notions concerning the anatomy of the organs whose care is its mission ; and when we transfer the same aspirations to the subject which now occupies us, this fact surely authorizes us to hope that in the future we shall see new methods in the treatment of mental maladies, and modes of action more efficacious than those now at our disposal, arise from a better comprehended cerebral anatomy, and a more rationally directed cerebral physiology.

J. LUYS.

Chapter II

True Period of Emission of the Processes which produce Voluntary Motion — Spontaneous Reaction of the Sensorium— Motived Resolution . . , « • • 3*9

LIST OF ILLUSTRATIONS.

PAGE

Fig. i. — Diagram of a Section of the Cerebral Cortex . . 15

Fig. 2. — Cortical Cell of the Deeper Zones . . . .19

Fig. 3. — Diagram of Commissural Fibres of the Anterior

Regions of the Brain 27

Fig. 4.— Diagram of Commissural Fibres on the level of the

Corpus Striatum 29

Fig. 5. — Diagram of Converging Fibres, and their Relations

with the Central Grey Ganglions . . . -31

Fig. 6. — Diagram of the Sensori-Motor Processes of Cerebral

THE BRAIN.

Part I. Anatomy Of The Brain

CHAPTER I.

METHODS OF STUDY.

THE study of the nervous centres has always strongly attracted the anatomist as a field of labour ; and the reason of this is not far to seek. In the face of such a subject, not only does the very natural desire to penetrate the inmost secrets of the organization of the anatomical details under consideration come into play, but, further, there is that unconscious attraction which draws the human mind towards the unexplored regions of the unknown — towards those mysterious realms where the living forces of all our mental activities are silently elaborated, and where the solution of those eternal problems, regarding the relations of the physical organization of the living being to the acts of its psychic and intellectual life, evades us as we pursue it.

Hence it is that from century to century most of the great anatomists have, each in his turn, laboured in this direction. Hence Galen, Varolius, Willis, Malpighi, Vieussens, Vicq d'Azyr, Sommering, Reil, etc., have successively, in their immortal works, either described the organization of the nervous centres as they conceived of it at their own epoch, or expressed in their iconographies (with a more or less distinct glimpse of the truth) the objective fashion in which they saw the anatomical details they have successively represented.

In dealing with a subject so vast and so delicate, and a material so fragile and easily alterable as the nervous matter, the student is necessarily forced to depend on the different methods placed at his disposal by the arts and sciences of his own epoch. Hence the smallest technical discoveries frequently become of inestimable value ; and it may be said, without exaggeration, that the utilization of chromic acid,* which, by hardening the nerve-substance, fixes it, with all its natural relations, without altering it, has been one of those new methods in laboratory work which have most essentially contributed to the success of those great achievements in this particular domain of anatomical science which our own century has witnessed.

On the other hand, the perfecting of the magnifying power of microscopes has been of immense service, and has permitted the spirit of man to advance with vast strides into regions as yet unexplored, where it stands face to face with those ultimate anatomical units, the nerve-cells, of which our predecessors scarcely

* Hannover, in 1840, was the first to point out the hardening properties of chromic acid. (Robin, Traite du microscope, p. 297. J. B. Bailliere, 1871.)

caught a glimpse. Thus it is now possible to give exact descriptions of their configuration, whether we study their connections, their minute structure, or the different pathological deviations they may undergo.

The introduction of the microscope into the study of histology has been in our century for the world of the infinitely little, what at another period of human development the intervention of the telescope was for the exploration of the sidereal world. It has rendered distinctly visible all those myriads of elements which, from their extreme smallness, were concealed from the eyes of our predecessors. It has brought them to light, revealed the secrets of their minute organization, and opened to the investigations of anatomists an entire new world of unexpected ideas.

Following upon this discovery, as a natural consequence, came the revelation of the art — previously unknown in our laboratories — of making thin slices of nervous tissue, colouring them, rendering them transparent, and preserving them. The employment of reagents of all kinds, which, testing in some degree the special sensibility of each histological element, colours it in a particular manner, and sets in relief the peculiarities of its structure, has opened a new road for progress ; so that all over the civilized world, labourers, aided by physics and chemistry, have united their efforts, until we can say that the limits of the unknown recede, and that new conquests are perpetually being registered in our scientific reports.

But this is not all. In this kind of research it is not sufficient to see for ourselves the new facts met with on our road ; it is necessary to make others see them, to represent in faithful statements the details of nature we have examined, and to place the newly-registered facts beyond dispute.

Up to the present time it was the observer himself who pourtrayed, by means of his pencil, the objects which passed through the focus of his microscope. And, accordingly, we all know how widely these nominal drawings — even those made by masters of their profession— usually diverge from the truth ; simply because they can never express more than those details which the artist has perceived and recognized, and a species of unconscious selection from the objects which are passing before his eyes. It is, then, in presence of these desiderata, as regards graphic representation, in drawings made by hand that we feel the necessity of applying the marvellous resources now offered us by photography to the reproduction of microscopic objects.

The sensitized plate henceforward plays its part in the world of scientific investigation, in the study of the phenomena that occur in the world of the infinitely little, as well as in the study of those that occur in the world of the infinitely great — registering histological facts as well as astronomical phenomena, and thus becoming the impersonal and automatic pourtrayer of the most minute details that have impressed themselves upon it. Thus, wonderful to relate, photography, very much superior to drawing, not only reveals the objects which the eye perceives, but brings to light in addition a whole series of latent details, which await but the intervention of a simple lens to be successively recognized upon the prints when obtained.

These new means of investigation, which the scientific methods of the nineteenth century have placed within the reach of our generation, will, therefore, explain the progress accomplished, and show us once more that, in the long process of evolution which extends through ages, man only arrives step by step at the fragments of truth which he snatches, and that even his most persevering efforts only serve to cause the unknown to recede a few paces backwards. It is strange to find that, as fast as any progress is accomplished and new discoveries registered, new problems incessantly start up ; and that just when we thought we had arrived at the utmost limits of the known world, at the demonstration of elements, simple, fixed, definite, our perfected methods of study enable us to see new complexities and unexpected horizons.

Thus, for instance, by means of high powers, the histological elements of the nerve-cell, hitherto considered as the primordial and irreducible units of the system, become themselves divisible into secondary elements.

Photo-chemical histology, indeed, shows us that the protoplasm of the cell, formerly described as a homogeneous substance, is arranged in a fibrillary trellis-work; that its nucleus presents an arrangement of radiated fibres ; and that what was thought to be the nucleolus is itself a complex element. The nerve-cell thus becomes in its turn a little nervous organ sui generis. (See Fig. 2.)

The same analytic processes enable us, moreover, to demonstrate that the network, so dense and compact, which unites all the nerve-cells of the cerebral cortex, for instance, one with another, is so delicate that, when enlarged to 286 diameters, the fibres of which it is composed become visible, like single hairs in appearance and magnitude, etc.

What will be the end of these unforeseen details which present themselves in the train of each adaptation of a new method of study, to our researches into the nervous system ?

No one knows as yet. It seems as though the secrets of nervous organization escape from our eyes as fast as we press further into the regions where they conceal themselves, and while anticipating the new methods of analysis which the future holds in reserve, we cannot help thinking that there is still much to do, and that now, more than ever, we should remember that true saying of Serres : " We have been dissecting the brain since Galen's time, yet there is not an anatomist who has not left his successors something to do."

The labours of which I am about to give a rtsumi, are, then, but one of the phases of this long discussion concerning the structure of the nervous centres which has been going on for centuries.

If they do not establish the truth absolutely and finally, they will at least have the merit of being the result of contemporary science, and a sort of synthesis of the methods of work at our disposal.

The method I have employed for studying the organization of the cerebro-spinal centre in man, I have already explained in my first work.* It essentially consists in the preparation of a series of sections made methodically, millimetre by millimetre, vertically, hori-

* J. Luys, " Recherches sur l'anatomie, la physiologie et la pathologie du systeme nerveux." Paris, 1865, J. B. Bailliere.

zontally, and antero-posteriorly ; and — these sections being thus made according to the three dimensions of the solid mass which was to be studied — in reproducing them all photographically.

I set myself, then, to make a series of successive horizontal sections of the brain, previously hardened in a chromic acid solution, from apex to base, at intervals of about one millimetre, and as perfect as possible ; each being in its turn reproduced by photography.

I made similar sections of the brain in a vertical and antero-posterior direction, and at regular intervals from behind forwards.

These operations having been thus regularly conducted, this method enabled me to have representations of the reality as exact as possible ; to keep the natural relations of the most delicate portions of the nervous centres each by each, according to their normal connections, and, in fact, without deranging anything. Thus by comparing the sections, horizontal or vertical, one with another, I could follow a given order of nerve-fibres in its progress, see its point of origin, and its point of termination ; study the natural increase in complexity of the different kinds of nerve fibrils, millimetre by millimetre, changing nothing, lacerating nothing, and leaving everything pretty much in its normal position.*

* The plan of this work does not permit me to insist upon the innumerable difficulties I have surmounted, in arriving at the clear result already recorded in my photographic iconography. (Luys, " Iconographie des centres nerveux," J. B. Bailliere, Paris, 1872.)

In the first place I had to invent cutting instruments sufficiently delicate to make complete sections of the brain, of the thickness of about one millimetre.

But these pieces, when sufficiently hardened to undergo the action of the cutting instrument, had acquired, on coming out of the bath of chromic acid,

By means of these new photographic methods of reproduction, which are all the more precise because impersonal, I had only, then, to register the details the sun himself had printed, to place the prints in juxtaposition, to compare them one with another, and thus to make a single synthesis of the multiple elements of analysis I had thus obtained by the automatic co-operation of the light.

The general view of cerebral topography having thus been fixed by these processes, the regions of more delicate texture, the special points which it was necessary to study in their minute elements, were further sufficiently magnified and reproduced, with successively increasing powers. I could thus render visible to the naked eye, and exhibit on a plan, details of structure which, up to that time, had only been seen in isolation under the tube of the microscope. By this means the mind of the observer, penetrating successively from the known to the unknown, from well-defined regions to those which are not so as yet, can easily make itself familiar with the details of the minute structure of the final nerve elements.

The cerebro-spinal system in man and the vertebrates consists of three departments, independent one of another, and yet very intimately connected. These are : —

I. The cerebrum proper.

that peculiar uniform greenish colouring which renders them completely unfit for photogenic action. It was therefore necessary to discover a perfectly novel series of processes, in order to purify these sections from the chromic acid, and, without altering them, to impart to them photogenic properties. (See Journal d'Anatomie de Robin, Paris, 1872, for the whole series of the processes employed to bleach the sections tinted with chromic acid.)

2. The cerebellum and the apparatuses of cerebellar innervation annexed thereto.

3. The medulla spinalis and its encephalic expansions. In this study we shall occupy ourselves with the

cerebrum proper only.

The cerebrum consists of two lobes or hemispheres united to one another by a series of white transverse fibres, which form an anastomosis between the homologous regions of each lobe, so as to constitute a twin system, of which all the molecules are consonant one with another.

Each cerebral lobe, taken alone, presents for consideration in its turn : —

1. Masses of grey matter.

2. Agglomerations of white fibres.

The masses of grey matter, which are composed of many myriads of cells, and are the essentially active regions of the system, are arranged at the periphery in the form of a thin, undulating, continuous layer, which constitutes the cerebral cortex ; and in the central regions in the form of two grey ganglions, coupled together, which are simply the grey substance of the optic thalami and corpora striata (opto-striate ganglions).

The white substance, essentially composed of nerve-tubules in juxtaposition, occupies the spaces comprised between the cortical periphery and the central ganglions.

The fibres of which it consists, and which merely represent lines of union between such and such regions of the cortical periphery and such and such regions of the central ganglions, run, like a series of electric wires stretched between two stations, in two principal directions.

1. Some directly unite the different points of the cortical periphery with the central ganglions, and are lost in their mass.

These are like the spokes of a wheel which unite its circumference to the central nave, which serves as their point of support. We may therefore describe them under the name of converging fibres.

2. The others, on the contrary, have a transverse direction. They proceed from one hemisphere to the other, thus uniting the homologous regions of the brain, right and left.

It may therefore be said that they serve as an anastamosis and commissure between these homologous regions, and that they are thus the agents which produce unity of action between the two cerebral hemispheres. This order of fibres, by reason of its origin and connections, may legitimately be designated by the name of commissural fibres.

These data being admitted, it may be said that the anatomic formula by means of which we may define the structure of the cerebrum, of man as of the other vertebrates, is this : " The cerebrum is the sum total of the cerebral convolutions, united one with another, with those on the same side and with those on the other, and simultaneously with the central opto-striate ganglions."

We shall now pass in review the different agglomerations of the grey matter, and at the same time give a sketch of the principal details of the organization of the white matter.

CHAPTER II.

CORTEX OF THE BRAIN — THE GREY CORTICAL SUBSTANCE.

Every one knows the external appearance of the cortical substance of the brain. It is sufficient to recall that of the brains of sheep, as served at table, to see at a glance that the grey cortical substance presents the appearance of a grey undulating layer, folded a great number of times upon itself, and thus forming a series of multiple sinuosities of which the sole object is the obtaining of increased surface.

These foldings and refoldings, which attain their maximum of development in the human species, apparently obey some fixed laws as regards their distribution.* Some, in fact, have permanent characters which render them easily discoverable in all human brains ; others, and these form the greater number, present all possible varieties of external configuration, not only in different individuals, but even in the same individual, according as we inspect homologous regions in the right or left hemisphere.

Take, for instance, a sheet of tracing paper, apply

* See the interesting description of the topography of the cerebral convolutions given by Prof. Charcot in his lectures to the Faculty. — Progres Medical, 1875, p. 2S3, 353, &c.

it to a fresh vertical section of the brain, mark with a brushful of water-colour the contour of the cortical substance of one hemisphere, and fold the paper over ; you will thus see very clearly that the outline of the convolutions of one side does not adapt itself to those of the other. I have made such tracings repeatedly, and have never yet found a human brain completely symmetrical, completely balanced in its peripheral regions, and with the left regions of the cortical substance exactly corresponding to the homologous regions of the opposite side.

There is another peculiarity, which it is important to notice, in the external examination of the cortical substance.

In the adult, in vertical or horizontal sections of the brain, it is evident that the line of the summits of the convolutions is continuous, that their culminating points are all on the same level ; there is some uniformity in the distribution of the activity of nutrition over the whole mass.

As old age advances different appearances begin to show themselves, and in studying the different effects of senescence in all the organs, it is curious to observe its characteristics in the human brain.

We observe, then, that the grey substance becomes diminished in thickness ; that its colour changes to yellowish white in consequence of the passing of the nerve-cells into the granulo-fatty state; and that besides, the convolutions settle down in isolated groups, like mountains, undermined at their bases, which insensibly subside. Thus, in many old men in their dotage, we may note that the line joining the summits of certain cortex of the brain. 13

groups of convolutions becomes interrupted ; that a certain number of them are retracted and have sunk below the level of the surrounding convolutions ; and that thus, from the effect of time, there exists a slow and progressive absorption of the nervous substance.

In individuals who fall prematurely into dotage from alterations of the cerebral substance, under the action of mental diseases, we find the same atrophy of the cortical layer. Thus I have very frequently observed atrophy of the convolutions in young subjects attacked by paralytic dementia, persons affected by hallucinations, and patients who have suffered from melancholic delirium.

The thickness of the cortical substance in the adult is on the average about two to three millimetres. Generally it is more abundant in the anterior than the posterior regions. Its mass varies according to age, and especially according to race, Gratiolet remarking that in races of low stature the mass of the cortical substance is but small.*

Its colour presents some varieties. It is uniformly greyish, and as it were gelatinous, in the new-born infant ; in the child during its first years it is of a rosy grey ; in the old man it acquires somewhat of a yellowish-white colour, its vascularity being less distinct than in the adult. In the negro this substance is of a darker colour than in the white man,