Cerebral Localization—What Is Known, What 
Surmised, and What Is Its Surgical Value? 
Read in the Section on Practice of Medicine, at the Forty-fifth Annual Meet- 
ing of the American Medical Association, held in San 
Francisco, June 5-8, 1894. 
BY JOHN W. ROBERTSON. M. D. 
PROFESSOR NERVOUS AND MENTAL DISEASES UNIVERSITY OF CALIFORNIA, 
, SAN FRANCISCO. 
REPRINTED FROM 
THE JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, 
■ AUGUST 4, 1894. 
CHICAGO: 
PRINTER AT THE OFFICE OF THE JOURNAL OF THE ASSOCIATION, 
1894. CEREBRAL LOCALIZATION—WHAT IS 
KNOWN, WHAT SURMISED, AND 
WHAT IS ITS SURGICAL 
VALUE? 
The physiology of the nervous system and the 
functional differentiation of its component parts has 
been but recently investigated, and is now in many 
particulars so well established that it seems proper 
before entering the domain of neurologic pathology 
to briefly recapitulate, not only that which has been 
scientifically proven, but the many speculations of 
eminent investigators that are as yet mere hypotheses. 
Without going into a detailed history of the evolution 
of cerebral physiology, I will refer to the great advance 
made by the anatomists of the seventeenth century. 
Before that time anatomy and physiology were neces- 
sarily theoretical, for as a basis they rested on specu- 
lation and tradition, not on the dissection of the 
human body. But the opinions held regarding the 
nervous system were even more crude than those that 
prevailed regarding other portions of the body, for 
the philosophers, led by Aristotle and Herophilus, 
had outlined a physiology based on their psychologic 
theories, and twenty centuries had served but to con- 
found the already existing confusion. 
Willis accomplished for the nervous what his con- 
temporary, Harvey, did for the circulatory system. 
He not only delineated and named the cranial and 
spinal nerves, but recognized the important fact that 
the brain is not only divided into gray and white 
matter, and correctly explained the functions of each, 
but also showed that the gray matter was convoluted 
simply as a wise provision for inclosing the greatest 
surface in the smallest space, realizing that there was 
a direct ratio between intelligence and the volume of 
gray matter, and further suggesting the possibility of 
its function being still more differentiatgd- 2 
The next great advance in the differentiation of the 
nervous system was Sir Charles Bell’s discovery that 
the spinal nerves subserved the twofold purpose of 
sensation and motion, the one entering through the 
posterior root bearing sensation from the periphery, 
the other solely motor, making its exit by the anterior 
root. This he proved by experiments on living animals; 
and his results, published in 1811, were elaborated 
with so much detail that our own text-books do not 
contain any amplification of the theory there pro- 
pounded. When, in 1870, Fritsch and Hitzig an- 
nounced the result of their experiments on dogs and 
monkeys, they were but confirmatory of views already 
advanced by Hughlings Jackson, whose investigations, 
both clinical and post-mortem, had suggested the ex- 
istence on either side the fissure of Rolando, of special 
centers which presided over the movements of the 
leg and arm. But even earlier than this, Dax had 
pointed out the close relationship existing between 
aphasia, right-sided hemiplegia and injury of the 
frontal convolutions; though it was Broca who defi- 
nitely located the speech center at the base of the 
third frontal convolution of the left hemisphere. 
The original experiments performed by Fritsch and 
Hitzig consisted in the removal of a portion of the 
skull of dogs and monkeys, exposing the brain and 
irritating the cortex. Before this it had been believed 
that irritation of the cortex resulted only in convul- 
sions, but when electricity was selected as a stimulus 
and very weak currents used, it was found that irri- 
tation of certain convolutions produced definite mo- 
tions, and so localized were these areas that it was 
possible for the experimenters to foretell the motion 
that would follow the application of the electrodes to 
a given area. This conclusively proved that there 
was some definite relation existing between these 
localities and movements of various members of the 
body. 
Ferrier and Horsley in England and Munk in 
Germany, modifying the methods of Fritsch and 
Hitzig, have so extended and varied these experi- 3 
meats as to eliminate all possible errors; the areas 
have been so incised as to separate them from other 
cells of the cortex, and portions of the cortex con- 
taining these areas have been removed and the re- 
sulting paralyses noted. Thus have the old theories 
been revolutionized and most plausible arguments 
advanced to support the assertion that not only the 
special senses but that motion and sensation are 
located in well-defined and accurately differentiated 
regions of the cerebral cortex. 
So brilliant and so essentially scientific were these 
experiments that the deductions made from them as 
to cerebral localization have been accepted not only 
by the majority of physicians, whose judgment can 
not be based on personal investigation, but especially 
by many leading neurologists. But this acceptance 
is not universal, and it may be said that neurologists 
are ranged into three schools. 
The very weighty names of Brown-Sequard and 
Goltz appear among those who altogether repudiate 
localization in the sense that one portion of the cor- 
tex intrinsically so differs from another as to possess 
a different function. They believe that each half of 
the cerebrum acts as a whole, but that certain portions 
may be educated and probably do preside over the 
special senses, motion and sensation. 
The second school, represented by Exner, Ober- 
steiner, and other conservative neurologists, teach 
“that certain regions of the cortex are to a greater 
extent than the rest associated with certain functions." 
Obersteiner defines his position as follows: “Individ- 
ual centers and cortex fields are not to be considered 
as sharply outlined and definitely marked off from 
neighboring regions; the so-called centers are rather 
the spots of maximal relation to functions which fade 
away into neighboring areas. Hence it follows that 
the cortex fields to a certain extent overlap one 
another. We shall speak of the centers in this sense 
as comprehending the spots of maximal physiologic 
relation." 
The third, known as the English school of local- 4 
izers, is led by Ferrier, Horsley, and Beevor. These 
teach the absolute segregation of centers in the cor- 
tex; that they intrinsically differ the one from the 
other, and that consequently their functions differ, 
and that there are not only regions presiding over the 
special senses, sensation and motion, but divide the 
last into finger, hand, arm, mouth, etc., centers; and 
further contend that these areas are sharply defined, 
are easily located, and, when exsected, produce a per- 
manent paralysis in that member of the body over 
which they preside. 
It is this last which has brought this subject into 
such prominence. Granting that either the first or 
the second school be right, it is only a step forward 
in the study of cerebral physiology; but if the teach- 
ings of the abrupt localizers be correct, a vast field 
of practical importance has been opened and cerebral 
surgery will at least receive a scientific recognition, 
rather than occupy the invidious position it even yet 
holds among conservative surgeons. For this reason 
it seems well to review the work of these investiga- 5 
tors and to point out what they have demonstrated, 
as well as the many questions that are still under 
investigation, and to show that some, at least, are 
unsolvable. 
It has been proved: That when certain regions 
of the cortex of the brain of monkeys, dogs, and 
other animals are irritated by mild currents of elec- 
tricity, motion is produced in corresponding parts of 
the body. That portion of the cortex which has been 
shown to be closely associated with motion is known 
as the Rolandic region, from the fact that it is com- 
posed principally of the two convolutions which are 
separated by the fissure of Rolando, as well as the 
parietal lobule. 
This region is subdivided into special centers. 
Irritation of the parietal lobule and upper junction 
of ascending frontal and parietal convolutions pro- 
duces advance of the opposite hind limb, flexion of 
thighs and toes as in walking. .When the middle 
portion of the ascending convolution is irritated, 
movements of the hand and arm follow. The lower 
portions of the convolutions are in like manner shown 
to preside over, or at least to be closely associated 
with, movements of the mouth, tongue and nose. 
Posteriorly, near the angular gyrus, irritation results 
in movement of the eyes and eyelids, and still farther 
downward on the superior temporo-sphenoidal con- 
volution there is pricking of the opposite ear, head 
and eyes turn to the opposite side, and the pupils 
widely dilate. Other regions, though irritable, are 
not connected with coordinated movements, while 
much of the cortex is insensitive. Thus is it shown 
that motor activity, though present to the greatest 
extent in the so-called motor area, is not confined to 
it. These experiments have also demonstrated the 
fact that while each hemisphere is closely associated 
with the opposite half of the body, to a subordinate 
degree it also presides over the same side. 
It is surmised: that the brain of the monkey and 
other animals resembles the brain of man to such a 
degree that what is true of the one holds equally true 6 
of the other; that both in man and animals the brain 
is so differentiated that certain areas preside over 
allotted functions, and that they are capable of being 
subdivided. Especially is this true of motion. To a 
lesser extent it is true of the special senses, and the 
brain has been mapped out into centers of sensation, 
hearing, sight, smell, taste, and speech, and these 
have been located as follows:— 
Motion.—The ascending frontal and parietal con- 
volutions, their superior junction and the paracentral 
lobule, known as the Rolandic or motor region, 
have been subdivided into finger, hand, arm, mouth, 
etc., centers, every muscle or group of muscles being 
represented by a definite area in the brain cortex, and 
any given action or series of coordinated movements 
can be obtained by irritating the proper area of the 
denuded cortex. These conclusions are the result 
partly of comparison with animals and partly of path- 
ologic research, and may be thus summarized:— 7 
Superior parietal lobule (i), advance of hind limb. 
Upper portion ascending- parietal (2, 3, 4-), complex 
movements of leg, arm, and trunk as in swimming. 
Ascending parietal (5, 6, 7, 8), individual and com- 
bined movements of fingers and wrist of hand; pre- 
hensile movements. Posterior extremity of superior 
frontal convolution (9), extension forward of hand and 
arm. Ascending frontal (10), supination and flexion 
of forearm. Lower third of ascending frontal and 
junction of ascending frontal and ascending parietal 
(11, 12, 13, 14), movements of mouth and nose. 
Superior and middle frontal ([5) and supra marginal 
lobule and angular gyrus (16). Movements of mouth, 
eye deviates, pupils change and head turns (sight). 
First temporal (17), pricking ear (in animals), head 
turns and pupil dilates (as in hearing). 
Visual Center.—In Ferrier’s original experiments 
this center was located in the angular gyrus (16), as 
blindness resulted when this was destroyed. But 
other operators claim that sight is centered in the 
occipital lobe (16), and showed that when the gyrus 
only was destroyed and the life of the animal was 
prolonged beyond a few days, sight returned. On 
destroying the occipital lobe with the angular gyrus 
the resulting blindness was more prolonged. Ferrier 
says: “After extensive destruction of the occipito- 
angular region in one hemisphere, the temporary 
amblyopia of the opposite eye leaves a more endur- 
ing homonymous lateral hemiopia to the opposite 
side, yet unless the destruction of the cortex is abso- 
lutely complete (and in none of the recorded experi- 
ments was this the case), restoration occurs, to such 
an extent, at least, that the defect ceases to be percep- 
tible by any tests applicable to the lower animals.” 
In other words, provided this be the center, some 
other portion of the brain assumes the function and 
is able to successfully receive and transmit visual 
impressions. It is further claimed that the simulta- 
neous destruction of occipital regions in both hemi- 
spheres may produce permanent blindness, and Fer- 
rier even goes the length of claiming that these 8 
regions are the central expansions of the optic tracts 
and consequently structurally differ from other cen- 
ters, and that in his experiments atrophy of the 
nerves and tracts has followed destruction of these 
zones. But localizers are by no means agreed among 
themselves as to many of the minor facts, though the 
occipital lobe is the accepted center. 
Auditory Center.—Experiments made on the lower 
animals as to the center of hearing are, from the very 
nature of the facts to be elicited, extremely unsatis- 
factory. It has been found impossible to eliminate 
the complications incident to the difficulty of intelli- 
gently interpreting the phenomena following the 
various lesions. Experiments seem to point to the 
superior temporal convolutions, and it is claimed that 
post-mortem researches bear out this location. 
Olfactory Center.—This has been selected from 
purely anatomical considerations. The roots of the 
olfactory nerve h<ive been traced to the hippocampal 
region and the sense of smell has been assigned to 
the tip of the temporo-sphenoidal lobe. Compara- 
tive anatomy teaches us, however, that the olfactory 
bulb itself is a portion of the brain, and it would 
seem that if any portion of the brain were selected for 
special functions, this would alone preside over the 
olfactory sense. 
Tactile Center.—There is no question in cerebral 
localization more undermined and apparently more 
undeterminable than is this. It is well known that 
the sensory fibers when they pass through the internal 
capsule are differentiated from the motor tract, but the 
region to the cortex to which they are distributed has 
not been determined. Ferrier and his school locate 
this center in the hippocampal region, but the major- 
ity of neurologists agree with Flechsig, who believes 
that the cortical fields of motion and sensation overlap 
each other, both occupying the Rolandic region. 
Center of Speech.—By motor aphasia is meant an 
inability to articulate, not to properly understand and 
appreciate what is heard. This center, situated at the 
base of the third frontal convolution of the left hemi- 9 
sphere, known as Broca’s convolution, has received 
much attention at the hands of pathologists, and 
medical literature teems with post-mortem facts that 
prove the close relationship this region bears to articu- 
late speech. It has been further claimed that only in 
right-handed persons is this center on the left side, 
while in the left-handed it occupies a corresponding 
position in the right hemisphere. There is no fact in 
cerebral localization more generally recognized by the 
profession than is this speech center, and it may be a 
matter of surprise that it is not included among those 
questions of cerebral physiology which have been 
proven. Nevertheless, that this center presides solely 
over speech, and that its functions can not be assumed 
by other portions of the cortex, has by no means been 
demonstrated. It is not possible to here enter into a 
discussion of this point, but it can be stated positively 
that while many facts point to a connection between 
this center and articulate speech, it has been conclu- 
sively shown that tumors involving this region have 
not produced aphasia. One such well-authenticated 
case is sufficient to overcome any number of facts 
which are adduced in support of the theory of a well- 
defined speech center. Not only have tumors been 
found which interfered with the Broca convolution, 
but embolisms have been recorded in which this 
whole area was softened and disintegrated without 
causing a loss of speech. Leading authorities, notably 
Bateman in his recent work on aphasia, take the 
middle ground. While they recognize the close 
relationship between the destruction of the Broca 
center and aphasia, they deny absolutely that it is in 
the strict sense of the term a center. They believe 
that it, as well as other regions of the brain, bear 
some as yet undetermined relation to the faculty ot 
speech. With all the light before us the most that 
can be said is that when the Broca center is involved 
in some destructive process, there is often right-sided 
hemiplegia with motor aphasia. 
From the above summary it will be seen that very 
little has been irrefutably demonstrated. The great 10 
majority of questions that are of practical importance 
are by no means settled. The one fact that coordi- 
nated movements may follow electrical irritation of the 
motor area is regarded by some neurologists as simply 
one of the curiosities of physiology, and they by no 
means accept the deductions which the localizers have 
drawn from such experiments. 
Terrier explains these phenomena by supposing 
that cells in certain areas—not necessarily disasso- 
ciated because a sulcus happens to intervene—possess 
an essentially motor function, and that when irritated 
this irritation passes directly to the white fibers 
which spring from these cells, and that these fibers 
are collected into differentiated bundles, pass out 
through the internal capsule, become the anterior 
and lateral pyramidal tracts, and convey impressions 
through the anterior cornua into the anterior root. 
In other words, he teaches that the motor area is the 
cortical expansion of the motor tract, and that con- 
sequently the cells from which the fibers spring are 
functionally differentiated from other cortical cells. 
Those who are not localizers find much to criticize 
even here. No one familiar with Ferrier’s work 
doubts the experiments recorded. What they are not 
willing to accept is the legitimacy of his conclusions. 
Granting that the brain of the monkey differs from 
that of man merely in number and complexity of 
convolutions, rather than any intrinsic quality, and 
that the cells of the cortex are irritable, they still 
maintain that each cell is so closely connected not 
only with adjacent cells and those in neighboring 
areas, as well as widely separated regions even of 
the opposite hemisphere, that no irritant could be 
applied which would not equally irritate all the rami- 
fications and connections of these cells. But even the 
irritability of the cortex is denied. It is well known 
that nerve fibers can be irritated by many agents, 
both chemical and physical, but it has not yet been 
proved that the cerebral cortex is susceptible to other 
than electrical irritation, and this electrical irritation 
can be attributed to its quality of diffusion. It has 11 
been shown that when the exposed sciatic nerve of a 
frog or the still more delicate galvanometer was con- 
nected with the brain, the application of even light 
currents at a distance resulted in movements of the 
leg or deflection of the needle, thus showing that 
there was extrapolar conduction. Therefore, it is 
claimed that the electricity does not necessarily 
irritate the cells of the cortex, but many penetrate 
to the white fibers as they pass through the internal 
capsule. It is conceded that in this location the fibers 
are differentiated, and that they are susceptible of 
irritation. The so-called motor region is therefore 
“motor” only because it happens to be contiguous 
to the internal capsule, and Dupuy, of Paris, points 
• out the further fact that this region is unusually rich 
in deeply penetrating blood vessels: “The pia mater 
over the Rolandic convolutions is almost a complete 
network of vasomotor fibers and cells, and blood- 
vessels which penetrate into the convolutions. One 
system of blood-vessels only ramifies and ends in the 
cortex proper; the other enters the white substance 
by means of larger vessels accompanied by nerves 
and ganglion cells. It follows from this arrangement 
that the cortex proper is much more vascular and the 
white substance or fibers a great deal less so, and 
moreover that while the vessels irritating the cortex 
are spread well over, those going into the white sub- 
stance are isolated from one another. Now I have 
shown that those points which when ‘excited’ by 
electricity give rise to a motor action, coincide with 
spots where arteries with nerves penetrate into the 
white matter or strands of fibers. The best method 
to demonstrate this fact consists in injecting one 
carotid artery after having marked with ink the posi- 
tion of the motor centers ascertained beforehand by 
means of electricity.” 
Ferrier and his school, while not denying the dif- 
fusibility of electricity, claim that in their experi- 
ments its action can not be thus explained. Ferrier 
says:— 
“Irritation of the ventricular aspect of the corpus 12 
striatum causes general contraction of the muscles 
of the opposite side of the body; and it is impossible 
by applying the electrodes to the surface of this gan- 
glion to produce differentiated contraction in any one 
muscle of a muscular group.” “We know there- 
fore by direct experiment what irritation of the basal 
ganglia should produce; but the phenomena of irrita- 
tion of the cortex are of a very different order.” 
And again: “The great and significant feature of the 
reactions produced by electrical excitation of the 
cortex is that they are definite and predictable and 
vary with the position of the electrodes.” But there 
is no fact more strongly urged by the localizers than 
that of the differentiation of white fibers in the corona 
radiata and the internal capsule, and Ferrier would 
be the last to deny that could these fibers after 
differentiation be separately irritated, corresponding 
movements would ensue. In fact, this is far better 
established than is cortical differentiation. Dupuy 
claims that the electricity following the penetrating 
blood-vessels and being so circumspectly applied to 
the strands is capable of producing coordinated move- 
ments—and at least in his recent writings does not 
say that this irritation necessarily takes place in the 
basic ganglia. 
Another point that has given rise to controversy is 
the interpretation of the results that follow destruc- 
tion of the cortex. Having measured the strength 
of the minimum current that will produce motion, 
the cortex is sliced off and left in situ. It is found 
that on reapplying the electrodes a stronger current 
is required to produce the same movement. The 
localizers claim that in the one case the electricity 
acted physiologically, in the other physically, and 
point to the increased strength of the current as 
proof. Their opponents explain the necessity of the 
increased currents because of the two new surfaces 
which have been created and the coagulation that 
necessarily takes place in the cut vessels, and they 
moreover urge that no better proof can be adduced 
that the electricity acts by diffusion of current than 13 
the fact that motion will follow the application of 
electricity to the cortex, even after it has been mechan- 
ically separated from the brain and lies merely in 
apposition. Another fact that is claimed will substan- 
tiate this same view is that when the cortex is frozen 
it is still susceptible of electrical irritation, a statement 
which Ferrier denies but other and later authorities 
consider well established. 
Another experiment of Frank’s consists in freez- 
ing- the motor center and then irritating the hard 
frozen surface. It is found that whereas before the 
freezing the motor action in the limb was longer in 
duration than the current used, and was epileptic, 
and besides only occurred after a lapse of about six 
and one-half hundredths of a second, when the same 
current is applied during the frozen state, the time of 
reaction is only about four and one-half hundredths of 
a second and the contraction is only tonic. The 
claim is made from these results that the reaction 
time is greater (six and one-half hundredths of a sec- 
ond) when the cortex is not frozen, because it reacts 
physiologically and the time is shorter (four and one- 
half hundredths of a second) when the cortex is frozen 
because it acts physically. This I consider a very 
unaccountable interpretation; it is -unnecessary to 
state that the white substance, as well as the cortex, 
is influenced by the freezing process and the irrita- 
bility of both endangered and altered. 
These cortical destructions and alterations of the 
motor centers are, perhaps, the most important 
proof the localizers have brought forward, but they 
are by no means agreed as to the interpretation of 
experiments supposed to be identical. For instance, 
Ferrier destroyed the angular gyrus with resulting 
hemianopsia, and so placed the visual center in this 
region, but others have shown that this blindness was 
temporary, and placed this center in the occipital 
region, where the results of destruction seemed more 
permanent; but no experiment yet performed seems 
conclusive, for the reason that complete removal of 
the cortex without destruction of the underlying 14 
fibers in the higher animal is not possible, while in 
simple-brained animals even great destruction is well 
borne with but few motor or sensory symptoms. 
Here, however, the localizers claim that automatism 
comes into play and can not therefore be compared 
with brains markedly convoluted. 
Another objection to experiments of this kind is 
that when the brain cortex is mutilated the animal’s 
disposition is so entirely changed that no just deduc- 
tions can be drawn by comparing it with a normal 
animal, with whom at best we can not intelligently 
communicate. 
The true and only test as to the truth of this theory 
that has so far been applied is the observation of 
lesions in the human brain. Numberless cases are 
on record where cortical lesions have resulted in par- 
alyses and disturbances of the special senses. Cor- 
tical destruction of the motor region is often followed 
by paralysis; in the frontal lobe by mental weakness; 
in the occipital lobe by visual disturbances, and in 
the temporal bv deafness. Left-sided paralyses accom- 
panied by aphasia are frequently found to have their 
origin in lesions near the base of the third frontal 
convolution. On the other hand, equally well-defined 
lesions impinging on or completely destroying these 
centers have not resulted in corresponding deficien- 
cies. However, in the vast majority of lesions due 
either to a tumor, apoplexy or embolism, the lesions 
are not circumscribed, and as a rule the destruction 
involves so many important divisions of the brain as 
to materially interfere with scientific deduction. 
The importance of these researches is undoubtedly 
great, for they have opened up a new and fertile field 
for the experimenter and have added vastly to our 
knowledge of the physiology of the brain. On the 
other hand, they have been a basis for the justifica- 
tions of the many operations performed for the 
removal of localized growths or deposits in or on the 
brain, and as such their accuracy and diagnostic value 
are rightly questioned. Surgeons have interpreted 15 
these researches in a manner that conservative inves- 
tigators can not approve. 
Our medical journals are filled with accounts of 
operations which have either justified the diagnosesr 
or where the results were not so bad as to completely 
confound and condemn both the operator and the 
operation. Unfortunately the many unsuccessful and 
otherwise disastrous operations remain unreported. 
As regards tumors, even were the localizers able to 
absolutely and definitely point the way to the sur- 
geon, yet post-mortems teach us that at least 75 per 
cent of such growths could not be successfully re- 
moved; and were all the results of such operations 
known, characterized as many of them are by mis- 
taken diagnoses and surgical mishaps, 95 per cent 
would more nearly represent the proportion of the 
operations which are either useless or criminal fail- 
ures. Granting that 5 per cent of the operations 
result in improvement or cure, this small proportion 
does not justify the readiness with which such opera- 
tions are undertaken. But surgeons have gone 
further than this. Not content to interfere with 
pathologic cerebral tissues, they have opened brains 
practically normal, removed the recognized centers, 
and noted results. This has frequently occurred in 
the so-called Jacksonian epilepsy, where conscious- 
ness is seldom lost and only one limb or group of 
muscles is involved, and the relief occasionally follow- 
ing such operations for all forms of epilepsy has been 
falsely attributed to the removal of a growth or pres- 
sure rather than to the well-known per se effects of 
operations in general Some of our recent text-books 
have even gone further and advised exploratory 
incisions as an aid in diagnosis, as if the trephining 
of the brain was as simple a procedure as is the 
opening of the peritoneal cavity, or the results which 
follow healing as insignificant. 
While granting the advance made by experiments 
on animals in elucidating the physiology of the brain, 
the modern cerebral surgery based on this is not jus- 16 
titled, either by reason of the possibility of accurate 
diagnosis or the probability that the operation per se 
may benefit. The results of operations, even those 
selected for publication, are not encouraging, much 
less do they lead us to regard the operation as one of 
minor surgery.