HOW THE BRAIN WORKS

I

Before beginning the study of the nerve-centres I shall remind the reader of a few very simple facts, which, doubtless, he already knows, but which, recalled, will render more apparent the part taken by the body in the functions of the mind.

In order to know how the brain works, it is sufficient to recall the pictures and visions which pass before us when we are absent-minded. How curious it is when the mind sets out on its fanciful wanderings! when, unconsciously, we leave the everyday world behind us and stand motionless, with open eyes, seeing and hearing nothing.

How often in the quiet of our study, while reading a book, have we not seen the words gradually fade one into another, until we found ourselves as though enveloped in a cloud, far away amid the recollections of childhood or the hopes of the future! And what wonderful forms grow out of the flames, the logs, and the sparks glowing under the ashes, when we draw close to the fire in lonely evenings!

It is an actual relief to many, this repose of attention, this extinction of the will which steals over us in the midst of life’s troubles, lifting the burden of care and allowing us to contemplate quietly the curious spectacle which, when left to itself, the brain at work presents. How rapidly things and thoughts are transformed, melting into each other without order, aim, or pause! How easily we glide by winding paths through time and space, while in endless succession new horizons and new countries rise before us! What airy phantoms look down from the clouds above, what voices and harmonies strike the ear in the waterfalls of the brooks, what living pictures peer at us from amongst the flowers and grasses on the bank! Then suddenly a flood of memories rushes over us and leaves us confused, bewildered, as it rolls on again to the dim horizon of consciousness. And in this rushing flood of thoughts and forms we see the familiar faces of those whom the grave seems to give back to us, and we hasten to meet them with smiling lips or with tears in our eyes.

II

And yet these are nought but dreams of the waking mind. Even when the force of attention and the energy of thought are greater, we still are carried away by the wilful, untamable current of cerebral activity; because the will can do nothing within the domain of the imagination, and because the brain is no slave who will obey our very nod. Who does not remember the painful and useless endeavours made to rid oneself of an annoying thought and that incapacity for mental work which afflicts us, without our knowing whence it came? How often have we sat for hours at the desk, with idle pen, our head in our hands, unable to wrest even one thought from the mind which we dared transmit to paper! How depressed we are on those days when the sources of the mind seem dried up, when we torture ourselves in vain, ransacking our brains and finding nothing but fragments, crumbs of thought which we reject angrily as worthless refuse!

We must resign ourselves. We feel ourselves humbled as though the door of our own house had been shut in our face. It is of no use to be sad and annoyed; even if we give way to furious passion, it does not help us. We stand behind a high wall which we cannot break down. An English physiologist compared the thinking man to a simple engine-driver. He does not move the trains, neither does he determine their departure or their stoppage, he merely guides their movement, directing them first in one direction then in another.

The brain is perpetually at work, and it is impossible for the mind to embrace its activities in every part. The greater the attention is in one part, the more vague is the knowledge which we have of contiguous parts, the less vivid are the impressions which the senses transmit from the outside world. We need only recall the well-known example of Archimedes who was killed by a Roman soldier during the siege of Syracuse, while he stood in calm contemplation of some geometrical figures.

The whole of our brain is never at work at one time; now it is the one half, then the other which is in action.

When looking at the sky or at a wall in a uniform light with only one eye, I found that the field of vision changed alternately from light to dark. This does not depend upon the eye but upon the brain, because unconsciously we use first one eye then the other; and, in the same way, the two hemispheres of the brain do not work simultaneously, sometimes it is the one sometimes the other which is in a state of activity. A French general had lost one half of his brain from a wound which clove the skull. He recovered and retained his intelligence and gaiety, but he used soon to grow tired during conversation and could only continue any intense mental work for a few minutes at a time.

There are many philosophers who maintain that a considerable portion of our cerebral activity is purely automatic, so that our mind is often in operation without our being conscious of it. When an idea, says Maudsley,[3] disappears from the horizon of consciousness, it need not vanish totally, but may remain, as it were, latent or veiled, continuing by its movements to awaken, to give rise to, other ideas without our being aware of this activity. But when our consciousness is unexpectedly drawn off from its work, or roused by something which had before occupied it, then we catch the idea at work.

This opinion is rendered probable by a few phenomena which I observed during my studies of the circulation of the blood in the brain, and we may easily convince ourselves also, if we reflect, how often, quite unexpectedly, names and events occur to us when we were least thinking of them, and which we were unable to recall for a long time and in spite of wearisome efforts, when we wished to do so. And we all know that we are unable to fall asleep at will, so little mastery have we over our thoughts. We direct our minds first to this object then to that, in order to draw it away from that which occupies it and keeps us awake. We try to suppress an idea which torments us by calling other ideas to our assistance in ousting it, and often wait powerless for the coming of that silent oblivion and calm of mind which alone can give us rest.

If, in the moments preceding sleep, when the mind is comparatively quiet, we make an effort to fix our thoughts on something, we notice how they vacillate, disappearing and reappearing, as though we were in a boat and our heads were lifted from time to time above the waves. Even when awake we find ourselves only too often in this humble bark in which every puff of wind drives us far from the shore we wish to reach, when impetuous currents of thought prevent our entering the haven, or when the waves open to plunge us into unfathomable depths out of which we can see no horizon.

III

But in order better to see the link which binds the substance of our organism to the activity of thought, the correlation between the nutrition of the body and the mental state, or, as one is accustomed to say, the relation between body and soul, let us carefully notice what takes place when a number of friends are assembled at table.

After a few cheerful remarks made by the most jovial as they take their places, a certain gloom spreads over the company. One might almost think only a few were sociably inclined. Someone attempts to break the ice, but it is a failure; one feels that the conversation is forced, jerky, altogether wanting in sparkle. Little by little the guests brighten up. A hum ensues, then a confused buzz, like the tuning of the instruments of an orchestra, which rapidly increases in pitch, as though each were trying to make his voice heard above his neighbour’s. It seems as though something in their brains had been loosened and the vocal cords had gradually got into working order. At dessert even the more taciturn, if they have done full justice to the banquet, pour forth an unceasing stream of conversation. Moody faces become smiling, and melancholy gives place to gaiety. The cross-fire of talk, the hot discussions, the frequent bursts of laughter, the lively play of feature, the witty interruptions, the excited gesticulations, all show a hundredfold increase of vital action.

And from the glowing faces, the sparkling eyes, we know that the blood is rushing in abundance to the brain. The tongue is loosed, ideas accumulate in the mind, as though some kind hand had set the rusty wheels of thought in motion and poured oil on the hinges of the vocal mechanism.

There is no need to say more. We have all experienced this transformation which takes place in the work of the brain. It enters on another phase when the wine begins to circulate. If we had not already met the guests on similar social occasions, we should be greatly surprised at their metamorphosis, and feel constrained to correct previous misconceptions of their character. Men, whom I had always thought silent and cold, I have seen, to my amazement, carrying on the most daring discussions with brilliant fluency, and rebutting sarcasms with such promptitude and success as to earn them loud applause. Other timid ones, known to all as slow, tiresome, clumsy talkers, find in the wine-glass a sparkling vivacity, a flow of speech which makes them more agreeable; nor do they hesitate to propose toasts and drink to the health of each of the guests. They rise, glass in hand, finding a witty word for each and showering compliments on all sides. Men, calm and sedate, in whom none suspected a poetic soul, are capable of rising and improvising verses, and we are full of admiration at their skill, and at the harmonious grace of rhythm, metaphor, and rhyme.

Each one feels something like inspiration within him, as though warmed by the quickening pulse of life.

But let us leave the joyous company: so far as our psychological study is concerned, we have already lingered too long, and it would be superfluous to follow them as they leave, in order to see how confident, kind, and courageous they have all become.

The next day each will resume his own character and his own business. If it happens that one of the guests meets another in the street, they smile as they shake hands, and words which are a revelation are heard: 'We were a lively party last night, eh? I scarcely recognised you, and as for some others, there was no keeping them quiet!'

IV

The analysis of memory better than anything else shows us the connection between the various parts of the brain which enter into activity in order to provide us with the elements that form speech.

We must distinguish two kinds of memory:

1. The fixation of impressions, whether these be images, or representations of movements, words, sounds or sensations.

2. The re-awakening of these impressions as recollection.

The phenomena of memory remain quite incomprehensible if we do not admit their intimate connection with physical changes of the nerve substance. An external impression acting upon receptive nerve-cells is retained by them permanently, as though it were photographed, if it be allowable to explain the unknown by a comparison with the known. It is the blood which carries those substances to the brain which are necessary to the functions of memory. Attention cannot be developed in all its intensity without causing considerable alterations in the circulation. Now when we are absent-minded, images leave no lasting impression on the memory, as no provision is then made by the physical changes in the organism accompanying attention for a more rapid circulation of blood in the cerebral hemispheres.

The old notion that the brain was a storehouse in which each idea had its nook where it might stay till needed, is truer than it appears. Modern science has proved that the matter is much more complicated than one thinks. It suffices that the blood should coagulate in the artery which carries it to some convolution, or that a tumour should destroy a part of the brain, for us to lose, as it were, a province of memory.

Let us first consider verbal memory. That region of the brain in which it is placed is, generally speaking, the parietal region of the left side; so that anyone who has had a blow on the temple at that side nearly always loses his speech, although he still remembers things and can pronounce their names when they are repeated to him by others, a sufficient proof that the movements of the tongue are not impeded. Sometimes it happens that a person in this condition looks in the dictionary for the missing word, in order to recover the pronunciation of it.

In learning a language, we believe that certain cells undertake functions which they did not before possess, that connections with other cells are established, like very intricate nets in which the impressions of nouns and verbs, the graphic representations of ideas and words, are collected. As we exercise ourselves in the language, the blood carries new elements to these cells, and the greater our attention, the stronger become the impressions. Oxidation does not destroy the impression once received, but it weakens it. If we have had no practice for some years in speaking a language, we meet with great difficulties, our communications being made in set, stiff words; but after a few days one regains the former fluency.

We might quote cases in which, through illness, a man has completely forgotten a language, recovering it as health returned. Others have forgotten several languages in the order of succession in which they had learnt them, regaining them later in the inverse order to that of acquisition.

When groping in the dim recesses of memory, we always perceive that there are associations and intimate connections amongst the phenomena of thought. The blood, making its way into certain parts of the brain, is like the light of a torch penetrating subterranean passages, on the walls of which are painted pictures of things we know. Often the blood-vessels do not yield, and we then wander in vain in that labyrinth, retracing our steps, roaming hither and thither, until suddenly we see an opening, and what we were seeking appears unexpectedly before us. The supposition that we here have to do with an effect of the blood, an expansion or contraction of the vessels, and with phenomena of nutrition, seems to be strengthened by the circumstance that sometimes, in consequence of violent emotion, a succession of things which before seemed totally forgotten suddenly reappears in our memory.

The link between physical phenomena and phenomena of memory is more apparent during fatigue and the refreshing state of repose. Memory may fail entirely from anÆmia, from poisoning by narcotics, innutrition of the brain, and in old age; for we all know how much better we remember the events of our youth than those of later occurrence.

Men who have had wounds or contusions on the head have been known to forget that they had children; authors have forgotten even the titles of their works; but as soon as the fever had passed, or the wound healed, they regained their memory. Others, during a fever, have related events and remembered names which they had quite forgotten previously, and which they were unable to recall after recovery.