The Principles of Psychology, Vols. 1-2

In man we are necessarily reduced to the observation post-mortem of cortical ablations produced by accident or disease (tumor, hemorrhage, softening, etc.). What results during life from such conditions is either localized spasm, or palsy of certain muscles of the opposite side. The cor tical regions which invariably produce these results are homologous with those which we have just been study ing in the dog, cat, a~e, etc. Figs. 8 and 9 show the result of

^ f Philosophical Transactions, vol. 179, pp. 6. 10 (1888). In a later paper (HM. p. 205) Messrs. Beevor and Horsley go into the localization still more minutely, showing spots from which single muscles or single digits can be made to contract. 169 cases carefully studied by Exner. The parts shaded are regions where lesions produced no motor disturbance. Those left white were, on the contrary, never injured with out motor disturbances of some sort. Where the injury to

the cortical substance is profound in man, the paralysis is permanent and is succeeded by muscular rigidity in the paralyzed parts, just as it may be in the monkey. (3) Descending degenerations show the intimate connec tion of the rolandic regions of the cortex with the motor tracts of the cord. When, either in man or in the lower ani mals, these regions are destroyed, a peculiar degenerative change known as secondary sclerosis is found to extend downwards through the white fibrous substance of the brain in a perfectly definite manner, affecting certain dis tinct strands which pass through the inner capsule, crura, and pons, into the anterior pyramids of the medulla oblongata, and from thence (partly crossing to the other side) downwards into the anterior (direct) and lateral (crossed) columns of the spinal cord.

(4) Anatomical proof of the continuity of the rolandic regions with these motor columns of the cord is also clearly given. Flechsig's ' Pyramidenbalm ' forms an uninter rupted strand (distinctly traceable in human embryos, before its fibres have acquired their white 'medullary sheath') passing upwards from the pyramids of the me dulla, and traversing the internal capsule and corona radiata to the convolutions in question (Fig. 10). None of the inferior gray matter of the brain seems to have any connec tion with this important fibrous strand. It passes directly from the cortex to the motor arrangements in the cord, de pending for its proper nutrition (as the facts of degenera tion show) on the influence of the cortical cells, just as motor nerves depend for their nutrition on that of the cells of the spinal cord. Electrical stimulation of this motor strand in any accessible part of its course has been nhown in dogs to produce movements analogous to those which excitement of the cortical surface calls forth.

One of the most instructive proofs of motor localization in the cortex is that furnished by the disease now called aphemia, or motor Aphasia. Motor aphasia is neither loss of voice nor paralysis of the tongue or lips. The patient's voice is as strong as ever, and all the innervations of his hypoglossal and facial nerves, except those necessary for speaking, may go on perfectly well. He can laugh and cry, and even sing ; but he either is unable to utter any words at all ; or a few meaningless stock phrases form his only speech ; or else he speaks incoherently and confusedly, mispronounc-

ing, misplacing, and misusing his words in various degrees. Sometimes his speech is a mere broth of unintelligible syl lables. In cases of pure motor aphasia the patient recog- FIG. lO.-Sehematic Transverse Section of Brain showing Motor Strand -After nizes his mistakes and suffers acutely from them. Now whenever a patient dies in such a condition as this, and an examination of his brain is permitted, it is found that the lowest frontal gyrus (see Fig. 11) is the seat of injury. Broca first noticed this fact in 1861, and since then the gyrus has gone by the name of Broca's convolution. The

jhematic Profile of T,eft Hemisphere, with the parts shaded whose ction causes motor (' Broca ') and sensory (' Weruicke ') Aphasia. injury in right-handed people is found on the left hemi sphere, and in left-handed people on the right hemisphere. Most people, in fact, are left-brained, that is, all then delicate and specialized movements are handed over to the charge of the left hemisphere. The ordinary righthandedness for such movements is only a consequence of that fact, a consequence which shows outwardly on account of that extensive decussation of the fibres whereby most of those from the left hemisphere pass to the right half of the body only. But the left-brainedness might exist in equal measure and not show outwardly. This would happen wherever organs on both sides of the body could be gov erned by the left hemisphere ; and just such a case seems offered by the vocal organs, in that highly delicate and special motor service which we call speech. Either hemi sphere can innervate them bilaterally, just as either seems able to innervate bilaterally the muscles of the trunk, ribs, and diaphragm. Of the special movements of speech, how-

ever, it would appear (from the facts of aphasia) that the left hemisphere in most persons habitually takes exclusive charge. With that hemisphere thrown out of gear, speech is undone ; even though the opposite hemisphere still be there for the performance of less specialized acts, such as the various movements required in eating. It will be noticed that Broca's region is homologous with the parts ascertained to produce movements of the lips, tongue, and larynx when excited by electric currents in apes (cf. Fig. 6, p. 34). The evidence is therefore as com plete as it well can be that the motor incitations to these organs leave the brain by the lower frontal region.

Yictims of motor aphasia generally have other disorders. One which interests us in this connection has been called agraphia: they have lost the power to ivrite. They can read writing and understand it ; but either cannot use the pen at all or make egregious mistakes with it. The seat of the lesion here is less well determined, owing to an in sufficient number of good cases to conclude from.* There is no doubt, however, that it is (in right-handed people) on the left side, and little doubt that it consists of elements of the hand-and-arm region specialized for that service. The symptom may exist when there is little or no disability in the hand for other uses. If it does not get well, the patient usually educates his right hemisphere, i.e. learns to write with his left hand. In other cases of which we shall say more a few pages later on, the patient can write both spontaneously and at dictation, but cannot read even what he has himself written ! All these phenomena are now quite clearly explained by separate brain-centres for the various feelings and movements and tracts for associate ing these together. But their minute discussion belongs to medicine rather than to general psychology, and I can only use them here to illustrate the principles of motor locali zation, f Under the heads of sight and hearing I shall have a little more to say.

* Nothuagel und Naunyn ; Die Localization in den Geliirnkrankheiten (Wiesbaden, 1887), p. 34. f An accessible account of the history of our knowledge of motor aphasia is in W. A. Hammond's ' Treatise on the Diseases .of the Nervous System,' chapter vn. The different lines of proof which I have taken up establish conclusively the proposition that all the motor impulses which leave the cortex pass out, in healthy animals, from the convolutions about the fissure of Rolando.

When, however, it comes to denning precisely what is involved in a motor impulse leaving the cortex, things grow more obscure. Does the impulse start independently from the convolutions in question, or does it start elsewhere and merely flow through ? And to what particular phase of psychic activity does the activity of these centres corre spond '? Opinions and authorities here divide ; but it will be better, before entering into these deeper aspects of the problem, to cast a glance at the facts which have been made out concerning the relations of the cortex to sight, hearing, and smell.

Ferrier was the first in the field here. He found, when the angular convolution (that lying between the ' intra parietal ' and * external occipital ' fissures, and bending round the top of the fissure of Sylvius, in Fig. 6) was ex cited in the monkey, that movements of the eyes and head as if for vision occurred ; and that when it was extirpated, what he supposed to be total and permanent blindness of the opposite eye followed. Munk almost immediately declared total and permanent blindness to follow from de struction of the occipital lobe in monkeys as well as dogs, and said that the angular gyrus had nothing to do with sight, but was only the centre for tactile sensibility of the eyeball. Munk's absolute tone about his observations and his theo retic arrogance have led to his ruin as an authority. But he did two things of permanent value. He was the first to distinguish in these vivisections between sensorial and psychic blindness, and to describe the phenomenon of resti tution of the visual function after its first impairment by an operation ; and the first to notice the hemiopic character of the visual disturbances which result when only one hemisphere is injured. Sensorial blindness is absolute insensibility to light ; psychic blindness is inability to rec ognize the meaning of the optical impressions, as when we

see a page of Chinese print but it suggests nothing to us. A hemiopic disturbance of vision is one in which neither retina is affected in its totality, but in which, for example, the left portion of each retina is blind, so that the animal sees nothing situated in space towards its right. Later observations have corroborated this hemiopic character of all the disturbances of sight from injury to a single hemi sphere in the higher animals ; and the question whether an animal's apparent blindness is sensorial or only psychic has, since Munk's first publications, been the most urgent one to answer, in all observations relative to the function of sight.

Goltz almost simultaneously with Ferrier and Munk reported experiments which led him to deny that the visual function was essentially bound up with any one localized portion of the hemispheres. Other divergent results soon came in from many quarters, so that, without going into the history of the matter any more, I may report the existing state of the case as follows : * In fishes, frogs, and lizards vision persists when the hemispheres are entirely removed. This is admitted for frogs and fishes even by Munk, who denies it for birds.

All of Munk's birds seemed totally blind (blind sensorially) after removal of the hemispheres by his operation. The following of a candle by the head and winking at a threatened blow, which are ordinarily held to prove the retention of crude optical sensations by the lower centres in supposed hemisphereless pigeons, are by Munk ascribed to vestiges of the visual sphere of the cortex left behind by the imperfection of the operation. But Schrader, who operated after Munk and with every apparent guarantee of completeness, found that all his pigeons saw after two or three weeks had elapsed, and the inhibitions resulting from the wound had passed away. They invariably avoided even the slightest obstacles, flew very regularly towards certain perches, etc., differing toto ccelo in these respects with certain simply blinded pigeons who were kept with

* The history up to 1885 may be found in A. Christian! : Zur Physi ologie des Gehirnes 'Berlin. 18sT>\. them for comparison. They did not pick up food strewn on the ground, however. Schrader found that they would do this if even a small part of the frontal region of the hemispheres was left, and ascribes their non-self-feeding when deprived of their occipital cerebrum not to a visual, but to a motor, defect, a sort of alimentary aphasia.* In presence of such discord as that between Munk and his opponents one must carefully note how differently sig nificant is loss, from preservation, of a function after an opera tion on the brain. The loss of the function does not neces sarily show that it is dependent on the part cut out ; but its preservation does show that it is not dependent : and this is true though the loss should be observed ninety-nine times and the preservation only once in a hundred similar excisions. That birds and mammals can be blinded by cortical abla tion is undoubted ; the only question is, must they be so ? Only then can the cortex be certainly called the * seat of sight.' The blindness may always be due to one of those remote effects of the wound on distant parts, inhibitions, extensions of inflammation, — interferences, in a word, — upon which Brown-Sequard and Goltz have rightly insisted, and the importance of which becomes more manifest every day. Such effects are transient ; whereas the symptoms of deprivation (Ausfallserscheinungen, as Goltz calls them) which come from the actual loss of the cut-out region must from the nature of the case be permanent. Blindness in the pigeons, so far as it passes away, cannot possibly be charged to their seat of vision being lost, but only to some influence which temporarily depresses the activity of that seat. The same is true mutatis mutandis of all the other effects of operations, and as we pass to mammals we shall see still more the importance of the remark.

In rabbits loss of the entire cortex seems compatible with the preservation of enough sight to guide the poor animals' movements, and enable them to avoid obstacles. Christian!' s observations and discussions seem conclusively * Pfl tiger's Archiv, vol. 44, p. 176. Munk (Berlin Academy Sitzsungsberichte, 1889, xxxi) returns to the charge, denying the extirpations of Schrader to be complete : ' ' Microscopic portions of the SelispMre must to have established this, although Munk found that all his animals were made totally blind.*

In dogs also Munk found absolute stone-blindness after ablation of the occipital lobes. He went farther and mapped out determinate portions of the cortex thereupon, which he considered correlated with definite segments of the two retinae, so that destruction of given portions of the cor tex produces blindness of the retinal centre, top, bottom, or right or left side, of the same or opposite eye. There seems little doubt that this definite correlation is mythologi cal. Other observers, Hitzig, Goltz, Luciani, Loeb, Exner, etc., find, whatever part of the cortex may be ablated on one side, that there usually results a hemiopic disturbance of loth eyes, slight and transient when the anterior lobes are the parts attacked, grave when an occipital lobe is the seat of injury, and lasting in proportion to the latter's extent. According to Loeb, the defect is a dimness of vis ion (' hemiamblyopia') in which (however severe) the centres remain the best seeing portions of the retina, just as they are in normal dogs. The lateral or temporal part of each retina seems to be in exclusive connection with the cortex of its own side. The centre and nasal part of each seems, on the contrary, to be connected with the cortex of the opposite hemispheres. Loeb, who takes broader views than any one, conceives the hemiamblyopia as he con ceives the motor disturbances, namely, as the expression of an increased inertia in the whole optical machinery, of which the result is to make the animal respond with greater effort to impressions coming from the half of space opposed to the side of the lesion. If a dog has right hemiamblyopia, say, and two pieces of meat are hung before him at once, he invariably turns first to the one on his left. But if the lesion be a slight one, shaking slightly the piece of meat on his right (this makes of it a stronger stimulus) makes him seize upon it first.

If only one piece of meat be offered, he takes it, on whichever side it be. When both occipital lobes are extensively destroyed total blindness may result. Munk maps out his ' Sehsphare ' definitely, and says that blindness must result when the entire shaded part, marked A, A, in Figs. 12 and 13, is involved in the lesion. Discrepant reports of other observations he explains as due to incomplete The Dog's visual centre according to Munk, the entire striated region, A, A, being the exclusive seat of vision, and the dark central circle, A', being correlated with the retinal centre of the opposite eye.

ablation. Luciani, Goltz, and Lannegrace, however, con tend that they have made complete bilateral extirpations of Munk's Sehsphare more than once, and found a sort of crude indiscriminating sight of objects to return in a few Aveeks.* The question whether a dog is blind or not is harder to solve than would at first appear ; for simply blinded dogs, in places to which they are accustomed, show little of their loss and avoid all obstacles; whilst dogs whose occipital lobes are gone may run against things fre quently and yet see notwithstanding. The best proof that they may see is that which Goltz's dogs furnished : they carefully avoided, as it seemed, strips of sunshine or paper on the floor, as if they were solid obstacles. This no really blind dog would do. Luciani tested his dogs when hungry (a condition which sharpens their attention) by strewing

pieces of meat and pieces of cork before them. If they went straight at them, they saw; and if they chose the meat and left the cork, they saw discriminatingly. The quarrel is very acrimonious ; indeed the subject of localization of functions in the brain seems to have a peculiar effect on the temper of those who cultivate it experimentally. The amount of preserved vision which Goltz and Luciani report seems hardly to be worth considering, on the one hand; and on the other, Munk admits in his penultimate paper that out of 85 dogs he only ' succeeded ' 4 times in his opera tion of producing complete blindness by complete extirpa tion of his '-Sehsphare.' * The safe conclusion for us is that Luciani's diagram, Fig. 14, represents something like the

FIG. 14.— Distribution of the Visual Function in the Cortex, according to Luciani. truth. The occipital lobes are far more important for vision than any other part of the cortex, so that their com plete destruction makes the animal almost blind. As for the crude sensibility to light which may then remain, noth ing exact is known either about its nature or its seat. In the monkey, doctors also disagree. The truth seems, however, to be that the occipital lobes in this animal also are the part connected most intimately with the visual function. The function would seem to go on when very small portions of them are left, for Ferrier found no ' appreciable impair ment ' of it after almost complete destruction of them on both sides. On the other hand, he found complete and perma nent blindness to ensue when they and the angular gyri in addition were destroyed on both sides. Munk, as well as

Brown and Schaefer, found no disturbance of sight from destroying the angular gyri alone, although Ferrier found blindness to ensue. This blindness was probably due to inhibitions exerted in distans, or to cutting of the white optical fibres passing under the angular gyri on their way to the occipital lobes. Brown and Schaefer got complete and permanent blindness in one monkey from total destruc tion of both occipital lobes. Luciani and Seppili, perform ing this operation on two monkeys, found that the animals were only mentally, not sensorially, blind. After some weeks they saw their food, but could not distinguish by sight between figs and pieces of cork. Luciani and Seppili seem, however, not to have extirpated the entire lobes. When one lobe only is injured the affection of sight is hemiopic in monkeys: in this all observers agree. On the whole, then, Munk's original location of vision ID the occipital lobes is confirmed by the later evidence.*

In man we have more exact results, since we are not driven to interpret the vision from the outward conduct. On the other hand, however, we cannot vivisect, but must wait for pathological lesions to turn up. The pathologists who have discussed these (the literature is tedious ad libi tum) conclude that the occipital lobes are the indispensable part for vision in man. Hemiopic disturbance in both eyes comes from lesion of either one of them, and total blindness, sensorial as well as psychic, from destruction of both.

Hemiopia may also result from lesion in other parts, especially the neighboring angular and supra-marginal gyri, and it may accompany extensive injury in the motor region of the cortex. In these cases it seems probable that it is due to an actio in distans, probably to the interruption oi * H. Munk: Functionen der Grosshirnrinde (Berlin, 1881), pp. 36-40 Ferrier : Functions, etc.,2ded., chap, ix, pt. i. Brown and Schaefer. Philos. Transactions, vol. 179, p. 321. Luciani u. Seppili, op. cit. pp. 131-138. Lannegrace found traces of sight with both occipital lobes de stroyed, and in one monkey even when angular gyri and occipital lobes were destroyed altogether. His paper is in the Archives de Medeciue Experimentale for January and March, 1889. I only know it from the abstract in the Neurologisches Centralblatt, 1889, pp. 108-420. The reporter doubts the evidence of vision in the monkey. It appears to have consisted in avoiding obstacles and in emotional disturbance in the presence of men.

fibres proceeding from the occipital lobe. There seem to be a few cases on record where there was injury to the occipital lobes without visual defect. Ferrier has collected as many as possible to prove his localization in the angular gyrus.* A strict application of logical principles would make one of these cases outweigh one hundred contrary ones. And yet, remembering how imperfect observations may be, and how individual brains may vary, it would certainly be rash for their sake to throw away the enormous amount of positive evidence for the occipital lobes. Individual variability is always a possible explanation of an anomalous case. There is no more prominent anatomical fact than that of the ' decussation of the pyramids,' nor any more usual pathologi cal fact than its consequence, that left-handed hemorrhages into the motor region produce right-handed paralyses. And yet the decussation is variable in amount, and seems sometimes to be absent altogether, f If, in such a case as this last, the left brain were to become the seat of apoplexy, the left and not the right half of the body would be the one to suffer paralysis.

The schema on the opposite page, copied from Dr. Seguin, expresses, on the whole, the probable truth about the regions concerned in vision. Not the entire occipital lobes, but the so-called cunei, and the first convolutions, are the cortical parts most intimately concerned. Nothnagel agrees with Seguin in this limitation of the essential tracts. :[ A most interesting effect of cortical disorder is mental blindness. This consists not so much in insensibility to optical impressions, as in inability to understand them. Psychologically it is interpretable as loss of associations be tween optical sensations and what they signify ; and any interruption of the paths between the optic centres and the centres for other ideas ought to bring it about. Thus,

| E. C. Seguin : Hemianopsia of Cerebral Origin, in Journal of Nervous and Mental Disease, vol. xnr. p. 30. Notbuagel und Naunyn : Ueber die Localization der Gehirnkrankbeiten (Wiesbaden, 1887), p. 10. printed letters of the alphabet, or words, signify certain sounds and certain articulatory movements. If the con nection between the articulating or auditory centres, on the one hand, and the visual centres on the other, be ruptured FIQ. 15.— Scheme of the mechanism of vision, after Seguin. The cuneus convolution (0u) of the right occipital lobe is supposed to be injured, and all the parts which lead to it are darkly shaded to show that they fail to exert their function. F O are the intra-hemispheric optical fibres. P. O. C. is the region of the lower optic cen tres (corpora geuiculata and quadrigemina). T. O. D. is the right optic tract- C the chiasma; F. L. D. are the fibres going to the lateral or temporal half 2' of the rteht retina; and F. C. 8 are those going to the central or nasal half of the left retina O. D. is the right, and O. S. the left eyeball. The rightward half of each is there fore blind: in other words, the right nasal field, R. N. F., and the left temporal field L. T. F., have become invisible to the subject with the lesion at Cu.

we ought a priori to expect that the sight of words would fail to awaken the idea of their sound, or the movement for pronouncing them. We ought, in short, to have alexia, or inability to read : and this is just what we do have in many cases of extensive injury about the fronto-teinporal regions, as a complication of aphasic disease. Nothnagel suggests that whilst the cuneus is the seat of optical sensations, the other parts of the occipital lobe may be the field of optical memories and ideas, from the loss of which mental blind ness should ensue. In fact, all the medical authors speak of mental blindness as if it must consist in the loss of visual images from the memory. It seems to me, however, that this is a psychological misapprehension. A man whose power of visual imagination has decayed (no unusual phe nomenon in its lighter grades) is not mentally blind in the least, for he recognizes perfectly all that he sees. On the other hand, he may be mentally blind, with his optical imagination well preserved ; as in the interesting case pub lished by Wilbrand in 1887.* In the still more interest ing case of mental blindness recently published by Lissauer,t though the patient made the most ludicrous mistakes, call ing for instance a clothes-brush a pair of spectacles, an um brella a plant with flowers, an apple a portrait of a lady, etc. etc., he seemed, according to the reporter, to have his men tal images fairly well preserved. It is in fact the momen tary loss of our wow-optical images which makes us mentally blind, just as it is that of our wow-auditory images which makes us mentally deaf. I am mentally deaf if, hearing a bell, I can't recall how it looks; and mentally blind if, see ing it, I can't recall its sound or its name. As a matter of fact, I should have to be not merely mentally blind, but stone-blind, if all my visual images were lost.

For although I am blind to the right half of the field of view if my left occipital region is injured, and to the left half if my right region is injured, such hemianopsia does not deprive me of visual images, experience seeming to show that the unaffected hemisphere is always sufficient for pro duction of these. To abolish them entirely I should have to be deprived of both occipital lobes, and that would de prive me not only of my inward images of sight, but of my