Mind, Brain and Adaptation in the Nineteenth
Century: Cerebral Localization and Its Biological Context from Gall to Ferrier
by
[ Contents | Preface | Introduction |
Chapter: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Bibliography ]
7
FRITSCH AND HITZIG AND THE
LOCALIZED ELECTRICAL EXCITABILITY OF THE CEREBRAL HEMISPHERES
All this has never yet been seen — But Scientists who
ought to know Assure us that it Must Be So: O, Let us never, never doubt What
nobody is Sure About!
H. Belloc
In 1870, Gustav Fritsch and Eduard Hitzig published a
paper entitled 'On the Electrical Excitability of the Cerebrum',[1] which
demonstrated by experiment that
A part of the convexity of the hemisphere of the brain
of the dog is motor . . . another part is not motor. The motor part, in general,
is more in front, the non-motor part more behind. By electrical stimulation of
the motor part, one obtains combined muscular contractions of the opposite side
of the body.[2]
This finding must be set apart from the foregoing
analysis for two reasons. It stands apart, first, because of its significance.
The work of Fritsch and Hitzig was a truly epoch-making classical experiment in
the sense that all subsequent work in cerebral physiology was done with
reference to this single publication. It dethroned a doctrine that had reigned
for fifty years, and its appearance introduced order into the confused picture
indicated above. The second reason is less obvious. It has to do with the
context of the experiment and the psychological theory with which it is allied.
Fritsch and Hitzig's psychological views neither arose from nor were they
compatible with the sensory-motor associationist tradition which has been traced
from Locke to Bain, Spencer, and Jackson. Their finding was one of the
two direct stimuli for Ferrier's experiments, but their psychophysiology was
part of the tradition which Jackson explicitly rejected. Consequently, the
finding of Fritsch and Hitzig must be considered separately from its
interpretation by them. This separation is relatively easy, since their comments
1 The original publication was Uber die elektrische
Erregbarkeit des Grosshirns', and it appeared in Arch. f. Anat.,
Physiol. und wissenschaftl. Mediz., Leipzig, 37, 1870, 300-32. All
quotations are taken from the translation in von Bonin, 1960, and page
references refer to it.
2 Fritsch and Hitzig, 1870, p. 81.
225
on psychophysiology are incidental to their main thesis
about the ‘central places of muscular movement'.
Gustav Fritsch and Eduard Hitzig were two young German
physicians. Their experiments were conducted on a dressing table in a small
Berlin house, because the University had no space for such studies.[1] Hitzig
became a renowned psychiatrist with a reputation for 'incorrigible conceit and
vanity complicated by Prussianism'.[2] He continued to play a major role in the
experimental work on localization in the ensuing decades and gave the 'Hughlings
Jackson Lecture' in 1900. Fritsch was a man of independent means who spent much
of his life travelling. His 1870 paper with Hitzig was his only important
contribution to medicine.[3]
Their report begins with a statement of the anomalous
positions of the hemispheres with respect to the law of specific energies of the
rest of the nervous system. 'Physiology ascribes to all nerves as a necessary
condition the property of excitability, that is to say, the ability to answer by
its specific energy all influences by which its properties are changed with a
certain speed.’[4] While the artificial excitability of the brain stem and
spinal cord had been hotly disputed, 'since the beginning of the century we were
quite generally convinced that the hemispheres were completely inexcitable for
all modes of excitation generally used in physiology'.[5] They review the
negative findings of Longet (1842), Magendie (1839), Matteucci (1843), and
others, setting Flourens aside for fuller treatment. Their quotations from Weber
and Schiff are instructive. Weber shows the confidence with which the dogma was
held.
If one can conclude from the present standpoint of
science that there are no motor fibers in a nervous part in which after
excitation no contractions occur, one can say with the greatest certainty there
is not one fiber in the hemisphere of the brain which goes to voluntary muscles.
Not a single observer saw movements of such muscles after stimulation of the
central parts.[6]
Schiff is equally certain and extends the
inexcitability from somatic muscular motion to the intestines, which also remain
quiescent after excitation of the lobes of the brain.[7] One can vicariously
experience the
1 Haymaker, 1953, pp. 138-42.
2 von Bonin, 1960, p. xii.
3 Ibid. Cf. Grundfest, 1963.
4 Fritsch and Hitzig, 1870, p. 73. Helmholtz had
measured the velocity of a nerve impulse in a motor nerve in 1850. See Boring,
1950, pp. 413, 47-9. Helmholtz's original report is translated and reprinted in
Dennis, 1948, pp. 197-8. On specific energies of nerves, see Boring 1950, pp.
80-95. This topic deserves further study.
5 Fritsch and Hitzig, 1870. p. 73.
6 Ibid., p. 75.
7 Ibid.
226
inconoclastic excitement with which Fritsch and Hitzig
conclude their review. 'Even in other fields than in physiology, there can
hardly be a question about an opinion which seems so completely settled as that
of the excitability of the cerebral hemisphere. It would be easy to give more
citations in the same vein if there would be any point to it.'[l]
Flourens' findings were discussed in greater detail.
There must be no question about the respect in which Fritsch and Hitzig held
him. At the beginning of their review they say. 'This gifted and lucky observer
by using as clean a method as possible came to results which deserve to be
considered as a basis for all later experiments in this field.’[2] Flourens'
ablations on birds and mammals had shown the 'signs of will and consciousness of
sensations disappear, while nevertheless, by stimuli coming from the outside,
quiet engine-like movements could be produced in all parts of the body'.[3] He
had quite naturally concluded that 'the cerebral hemispheres were not the seat
of the immediate principle of muscular movements but only the seat of volition
and sensation'.[4]
Given Flourens' methods, Fritsch and Hitzig grant that
these conclusions seemed satisfying. However, Flourens' further findings and the
concepts associated with them were 'difficult to harmonize . . . with experience
gained in other ways'.[5] These further results had led Flourens to believe in
cortical equipotentiality. If he ablated a hemisphere, the resulting blindness
and occasional weakness on the opposite side were transient. Ablation of the
grey matter of both cortices (apparently in a pigeon) was also followed by
complete recovery. Progressive slicing away of the hemispheres led to 'a uniform
gradual decrease of sensory perceptions and volition', which was regained within
a few days, provided a sufficient amount of tissue was left intact. If the
extirpations exceeded a certain limit all faculties disappeared and were not
recovered. 'Flourens concluded that the cerebral lobes with their whole mass
subserved their functions, and that there is no special seat either for the
different faculties or for the different sensations.' Also, an intact remaining
part of the hemispheres 'could relearn the complete use of all functions'.[6]
The resulting view of 'the central places of muscular
movement' was that there were muscular mechanisms in most parts of the brain
stem and cord which could be excited reflexly from the periphery or centrally
'by way of volition or of the impulse of the soul'. The soul was believed
1 Fritsch and Hitzig, 1870, p. 75
2 Ibid., p. 76.
3 Ibid.
4 Ibid.
5 Ibid.
6 Ibid., pp. 76-7.
227
to have its seat in the grey matter of the hemispheres,
'without however, the parts of the psychic center being localizable on to parts
of the organic center'. Unfortunately, the investigation of the probable seat or
'nearest tools' of the soul was closed, 'since the substrate will not answer
with an overt reaction to any normal stimulus'.[l]
Fritsch and Hitzig thus raised three closely related
issues: the excitability of the hemispheres, localization of functions, and the
relation of the hemispheres to the immediate principle of muscular movements.
Prior to their own experiments there had been equivocal results which bore on
the traditional views on each of these points. In 1756, Haller and Zinn had seen
convulsive movements after lesions of the white matter of the brain, but the
limitation of the stimuli they used was not precise, and their findings were
explained away as the likely result of pushing their instruments into the
medulla oblongata.[2] In 1867, Eckhard mentioned an unspecified source which
noted movements of the anterior extremities on ablation of the anterior
lobes.[3] Neither of these results had any effect on the prevailing doctrines.
Clinical findings had been discounted because of the notorious difficulties
involved in interpreting post-mortem examinations. In any case, many congenital
and acquired defects of parts of the brain involved no interference with
cerebral functions. Nevertheless, it was such clinical findings which
contributed to the gradual modification of the prevailing view. Bouillaud and
Broca found aphasia 'caused by destruction of a small eccentric part of the
brain', and cases had been reported in the literature of monoplegias of an arm
or leg associated with postmortem findings of 'small defects of the cerebral
hemispheres'.[4] As early as 1834, Andral had expressed the frustration which
these results engendered: in the present state of the science it is impossible
to assign a distinct cerebral seat for limb movements, although the findings of
monoplegias leave no doubt that such a seat exists.[5]
Other clinical results came from cases involving the
corpus striatum and thalamus. As long as there was no question of a role for the
cortex in movements, these had been taken into account by physiologists.
However, once Fritsch and Hitzig began to take seriously the possibility of
involvement of the cortex, they became wary of reasoning on the basis of such
cases, since the corpus striatum and thalamus contained conduction pathways from
the hemispheres and therefore could not
1 Fritsch and Hitzig, 1870, pp. 77-8.
2 Ibid., pp. 73-4.
3 Ibid., p. 75.
4 Ibid., p. 78.
5 Ibid.
228
give certain evidence regarding 'the first locus where
the lost movement began'.[1]
Clinical findings in favour of both localization and
cortical representation of movements were supported by morphological
investigations, notably those of Meynert. He considered the cerebral cortex to
be a 'focus of perceptions' and argued that it could be 'subdivided into many,
more or less circumscribed parts, the importance of which for the various
perceptions is due to the nerve fibers of its so-called projection system'.[2]
Fritsch and Hitzig refer to Meynert as one of the few neurologists prior to
their report who had 'talked in favour of a strict localization of psychological
faculties, although differently from Gall'.[3] This is the only mention of Gall
in their paper. However, it may help to see the significance of his concepts for
their work if it is recalled that what Flourens, Bouillaud, and Broca said about
localization is directly related to Gall, and that these figures provided the
issues which Fritsch and Hitzig are addressing. Their conclusion is that 'Such
facts show that the origin of at least some function of the soul is bound up
with circumscribed parts of the brain'.[4] It is against this background that
they began their own work.[5] 'In the meantime, by the results of our own
investigations, the premises for many conclusions about the basic properties of
the brain are changed not a little.’[6]
In a previous experiment Hitzig had elicited eye
movements by conducting galvanic currents through the 'posterior part' and
temporal region of the head of a man. He claimed that these were 'the first
movements of voluntary muscles elicited by direct stimulation of the central
organ in man'.[7] The question arose whether the temporal stimulations involved
spread of current to subcortical centres 'or whether
1 Fritsch and Hitzig, 1870, p. 78.
2 Ibid., p. 79.
3 Ibid., p. 92.
4 Ibid., p. 78.
5 Jackson’s name is conspicuously absent from Fritsch
and Hitzigs's otherwise thorough review of work leading up to their discovery.
It is true that in his Hughlings Jackson Lecture in 1900, Hitzig claimed that he
was the first to confirm by experiment and to define more closely what Jackson
had concluded from clinical facts. However, I have seen no evidence that
Jackson's ideas played any role in leading Fritsch and Hitzig to conduct their
experiments. The relationship seems to be that they arrived at their views on
the basis of the work listed in their paper. Their findings, along with
Jackson's theories, inspired Ferrier to conduct his experiments. The discoveries
of Fritsch and Hitzig, and of Ferrier were, in turn, taken up by Jackson as
confirming his earlier views and as a sure basis for extending them. A false
impression could be gained from the way Sir Francis Walshe quotes Hitzig's
remark about confirming Jackson. (Walshe, 1961, p. 119)
6 Fritsch and Hitzig, 1870, p. 79.
7 Fritsch and Hitzig, 1870, p. 79. Walker reports that
Fritsch is said to have 'observed, while dressing a head wound some years
earlier, that mechanical irritation of the brain caused twitching of the
contralateral limbs'. He gives no reference, and no mention is made of this in
the 1870 article. (Walker, 1957, p. 106.)
229
the cerebral hemispheres in contrast to the general
assumption were after all electrically excitable'.[1] A preliminary experiment
on a rabbit by Hitzig gave a positive result, and he and Fritsch undertook a
large number of further experiments on dogs which gave 'results . . . uniform
even to the smallest details'.
Their findings overthrew three theories that had stood
since Flourens: they established cortical excitability, a role for the cortex in
the mechanism of movements, and cerebral localization. 'The possibility to
stimulate narrowly delimited groups of muscles is restricted to very small foci
which we shall call centers.'[2] Five centres were specified in constant loci
(see Fig. i): for the muscles of the neck, the extensorsand adductors of the
anterior leg, flexion and rotation of the same leg, the posterior leg, and the
facial nerve. Using minimal intensity of stimulation, the areas between these
centres were not excitable, though a greater intensity or separation of the
electrodes led to generalized movements on both sides of the body, and tetanic
stimulation led to after-movements which, in two cases, developed into
generalized epileptic attacks.
1 Fritsch and Hitzig, 18070, P. 79.
2 Ibid., p. 81
230
Two points should be made about their presentation.
First, their meticulous attention to operative techniques (especially the
necessity to control bleeding) and stimulation parameters, is a new and
important feature of their paper as compared with earlier work. The technology
of neurophysiological research becomes more and more a matter of central concern
in subsequent work. A second matter of increasing importance was a standard
nomenclature of cerebral areas. This was provided for Fritsch and Hitzig by
Richard Owen's On the Anatomy of the Vertebrates (1868).[1]
Much of their discussion is concerned with issues that
took a decade to settle. Were they really stimulating the cortex, or were
current loops spreading to lower centres? They conducted experiments which
convinced them that it was the convexity itself which was producing the
contractions. Were the fibres alone, or the cells as well, excitable? This was a
confusing question in 1870, which they felt unable to decide. One reason for
their indecision is reflected in its statement as a dichotomy: fibres or fibres and cells. It should be remembered that the explicit statement of the
neurone theory was almost twenty years away. Fritsch and Hitzig tentatively
attempt to eliminate the dichotomous issue with an early statement of the
theory. 'Since no other reason can be found why the fibers should come closer to
the ganglion cells just here than to meet their fate to enter into them, one can
assume that these ganglionic masses are predestined to produce organic stimuli
just for these nerve fibers.’[2] They are quite properly not over-concerned with
this last issue in their first publication, nor are they particularly worried
about other questions they left open, such as the relation between the poles of
their stimulating instrument or the character of the muscular twitches obtained.
'The new facts which were shown by these investigations are so manifold, and
their consequences go into so many directions, that it would be of little
advantage to try to follow all these trails at once.’[3]
They insist on only two firm conclusions. The first,
'that central
1 Standard cerebral anatomy has become the cornerstone
of method in cerebral physiology. In 1908, Victor Horsley and A. H. Clarke
designed a stercotaxic instrument which made it possible to use a standard atlas
and standard three-dimensional co-ordinates for specifying any point on the
surface and, more importantly, in the deeper portions of the brain. Subsequent
developments of this technique have led to very impressive localized
stimulation, ablation, electrical recording, and implantation of pharmacologic
substances. 0.5 mm is the current acceptable standard of error for a good
instrument and atlas. The original instrument was described in Horsley and
Clarke, 1908. Several articles describing current stereotaxic technology appear
in Sheer, 1961. The enormous bibliography to that work is a rich mine of
sources.
2 Fritsch and Hitzig, 1870, p. 93.
3 Ibid., p. 84.
231
nervous structures answer our stimuli with overt
reactions',[l] eliminates the anomaly with which they opened their paper. The
hemispheres, like all other nervous structures, have the property of
excitability that had formerly been denied to them alone. The second certain
conclusion is that 'a large part of the nervous masses composing the
hemispheres, about half of it, stands in immediate connection with muscular
movements, while another part has evidently directly nothing to do with it’.[2]
Fritsch and Hitzig reveal the two most important
principles of the new era in cerebral physiology which this paper begins as they
attempt to answer the very pertinent question of 'how it came about that so many
earlier investigators, among them the most illustrious names came to opposite
results. To this we have only one answer, "Methods give the results"'.[3] This
statement is double-edged. It recalls Flourens' identical statement as he
advocated the experimental method rather than Gall's anecdotal and correlative
approach. Since it is being used by Fritsch and Hitzig as they overthrow
Flourens' findings, the statement also shows that new methods give new results.
From 1870 to the present day, this technology has provided increasingly more
refined and fruitful techniques, which have largely determined the progress of
experimental work: new surgical and aseptic techniques, stimulation sources,
electrodes and methods of placing them accurately (and, later, of implanting
them permanently). Beginning in the second quarter of the present century, the
above methods were aided by the addition of very elaborate methods of recording
the electrical activity of the brain as a whole, and very tiny regions of it
down to a single neurone. Some appreciation of these advances can be gathered by
comparing a modern stimulating and recording console with their measure of
stimulus intensity-that which 'produced just a sensation on the tongue when it
was touched by the heads'.[4]
Their answer to previous failures was not only
concerned with methods. In fact, they acknowledge that assumptions had,
in large measure, determined the results.
It is impossible that our predecessors have laid bare
the whole convexity, for otherwise they must have obtained contractions. The
posterior lateral wall of the cranial vault of the dog, under which there are no
motor parts, recommends itself by its configuration for the first trephine
opening. Here one most likely began the operation and then did not go forward,
assuming erroneously, that the various parts of the surface were equivalent. One
based
1 Fritsch and Hitzig, 1870, p. 91.
2 Ibid., p. 92.
3 Ibid., p. 90.
4 Ibid., p. 81.
232
oneself on the supposition still widely disseminated
and mentioned in the beginning, that all psychological functions are present in
all parts of the cortex. Had one only thought of the localization of
psychological functions, one would have considered the seemingly inexcitability
of certain parts as something quite obvious and would have examined every part
separately.[1]
Their paper closes ,with a reiteration of this
rejection of cerebral equipotentiality and its replacement by cerebral
localization.
This shows clearly, that in the former colossal
destructions of the brain, either other parts have been chosen or that the final
mechanisms of movements were not particularly noticed. It further appears, from
the sum of all our experiments that the soul is not, as Flourens and others
after him had thought, a function of the whole of the hemispheres, the
expression of which one might destroy by mechanical means in the whole, but not
in its various parts but that on the contrary, certainly some psychological
functions and perhaps all of them, in order to enter matter or originate from it
need certain circumscribed centers of the cortex.[2]
The assumption of cerebral localization which was given
its first firm experimental support in this publication by Fritsch and Hitzig
was to dominate cerebral research (with dissent that took its meaning by
contrast) until the 1930's, and is again the ruling assumption in clinical and
experimental work.[3]
Ontological Dualism and Interaction in
Fritsch and Hitzig
The phrasing of the closing sentence in their paper
raises the issue of the philosophic assumptions underlying Fritsch and Hitzig's
experiments and their incompatibility with the assumptions of the associationist
tradition to which Jackson and Ferrier belonged. Put simply, Fritsch and Hitzig
were ontological dualists and believed in separate substances of mind and its
mechanisms. The brain is the material instrument of the immaterial soul, and the
grey matter of the cortices constituted the 'first tools of the soul.[4] The
soul can execute its orders by its property or faculty of will, and this
provides an impulse which excites the motor mechanisms by interaction.
Excitation by a mental act is an alternative means of exciting the motor
mechanisms; reflex excitation from the periphery by purely physiological means
being the other. They differed from Flourens, who held a similar interactionist
view, in that they were prepared to localize at least some of the functions of
the soul and to place some of its instruments for muscular
1 Fritsch and Hitzig, 1870, p. 90.
2 Ibid., p. 96.
3 See Zangwill, 1961; Krech, 1962.
4 Fritsch and Hitzig, 1870, p. 77.
233
motion in the hemispheres. Flourens had reserved the
hemispheres for sensation and volition, holistic functions served by an
equipotential and inexcitable cerebral mass.
Fritsch and Hitzig were not prepared to say that they
had found the centres of volition or even that their centres were the first
mechanical link in the execution of volitions. The methods they used could not
tell them if their stimuli led to the same movements as normal mental and
physiological mechanisms. The last sections of their paper are concerned with a
tentatively-held view that their centres served an intermediate function between
'that part of the brain which harbors the origin of the volition of the
movement' and lower muscular mechanisms which were less well-coordinated.[l]
They conducted ablation experiments which, they believed, left room for 'purely
psychological possibilities' 'more central' than their motor centres. These were
presented very briefly and interpreted very tentatively. The result of ablating
the centre for the right anterior extremity was not complete paralysis but only
impairment of the ability to move the limb. They saw this finding as supportive
of the existence of 'still other centers and pathways to originate and to run to
the muscles of that leg'.[2] The further interpretation of the partial nature of
the impairment is reserved, but the whole discussion is in the service of an
interactionist conception.
There is nothing to be gained for present purposes from
a detailed examination of their interactionism and the complex problems it
involves. (For example, like Flourens, they were involved in a double
interaction: between will and its material substrate in the first instance, and
then between the mental act of will and the muscular mechanisms it activates.)
The point to be made is that the psychophysical parallelism of the
Spencer-Jackson-Ferrier view eliminates all these complex issues by precluding
interaction and even the discussion of psychological faculties in a
physiological context. The support for his concepts which Jackson derived from
Fritsch and Hitzig is confined to the involvement of the hemispheres in
movement. The stimulus they gave to Ferrier is confined to their demonstration
of the localized electrical excitability of the cerebral hemispheres. The
philosophical assumptions of the Germans' view were anathema to the Englishmen,
whose parallelism allowed them the luxury of ontological agnosticism while they
got on with their work.
1 Fritsch and Hitzig, 1870, p. 92.
2 Ibid. p. 96.