THE TOPOGRAPHY OF THE BRAIN.

As late as twenty years ago physiologists and clinicians agreed in declaring the cortex of the brain to be functionally homogeneous. Flourens's experiments had decisively negatived Gall's very ingenious but purely hypothetical conception, and any effort to prove localization would, at that day, have seemed like a reversion to a system already tried and condemned. It was freely admitted that, from experiments made on pigeons, one might infer the mode of brain functionment in man. Medicine was under the yoke of the then dominant teachings of physiology, nor was there so much as a thought of reaction. Clinical observers, indeed, had long before known that motor troubles consequent on a lesion of the brain imply localization of such lesion in the hemisphere on the side opposite to that paralyzed; but that was then the sum of the topographical diagnosis.

Broca, in 1863, showed that the impairment of the power of articulate speech, which he calls aphemia, is connected with a brain affection that is always localized in a clearly circumscribed region of the left hemisphere. At first the fact was called in question. When proofs had been multiplied in its favor men contented themselves with simply admitting it, little noting that this very definite localization was a first attack on Flourens's doctrine, which must now undergo revision. But the topographical anatomy of the cerebral convolutions was then too little known to enable one to "find his bearings" on the surface of the brain, and the reaction against Flourens's ideas would at that time have met with insurmountable obstacles.

The thorough researches of Leuret and Gratiolet, and of their successors, Ecker, Broca, Gromier, by making us acquainted with the morphology of the external surface of the brain, removed these first anatomical difficulties. The experiments of

Fritsch and Hitzig in Germany, in 1870, and shortly afterward those of Ferrier, in England, modified the ideas which prevailed. They showed, on the one hand, that the gray matter of the brain is not incapable of excitation, as had been supposed; that electric excitation of this gray matter calls forth motor reactions; on the other hand, they prove-an important point-that the effects produced differ according to the part of the cortex that is excited. From that date, properly speaking, began researches into motor localizations in the brain. Since then such researches have been prosecuted in two directions; for while the physiologists reproduced, with various results, the experiments of Fritsch, of Hitzig, and of Ferrier, the clinicians were also at work. And I may be permitted to say that the researches in this latter direction began in France, and that I have had some share in them. My first researches, made jointly with Professor Pitres, then my interne, were the starting-point for studies that have been for ten years prosecuted with remarkable activity in France, where a great number of investigators have contributed their share of facts, in England by Jackson and Ferrier, in Germany by Nothnagel.

On considering how far we have advanced in the study of localization in the cortex while pursuing these two pathsexperimentation on animals and anatomo-clinical observation of man-one is struck with the fact that while among clinicians there is perfect agreement, at least on the essential points, among the physiologists there is marked disagreement. The divergence of views is due, perhaps, mainly to the fact that the experimenters have cared less about determining the relations between a given affection and a lesion of one or another part of the cortex, than about discovering the inner mechanism of the relation between the two. That which, in the eyes of the clinician, whose thoughts are ever of diagnostics, is the point of capital importance, thus becomes an accessory datum for the experimenter, who thinks more about theory. Now, the theories that have been advanced, one after another, to account for the phenomena observed to follow excitation or destruction of the cortex are as numerous as they are uncertain. Take the fundamental facts alleged by Fritsch, Hitzig, and later by Ferrier, viz., that exci

tation of certain parts of the gray matter determines localized convulsions; that, on the contrary, ablation of these parts produces paralysis; these facts, while admitted in their general tenor, have been interpreted in very different ways. According to some writers, Ferrier, for instance, the cortex comprises true motor centers; others, as Hitzig, Fritsch, Schiff, Munk, hold the excitable points to be sensitive centers, excitation of which determines movement in virtue of a sort of reflex action, while destruction of these centers produces paralysis through loss of conscious sensibility. Many physiologists, as Tamburini, Luciani, and Seppeli, hold this "excitable zone" to be both motor and sensitive. Vulpian held that it is simply the place of convergence for influences emanating from all the other parts of the encephalon, and that it has no activity of its own. Finally, according to Dr. Brown-Séquard, the excitable points of the cortex have neither motor nor sensitivo-sensorial functions; excitation applied to them does but traverse them, passing on to organs of movement situate lower down; their destruction does not act by suppression, but by irritation at a distance. Such is the theory of dynamogenic, or inhibitory, action at a distance. As has been justly remarked by François Franck:

"It must be admitted that all the interpretations now conceivable are absolutely provisional; nay, it were rash and illogical to believe that any question whatever touching the mechanism of the brain, and in particular this one, has been definitely settled."

Certainly the study of these questions is by no means void of interest, and the clinician may not stand indifferent toward the efforts made to determine the instrumental process whereby a given lesion of the cortex produces such or such a convulsion, such or such a paralysis. But he must not forget that this determination is a secondary task; and, in any case, theoretic considerations cannot fairly be suffered to call in question the positive teachings of anatomo-clinical observation.

Then, it is to be borne in mind that experimentation with animals that are nearest to man, still more with those far removed from man on the zoological scale, cannot, however faultless its technique, however definite its results, solve finally the problems

raised by the pathology of the human brain. In brain it is, above all, that we differ from animals. That organ attains in man a degree of development and of perfection not reached in any other species. Its functions become complex, while at the same time its morphology undergoes important modifications. Now, it is perfectly clear that as regards questions of localization morphological details are of the first importance. As for functions, even if we take account only of those common to men and animals, they are not performed in all in the same way. The higher an organism stands in the animal scale, the more strictly are the purely reflex functions subordinated to the functions of the higher centers. A decapitated frog performs with its legs co-ordinated automatic movements; not so a decapitated dog. In the dog, brain lesions, even of considerable extent, produce only incomplete paralysis, often passing away, while in man the like lesions cause incurable functional troubles. These examples are enough to show that, particularly as regards brain functions, the utmost reserve is necessary in drawing inferences from animals to man. The results of experimentation, however ingenious, however skillfully conducted, can give only presumptions more or less strong, but never absolute demonstration.

Hence, the only really decisive data touching the cerebral pathology of man are, in my opinion, those developed according to the principles of the anatomo-clinical method. That method consists in ever confronting the functional disorders observed during life with the lesions discovered and carefully located after death. This is the method that enabled Laennec to throw light on the difficult subject of diagnosing pulmonary affections, and it has also materially helped the diagnosis of diseases of the liver, kidneys, and spinal cord. To it, I may justly say, do we owe whatever definite knowledge we have of brain pathology. As for the localization of certain cerebral functions, here this method is not only the best, but the only one that can be employed. What light, for instance, could experimentation have thrown upon the question as to the seat of the functions of speech-functions which are special to man?

No doubt observations restricted to the domain of man, and deprived of the powerful lever of experimentation, may, at first

sight, seem doomed to play a subordinate and inconspicuous role, but that is so only in appearance. As I had occasion to write, some twelve years ago:

"The conditions of a truly spontaneous experiment in man are presented every day in pathological circumstances. To profit by them, we have only to learn to comply with the necessities of a situation no doubt very different in many respects from that which experiment purposely brings about in the ani mal, but which is not always more complex. If it is true that observations made, in the light of physiology, on man in disease, usually require more time, more patience, than corresponding studies of animals under experiment; if it is true that in man the conditions of the phenomena cannot be, as they are in the laboratory, either modified or reproduced at the will of the observer; so, too, is it true that disease often determines in the body of the patient lesions more strictly limited to one organ or one tissue; in other words, more systematic and more compatible with persistence of life, and with the integrity of functions not directly concerned; consequently they lend themselves better to methodical and protracted analysis than do mutilations produced in animals by even the most skillful physiologist.” *

But in order to be employed with profit, anatomo-clinical observations must not be gathered at hap-hazard. On the contrary, they have to be tested methodically and classified according to certain rules that I have taken pains to define from the beginning of my studies on cerebral localizations. It is plain, for instance, as I have elsewhere said, that irritative lesions are a very different thing from destructive lesions; nor must we confound lesions newly produced (accompanied, as they almost necessarily are, by phenomena having their seat either near by or at a distance) with old lesions, in which the morbid process being, in a measure, at an end, is now clinically represented only by the mere inactivity of the parts that have been diseased or destroyed. Just because these distinctions have not been sufficiently noted by authors, most of the old observations are useless as regards the question of localizations. When we add that in these observations the designation of the lesioned convolutions is commonly vague and lacking in precision, it is seen that such data give but little light. Hence, as Nothnagel justly says of the many cases of brain lesions that are recorded, having been collected in the course of ages, unfortunately only a very few

* "Revue Scientifique," Nov. 11, 1876.