Mind, Brain and Adaptation in the Nineteenth Century: Cerebral Localization and Its Biological Context from Gall to Ferrier
by
Robert M. Young
[ Contents | Preface | Introduction | Chapter: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Bibliography ]
6
SPENCER, JACKSON, CARPENTER, AND THE APPLICATION
OF SENSORY-MOTOR LOCALIZATION TO THE CEREBRAL CORTICES
We must remember, too, that many doctrines were stated years ago in principle which were then novel and much disputed, but are now so generally accepted that we are in danger of ceasing to think of the very early propounders of those doctrines.
John Hughlings Jackson, 1881.
Spencer and Jackson
The aspects of Spencer's evolutionary associationism which had the most direct influence on the history of the study of the brain can be best appreciated in the context of their immediate effects. Magoun points out that there can be no question of 'the predominant influence of Spencer upon Hughlings Jackson and, through him upon the formation of evolutionary concepts of the organization and function of the brain in Western neurological thought'.[l] This influence began early and continued throughout Jackson's career. When he first arrived in London after completing his medical training in 1859 (aged twenty-four), he had already become so thoroughly interested in Spencer's evolutionary psychology that he 'had fully resolved to give up medicine and devote himself to philosophy'.[2] He was dissuaded from this course by Sir Jonathan Hutchinson,[3] but his interest in Spencer's philosophical and psychological views dominated his distinguished career as a pioneer neurologist and theoretician whose writings and example have strongly influenced subsequent clinical work. Jackson was to neurology what Bain was to psychology: a figure who almost single-handedly gave the discipline an identity apart from its parent sciences. His appointment as Assistant Physician to the National Hospital, Queen Square, in 1862 (where he continued to work for forty-five years), was the beginning of an influence exerted by the man and the institution which became predominant in the English-speaking world. His biographer says,
1 Magoun, 1961, p. 17.
2 Jackson, 1931, 1, ix. Cf. Jasper, 1960, p. 97.
3 Hutchinson, 1925, pp. 28-9.
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There is little doubt that the advent of Jackson infused a new spirit into neurology, and was the beginning of that systematic orderliness which now [1925] characterizes neurology, more perhaps than any other branch of medical science. Although his influence on neurology cannot be over-estimated, it must also be remembered that his contributions to the physiology of the nervous system are no less valuable.[1]
The claim that he was 'the founder of modern neurology'[2] is therefore not a gross exaggeration.[3] Again, like Bain, he was the founder (along with Ferrier and others) of the first English journal devoted exclusively to his field of interest: Brain (1877-).[4]
Darwin's work is referred to once in Jackson's Selected Writings; the context gives a clear picture of the source of Jackson's views on evolution. 'I need scarcely mention the name of Herbert Spencer, except to express my vast indebtedness to him; the first edition of his Principles of Psychology appeared so long ago as 1855, five years before the publication of the Origin of Species.’[5]
Spencer is by far the most often-quoted figure in Jackson's writings. There is hardly a single matter of principle or detail for which he does not at some point cite Spencer as source, inspiration, or authority. These citations, which appear at the head of many of his publications, are always made with great diffidence. 'I should say that a very great part of this paper is nothing more than an application of certain of Herbert Spencer's principles, stated in his Psychology, were it not that I dare not risk misleading readers by imputing crudities of my own to this distinguished man.'[6] 'I should consider it a great calamity, were
1 Taylor, 1925, p. 12.
2 Riese, 1959, p. 199.
3 A parallel influence in France was exerted by Jean-Martin Charcot (1825-93) and the Hospital of Sâlpetrière. See Guillain, translated Bailey, 1959; Charcot, translated Sigerson, 1881, Charcot, translated Hadden, 1883. Cf. Haymaker, 1953, pp. 266-9; Thorwald, translated Winston, 1960, Chapter I.
4 Jackson's life, his clinical work and his theories. will not receive a full treatment here. His work has been most ably expounded by Sir Francis Walshe and Henry Head. (Walshe, 1948, 1953, 1954, 1957, 1958, 1961; Head, 1926, 1, 30-53, 134-41). The sources of Jackson's views are (somewhat unevenly) reviewed by Riese, 1949, 1956, 1959; Riese and Hoff, 1950-51. The classical study of the history of the investigation of epilepsy is Temkin's The Falling Sickness (1945; see especially pp. 288-324). Jackson's influence on psychiatry, especially on Freud, is very well dealt with by Stengel (1953, 1954, 1963). Biographical information is available in three short essays by his mentor (Hutchinson), a colleague (Mercier), and a pupil (Taylor) in Jackson, 1925, pp. 1-46. Other useful information on his life and work may be found in Jefferson, 1960, pp. 35-44, 122-4; Jasper, 1960; Brain, 1958; Haymaker, 1953, pp. 308-11; Thorwald, 1960, Chapter I; Levin, 1953, 1960. Jackson's papers are scattered through many obscure journals. The works which are relatively easily accessible include the papers on aphasia and the bibliography reprinted by Head in Brain 38, 1915, 190, the Neurological Fragments (1925); and two volumes of Selected Writings prepared by Taylor (1931); cf. Greenblatt, 1965, which includes a bibliography of Jackson's early publications.
5 Jackson, 1931, II, 39.5.
6 Ibid., II, 40.
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any crudities of mine imputed to a man to whom I feel profoundly indebted.’[1]
The unifying conception of Jackson's work is the application of the theory of evolution to the structure, functions, and diseases of the nervous system. He saw his own investigations in the following context:
Here, for the first time in this article I use the term Dissolution, I most gratefully acknowledge my vast debt to Herbert Spencer. What I have to say of the constitution of the nervous system appears to me to be little more than illustrating his doctrine on nervous evolution by what I may metaphorically speak of as the experiments of disease. I should make more definite acknowledgements were it not that I do not wish to mislead the reader, if, by any misunderstandings of his doctrines on my part, I impute to Mr. Spencer particular opinions he might not endorse. Anyone interested in diseases of the nervous system should carefully study Spencer's Psychology.[2]
This is not the place to review Jackson's applications of nervous system evolution in detail. Many of them fall outside of the temporal limitations of the present study and were derived from the more explicitly neurological second edition of the Principles of Psychology. Given the all-pervasive influence of Spencer on Jackson, two aspects of his evolutionary neuropsychology are of direct relevance to the issues being considered here. It served as a new basis for the extension of the sensory-motor view from the spinal cord to the hemispheres, and for a belief in the cerebral localization of sensory and motor processes.
Spencer's principles of continuity and evolution provided Jackson with a single, consistent set of variables for specifying the physiological and psychological elements of which experience, thought, and behaviour are composed: sensations (or impressions) and motions. All complex mental phenomena are made up of these simple elements-from the simplest reflex to the most sublime thoughts and emotions.[3] All functions and faculties can be explained in these terms. The application
1 Jackson, 1931, II, 80, 346. This form of acknowledgement is repeated again and again. Cf. Jackson, 1931, I, 238, 375; Jackson, 1931, II 45, 98, 431-2.
2 Jackson, 1931, 1, 147. Dr Charles Mercier, Jackson’s colleague and friend, contributed the following judgement on Jackson’s allegiance to Spencer:’ He had also a great admiration for Herbert Spencer, with which he inoculated me, but I always thought-and in this I think Sir Jonathan Hutchinson agrees- that Dr Jackson gave Spencer far too much credit as the founder and suggester of Dr. Jackson’s own doctrines. In this opinion I have been confirmed by reading Spencer’s Autobiography, which destroyed not only my respect for man, but also illogically perhaps, my faith in his doctrines. It seems impossible that the opinions of a man who depicts himself as the glorified quintessence of a pig be worth anything.’ (Mercier, 1925 pp. 42-3). Cf. ‘Two’, 1906.
3 Cf. Spencer, 1904, 1, 470-1.
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to emotions has been noted.[1] Ideas 'are nothing else than weak repetitions of the psychical states caused in us by actual impressions and motions-partial excitements of the same nervous agents'.[2]
The tradition of sensation and association had, in principle, a single hypothesis which explained the origins of all experience. Through Mueller and Bain this explanation was applied to motion and linked closely with the nervous system, including specific sensory modalities. But, until the advent of the evolutionary theory, the consistent application of a sensory-motor psychophysiology was faltering in one respect or another, whether instinct, emotion, or various higher processes. The extension of the principles throughout the brain was held back by the theories of Flourens and the findings of those who worked in his shadow. Spencer eliminated all reason for hesitation, and Jackson grasped this fact. Impressions and motions became the elements of nervous processes in one aspect and of psychological processes in the other. The principles of Haller, Bell, and Magendie drove all other elements from the nervous system as Spencer had from the mind, and the theory of evolution supported both. The applications of these principles will be considered presently.
The same theory of evolution provided a new basis for the conception of cerebral localization which Jackson adopted from Spencer. Writing on this topic in 1867 and 1868, Jackson says, 'I would especially draw attention to the quotations from Spencer's Psychology, as the doctrine on localization I here try to illustrate further is, I believe, the one he has put forward’.[3] The passages which Jackson mention[4] reveal the attitude which Spencer maintained toward phrenology in his later work. (They are rearranged but not changed in later editions of the Principles.)
The phrenological views which had played an important part in the early development of adaptive and biological thinking and led Spencer to formulate his evolutionary psychology are now considered in the light of the hereditary transmission of complex emotions. What is left of his early phrenological organ-function view now appears as a corollary of evolutionary associationism.
That an organized tendency towards certain complex aggregations of psychical states, supposes a structural modification of the nervous system-a special set of complex nervous connections whereby the numerous excitations constituting the emotion may be co-ordinated-no one having even a superficial knowledge of Physiology can doubt. As every student of the
1 Above, pp. 182-3.
2 Spencer, 1855, p. 568.
3 Jackson, 1931, II, 216.
4 Ibid., II, 234.
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nervous system knows, the combination of any set of impressions, or motions, or both, implies a ganglion in which the various nerve-fibres concerned are put in connection.[1]
Thus, there must be greater and smaller ganglionic masses which coordinate the more or less complex emotions and which constitute their seats. Spencer recognizes that the controversies engendered by some of 'the unscientific reasonings of the phrenologists' had quite naturally led physiologists to deny or ignore localization of functions in the cerebrum.
But no physiologist who calmly considers the question in connection with the general truths of his science, can long resist the conviction that different parts of the cerebrum subserve different kinds of mental action. Localization of function is the law of all organization whatever: separateness of duty is universally accompanied with separateness of structure: and it would be marvellous were an exception to exist in the cerebral hemispheres. Let it be granted that the cerebral hemispheres are the seat of the higher psychical activities; let it be granted that among these higher psychical activities there are distinctions of kind, which, though not definite, are yet practically recognizable; and it cannot be denied, without going in direct opposition to established physiological principles, that these more or less distinct kinds of psychical activity must be carried on in more or less distinct parts of the cerebral hemispheres.[2]
Everything known about the peripheral nervous system supports this view.
It is proved experimentally, that every bundle of nerve-fibres and every ganglion, has a special duty; and that each part of every such bundle and every such ganglion, has a duty still more special. Can it be, then, that in the great hemispherical ganglia alone, this specialization of duty does not hold?[3]
Everything known about the spinal cord further supports this view, including specialization of function with no perceptible differences in structure.
The specialization of function in the hemispheres is analogous to that in the spinal cord.[4] Thus, the principle of continuity provides an evolutionary basis for extending the Bell-Magendie law to the hemispheres in support of cerebral localization. The functional division of the spinal roots plays a double role in the views which Spencer sharpens
1 Spencer, 1855, pp. 606-7.
2 Ibid., p. 607.
3 Ibid., p. 608.
4 Ibid.
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and passes on to Jackson: the fact of the division supports a general principle of functional specialization of structures, while the nature of the division provides the sensory-motor categories of functional analysis which are applied to all physiological and psychological processes.
Thus, Spencer accepts the 'fundamental proposition'[l] of cerebral localization.
Indeed, any other hypothesis seems to me, on the face of it, untenable. Either there is some arrangement, some organization in the cerebrum, or there is none. If there is no organization, the cerebrum is a chaotic mass of fibres, incapable of performing any orderly action. If there is some organization, it must consist in the same 'physiological division of labour' in which all organization consists; and there is no division of labour, physiological or other, of which we have any example, or can form any conception, but what involves the concentration of special kinds of activity in special places.[2]
It should be recalled that the association psychologists and most physiologists since Gall had been opposed to cerebral localization. Spencer reintroduced this concept. The development of his thinking on this topic can be seen as a circuitous path by which he started from, left, and finally returned to Gall's first physiological proof of the plurality of the organs of the soul: 'In all organized beings, different phenomena suppose different apparatus; consequently, the various functions of the brain likewise suppose different organs.’[3] It should be clear, though, that the developments from Haller to Bell-Magendie to Spencer involve a very different conception of the functions of the brain from the one Gall put forth.
'But to coincide with the doctrine of the phrenologists in its most abstract shape, is by no means to coincide with their concrete embodiments of it.’[4] He objects to their 'great . . . unwillingness to listen to any criticisms on the detailed scheme rashly promulgated as finally settled' and to the fact that phrenology represents itself as 'a complete system of Psychology'.[5] Most important, he opposes both the attempt to demarcate organs precisely in the brain and to set up rigid concepts of the functions. It was this undogmatic aspect of Spencer's scheme that most appealed to Jackson. 'The only localization which we may presume to exist, and which the necessities of the case imply, is one of a comparatively vague kind-one which does not suppose specific limits, but an insensible shading-off.'[6] The mental plexuses answering to relations
1 Spencer, 1855, p. 611.
2 Ibid., p. 608.
3 Gall, 1835, II, 254. Cf. Gall, 1835, VI, 307.
4 Spencer, 1855, p. 608.
5 Ibid., p. 609.
6 Ibid.
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in the external world cannot be represented in the nervous system by anything less complex and overlapping than the phenomena to which they correspond.
Nor can the categories of function be any less flexible than the ‘phenomena habitually surrounding any race of organisms'.[1] Spencer was quite right to insist on flexible categories corresponding to the progressive adaptations implied by evolution and to reject Gall's static, fixed faculties based on the pre-established adaptations of the chain of being. 'So little specific are the faculties, that no one of them is quite the same in different persons: they severally differ as the several features differ.’[2] Gall's faculties were formulated in anticipation of this objection and were supposed to be rich and subtle enough in their various combinations to account for individual differences. But Spencer is correct on the more basic issue of the changing nature of the functions through evolution. Finally, Spencer attacks the organology itself-the simple view of one faculty to one organ-and insists that the seat of an emotion is merely the 'centre of co-ordination' of a number of complex aggregates of sensory and motor fibres distributed throughout the cerebrum.[3]
This is all that remains of Spencer's early phrenological allegiance. His conclusion on the discipline itself is that 'At best, Phrenology can be but an appendix to Psychology proper; and one of but comparative unimportance, scientifically considered'.[4] However, it has been argued here that much of his psychology grew out of his phrenological beginnings, and that the transformations his views underwent during his development show the continuity of some of the basic aims and approaches of phrenology with the adaptive and biological aspects of Spencer's psychology. Nevertheless, evolutionary sensory-motor psycho-physiology is incompatible with the static chain of being and the faculty psychology of phrenology, and the concept of cerebral localization which carries over from the phrenological period in Spencer's development is a very different concept from that of Gall.[5]
1 Spencer, 1855, p. 610.
2 Ibid.
3 Spencer, 1855, pp. 610-11
4 Ibid., p. 609.
5 It is extremely likely that phrenology remained an occasional topic of conversation with Spencer, since he continued to make periodic week-long visits to Mr and Mrs Charles Bray. Bray was a free-thinking manufacturer who was a close friend of George Combe and an ardent phrenologist. He wrote phrenological works in his abundant leisure and remained a sincere and complete believer throughout his life. His works are The Education of the Feelings (1838); The Philosophy of Necessity (1841); Phases of Opinion and Experience During a Long Life (1885). He and his wife were close friends of George Eliot, and he was responsible for her interest in the subject. He succeeded in getting her to sit for a phrenological 'delineation' and, through her, aroused G. H. Lewes' interest in phrenology. Spencer had become friends with the Brays through George Eliot, and he notes visits with them twice in 1852, in 1856,
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Hughlings Jackson Extends Sensory-Motor Psychophysiology to the Cerebral Cortices
Spencer's rather vague notion of localization is combined by Jackson with a thoroughgoing sensory-motor view of all mental processes, and this is applied to the cerebral cortices. The extension of the sensorymotor paradigm to the cortex had been implicit in earlier analyses which identified higher mental processes with the cortices and treated these in associationist terms, but it had not been made central to any theory of the functional organization of the hemispheres which influenced the major figures under review here. Jackson based his argument on two theories: '[Thomas] Laycock's hypothesis of Reflex Cerebral Action and Spencer's hypothesis of Nervous Evolution'.[1]
Jackson had been associated with Laycock (later professor of medicine at Edinburgh) early in his medical career at the York Dispensary, and it has been presumed that he first stimulated Jackson's interest in the nervous system.[2] In acknowledging his debt, Jackson quotes a version of Laycock's doctrine which was first put forth in 1840, In 1845, Laycock said,
Four years have elapsed since I published my opinion, supported by such arguments as I could then state, that the brain, although the organ of consciousness, is subject to the laws of reflex action, and that, in this respect, it does not differ from the other ganglia of the nervous system. I was led to this opinion by the general principle that the ganglia within the cranium, being a continuation of the spinal cord, must necessarily be regulated, as to their reaction on external agencies, by laws identical with those governing the spinal ganglia, and their analogues in the lower animals.[3]
The reflex aspect of Laycock's view played an important part in Jackson's theories, but it is less important for present purposes than the principle of continuity of functional organization between lower and higher centres in the nervous system. This continuity justified the extension of the Bell-Magendie law to the highest centres in the nervous system. Jackson took it to be 'a necessary implication of the doctrine of nervous evolution as this is stated by Spencer'.[4] In another place
1862 and (with Mrs Bray) 1886. (Spencer, 1904, 1, 407, 434, 484; Spencer, 1904, II, 84, 411.) See also Cross, n.d. pp. 45, 56-7, 169-70; Jefferson, 1960, pp. 40-42; Haight, 1968, for information on the Brays and George Eliot.
1 Jackson, 1931, I, 123.
2 Ibid., I, ix. Cf. Jasper, 1960, p. 97.
3 Ibid., I, 167. The same quotation heads his paper (1875) claiming that he had attributed motor functions to the cortex prior to Fritsch and Hitzig (Ibid., I, 37). Emphasis added by Jackson. Mr. Roger Smith, King's College, Cambridge, is making a study of the theories of Laycock. Cf. Young, 1966, pp. 25-6.
4 Ibid., I, 42.
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(after he has the supporting evidence of Hitzig and Ferrier), Jackson says,
If the doctrine of evolution be true, all nervous centres must be of sensori-motor constitution. A priori, it seems reasonable to suppose that, if the highest centres have the same composition as the lower, being, like the lower, made up of cells and fibres, they have also the same constitution. It would be marvellous if, at a certain level, whether we call it one of evolution or not, there were a sudden change into centres of a different kind of constitution. Is it not enough difference that the highest centres of one nervous system are greatly more complicated than the lower?[l]
In a long preface (written in 1875) to a republication of an earlier paper (1873), he reviews his previous writings to support his claim to priority in viewing the convolutions as containing nervous arrangements representing movements.[2] This view had become automatic with him and was not explicitly stated except in a footnote. He nowhere tried to prove it, he says, since 'I cannot conceive of what other materials the cerebral hemispheres can be composed than of nervous arrangements representing impressions and movements'.[3] 'In fact, in every paper written during and since 1866, whether on chorea, convulsions, or on the physiology of language, I have always written on the assumption that the cerebral hemisphere is made up of processes representing impressions and movements.’[4] The famous footnote, written in 1870 and quoted again and again by Jackson, says,
It is asserted by some that the cerebrum is the organ of mind, and that it is not a motor organ. Some think the cerebrum is to be likened to an instrumentalist, and the motor centres to the instrument; one part is for ideas, and the other for movements. It may then be asked, How can discharge of part of a mental organ produce motor symptoms only? I say motor symptoms only, because, to give sharpness to the argument, I will suppose a case in which there is unilateral spasm without loss of consciousness. But of what ‘substance’ an the organ of mind be composed, unless of processes representing movements and impressions; and how can the convolutions differ from the inferior centres, except as parts representing more intricate co-ordinations of impressions and movements in time and space than they do? Are we to believe that the hemisphere is built on a plan fundamentally different from that of the motor tract? What can an 'idea', say of a ball, be, except a process representing certain impressions of surface and particular muscular adjustments? What is recollection, but a revivification of such processes which, in the past, have become part of the organism itself? What is delirium, except the disorderly revival of sensori-motor processes received in the past:
1 Jackson, 1931, II, 63.
2 Jackson, 1931, I, 37.
3 Ibid., I, 42.
4 Ibid.
206
What is a mistake in a word, but a wrong movement, a chorea? Giddiness can be but the temporary loss or disorder of certain relations in space, chiefly made up of muscular feelings. Surely the conclusion is irresistible, that 'mental' symptoms from disease of the hemisphere are fundamentally like hemiplegia, chorea and convulsions, however specially different. They must all be due to lack, or to disorderly development, of sensori-motor processes.[1]
This quotation has been given in full, since it provides the basic statement of Jackson's whole position. As it stands it is a unified view of neurological symptomatology. It was elaborated by him into a general theory of the functional organization of the nervous system, and constituted the last stage of the integration of the association psychology with sensory-motor physiology. It involved an explicit rejection of the aspects of the clinical and physiological work which had hindered a unified view: the faculty formulation of Broca, and the unwillingness of Flourens, Magendie, Mueller, and others to treat the organ of mind -the highest centres-in consistently physiological terms.
Broca owned both his concept of localization and its formulation in terms of faculties to phrenology. Jackson had been prepared in 1864 to speak in terms of a 'faculty of language' which 'resides' in a given convolution or vascular region. But by 1866 he found it 'incredible that "speech" can "reside" in any limited spot'.[2] The formulation in terms of localization of faculties was rejected. 'I think, then, that the so-called "faculty" of language has no existence. It was replaced by a motor view which Jackson derived from Bain.[4] The anatomical
1 Jackson, 1931, I, 26. Quoted again, pp. 42, 58; Jackson, 1931, II, 63-4, 67, etc.
2 Jackson, 1931, II, 233-4.
3 Ibid., II, 123. Jackson and Broca are reputed to have clashed publicly over their respective views of aphasia at a meeting of the British Association in 1868. Broca is said to have carried the day. (Haymaker, 1953, pp. 260-1.) Broca opened the discussion on the physiology of speech and was followed by Jackson. There is no record of their discussion in the Proceedings of the British Association. Broca's paper was published and contains no reference to Jackson's views. He defends the existence of a faculty of articulate language which is independent of other functions, and considers the issue of whether or not it has a localized seat in the brain, still open. The greater part of the paper is concerned with the nomenclature of speech disorders and the differential diagnosis among four classes: 'alogia' (due to loss of the ideas for words), 'verbal amnesia' (due to loss of the memory of words), 'aphemia' (loss of the ability to repeat words, although their meaning is understood), and 'mechanical alalia' (impairment of the agencies for articulation). The term 'aphasia' is reserved for cases where one of the above diagnoses is not yet established. (Broca, 1869. Cf. Head, 1926, I, 26-7.) A synopsis of Jackson's argument appeared, but it conveys little sense of the conflict between their views. He says that disease separates healthy language into intellectual and emotional aspects, and that the impairment in aphasia is one of intellectual expression by movements; those most special (those of speech) suffering most, simpler ones (such as gestures) suffering least. (Head, 1926, I, 34-5.)
4 See above, p. 110.
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substrata of words are motor processes, and the defect in aphasia is one of articulatory movements.[1] Jackson calls this view 'but a particular expansion of views which Bain has long taught, and which, indeed, he has applied to speech'.
'When we recall,' he says, 'the impression of a word or a sentence, if we do not speak it out, we feel the twitter of the organs just about to come to that point. The articulating parts,-the larynx, the tongue, the lips,-are all sensibly excited; a suppressed articulation is, in fact, the material of our recollection, the intellectual manifestation, the idea of speech'.[2]
Similarly, in i864, he was prepared to speak of the corpus striatum ('the highest part of the motor tract') as 'the point of emission of the orders of the "will" to the muscles'.[3] This was the traditional formulation used by Magendie, Mueller, Todd and Bowman, Carpenter, Bain, and others and was implicit in the separation of sensory-motor analysis of lower centres from vague reference to the functions of will, intelligence, sensation, and so on, in the hemispheres. It left a hiatus in the analysis which Jackson sets out to eliminate, again as an extension of Spencer's psychophysiology. He cites his own previous confusion of mental and physiological states and terms, as 'an additional reason why I should point out the evil results of the confusion'.[4] His criticism is aimed at those who 'speak as if at some place in the higher parts of the nervous system we abruptly cease to have to do with impressions and movements, and begin all at once to have to do with mental states'.[5]
There are motor centres, and above these are centres for ideas, for memory, volition, etc., which 'play on' the motor centres. . . . There are in use such expressions as that an 'idea produces a movement'. It would be a marvellous thing if there were any such sudden and total change in function. Supposing that we do begin in the cerebrum to have to do with mental states, does it follow that we cease to have to do with impressions and movements? For have we not to do with the nature of the material basis of the mental states ?[6]
Those who speak of 'centres for memory of words', or of 'centres for ideas' of any kind, as arbitrarily acting on and governing motor centres, are, as regards their method, essentially like those who speak of the soul producing movements, etc. The difference is that the former practically talk as if the soul were a solid one, made up of fibres and cells. This physiologico-materialistic method practically ignores anatomy and physiology. It leads to verbal explanations, such as that an aphasic does not speak 'because he has lost the memory for words'; that 'chorea is a disorder of volition'; that
1 Jackson, 1931, I, 39.
2 Ibid., I, 50- 1. Cf. the theories of J. B. Watson.
3 Jackson, 1931, II, 233. Cf. 121, 122, 127.
4 Jackson, 1931, I, 48.
5 Ibid.
6 Ibid.
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'ideas are formed in the cortical grey matter of the brain, and produce movements by acting on lower centres'; 'that we combine two retinal impressions by a mental act'; it leads to the free use of such phrases as ‘volitional impulses', 'by an act of memory', etc.[1]
Jackson is opposed to this mixture of morphological and physiological terms. His objections are based on the philosophical assumption of psychophysical parallelism and involve a rigid conception of the proper domain of physiology.
It is sometimes objected that we cannot 'understand' 'how energising of nervous processes, representing movements, can give or share in giving us ideas'. This is a very naïve objection. We cannot understand how any conceivable arrangement of any sort of matter can give us mental states of any kind. Is it more difficult to understand why we remember a word during energising of cells and fibres because we believe those cells and fibres represent articulatory movements? I do not concern myself with mental states at all, except indirectly in seeking their anatomical substrata. I do not trouble myself about the mode of connection between mind and matter. It is enough to assume a parallelism. That along with excitations or discharges of nervous arrangements in the cerebrum, mental states occur, I, of course, admit; but how this is I do not inquire; indeed, so far as clinical medicine is concerned, I do not care.[2]
His position is that mental states arise during, not from, physiological processes.
'Sensations', in the sense of 'mental states', arise, I submit, during energising of motor as well as of 'sensory' nerve processes-with the 'out-going' as well as with the 'in-going' current. I say 'arise during'; I have used no expressions which imply, even remotely, that in the penetralia of the highest centres, physical vibrations, however fine they may become, fine away into mental states-such as for example that molecular changes in optic nerves and centres turn into sensations of colour.[3]
The result for his analysis is that 'faculties' and their corresponding processes, such as volition, ideation, reasoning, and emotion, are 'artificially distinguished' aspects of consciousness. During the activity of the highest centres these are simultaneously displayed. These centres represent, not the faculties, but movements of all parts of the body. In health they function normally; in disease they are disordered. However, there is no incongruity between obvious disorders of motion such as epilepsy and less obvious ones like insanity: both are diseases of sensory-motor processes.[4]
1 Jackson, 1931, 1, 51-2.
2 Jackson, 1931, I, 52. Cf. Freud, 1891, pp. 52-7, 56, 61.
3 Ibid., I, 55.
4 Jackson, 1931, II, 66.
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The result for physiology is that it is concerned with the 'degrees and conditions of excitation or discharge of nervous centres. . . . Physiology deals with the functions of nervous arrangements'.[l] He does not deny that the functions of the hemispheres include
‘ideation,' 'consciousness,' etc. Sensori-motor processes are the physical side of, or, as I prefer to say, form the anatomical substrata of, mental states. It is with these substrata only that we, in our character as physicians and physiologists, are directly concerned.[2]
Neural physiology is concerned only with the varying conditions of the anatomical arrangements of nerve cells and fibres-with the physics of the nervous system.[3]
The proper activity of the physiologist involves resolving all the functions of the various structures of the brain into sensory-motor processes. Jackson's scheme of localization was concerned only with these.
Jackson's analysis marked the end of the long movement away from the attempt to define physiology in terms of correlation of faculties with organs: the attempt to localize mental functions. The mental aspect was reduced to the conscious parallel of sensory-motor substrata. This formal hypothesis about the relations of mental with physiological phenomena was coupled with a genetic hypothesis which analysed all complex mental contents and processes into simple sensory and motor elements. This does not mean that movements or cerebral arrangements serve in mentation as a subjective activity. Words serve in mentation, but these, in turn, are defined as the concomitants of discharge of cerebral arrangements representing articulatory movements. The foregoing analysis has attempted to demonstrate this for Bain and Spencer. Jackson shared the view,[4] and Ferrier followed him. In about fifty years, cerebral localization had moved from a conception of physiology dominated by psychological faculties with no precise designation of the related material processes, to a physiology of sensory-motor processes which dominated the psychological functions by placing them in a sensory-motor framework. For Gall the functions of the brain were the faculties; physiology was defined as the study of these. For Jackson and Ferrier the only functions proper to physiology were sensory-motor phenomena. There was no place left for Gall's faculties except as artificial abstractions. The concomitants of sensory-motor phenomena were ideas of sensation and movements, and associated
1 Jackson, 1931, 1, 56.
2 Ibid., I, 49.
3 Ibid., 1, 52.
4 Cf. Jackson, 1931, I, 81-2.
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complexes built up from these elements. With Jackson's analysis, the development of the concept of function was completed in the form it would retain until the end of the nineteenth century. The concept of localization, however, underwent further development, and the whole approach still lacked experimental demonstration. It should be noticed that Spencer, Jackson, and Ferrier had no interest in the biological issue of what are the functions of the brain.
William Carpenter and the Climate of Opinion in 1870
Jefferson has provided an excellent picture of the coexistence of irreconcilable views, and the hesitancy on the part of everyone concerned to juxtapose their findings in such a way as to include the cortex in the motor system. Two dogmas coexisted with their contraries. First, the cortex had been found inexcitable on mechanical and electrical stimulation. Second, the corpus striatum was the highest motor ganglion. However, clinical findings and theoretical considerations indicated that the convolutions were involved in convulsions and paralyses, and that they contained nervous arrangements and processes ‘representing movements and impressiona.’[1] Jefferson's summary of the state of affairs is excellent.
From Haller (1755) and Lorry (1760) to Legallois, onwards to the best observer of them all, Flourens, and on again to Magendie and everyone else, all were agreed upon this-the brain was unresponsive except at the lower and lowest levels. The hemispheres were the seat of the 'will'; they excited movement by playing on these motor mechanisms. But how they did so no one knew and no nice man would ask![2]
Longet (1842), in confirming once again that the cortex was inexcitable, granted that in cerebral disease affections of the brain were able to produce epileptiform phenomena. He could reconcile these phenomena only by saying that 'in men disease can stir in the bosom of the brain irritations such as artificial and immediate stimulation cannot provoke'.[3] R. B. Todd had produced epileptic movements by mid-brain stimulation in 1849, but no one seems to have taken any notice, and the artificial stimulation of epileptiform movements was discovered anew by Fritsch and Hitzig, and Ferrier twenty years later. Todd stressed that the prevailing spinal and medullary theories of epilepsy could not explain the many fits in which loss of consciousness was the only symptom (now known as petit mal seizures).[4] In their
1 Jackson, 1931, I, 26, 37.
2 Jefferson, 1960, p. 116.
3 Quoted in Jefferson, 1960, p. 118.
4 Jefferson, 1960, pp. 118-9.
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authoritative Physiology, Todd and Bowman had extended the Bell-Magendie law only as far as the thalami for sensation and the corpora striata for motion.[1]
The corpora striata seem to have held the loyalties of all as the major motor organs. When, in 1865, Luys assigned discrete motor functions to cortical cells on histological grounds, he still held that the corpora striata were the effective motor organs.[2] Carpenter's standard text on Physiology held in 1869 that the corpus striatum was the motor ganglion and the thalamus the sensory.[3]
William Carpenter's writings provide a clear picture of the orthodox view, and an opportunity to contrast this with the new approach of Spencer and Jackson. He is a convenient figure for this purpose in that he exemplifies Palmer's dictum that 'The tendencies of an age appear more distinctly in its writers of inferior rank than in those of commanding genius'.[4] Carpenter was explicit on topics where more subtle thinkers were troubled, uncertain, and ambiguous. He was a leading expositor of experimental physiology, and his Principles of Human Physiology was, according to T. H. Huxley, the standard English work between 1842 and the early 1870s.[5] It went through five English and several American editions under his hand by 1855, and four more (edited by others) appeared by 1881. This work, along with his General and Comparative Physiology, played a large part in establishing physiology as an autonomous discipline in Britain.[6] His impressive bibliography shows that he was at the centre of biological and physiological debate until his death in 1885.[7] Early in Carpenter's career, J. S. Mill wrote to Comte that he considered him 'the most philosophical of all those in England who study the laws of the living body, who has written the best treatise on general and human physiology which we possess in our language'. At that time (1843) Mill lamented that Carpenter had, as yet, found no financial support for his research.[8] This situation soon changed, and Carpenter's official positions included Lectureships at the Royal Institution and the British Museum, and the Professorship of Physiology and Forensic Medicine at University College and Hospital, London.
1 See above, pp. 111-2.
2 Jefferson, 1960, pp. 121-2.
3 Ibid., p. 114.
4 Quoted in Lovejoy, 1936, p. 20. Mr Roger Smith of King's College, Cambridge is involved in a detailed study of Carpenter's views on the functions of the nervous system which is likely to alter considerably the account which I have given of him as a representative figure. I am indebted to him for his criticisms but do not wish to anticipate publication of his own interpretation. See below p. 212n.
5 Quoted in Carpenter, 1888, p. 66.
6 Carpenter, 1888, p. 64. Cf. pp. 64-9 for the views of Sir James Paget, Huxley, etc.
7 Ibid., pp. 467-83.
8 Mineka, 1963, p. 567.
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He was also a Fellow of the Royal Society, President of the British Association (1872), Editor of the Medico-Chirurgical Review, and Registrar of London University for twenty-three years until his retirement in 1879. At the end of his career a colleague summarized Carpenter's contribution:
The great work of his life was, after all, that he gathered up the new knowledge, digested it and put it before the world in a coherent and logical form. Stated in this way, the task accomplished may not seem much. In effect it was of the deepest importance. In my judgment he laid the foundations of that breadth and comprehensiveness of the English biological school, which will, I hope, be its lasting heritage.[1]
At least as early as 1846, Carpenter had stated the limits of the principle of continuity with respect to the sensory-motor view of the nervous system.[2]
1 Thiselton-Dyer, quoted in Carpenter, 1888, p. 142. In the following discussion Carpenter's views will be presented as representative of the prevailing climate of opinion before 1870. It should be stressed, however, that the original aspects of his work are not being discussed and are not representative. His theories of 'unconscious cerebration' and the common centre of sensation are not relevant to the present discussion. See Walshe, 1957, where Carpenter's theories are outlined and used as a stick with which to beat Penfield and discredit his concept of a 'centrencephalic integrating system'.
Carpenter's psychological writings were closely integrated with his physiological treatises, and T. H. Huxley called him a leading figure in 'the foundation of a rational, that is, to say, a physiological psychology'. (Quoted in Carpenter, 1888, p. 67.) Carpenter may be said to have played the same role from the physiological side that Bain did from the psychological in integrating the two disciplines. He added sections on Psychology to the fourth and fifth editions of his Principles. The growth of new physiological discoveries pushed this matter out of subsequent editions, but it was expanded and issued separately in 1874 as Mental Physiology (a title which was very significant of developments in the period). The psychological matter in this work is not discussed in the text, since it is drawn directly from the association psychology (except for the original matters mentioned above). His biographer reports that 'He had been trained by his father in the principles of Hartley; his psychological text-book had been James Mill's Analysis of the Human Mind; and his acquaintance with John Stuart Mill, and the perusal of his treatise on Logic, had not tended to weaken the general notions thus impressed upon him'. (Carpenter, 1888, p. 38.) To complete the picture, it is noteworthy that he was drawing heavily from Bain even before the publication of Bain's major work. He acknowledges his debt in Carpenter, 1855, p. 580. Conversely, Bain was very impressed by Carpenter's physiological writings and drew on them in his treatment of the nervous system (Bain, 1904, pp. 132-3, 164).
2 These passages come from Carpenter's analysis of a work on phrenology (1846, see above, pp. 164-5). I have not read the first edition of Carpenter's Principles and do not know when he first held these views. Carpenter's analysis of phrenology is not being discussed in the text, but it should be noted that it adds further weight to the argument that the assumptions of later brain research developed partly on the basis of and partly in reaction to the issues posed by the phrenologists. In this article Carpenter acknowledged the debts of both neurophysiology and psychology (especially comparative) to Gall, while lamenting the excesses and poor standards of evidence of the cranioscopists and opposing their view of the cerebellum (Carpenter, 1846, pp. 520-5, 529-43). He adds that important advances in the understanding of reflex actions and related phenomena had occurred since Gall's time (p. 520). The care which Carpenter took in examining Noble's phrenological work is noteworthy in itself.
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Knowing, as we do, that the sensory ganglia not only receive the sensory nerves, but are connected, by their implantation on the fibrous tracts of the medulla oblongata, with the motor system, we can at once understand the channel through which sensations should thus produce movements, without involving any higher act of the mind, or any exertion of the will. In the case of common or tactile sensation, there seems good reason for regarding the corpora striata as the motor portion of the ganglionic mass, of which the thalami optici constitute the sensory; the relation between them being, as well pointed out by Messrs. Todd and Bowman, the same as that which subsists between the anterior and posterior peaks of vesicular matter in the spinal cord.[l]
He makes an explicit separation of the thalami and corpora striata on the one hand from the cerebrum on the other. He refers to the cerebral hemispheres as 'distinguished from other ganglionic masses by their superadded character, having no direct connexion with any of the nerves, but being implanted, as it were, upon the summit of the strands which pass upwards from the nervous centres of the trunk'.[2] In a later passage he repeats (and italicizes) this point and adds that as the cerebrum 'receives sensations through the medium of the various ganglia, in which the sensory nerves terminate, so it executes the mandates of the will through the motor fibres which originate from those same ganglia, or from others in immediate connexion with them'. He emphasizes the independence of the cerebrum from the thalami and corpora striata.[3] Although the cerebrum receives sensations, Carpenter denies that this means that sensations are localized in the cortices. He was much more explicit on this point than many of his predecessors. He points out that Flourens, who had originally said that cortical ablation destroys all sensibility, 'substituted, in the second edition of his Experimental Researches, the term perception for sensation, whenever he speaks of the function which is destroyed by the removal of the cerebrum'.[4]
Having argued that the corpora striata and thalami are the highest motor and sensory ganglia, Carpenter attributes to the cerebrum the functions which are not accounted for by lower centres. It 'has no concern in the purely excito-motor actions'.[5] Nor is it the seat of pleasures and pains. Rather, it is the seat of ideas respecting the objects of sensation: 'perception, memory, and conception (or storing and recalling ideas).[6] The cerebrum is 'restricted to intellectual operations;
1 Carpenter, 1846, p. 505.
2 Ibid., p. 500.
3 Ibid., p. 510. Cf. p. 517.
4 Ibid., p. 508; see above, p. 69.
5 Ibid., p. 512.
6 Ibid., pp. 510-12.
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understanding, by that term, the operations which are concerned in the formation of a voluntary determination'.[1]
In the fourth edition of his Principles, Carpenter reviews the evidence for his position.
All the results of experiments concur to establish the fact, that no irritation, either of the vesicular or of the fibrous substance, produces either sensation or motion. These results are borne-out by pathological observations in Man; for it has been frequently remarked, when it has been necessary to separate protruded portions of the Brain from the remainder, that this has given-rise to no sensation, even in cases in which the mind has been perfectly clear at the time, nor has any convulsive action been produced.[2]
This last phrase points to the issue which will be seen to trouble Jackson most. Carpenter repeats the argument given in the earlier paper,[3] and stresses the separation of the lower, automatic sensory-motor centres from the superadded cerebrum, whose functions are those of mind: perception, intelligence, and will. The sensory-motor centres are the instruments of consciousness and will.[4]
Finally, Carpenter reiterates the identical views in his Mental Physiology, written just before the appearance of Ferrier's work.[5] This book is a very useful document. Its text is pre-Ferrier, and an appendix was added to take account of Ferrier's first findings. The text of the appendix is almost identical with a paper which Carpenter delivered at the Annual Conversazione at the West Riding Lunatic Asylum in November of 1873.[6] That Carpenter was induced (by Crichton-Browne) to travel to Wakefield and deliver the address at the site of Ferrier's experiments indicates the significance which was immediately attached to his findings. That Carpenter shared this evaluation is further indicated by his adding it to his book after it was in page proofs. He says in his introduction that he ranks Ferrier's findings among 'the greatest advances in the Physiology of the Nervous System which have been made during the last fifty years'.[7] That Carpenter and Ferrier belonged to very different generations in physiological thought is indicated by the fact that Carpenter's review of Ferrier's results interprets the evidence as being in favour of the corpora striata as the primary motor
1 Carpenter, 1846, p. 515. Cf. p. 517.
2 Carpenter, 1855, p. 534.
3 See Ibid., pp. 534-5, 489-90, 497-.511
4 Ibid., pp. 508-11.
5 Carpenter, 1874a, pp. 99-100.
6 Carpenter, 1874, p. 1. It appears that he did not take cognizance of the findings of Fritsch and Hitzig until after he delivered the address. See Carpenter, 1874, p. 10.
7 Ibid., p. 2.
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centres and the optic thalami as the sensory.[1] He remained convinced that 'the Cerebrum does not act immediately on the motor nerves, but that it plays downwards on the motor centres contained within the Axial Cord; from which, and not from the Cerebral convolutions, the motor nerves take their real departure'.[2] The point must not be missed that Carpenter is here reiterating the old view of the separation 'of the cortex from the sensory-motor centres in his comments on the very work which would finally overthrow this discontinuity. He still saw the cerebrum as a separate, superadded organ, although he did mention the fibres connecting it with the striata and thalami, an acknowledgement which is at variance with his earlier claim that the cerebrum had no direct connection with any of the lower centres.[3] Even so, he recalls Flourens' experiments to support the belief that the cerebrum is independent of the thalami and striata.[4] The juxtaposition of the old and the new is dramatized by the fact that Carpenter somehow manages to reiterate his former views and to praise Ferrier's findings. For example, he points out that one of the strongest arguments in favour of the validity of Ferrier's work is 'that Dr. Ferrier can predict with almost positive certainty the movements he will call forth by the localized stimulation of certain parts of the Cerebral convolutions; and that very dissimilar movements follow the application of the stimulus to points nearly adjacent'.[5] In so far as he questions Ferrier's findings, he suggests that they may be secondary phenomena produced by hyperaemia.[6] However, in his conclusion he grants that there are motor centres 'which are now proved to be definitely localized in the Cerebral convolutions' and which call forth coordinated movements when electrically stimulated.[7] Nevertheless, Carpenter somehow fails to grasp that Ferrier's findings contradict his own doctrine of the separation of the cortex from the lower centres and draws the implausible consequence that 'the office of the Cerebrum is not immediately to evoke, but to co-ordinate and direct, the muscular contractions' excited through lower centres.[8]
1 Carpenter, 1874a, p. 715.
2 Ibid., p. 719.
3 Carpenter, 1874 pp. 7-8.
4 Ibid.
5 Ibid., p. 2.
6 Ibid., pp. 10-12.
7 Ibid., pp. 18-19
8 Ibid., p. 20. There may be a simple explanation for this, given by Carpenter in introduction to the printed version of his address at the West Riding Lunatic Asylum: while he grasped that Ferrier's findings were very significant, he did not look closely enough into the experimental findings to see their detailed implications. He said, 'the time I can spare from Official duty has been so completely engrossed for several years past by other studies, that I could not presume to enter into such a critical examination of these results as would be required to satisfy Physiologists who have paid special attention to this department of inquiry.' He delivered the address with no thought of its eventual publication. (Ibid., pp. 1-2.)
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Carpenter's ability to ignore the implications of new facts and to make them fit old doctrines in the period after 1870 is complemented by Jackson's difficulty (in the period just before 1870) in seeing that new facts, seen in the light of new doctrines, should transcend the orthodox belief in the corpora striata as the highest motor centres. Before turning to Jackson's difficulties, however, it is important to appreciate just how far physiological doctrine was at variance with anatomical fact. What anatomical basis was there for making a separation between the corpora striata and thalami on the one hand and the cortices on the other? The experimental evidence for this has been reviewed. Similarly, it is clear that at least since Flourens, this evidence conveniently supported philosophical prejudices which separated the mind and its organs from the sensory-motor view of the rest of the nervous system. How does this position relate to modern conceptions of the anatomy, relations, and functions of the structures involved?
It is perfectly understandable that the investigators of the brain in the nineteenth century related the sensory tracts to the optic thalamus and the motor tracts to the corpus striatum. Todd and Bowman were quite right in tracing the posterior columns of the spinal cord to the thalami and the anterior columns to the corpora striata. But why did they stop there? It appears that their preconceptions allowed them to see this far and no farther. Neither the thalami nor the corpora striata are the termini of the tracts which are seen to pass into them.
The situation with respect to the thalami is easier to understand and to reconcile with modern knowledge than that concerning the corpora striata. The spino-thalamic tract passes into the nuclei of the thalamus, carrying sensory impulses from the periphery. However, these nuclei serve only as relay stations. The spinothalamic tract synapses with the fibres of the thalamo-cortical tract which relays sensory impulses (partly by way of the anterior limb of the internal capsule) to the primary sensory projection areas of the cerebral cortices. Thus, the thalami do have sensory functions. The error of the nineteenth-century physiologists was therefore not anatomical. It was also recognized that the thalami passed information on to the cortices, though the fibres involved were sometimes conveniently ignored. However, until the sensory functions of the cerebral cortices were discovered in the mid-1870's, a physiological distinction was made between the functions of the thalami and those of the cortices. It was believed that the thalami were the highest sensory centres and served to connect the sensations coming from the external world with the organ of mind, where physical
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sensations became mental perceptions and served as the elements of ideas and the matter for intellectual operations. Since the association psychology had always been sensationalist, there was little resistance to extending the sensory tract to the cerebral cortices, and the literature does not mark the change of emphasis and the relative downgrading of the thalami as an important problem. The thalami were soon seen in proper perspective as relay stations for sensory impulses on their way to the cortices, the problem of the relations between sensations and perceptions ceased to have a convenient anatomical analogue, and the issue reverted to its proper philosophical context.
The situation with respect to the corpora striata is at once less clear and more interesting. Modern neuroanatomy and physiology provide almost no basis for the view which was so tenaciously held by most physiologists before (and by many after) 1870. In order to separate the corpora striata from the cerebral cortices, it was necessary to create a discontinuity where none exists. How did this happen? In order to appreciate the enormous influence of preconception, it may help to present the modern view and then try to reconcile it with the findings of earlier workers. First, the term 'corpus striatum' refers to no simple anatomical structure. It is a collective term sometimes used to refer to a number of closely related nuclei: the caudate and lenticular nuclei. 'Lenticular nucleus,' in turn is a collective term for the putamen and globus pallidus. Each of these structures was named for its shape. Their functions are very imperfectly understood today, and the most that can be said is that they are part of an 'extrapyramidal motor system', injury to which produces characteristic motor dysfunction, e.g., the tremor of Parkinsonism. Their functions in normal life are not understood at all. What is clear is that they do not play an important part in the direct control of muscular movements, the function which was assigned to them by all major investigators by 1870. How, then, did this enormous blunder occur?
The name 'corpus striatum' refers to the characteristic striated appearance of the collection of structures discussed above when they are sectioned and examined grossly. The striate appearance is produced by connecting bands of grey matter passing between the caudate and lenticular nuclei through the white matter of the internal capsule. It is the internal capsule which explains the findings of the nineteenthcentury investigators. This structure is made up of fibres passing to and from the cortices. En route they pass between the caudate and lenticular nuclei. The cortico-spinal or pyramidal tract which carries motor
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impulses from the cortex to the spinal nerves (which, in turn, control muscular contractions), passes through part of the internal capsule on its way to the pyramids. Thus, the primary motor pathway occupies the posterior third of the anterior limb, the genu, and the anterior two thirds of the posterior limb of the internal capsule.[1]
The point of this anatomical description is to show how the nineteenth-century investigators came to associate the corpus striatum with muscular motion. Their descriptions and illustrations show that they meant the same thing by the term corpus striatum that we do today. What they failed to appreciate is that the motor tract is merely passing through on its way from the cortex (to which they denied primary motor functions) to the spinal cord. They did not deny that the corpora striata were related to the organ of will in the hemispheres, since the will was supposed to give orders which were executed by the putative motor centres in the corpora striata. Nor would a modern investigator deny that stimulation of the corpora striata produces muscular motions. Stimulation of the cortico-spinal tract at any point produces movement of the relevant muscles. Thus, the physiological findings are valid. Similarly, until 1870, cortical stimulation consistently failed to produce muscular contractions. The consequence seemed clear. However, no one noticed the continuity between the white matter of the corpora striata and the hemispheres. In fact, Carpenter (supported by Todd and Bowman on physiological grounds, and Kölliker on histological evidence) claimed that the radiating fibres of the hemispheres 'take a fresh departure' from the thalami and corpora striata.[2] As has been shown, the former claim is valid, while the latter has no anatomical basis.
The only conclusion that can fairly be reached on the fundamental role ascribed to the (in this context fundamentally unimportant) corpora striata is that the incidental passing through of the fibres of the motor tract which, when stimulated, gave violent muscular contractions and convulsions, combined with the failure to evoke contractions from cortical stimulation, proved too convenient a set of findings for those who wanted to separate the organ of the will from mundane muscular movements. This coalescence of physiological findings (positive and
1 The anatomical and physiological matter of the foregoing discussion has been drawn from Peele, 1954; Brain, 5th ed., 1955; Dorland, 23rd ed., 1957; and consultation with professional neuroanatomists and neurologists. I should like to thank Sir Francis Walshe for referring me to the works of Carpenter.
2 Carpenter, 1855, p. 490. Cf. Jefferson, 1960, p. 115, for an earlier (1827) illustration which shows the pyramids ending in the corpus striatum.
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negative) with psychological convictions and philosophical assumptions led them to see just what they wanted in a way that is reminiscent of the anatomists who dissected bodies only to confirm what Galen had written centuries before. Their assumptions prepared (or permitted) them to see only so much. For important philosophical reasons the cortex was considered separate in function from the sensory-motor system. What they saw was what they expected: discontinuity. It had been a great step to admit that the brain was the organ of the mind. To reduce mind to crude sensory-motor terms was asking too much of most investigators of the pre-Spencerian school.
The belief in the pre-eminence of the corpora striata did not disappear with the findings of Fritsch and Hitzig, and Ferrier, and Carpenter's response has already been noted. Similarly, the Report to the British Association which called Ferrier's findings 'the most important work which has been accomplished in physiology for a very considerable time past'[l] and explicitly argued that the convolutions of the cerebrum were shown by Ferrier to be concerned with muscular movements and not entirely with purely intellectual operations,[2] contained the following passage on the same page: 'that the corpus striatum is concerned in motion, while the optic thalamus is concerned in sensation, and that intellectual operations are manifested specially through the cerebral hemispheres, are conclusions which were indicated by the study of diseased conditions’,[3] and Ferrier's experiments are said to confirm this doctrine.[4] The origin of the pyramidal tract was shown by Betz to be in the cortex, where, he said, the great pyramidal cells were found in just those parts of the cortex which Fritsch and Hitzig had found excitable.[5] This was in 1874. In 1876, William Broadbent was referring to the corpus striatum as 'the motor ganglion for the entire opposite half of the body. It translates volitions into actions, or puts in execution the commands of the Intellect'.[6] This passage was quoted by Bastian in 1880, as the best expression of a view which he supported.[7] He goes on to discuss Ferrier's findings in detail, but he retains an important motor role for the corpora striata.[8] As late as 1886, Jackson indicated that most physicians thought epilepsy to be a dysfunction of sub-cortical and medullary centres.[9] It is not until 1890 that one finds, in Foster's standard Text Book of Physiology, the modern view which sees the fibres of the cortico-spinal tract merely passing through the corpora striata,
1 Rutherford, 1874, p. 122.
2 Ibid., p. 121.
3 Ibid.
4 Ibid., p. 122.
5 Jefferson, 1960, p. 121.
6 Quoted in Bastian, 1880, p. 567.
7 Ibid., pp. 564-7.
8 Ibid., pp. 569-88.
9 Jefferson, 1960, p. 116.
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structures whose functions are unknown.[1] It is with this subsequent history in mind that one must return to the 1860's and examine Jackson's tentative attempts to implicate the cerebral cortices in muscular motions.
Jackson's Ambiguous Position
Jackson's case is instructive and is worth considering in detail, not for the sake of priority (no claim is feasible that Jackson predicted Fritsch and Hitzig's findings), but because it emphasizes the slowness with which the elements of a thoroughgoing sensory-motor view, which, included the cortex and its functions, were finally brought together. All the necessary conceptions had existed in the literature at least since Mueller, and they had been developed into a thoroughgoing sensory-motor psychophysiology by Bain and Spencer, but Jackson's work shows that there was an extreme reluctance to apply them unequivocally to the cortex, even though there were data in abundance to justify the application, and even though it was required by Spencer and Jackson's evolutionary view of the continuity of functional organization of the nervous system.
If Jackson's statements on the convolutions and the corpus striatum up to 1870 are brought together and compared, the simple truth is that they defy integration into a consistent, unified view. Two positions remain constant: (1) The corpus striatum was considered the highest part of the motor tract,[2] and the movement of limbs and of speech were represented there.[3] (2) The convolutions, usually referred to as 'convolutions near the corpus striatum', represented impressions and movements.[4] As early as 1866, he began making statements which sometimes juxtaposed these views and sometimes ignored one while advocating the other with regard to disease. Thus, in one article he names the corpus striatum 'the highest part of the motor tract', through which 'we are able to direct our limbs voluntarily'.[5] But two years later
1 Foster, 5th ed., 1890, pp. 970-8. The present study is confined to the period which begins with empirical localizations, and I have not looked into the earlier history of views on the functions of the corpus striatum. Meyer (1960, p. 789) attributed the origin of the view to Thomas Willis. I have not read Willis' works and can only report that other secondary sources do not support this attribution. Willis' role in the founding of comparative neurology and the shift of emphasis from the ventricles to the solid parts of the brain deserves a much more careful treatment at the hands of historians than it appears to have had until now.
2 Jackson, 1931, II, 127, 122-3.
3 Ibid., 11, 216, 244; Jackson, 1931, I, pp. 26-7.
4 Jackson, 1931, I, 27, 38; Jackson, 1931, II, 123.
5 Jackson, 1931, II, 122-3. Jackson's emphasis is irrelevant to my point.
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he was using a looser formulation for movements of the limbs: they are 'represented in each part near the corpus striatum'.[1] He next refers to ‘convolutions near the corpus striatum for superintending those delicate movements of the hands which are under the immediate control of the mind'. These convolutions are spoken of as 'higher centres of movement', and disease of them can cause chorea.[2] However, he is occasionally less explicit, naming only 'the locality of the corpus striatum'.[3]
Jackson's style is always vague, but it appears that his lack of explicitness here is the result of hesitancy and/or muddle rather than his usual style. He regards the corpus striatum as the seat of the lesion in hemiplegia[4] and in convulsions beginning unilaterally.[5] But where aphasia is concerned, he is less explicit. The arrangements of fibres and cells representing the movements of speech lie 'close upon the corpus striatum' in one reference and are located in convolutions near the corpus striatum in another on the same page.[6] The confusion about the highest motor centres is made explicit in the last reference where, having localized the movements of speech and the lesion of aphasia in the convolutions, he says that these cause symptoms by affecting the corpus striatum, which alone is the place where the will can move muscles: 'disease near the corpus striatum produces defect of expression (by words, writing, signs, etc.), to a great extent, because this is the way out from the hemisphere to organs which the will can set in motion'.[7] This was written in 1866. Two years later he reported a case of 'Corpus Striatum Epilepsy' which involved a postmortem finding of blood, the bulk of which 'lay in one spot over the frontal convolutions, and was so placed as, I imagined, to squeeze the corpus striatum'.[8] The discussion refers all symptoms to the corpus striatum and does not mention the convolutions. In this case Jackson was clearly wedded to the corpus striatum in spite of a striking finding which pointed to the convolutions.
By 1870 he was to implicate the convolutions in severe convulsions: 'As the convolutions are rich in grey matter I suppose them to be to blame, in severe convulsions at all events'. However, he immediately reverts to the corpus striatum in the rest of the sentence: 'but as the corpus striatum also contains much grey matter I cannot deny that it may be sometimes the part to blame in slighter convulsions. Indeed, if the discharge does begin in convolutions, no doubt the grey matter
1 Jackson, 1931, II, p. 241. Jackson's emphasis is irrelevant to my point.
2 Ibid., II, 240-1, 122-3.
3 Ibid., II, 239.
4 Ibid., II, 239, 246.
5 Jackson, 1931, I, 38.
6 Jackson, 1931, II, 123.
7 Ibid.
8 Ibid., II, 218.
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of lower motor centres, even if these centres be healthy, will be discharged secondarily by the violent impulse received from the primary discharge’.[1]
After the findings of Fritsch and Hitzig and Ferrier, Jackson's hesitancy and/or confusion disappeared, and he attempted to rehabilitate his former views with the wisdom of hindsight, claiming that his only real error was in assigning the lesion of unilateral epilepsy to the corpus striatum, rather than to the convolutions near to it.[2] He also held, as part of his hierarchical view of the nervous system, a conception of these convolutions as representing 'over again, but in new and more complex combinations, the very same movements which are represented in the corpus striatum. They are, I believe, the corpus striatum "raised to a higher power"'.[3]
The accusation of vagueness against many of Jackson's statements should be mitigated in the light of the fact that he was dealing with clinical phenomena at a time when the underlying neurophysiological processes were not known and could not provide a precise set of correlates for his gross observations of symptoms and lesions. For example, his failure to make a clear demarcation between the convolutions and the corpus striatum in cases of epilepsy is partially explained by his seeing them both as parts supplied by the middle cerebral artery.[4]
The purpose of the foregoing analysis will have been served if it communicates some of the confusion about the convolutions among physiologists and clinicians up to 1870. Clinical views based on the associationist sensory-motor psychophysiology were directly implicating the cortex with more or less hesitancy, but the strictly experimental data from physiology gave an unequivocal answer: the cortex was inexcitable to artificial stimulation, whether mechanical, chemical, or electrical.
Although the subject matter of the last several chapters, beginning with the association psychology, has all been properly included within the experimental tradition, it should be noted that no new experiments fundamentally affecting the aspects of brain physiology which are being considered here were conducted between 1822 and 1870. The intervening years were occupied with the progressive extension of the sensory-motor view to the brain in the (non-experimental) writings of association psychologists in the light of clinical and clinico-pathological findings. In a sense, then, no strictly experimental work was
1 Jackson, 1931, I, 9.
2 Ibid., I, 38.
3 Ibid., 1, 68. Cf. 114-15.
4 Ibid., I, 9.
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going on between 1822 and 1870. Experimental neurophysiology was dominated by three firmly-based findings: the Bell-Magendie law, the regulatory function of the cerebellum, and the inexcitability of the cortex. A fourth aspect of the climate of ideas was in an equivocal position: cerebral equipotentiality had been challenged by the clinical findings of Bouillaud and Broca in France, and cerebral localization was being considered (though less heatedly and in very different functional and anatomical terms) by Spencer and Jackson. Three of these four reigning ideas were primarily the results of Flourens' findings and preconceptions. Consequently, Fritsch and Hitzig address their experimental findings back through fifty years to Flourens.