Localization of the Functions in the Brain

David Ferrier

Hitherto we have considered the brain chiefly in its objective or physiological aspects, and the conclusion has been arrived at that the brain is a complex system of centres of motion and centres of sensation.

In their subjective aspect the functions of the brain are synonymous with mental operations, the consideration of which belongs to the science of psychology and the subjective method of investigation. No purely physiological investigation can explain the phenomena of consciousness. By throwing light, however, on the anatomical substrata of consciousness, physiological experiment may serve to elucidate some of the at present obscure relations between normal and abnormal conditions of the brain, and normal and abnormal psychical manifestations.

It is not the object of this work to attempt an analysis of mind or the laws of mental operations, but simply to discuss, in the light of the facts revealed by the experimental investigations recorded in the preceding chapters, some of those relations between the physiological and psychological functions of the brain which present themselves to the consideration of the physician and medical psychologist.

That the brain is the organ of the mind, and that mental operations are possible only in and through the brain, is now so thoroughly well established and recognized that we may without further question start from this as an ultimate fact.

But how it is that molecular changes in the brain cells coincide with modifications of consciousness; how, for instance, the vibrations of light falling on the retina excite the modification of consciousness termed a visual sensation, is a problem which cannot be solved. We may succeed in determining the exact nature of the molecular changes which occur in the brain cells when a sensation is experienced, but this will not bring us one whir nearer the explanation of the ultimate nature of that which constitutes the sensation. The one is objective and the other subjective, and neither can be expressed in terms of the other. We cannot say that they are identical, or even that the one passes into the other; but only, as Laycock expresses it, that the two are correlated, or, with Bain, that the physical changes and the psychical modifications are the objective and subjective sides of a "double-faced unity."

"We have every reason for believing that there is, in company with [p.340] all our mental processes, an unbroken material succession. From the ingress of a sensation, to the outgoing responses in action, the mental succession is not for an instant dissevered from a physical succession. A new prospect bursts upon the view; there is a mental result of sensation, emotion, thought, terminating in outward displays of speech or gesture. Parallel to this mental series is the physical series of facts, the successive agitation of the physical organs . . . While we go the round of the mental circle of sensation, emotion and thought, there is an unbroken physical circle of effects. It would be incompatible with everything we know of cerebral action, to suppose that the physical chain ends abruptly in a physical void, occupied by an immaterial substance; which immaterial substance, after working alone, imparts its results to the other edge of the physical break, and determines the active response—two shores of the material, with an intervening ocean of the immaterial. There is, in fact, no rupture of nervous continuity. The only tenable supposition is, that mental and physical proceed together, as undivided twins. When, therefore, we speak of a mental cause, a mental agency, we have always a two-sided cause; the effect produced is not the effect of mind alone, but of mind in company with body." (Bain, "Mind and Body," 1873, p. 131.)

In accordance with this position it must follow from the experimental data that mental operations in the last analysis must be merely the subjective side of sensory and motor substrata. This view has been repeatedly and clearly enunciated by Hughlings-Jackson, with whose physiological and psychological deductions from clinical and pathological data I frequently find myself in complete accordance. ("Clinical and Physiological Researches on the Nervous System." Reprints from "Lancet," 1873.)

The physiological activity of the brain is not, however, altogether co-extensive with its psychological functions. The brain as an organ of motion and sensation, or presentative consciousness, is a single organ composed of two halves; the brain as an organ of ideation, or re-presentative consciousness, is a dual organ, each hemisphere complete in itself. When one hemisphere is removed or destroyed by disease, motion and sensation are abolished unilaterally, but mental operations are still capable of being carried on in their completeness through the agency oft he one hemisphere. The individual who is paralysed as to sensation and motion by disease of the opposite side of the brain (say the right), is not paralysed mentally, for he can still feel and will and think, and intelligently comprehend with the one hemisphere. If these functions are not carried on with the same vigour as before, they at least do not appear to suffer in respect of completeness.

In order that impressions made on the individual organs of sense shall excite the subjective modification called a sensation, it is necessary that they reach and induce certain molecular changes in the cells of their respective cortical centres.

If the angular gyrus (gyri) is destroyed or functionally inactive, impressions made on the retina and optical apparatus cause the same physical modifications as usual, but do not affect consciousness. The changes produced have no subjective side.

The optical apparatus without the angular gyrus may be compared to the camera without the sensitised plate. The rays of light are focussed as usual, but produce no chemical action, and leave no trace when the object is withdrawn, or the light from it shut off. The angular gyrus is like the sensitive plate. The cells undergo certain molecular modifications which coincide with certain subjective changes constituting the consciousness of the impression or special visual sensation. And as the sensitive plate records, in certain chemical decompositions, the form of the object presented to the camera, so the angular gyrus records in cell modifications the visual characters of the object looked at. We may push the analogy still further. Just as the chemical decomposition effected by the rays of light may be fixed and form a permanent image of the object capable of being looked at, so the cell modifications which coincided with the presentation of the object to the eye, remain permanently, constituting the organic memory of the object itself. When the same cell modifications are again excited, the object is re-presented or rises up in idea. It is not meant by this analogy that the objects are photographed in the angular gyrus, as objects are photographed on the plate, but merely that permanent cell modifications are induced, which are the physiological representatives of the optical characters of the object presented to the eye. The optical characters are purely light vibrations, and few objects are known by these alone. The object appeals to other senses, and perhaps to movements, and the idea of the object as a whole is the revival of the cell modifications in each of the centres concerned in the act of cognition. For what is true of the angular gyrus or sight centre is true, mutatis mutandis, of the other sensory centres. Each is the organic basis of consciousness of its own special sensory impressions, and each is the organic basis of the memory of such impressions in the form of certain cell modifications, the reinduction of which is the re-presentation or revival in idea of the individual sensory characters of the object. The organic cohesion of these elements by association renders it possible for the re-excitation of the one set of characters to recall the whole. [p.342]

The sensory centres, therefore, are to be regarded not merely as the organs of consciousness of immediate sensory impressions, but as the organic register of special sensory experiences. This organic memory is the physical basis of Retentiveness, and the property of re-excitability is the organic basis of Recollection and Ideation. We have thus a physiological foundation of the law arrived at on other grounds by Bain, viz. that "the renewed feeling occupies the very same parts, and in the same manner as the original feeling." According to Spencer, the renewal of the feeling is the faint revivification of the same processes which are strongly excited by presentation of the object. The molecular thrill, if we may so term it, of present sensation extending from the peripherical organ of sense, is in the ideal sensation revived, but, as a rule, not so powerfully as to extend to the periphery; though, in rare instances, the central revivification may be so intense as actually to re-induce the peripherical impression. This occurs in certain morbid states such as are described under the name of "fixed ideas," or in sensory hallucinations from diseased conditions of the brain, as in epilepsy and insanity.

The organic memory of sensory impressions is the fundamental basis of knowledge. If the sense impressions were evanescent, or endured only so long as the object was present, the range of conscious intelligent action would be limited to the present, and we should have no real knowledge. Knowledge implies the consciousness of agreement or difference. We can only be said to know when we recognise identity, or difference between past and present conscious modifications. We know that a certain colour is green by recognising a similarity or identity between the present and a certain past colour sensation, or a difference between this and some other colour in the spectrum. If we had no organic memory of the past capable of re-excitation to serve as the basis of comparison, we should be unable to recognise either agreement or difference. We might be conscious from moment to moment, but there would be no continuation in time, and knowledge would be impossible. The foundation of the consciousness of agreement is the re-excitation by the present of the same molecular processes which coincided with a past impression; and of difference, a transition from one physical modification to another. The sensory centres, therefore, besides being the organs of sensation or consciousness of immediate impressions, contain, in the persistence and revivability of the coincident physical modifications, the materials and possibilities of simple and complex cognitions, in so far as these are dependent on sensory experience alone. [p.343]

The destruction of the sight centre, therefore, not only makes the individual blind presentatively, but blind re-presentatively or ideally, and all memories into which visual characters enter in part or whole become mangled and imperfect, or are utterly rooted out of consciousness. The destruction of the eye renders the individual blind only presentatively, but his visual memory and visual ideation remain unaffected. And it would be extremely interesting to ascertain whether, in an individual born blind, the sight centre presents any peculiarities either as regards the forms of the cells, or their processes or otherwise, differing from those of the normal brain. If such were detectable, we should come near arriving at the characters of the physical basis of an idea.

In the remarkable and, in a physio-psychological sense, highly instructive condition termed aphasia, many of the principles above laid down are strikingly exemplified.

The subject of aphasia is deprived of the faculty of articulate speech, and also very generally of the faculty of expressing his thoughts in writing, while he continues intelligently to comprehend the meaning of words spoken to him, or, it may be, to appreciate the meaning of written language. An aphasic individual knows perfectly well, as exhibited by his gestures, if a thing is called by its right name or not, but he cannot utter the word himself, or write it when it is suggested to him. In his attempts, only an automatic or interjectional expression or some unintelligible jargon escapes his lips, or unmeaning scrawls are set down on paper as writing.

This affection is usually, at first at least, associated with a greater or less degree of right hemiplegia, but the motor affection of the right side, chiefly of the right arm, is often slight and transient, or may be wanting from the first, the only indication of motor paralysis being a paretic or weak condition of the oral muscles of the right side.

The inability to speak is not due to paralysis of the muscles of articulation, for these are set in action and employed for purposes of mastication and deglutition by the aphasic individual.

The cause of this affection was shown by Broca—and his observations have been confirmed by thousands of other cases—to be associated with disease in the region of the posterior extremity of the third left frontal convolution, where it abuts on the fissure of Sylvius, and overlaps the island of Reil, a region which I have shown corresponds with the situation of the motor centres of articulation in the monkey.

One of the most common causes of the affection is softening of this region, consequent on sudden stoppage of the circulation by embolic plugging of the arterial channels which convey its blood supply, by which the functional activity of the part is temporarily or permanently suspended.

Owing to the proximity and common vascular supply of the motor centres of the hand and facial muscles, it is easy to see how they also become implicated in the lesion of the centres of articulation, and why, therefore, dextral and facial motor paralysis should so commonly occur along with aphasia. This may be taken as further evidence in proof of the fact that lesions of the cortical motor centres cause motor paralysis on the opposite side.

The escape of the articulatory muscles from paralysis in unilateral lesion of the centres of articulation is accounted for by the bilateral influence of each centre which has been experimentally demonstrated.

The loss of speech actually or in idea from destruction of the centres of articulation is not more difficult of explanation on the principles laid down in this chapter, than the loss of sight presentatively or representatively from destruction of the angular gyri. That which constitutes the apparent difficulty is the explanation of speechlessness without motor paralysis from unilateral lesion of the centres of articulation in the left hemisphere.

This difficulty is explicable on the principles laid down in reference to motor acquisitions in general. As the right side of the body is more especially concerned in volitional motor acts, so the education is principally in the motor centres of the left hemisphere, and these centres are more especially the organic basis of motor acquisitions. The left articulatory centres, as has been argued by more than one observer, preponderate over the right in the initiation of motor acts of articulation. They are, therefore, more especially the organic basis of the memory of articulations and of their revival in idea. The destruction of the left articulatory centres removes the motor limb of the cohesions which have been formed by long education between the centres of hearing and sight, and between the centres of ideation in general.

Sounds actual or revived fail to excite corresponding articulations actually or in idea. The individual is speechless, the motor part of the sensori-motor cohesion, sound-articulation, being broken. The sight of written symbols also fails to reproduce the equivalent articulatory action, actually or in idea. The individual is speechless, because the motor element of the sensori-motor cohesion, sight-articulation, is broken.

Ideally revived sights, sounds, touches, tastes, smells fail to call up the symbolic articulations, hence the individual cannot express his ideas in language, and in so far as language or internal speech is necessary to complex trains of thought, in that proportion is thought impaired. Thought, however, may be carried on without language, but it is thought in particulars, and is as cumbrous and limited as mathematical calculations without algebraical symbols. Thought, as has been observed by Bain, is in a great measure carried on by internal speech, i.e., through the ideal or faint re-excitation of the articulatory processes which are symbolic of ideas. This is shown by the unconsciously executed movements of the lips and tongue which all persons exhibit more or less, and some so obviously that the unconscious processes rise almost to the point of whispering. So also the blind deaf-mute Laura Bridgman, whose language was symbolic movements of the fingers, during thought or when dreaming, unconsciously executed the same movements as she was accustomed to make in the actual exercise of her manual speech.

And just as ideas tend to excite their symbolic representations in articulation or in manual movements, so does the actual or ideal revival of the articulatory or manual movements tend by association to call up the other limbs of the cohesions, whether simple sights, sounds, tastes, smells, or their combinations. The importance of this connection between the articulating centres and the centres of ideation in general, will be shown more fully in reference to the voluntary revival of ideas and control of ideation.

We have seen that a person aphasic from destruction of his speech centre (as we may for shortness call the articulatory motor centres of the left hemisphere) still remains capable of appreciating the meaning of words uttered in his hearing. In this respect he does not (and there is no reason why he should) differ from a normal individual. His centres of sight, hearing, etc., being unimpaired, he is as capable as before of sight, auditory, tactile, gustatory and olfactory ideation. The difference consists in the fact that in the aphasic individual the word spoken, though it calls up the idea or meaning, cannot call up the word itself actually or in idea, owing to the centres of word execution and word ideation being destroyed. The appreciation of the meaning of spoken words is readily accounted for by the fact that in the process of education an association is formed directly between certain sounds and certain objects of sense, simultaneously with, if not antecedent to, the formation of the cohesive association between these sounds and certain acts of articulation. The cohesion or association between sound and meaning remains unimpaired in aphasia; it is the cohesion between sound and articulation which is broken, by removal of the motor factor of the organic nexus.

The association between visible symbols and things signified is, however, secondary to the associations formed between sounds and things signified, and between sounds and articulations, for speech precedes the art of writing. In the first instance, when an individual is learning to read, visible symbols are translated into articulations and revived sounds before they call up the things signified. This translation occurs in all at first, and continues apparent in those persons not much accustomed to reading, for they only understand by articulating in a more or less suppressed manner all the while. Just as an individual in learning a foreign language is at first obliged to translate the words into his vernacular before he reaches the meaning, but comes by familiarity and practice to associate the new words with their meaning directly without the aid of the vernacular, and even to think in the new language, so it is possible that by long experience in reading, a direct association may be established between visible symbols and things signified, without the mediation of articulation. In such a case a person who has his speech centre disorganised will still be able to comprehend the meaning of written language. A person, on the other hand, who has not established the direct association between visible symbols and things signified, and is still obliged to translate through articulation, will, by destruction of his speech centre, fail to comprehend written language, though he may still understand spoken language.

In learning to write a new association has to be grafted on to the association already formed between sounds and articulations. The new cohesion is between sounds and certain symbolic manual movements guided by sight, which symbolic tracings are the equivalents of certain acts of articulation. In the first instance this association between sounds, or sounds and things signified, and manual movements, takes place through the mediation of the centres of articulation, for the sounds or ideas are first reproduced actually or internally by articulations before their equivalence in written symbols is established and recognised.

By education, and by the familiarity engendered of long practice in expressing ideas by written symbols, a direct association becomes established between sounds and ideas, and symbolic manual movements, without the intermediation of articulation; and in proportion as the translation through articulation is dispensed with, in that proportion will an individual continue able to write who is aphasic from disease of his speech centre. [p.347]

In the great majority of cases of aphasia, met with in hospitals, the direct association between sounds and ideas and manual equivalents of articulations has not been established, except for very simple and constantly repeated acts of writing such as signing one’s name: and hence, as the intervention of articulation is still necessary before ideas can be expressed in writing, destruction of the speech centre causes not merely aphasia, but also agraphia.

Examples of all these different conditions are to be met with in aphasia. Some can neither speak nor write; some can write but cannot speak; some can write their names but cannot write anything else; all can comprehend spoken language; many can comprehend written language; others not at all, or very imperfectly. Between the normal condition of the speech centre and its total destruction, many intermediate abnormal conditions occur, which exemplify themselves as partial aphasia, and partial disorders of speech. In some cases there seems to be such a perturbation of the centres, that though the individual is not aphasic in the sense of being speechless, yet the associations between certain articulations and certain ideas are so disturbed that in attempts to speak only an incoherent jumble of words comes forth. This is a condition of ataxia rather than aphasia in the proper sense of the term.

The speech centre is, as has been stated, in the great majority of instances situated in the left hemisphere. But there is no reason, beyond education and heredity, why this should necessarily be so. It is quite conceivable that the articulating centres of the right hemisphere should be educated in a similar manner. A person who has lost the use of his right hand may by education and practice acquire with his left all the cunning of the right. In such a case the manual motor centres of the right hemisphere become the centres of motor acquisitions similar to those of the left. As regards the articulating centres, the rule seems to be that they are educated, and become the organic seat of volitional acquisitions on the same side as the manual centres. Hence, as most people are right-handed, the education of the centres of volitional movements takes place in the left hemisphere. This is borne out in a striking manner by the occurrence of cases of aphasia with left hemiplegia in left-handed people. Several cases of this kind have now been put on record. (Vide These Mongie, Paris, 1866; quoted by Lepine, "La Localisation dans les Maladies Cerebrales," Paris, 1875. Russell, "Med. Times and Gazette," July 11, Oct. 24, 1874. Case (unpublished) communicated to me by my friend Dr. Lauder Brunton, of St. Bartholomew’s Hospital.) [p.348]

These cases more than counterbalance any exception to the rule that the articulating centres are educated volitionally on the same side as the manual motor centres. The rule need not be regarded as absolute, and we may admit exceptions without invalidating a single conclusion respecting the pathology of aphasia as above laid down.

Though the left articulatory centre is the one commonly and specially educated in speech, it is quite conceivable that a person who has become aphasic by reason of total and permanent destruction of the left speech centre, may reacquire the faculty of speech by education of the right articulatory centres. To a certain extent they have undergone education along with those of the left through associated action, registering automatically, as Hughlings-Jackson puts it, the volitional acts of the left. This automatic may be educated into volitional power, though at the age at which aphasia usually occurs, there is less capacity and plasticity in the nerve centres for forming new cohesions and associations. The rapid recovery which so frequently occurs in cases of aphasia, especially of the kind due to embolic plugging of the nutrient arteries of the left centres, is not so much to be regarded as an indication of the education of the right centres, but rather of the re-establishment of the circulation and nutrition in parts only temporarily rendered functionless.

But there are other cases which would seem to show that recovery of speech may take place after a lesion which has caused complete and permanent destruction of the left speech centre. A case which seems to me to be of this nature has been reported by Drs. Batty, Tuke and Fraser ("Journal of Mental Science," April, 1872), who, however, have adduced it as an instance opposed to the localisation of a speech centre, which in one sense, i.e., as against absolute unilateral localisation, it certainly is. The case in essentials is that of a female patient who was rendered unconscious by the occurrence of cerebral hemorrhage. On her recovery she was found totally speechless, and she remained so for an indefinite period. In process of time, however, the faculty of speech was restored in great measure, though never quite perfectly. "During the whole period of her residence two peculiarities in her speech were observed—a thickness of articulation resembling that of general paralysis, and a hesitancy when about to name anything, the latter increasing very much some months previous to her death.

"The thickness seemed apparently due to slight immobility of the upper lip when speaking, but there was no paralysis when the lip was voluntarily compressed against its fellow. The inaction of the upper lip was observed by all."The hesitancy was most marked when she came to a noun, the hiatus varying in duration according to the uncommonness of the word. Latterly, she could not recall even the commonest terms, and periphrases or gestures were used to indicate her meaning. She was always relieved and pleased if the words were given her, when she invariably repeated them. For example, she would say, ’Give me a glass of—.’ If asked if it was ’water?’ she said, ’No.’ ’Wine?’ ’No.’ ’Whisky?’ ’Yes, whisky.’ Never did she hesitate to articulate the word when she heard it."

Death occurred fifteen years after the seizure, and it was found post mortem that there was total destruction and loss of substance in the cortical region in the left hemisphere corresponding with the position of the centres of articulation, This seems to me one of the clearest cases of re-acquisition of the faculty of speech by education of the articulating centres of the right side. That speech was lost in the first instance is in harmony with the usual effect of lesion of the left speech centre. Education of the right side had not become quite perfect even after fifteen years, and that peculiar hesitancy, and the fact, which the authors themselves have specially noted in italics, that speech often required the aid of suggestion, is in accordance with the less volitional and greater automatic power of the right hemisphere. Aphasia being essentially due to the destruction, temporary or permanent, of the centres of excitation and organic registration of acts of articulation, is a significant proof of the fact that there is no break between the physiological and psychological functions of the brain, and that the objective and subjective are not separated from each other by an unbridgeable gulf.

We have now traced the development of the volitional control of the movements, and the mode in which the memory of volitional acts becomes organised in the motor centres. The conclusion reached is that the volitional control of the movements becomes established when an organic cohesion is welded between a consciously discriminated feeling and a definite and differentiated motor act. The volitional control of the individual movements having once been established the work of education advances, and the conditions of volition become more and more complex. The volition of the untutored and inexperienced infant is of a more or less impulsive character, its action being conditioned mainly by impressions or ideas of the moment. Associations have not yet been formed between the pleasurable and painful remote consequences of actions. Experientia docet. A child which has acquired the differentiated control of its hands is impelled to touch and handle whatever [p.350] strongly attracts its sight. The sight of a bright flame stimulates a desire to handle it. This is followed by severe bodily pain, and an association is formed between touching a certain brilliant object and severe suffering. The vivid memory of pain experienced on a former occasion, is sufficient to counteract the impulse to touch when the child is again placed in similar circumstances. Here we have a simple case of the conflict of motives, and the inhibition or neutralisation of one motive by another and stronger. Action, if it results at all, is conditioned by the stronger. Similarly, a hungry dog is impelled by the sight of food to seize and eat. Should the present gratification bring with it as a consequence the severe pain of a whipping, when certain articles of food have been seized, an association is formed between eating certain food and severe bodily pain; so that on a future occasion the memory of pain arises simultaneously with the desire to gratify hunger, and, in proportion to the vividness of the memory of pain, the impulse of appetite is neutralised and counteracted. The dog is said to have learnt to curb its appetite.

As experience increases, the associations between acts and consequences increase in complexity. Both by personal experience, as well as by the observed experience and testimony of others, associations are established between actions and their remote consequences as pleasures or pains, and it is found that present gratification may bring a greater and future pain, and actions causing present pain may bring a greater pleasure. As the great law of life is vivere convenientur naturae—to secure pleasure and avoid pain in the highest and most general sense, and not for the moment only (a law which cannot be transgressed with impunity)—factions are conditioned no longer, as in the infant or untutored animal, by present desires or feelings alone, but by present desires modified by the ideally revived feelings of pleasure or pain near and remote, which experience has associated with definite actions. The motive to action is thus the resultant of a complex system of forces; the more complex, the wider the experience, and the more numerous the associations formed between actions and their consequences, near and remote. Actions so conditioned are regarded as mature or deliberate, in contradistinction to impulsive volitions, but the difference is not in kind, but only in degree of complexity; for in the end, actions conditioned by the resultant of a complex system, of associations are of essentially the same character as those conditioned by the simple stimulus of a present feeling or desire, where no other associations have as yet been formed capable of modifying it. [p.351]

But what is normal in the infant or untutored animal, may be positive insanity on the part of the educated adult. If in him actions are conditioned merely by present feelings or desires, irrespective of, or in spite of, the associations formed by experience between such acts and their consequences as pains, there is a reversion to the infantile type of volition; the only difference being, that in the one case no opposing associations have as yet been formed, while in the other, though formed, they prove of no avail. An individual who so acts, acts irrationally; and if in anyone, notwithstanding the opposing influence of past associations, a present feeling or desire reaches such a pitch of intensity as to overbalance these associations, the individual is said to act in spite of himself, or, metaphorically, against his will. Such tendencies occur more or less in all, but they are exemplified more especially in certain forms of insanity, in which the individual becomes the victim of some morbid desire, and is impelled irresistibly, and to his horror, to commit some act fraught with dreadful consequences.

The tendency of feelings or desires to expend themselves in action leads to the consideration of another faculty which plays an important part in the regulation and control of ideation and action.

The primordial elements of the volitional acts of the infant, and also of the adult, are capable of being reduced in ultimate physiological analysis to reaction between the centres of sensation and those of motion.

But besides the power to act in response to feelings or desires, there is also the power to inhibit or restrain action, notwithstanding the tendency of feelings or desires to manifest themselves in active motor outbursts.

Inhibition of action is either direct or indirect.

As an example of indirect inhibition, we may take the inhibition of reflex action, which is caused by a simultaneous stronger sensory stimulus. This is paralleled in volitional action by the inhibition or neutralisation of one motive by another and stronger.

As an example of direct inhibition, we may take the inhibitory action of the vagus upon the heart. This is due to an influence of the vagus on the cardiac motor ganglia by which their activity is restrained. "The heart contains within itself numerous ganglia, which keep up its rhythmical contractions even for some time after it has been removed from the body. The terminal branches of the vagus nerve in the heart are connected in some way with these ganglia, and whenever it is irritated the ganglia cease to act on the muscular substance, and the heart stands completely still in a relaxed condition. The branches of the vagus which have this action resemble motor nerves in their conveying an irritation applied to them towards the periphery, and not towards the centre, and also in their origin, for although they run in the vagus they are really derived from the spinal accessory nerve, and only join the vagus near its origin. The other fibres of the spinal accessory go to muscles, and when they are excited they set the muscles in action, but those going to the heart do not end in the muscular fibres, but in the ganglia, and they produce rest instead of motion, relaxation instead of contraction." (Lauder-Brunton, "On Inhibition, Peripheral and Central," "West Riding Lunatic Asylum Medical Reports," vol. iv., p. 181.)

The centres of direct inhibition are thus truly motor in character, but their action is expended in the motor centres proper.

As an illustration of volitional inhibition we may take the power, accompanied with the feeling of effort, to rein in and inhibit the tendency of powerful feelings to exhibit themselves in action. The battle between inhibition and the tendency to active motor outburst, is indicated by the tension into which the muscles are thrown, and yet kept reined in, so that under a comparatively calm exterior there may be a raging fire, threatening to burst all bonds.

The inhibitory centres are not equally developed or educated in all, nor are they equally developed in the same individual in respect to particular tendencies to action. But this faculty of inhibition appears to me to be a fundamental element in the attentive concentration of consciousness and control of ideation.

It has been properly remarked that we have no direct volitional control over the centres of ideation. Ideas once excited centrally or from peripherical impressions tend to excite each other in a purely reflex manner, as Laycock and Carpenter have pointed out. Left to themselves ideas excite ideas along the lines of association of contiguity and similarity—coherently in the waking state, when all the centres and senses are functionally active; incoherently in dreams and delirium, where the various centres are functioning irregularly.

But we have the power of concentrating attention on one idea, or class of ideas, and their immediate associates, to the exclusion of all others, a power differently developed in different individuals. We can thus modify and control the current of ideation, and we can also, to a certain extent, voluntarily call up and retain in consciousness particular ideas and particular associations of ideas.

On what physiological basis this psychological faculty rests is an extremely difficult question, and is one scarcely capable of experimental determination. The following considerations are therefore more properly speculations than deductions from experimental data.

Both the voluntary excitation of ideas and the concentration of consciousness by which the current of ideation is controlled, seem to be essentially dependent on the motor centres. The fact that attention involves the activity of the motor powers has been clearly enunciated by Bain and Wundt.

Bain ("The Emotions and the Will," 3rd ed. 1875) remarks as follow:—"It is not obvious at first sight that the retention of an idea in the mind is operated by voluntary muscles. Which movements are operating when I am cogitating a circle, or recollecting St. Paul’s? There can be no answer given to this, unless on the assumption that the mental or revived image occupies the same place in the brain and other parts of the system as the original sensation did, a position supported by a number of reasons adduced in my former volume ("Contiguity," §10). Now there being a muscular element in our sensations, especially of the higher senses—touch, hearing, sight—this element must somehow or other have a place in the after remembrance of the idea.
"The ideal circle is a restoring of those currents that would prompt the sweep of the eye round an ideal circle; the difference lies in the last stage, or in stopping short of the actual movement performed by the organ" (p. 370).

In these sentences, and particularly the last, Bain seems to me to have dearly indicated the elements of attention, which I conceive to be a combination of the activity of the motor, and of the inhibitory-motor centres.

In calling up an idea, or when engaged in the attentive consideration of some idea or ideas, we are in reality throwing into action, but in an inhibited or suppressed manner, the movements with which the sensory factors of idealion are associated in organic cohesion.

We think of form by initiating and then inhibiting the movements of the eyes or hands through which and by which ideas of form have been gained and persist. And just as sensory impressions or sensory ideas tend by association to call up ideal or actual movements, so conversely, the excitation of movements tends to call up by association the various sensory factors which combine with these particular movements to form complex ideas. In the case of ideas, the motor element of which is not apparent, the method of excitation can be referred to the articulatory movements with which as symbols ideas are associated. This is, in fact, the most usual method of recalling ideas in general. We recall an object in idea by pronouncing the name in a suppressed manner. We think, therefore, and direct the current of thought in a great measure by means of internal speech. [p.354]

This is essentially the case with respect to the recalling of abstract ideas as contradistinguished from concrete and particular.

The abstract qualities and relations of objects exist only by reason of words, and we think of the concrete or particular instances out of which the general or abstract have been formed, by making the symbolic movements of articulation with which these ideas cohere.

An aphasic individual is incapable of abstract ideation or trains of thought. He thinks only in particulars, and his thoughts are conditioned mainly by present impressions on his organs of sense, arousing ideas according to the usual laws of association.

The recall of an idea being thus apparently dependent on excitation of the motor element of its composition, the power of fixing the attention and concentrating consciousness depends, further, on inhibition of the movement.

During the time we are engaged in attentive ideation we suppress actual movements, but keep up in a state of greater or less tension the centres of the movement or movements with which the various sensory factors of ideation cohere.

By checking the tendency to outward diffusion in actual motion, we thereby increase the internal diffusion, and concentrate consciousness. For the degree of consciousness is inversely proportional to the amount of external diffusion in action. In the deepest attention, every movement which would diminish internal diffusion is likewise inhibited. Hence, in deep thought, even automatic actions are inhibited, and a man who becomes deep in thought while he walks, may be observed to stand still.

The excitation of the motor centres, inhibited from external diffusion, expends its force internally along the lines of organic cohesion, and the various factors which have become organically coherent with any particular movement rise into consciousness. This inhibited excitation of a motor centre may be compared to tugging at a plant with branching roots. The tension causes a vibratile thrill to the remotest radicle. So the tension of the motor centre keeps in a state of conscious thrill the ideational centres organically coherent therewith. The centres of inhibition would therefore form the chief factor in the concentration of consciousness and the control of ideation. They have, however, no self-determining power of activity, but are called into action by the same stimuli which tend to excite actual movement. The centres of inhibition undergo education along with the centres of actual motion during the growth of volition. The education of the centres of inhibition introduces the element of deliberation into volition, for action at the instigation of present feelings is suspended until the various associations which have clustered round any individual act have arisen in consciousness. The resultant of the various associations, the revival of which is conditioned by the present feeling and the concentration of consciousness which it instigates, is the motive which ultimately determines the action.

In proportion to the development and degree of education of the centres of inhibition do acts of volition lose their impulsive character, and acquire the aspect of deliberation. Present impulses or feelings, instead of at once exciting action, as in the infant, stimulate the centres of inhibition simultaneously, and suspend action until, under the influence of attention, the associations engendered by past experience between actions and their pleasurable or painful consequences, near and remote, have arisen in consciousness. If the centres of inhibition, and thereby the faculty of attention, are weak, or present impulses unusually strong, volition is impulsive rather than deliberate.

The centres of inhibition being thus the essential factor of attention, constitute the organic basis of all the higher intellectual faculties. And in proportion to their development we should expect a corresponding intellectual power.

"A great profusion of remembered images, ideas, or notions, avails little for practical ends without the power of arrest or selection, which in its origin is purely voluntary. We may have the luxuriousness of a reverie or a dream, but not the compliance with a plan of operations, or with rules of composition." (Bain, p. 371.)

In proportion to the development of the faculty of attention are the intellectual and reflective powers manifested. This is in accordance with the anatomical development of the frontal lobes of the brain, and we have various experimental and pathological data for localising in these the centres of inhibition, the physiological substrata of this psychological faculty.

It has already been shown that electrical irritation of the antero-frontal lobes causes no motor manifestations, a fact which, though a negative one, is consistent with the view that, though not actually motor, they are inhibitory-motor, and expend their energy in inducing internal changes in the centres of actual motor execution. [p.356]

Centres of direct inhibition and nerves of inhibition are, as we have seen, all centrifugal, or motor, in character, and it has also been shown that the frontal regions are directly connected with the centrifugal, or motor, tracts of the peduncular expansion or corona radiata.

The removal of the frontal lobes causes no motor paralysis, or other evident physiological effects, but causes a form of mental degradation, which may be reduced in ultimate analysis to loss of the faculty of attention.

The powers of attention and concentration of thought are, further, small and imperfect in idiots with defective development of the frontal lobes, and disease of the frontal lobes is more especially characteristic of dementia or general mental degradation. The frontal regions which correspond to the non-excitable regions of the brain of the monkey are small or rudimentary in the lower animals, and their intelligence and powers of reflective thought correspond.

The development of the frontal lobes is greatest in man with the highest intellectual powers, and taking one man with another, the greatest intellectual power is characteristic of the one with the greatest frontal development.

The phrenologists have, I think, good grounds for localising the reflective faculties in the frontal regions of the brain, and there is nothing inherently improbable in the view that frontal development in special regions may be indicative of the power of concentration of thought and intellectual capacity in special directions.

In this chapter I have contented myself with indicating very briefly some of the more important psychological principles which seem to me fairly deducible from experimental investigation into the anatomical and physiological substrata of mind, principles which in many respects coincide with those expounded by Bain and Herbert Spencer.

Many other important points in cerebral physiology still remain to be considered, such as the relation of the encephalic centres to nutritive or trophic processes; the conditions of the normal activity of the brain; the physiological conditions of consciousness, etc.; but as these questions require discussion in the light more of the phenomena of disease in man, than of experiments on the lower animals, I propose to reserve these and similar topics for another treatise, specially devoted to the consideration of diseases of the brain.

(1), placed on the postero-parietal lobule, indicates the position of the centres for movements of the opposite leg and foot such as are concerned in locomotion.

(2), (3), (4), placed together on the convolutions bounding the upper extremity of the fissure of Rolando, include centres for various complex movements of the arms and legs, such as are concerned in climbing, swimming, etc.

(5), situated at the posterior extremity of the superior frontal convolution, at its junction with the ascending frontal, is the centre for the extension forwards of the arm and hand, as in putting forth the hand to touch something in front.

(6), situated on the ascending frontal, just behind the upper end of the posterior extremity of the middle frontal convolution, is the centre for the movements of the hand and forearm in which the biceps is particularly engaged, viz., supination of the hand and flexion of the forearm.

(7) and (8), centres for the elevators and depressors of the angle of the mouth respectively.

(9) and (10), included together in one, mark the centre for the movements of the lips and tongue, as in articulation. This is the region, disease of which causes aphasia, and is generally known as Broca’s convolution.

(11), the centre of the platysma, retraction of the angle of the mouth.

(12), a centre for lateral movements of the head and eyes, with elevation of the eyelids and dilation of pupil. [p.358]

(a), (b), (c), (d), placed on the ascending parietal convolution, indicate the centres of movement of the hand and wrist.

Circles (13) and (13’) placed on the supra-marginal lobule and angular gyrus, indicate the centre of vision.

Circles (14) placed on the superior temporo-sphenoidal convolution, indicate the situation of the centre of hearing.

The centre of smell is situated in the subiculum cornu Ammonis (inner surface of brain).

In close proximity, but not exactly defined as to limits, is the centre of taste.

The centre of touch is situated in the hippocampal region. [But feeling centres seem also to be located in the same regions as the corresponding motor centres.—Ed.]