Studies in the Osteopathic
The Physiology of Consciousness:
Louisa Burns, M.S., D.O., D.Sc.O.
CEREBRAL LOCALIZATION, SENSORY.
The part of the nervous system which is concerned
in those activities perceived in consciousness is that which occupies the
cerebral cortex. The cells of the cortex represent the highest development
of the neuron. They are best developed in man, and they are the first sufferers
when the nutrition of the nervous system is interfered with, or when poisons
are found in the circulating blood. It is true that certain poisons have
a selective action upon other cells of the nervous system, rather than
upon the cortical neurons; but, as a rule, those abnormalities which affect
the body at all, affect first the cells of the highest development, the
most specialized function, and the most rapid metabolism. These cells are
chiefly found within the nervous system, and the cortical neurons are most
highly developed, most perfectly specialized, and most energetic in metabolic
processes of all nerve cells.
Since consciousness is affected through the intermediation
of the cortical neurons, it follows that, so far as our present knowledge
goes, the physiology of the cortical neurons is the physiology of consciousness.
The functions of the cerebral cortex are localized
to a certain extent. The motor areas are very exactly defined—so exactly
that in certain cases this knowledge may be safely used in surgical procedures.
The sensory areas are less exactly defined. Sight, hearing and the somesthetic
areas are fairly well recognized; smell is less definitely limited upon
the cortex, while there is very little known concerning the localization
of taste. Other sensations seem to have no exact representation upon the
cortex, so far as our present knowledge is concerned.
Development of Localization
The placing of the different functions upon the
cortex rests upon some law which is not yet recognized. The beginning of
the cortical representation of somatic functions is found in the olfactory
cortex. The other somatic functions became represented at later periods
of development, but during the development among many classes of animals
the progress has followed practically identical lines, and the areas in
which certain functions are represented are the same for all classes of
mammals, except as the varying degrees of functional development of certain
areas may be associated with certain structural variations. It is not known
what relationship exists between functional development and structural
Apparently the different parts of the cortex are
practically alike at early stages of ontogenetic as well as phylogenetic
development. Yet areas which are practically identical become differentiated
into areas of specific function, or “specific nerve energies,” and these
areas are practically identical for all mammals. The problem thus presented
is not limited to nervous phylogeny and ontogeny, but it presents more
baffling puzzles, perhaps, in regard to nervous development than in the
development of the other structures of the body.
Given the placing of the primary sense areas and
the primary motor areas of the cortex, the development of the other part
s of the cortex seems logical enough. The areas adjacent to the primary
sense areas, the overflow areas, receive the effects of the stimulation
of the cells of these primary areas, and increasing complexity of neuron
relationships follows naturally enough. As the result of the increased
activity of the overflow areas, with the associated complexity of coordination
of nerve impulses, the stimulation and development of the intermediate
areas follows with equal facility.
The progressive assumption of the functions of coordination
by the overflow and intermediate areas is thus a matter simply of functional
relationships of the primary sensory and motor areas, and of the morphology
of the cortex itself. The conditions which modify the development of the
overflow and intermediate areas are apparent from the consideration of
the physiological relationships. In order that the overflow areas may be
well developed it is, of course, first necessary that the physiological
requirements of the cells themselves for normal nutritive conditions shall
be met; good blood, flowing freely under normal pressure, the efficient
removal of the wastes of metabolism, no less than the efficient feeding
and oxygenation of the nutrient fluids, are essential first of all to the
normal development of these areas. Given these physiological requirements,
the development of the primary areas depends upon their activity, and this
is dependent upon their stimulation. This is accomplished by means of the
sensory apparatus associated with each cortical primary area. The development
of the visual cortex depends upon the nerve impulses from the retinae;
the development of the auditory cortex depends upon the impulses from the
cochlea, of the somesthetic area, upon the impulses from the body, and
so for each of the primary sense areas of the cortex.
The development of the overflow areas depends upon
the activity of the primary areas, much as the development of the primary
areas depends upon the stimulation from the sensory apparatus. As the result
of the activities of the overflow areas the intermediate areas are stimulated,
and their development becomes possible.
The localization of the various functions of the
intermediate and overflow areas thus depends upon the structural and functional
relationships of the primary sensory and motor areas.
Localization of Overflow Areas
There is thus a certain localization of the associative
memories upon the cerebral cortex. The “overflow” areas of the sensory
and motor areas are functional in retaining within themselves, probably
as the result of variations in their functional activity, the effects of
any given stimulation. The effects produced upon these cells by stimulation
seem to be peculiarly far-reaching, so that subsequent stimulation in much
less degree suffices to cause the same or similar activity to occur again.
The activity thus initiated is associated with the conscious phenomenon
called memory. Memory is the consciousness associated with the activity
of neurons which repeat metabolic changes. The overflow areas are especially
adapted to the retention of the effects of metabolic changes, probably
partly because of their structural and physiological characteristics, and
partly because the overflow is larger than the primary area, and contains
cells variously related to the cells of the primary area. The overflow
areas are thus concerned in the associative memories of the activities
of the adjacent primary area.
Between the overflow areas there appear other areas
which give no response to cortical stimulation in animals, and whose injury
does not produce any marked symptoms in persons who are of deficient mentality,
or whose powers of classification are not well developed, whether they
are not capable of education, or whether they merely have failed to receive
education, in the broader sense.
These areas have been called “negative areas” or
“silent areas” for these reasons. It is probable that the term “intermediate
areas” is better, since this morphological term has no psychological significance.
There is reason to believe that these areas are capable of performing certain
functions when the demands of the higher civilization are made upon the
individual. Probably no person uses all of these areas. If the part of
the cortex which is unused by a certain person should be injured, no localizing
symptoms would follow the injury. But another person, in whom those particular
cells might happen to be well developed, suffering from that same injury,
would lose a large proportion of his powers of mentality, might become
insane, in fact. The fact that certain parts of the brain remain unused,
probably throughout life, accounts for the different result s of brain
injuries and diseases. The following cases illustrate the possibility of
serious brain lesions without recognizable localizing symptoms:
Localization of Lesions
Sachs and Berg, Medical Record, January 23, 1909:
Case of otitic brain abscess in woman. Symptoms were,
first headache, nausea and vomiting, not projectile. After that she seemed
more talkative than usual, but always apparently rational. About two weeks
later she complained of headache, and that day seemed to have forgotten
the names of the people in her home. She seemed able to talk freely enough,
but was unable to understand things said to her. There was at that time
slight rigidity of the neck, some right facial paralysis, some weakness
of right leg and arm. On the third day after this there was found some
paraphasia, but she was able to speak fairly well; she was not able to
understand the meaning of questions or commands. There was headache and
some somnolence. At operation an abscess containing more than two ounces
of pus was found about an inch below the surface of the left temporo-sphenoidal
R. D. Rudolph gave this case report before the Association
of American Physicians, Washington, D. C., 1909:
Woman of 46; symptoms had been those of neurasthenia.
There were “compression attacks” during the last six months of her life.
These were accompanied or preceded by blood-pressure rise from about 120,
the normal, to 200. The attacks were characterized by vomiting and profound
coma. She died in one of these attacks. At autopsy two tumors were found,
one growing from the pia mater over the left occipital lobe, the other
over the left brain just behind the ascending parietal convolution. There
were no localizing symptoms at any time.
Sachs, at the same meeting, gave this report:
A patient, a young man, had attacks of convulsive
seizures at intervals of three or four months. There were no other symptoms.
He died suddenly, and at the autopsy a large glioma was found occupying
almost the entire left hemisphere. It seemed hardly possible that no symptoms
should have appeared. The glioma had grown very slowly.
Many other cases are recorded. Injuries slowly produced
may be associated with compensatory activity of other parts of the cortex.
For the most part, however, the clinic records seem
to indicate that injury of any part of the brain is followed by a loss
of the function associated with that part of the brain. The lesions found
associated with those parts of the brain of more general function, and
lesions of parts of areas of broad extent, give symptoms of less exact
localizing significance than do lesions of small and definitely-located
functional areas. The functions which are performed by areas of broad cortical
extent are, for the most part, those of the earlier phylogenetic development.
The olfactory cortex is one of these areas.
The lack of localizing symptoms in cortical or ganglionar
lesions is due sometimes to the existence of pressure symptoms. The growth
of a tumor in any part of the brain increases the intracranial pressure
and lessens the blood supply to the entire brain. The pressure and the
lack of nutrition affect the functions of practically the entire nervous
system, since the abnormal condition of the brain affects the spinal centers
to a certain extent. Thus, the most prominent symptoms of brain lesions
may be characteristic of no particular area, and there may be even nothing
indicative of the brain lesions at all. Especially in the earlier stages
of the slowly-growing tumors, tubercles, etc., there may be difficulty
in making a diagnosis of brain lesion at all.
The primary visual area occupies the cuneate and
lingual gyri. In the human brain the visual area is placed rather more
upon the median aspect than is the case with animals. Because of the partial
decussation of the optic tracts, the retinal projection upon the cortex
is partially crossed in the human brain. The left occipital lobe receives
impulses from the left halves of both retinae; the right occipital lobe
receives impulses form the right halves of both retinae. The fovea of both
retinae is represented upon both sides of the brain. Thus, the injury of
the optic tracts at any point posterior to the chiasma is associated with
homolateral hemianopsia, with the loss of the contralateral fields of vision
and the retention of the field of direct vision of both retinae. The retina
is projected upon the cortex in an inverted manner, so that the lower right
half of each retina is projected upon the upper part of the right half
of the primary visual cortex , and the lower right half of each retina
is projected upon the upper half of the right primary visual area.
The Visual Cortex
The structure of this part of the cortex displays
certain peculiarities. The external layer of cells is not particularly
well developed. The external layer of large pyramids, found in practically
all parts of the cerebral cortex, are here represented by a layer of large
stellate cells, among which a few large pyramids, mostly atypical, appear.
The internal layer of large pyramids is present, and these pyramids are
really giant cells. The seventh layer of polymorphic cells is rather well
developed, both in the size of the cells and, in a certain degree, their
The association tracts from the primary visual area
are very intricate. This relationship of visual area is indicative of the
important place in life which the visual coordinations fulfill.
Fig. 8. Cell nest, from
human gyrus hippocampus. About 150 diameters. The cells are closely approximated,
with very small intercellular spaces. The more freely branching dendrites
of the pyramidal cells show similarity to the “tassel” cells of Cajal.
Whether there is any cortical area for the perception
of colors has not yet been demonstrated. The phenomena of color vision
present peculiarly baffling problems to the physiologist. The differences
between colors, from the physical standpoint, is comparable to the differences
between musical tones; that is, it should be perfectly proper to speak
of blue as a “higher” or a “faster” shade of red, or of yellow as a “lower”
or a “slower” shade of violet. Such ideas are primarily absurd in consciousness,
in which these colors are recognized as qualitatively different. The nerve
impulses carried by the optic tracts and the resulting activities of the
cortical neurons must be identical. How qualitative differences can be
based upon quantitative variations in vibration rate is most puzzling.
Origin of Visual Impulses
Visual impulses originate in the retina. The structures
of the eye are complex, and may be functional in causing considerable variations
in the nature of the impulses sent from the retina and from the essential
qualities of the objects seen; in other words, while the peripheral sense
organs are supposed to translate environmental qualitative and quantitative
variations into the language of nerve impulses, the eye seems to use considerable
latitude in the translation, so that a very “free” and idiomatic translation
may be made. Thus we have sent to the cortical areas the impulses concerned
in the consciousness of qualitative color senses based upon the quantitative
variations in vibration rate, that puzzling problem to which reference
has already been made.
Fig. 9. Terminations
of the olfactory tract fibers in the ala cineraes. Adult human brain. About
940 diameters. The cells of the ala cineraes are indicated by the dotted
lines; the fibers branching around them are from the olfactory tract.
Physiology of Visual Impulses
Primarily, vision is of a flat, plane surface. The
ideas of distance, form, size, space in three directions, and the other
ideas ordinarily supposed to be primarily derived by means of visual impulses,
arise as the result of the activity of the overflow and intermediate areas.
The Cheselden case was reported in 1727. A child
born blind was couched when he was between thirteen and fourteen years
of age. When the bandages were removed from his eyes he thought things
seen touched his eyes. He saw only plane, colored surfaces. Later, having
forgotten the name of a certain animal, he picked it up and said, “Puss,
so I shall know you next time.” The visual impulses seemed not to be associated
at first with any ideas of solid form, or of the names of things. Evidently,
the process of relating the activities of the visual areas to other areas
is a matter of a certain length of time.
A man, having been couched, began to see for the
first time. He experienced great difficulty at first in learning to eat.
For some time he found it difficult to restrain the fear associated with
the sight of an approaching fork or spoon toward his face as he fed himself.
Another patient, under the same circumstances, displayed the most active
delight in the colors first seen. Red, especially, filled him with a sort
of joy. He saw red roses upon a bush in the yard. He did not, of course,
recognize them, but he did so greatly admire their color that he was with
difficulty restrained from climbing out of the window in order to examine
them more closely. His incomplete coordinations failed to warn him of the
danger of climbing from a second-story window into a rosebush.
Fig. 10. Cells from
the human gyrus hippocampus, stained with iron hematoxylis. A. from the
hippocampus in general; B, cells of olfactory nest” adjacent to A. The
small intracellular spaces, and the close interfacing of the dendrites,
Such instances illustrate the fact that primarily
a colored surface only is seen, and that the complex knowledge we think
ourselves to receive by sight is, in fact, the result of the primary visual
sensations qualified and modified by the activities of the cells of other
areas of the cortex.
The Visual Overflow
The visual overflow surrounds the primary visual
area completely. Thus, the visual overflow is as extensive in comparison
with the primary visual area as it possibly could be. It neighbors the
auditory overflow toward the inferior part of its extent, and the somesthetic
toward its superior extent.
The structure of the visual overflow presents a type
intermediate between the structure of the primary visual area and that
of the typical cortex. The stratum zonale is very well developed and is
very rich in cell structure. The association fibers are plentiful. The
line of Bailarger is unusually well developed, both in the primary and
the overflow of the visual cortex. The great development of the fiber tracts
of this line is indicative of the great number and complexity of the relationships
of the visual impulses.
The cells of this area seem to be concerned in the
storing and reproduction of the visual memories. The stimulation of the
primary visual area by impulses of a sufficiently energetic or efficient
character causes the activity of cells of the neighboring overflow. The
activity of these cells, which probably include the cells of the stratum
zonale, affects their metabolism in such a manner as to lower their liminal
value. This decrease of liminal value appears to be permanent. Thus, the
reception of impulses from either the primary visual area or from other
cortical centers initiates their activity again. The initiation of the
activity of the neurons of the visual overflow areas by impulses from the
primary visual area is the origin of the visual memories; the stimulation
of the cells of the visual overflow area by impulses from other overflow
or intermediate areas causes the phenomenon of visual memories in consciousness.
Fig. 11. Cells from
human temporal lobe, about 200 diameters. A, same; M, inverted pyramids
The activities of the visual overflow areas are concerned
in the recognition of visual impulses as they are repeated. Together with
the areas intermediate between the visual overflow and the auditory and
somatic overflows, the ideas of solidity, distance, extension in three
directions and various other complex ideas are able to be interpreted in
consciousness. These are discussed more fully in connection with the somesthetic
and the language areas.
The primary and overflow visual areas give origin
to a number of tracts which relate the functions of vision and of visual
memories to practically all of the other parts of the cerebral cortex,
both of the same and the opposite sides. The very great importance of visual
images in intellectual development is thus apparent in the structure of
The environment is extended to the limits of vision.
This, alone, has great importance from the biological standpoint. Animals
are able to find food, and to protect themselves from danger much more
efficiently on account of the visual impulses.
By means of the visual overflow and the intermediate
areas the limits of the environment are indefinitely extended. The activity
of the intermediate areas, together with the effective motor impulses,
for example, invents lenses and other instruments, by means of which the
environment of civilized man is extended to the limits of telescopic vision
on one hand, and of microscopic vision on the other. By means of the intricate
and efficient fiber tracts of the cerebral hemispheres the impulses derived
from this infinite environment add to the wisdom and energy of living in
a sense almost beyond conception.
Visual impulses may be employed very efficiently
both in education and in therapeutics. Facts may be stated through the
intermediation of sight in a manner which affects t he activities of the
intermediate and motor areas speedily and energetically. The cartoon as
an educational factor owes its value to the fact that it presents its lesson
in a simple, concrete form, which stimulates the overflow and intermediate
areas much as they are stimulated by the presence of the objects pictured.
The moving picture is extremely efficient in a similar manner. Great harm
may be done by uncensored motion pictures.
The more highly developed the visual cortex is, and
the lower is the liminal value of the neuron systems which relate the visual
cortex to the other areas of the brain, the greater are the numbers of
associations which are concerned with the activities of the intermediate
areas and the resultant activities of the motor areas. These activities
are the basis for reason and judgment; hence, the more complex the visual
relationships, the wiser the judgments and the more efficient the motor
reactions of the individual.
In dealing with patients who are, for nervous reasons,
not so obedient as they ought to be, it is often possible to secure more
exact compliance with instructions if they are written. In dealing with
certain neurasthenic and hysterical patients it is sometimes a good thing
to give them “written orders.” These are merely instructions concerning
food, exercise, bathing, etc., written upon paper and sealed in an envelope.
Upon the outside of the envelope is written the hour at which the “prescription”
is to be taken. Such methods are efficient in certain cases. It is not
usually worth while to try to appeal to the “good sense” of hysterical
or neurasthenic patients who are not obedient to instructions. If they
had any common sense they would either obey the physician’s instructions
or go to some person whom they could better trust. But the use of such
methods of giving instructions in a manner which impels obedience and adds
the interest of curiosity is often a very good thing to do. The method
is especially adapted to children, and to adults of slightly deficient
The primary cortical auditory area occupies the central
part of the first temporal convolution, and probably the upper part of
the second convolution. (Figs. 11, 12.) The auditory overflow extends posteriorly
to meet the visual overflow of the occipital lobe, inferiorly to an extent
not yet defined, and anteriorly and slightly inferiorly into an area which
is concerned in the consciousness of musical tones. Neighboring the area
for the consciousness of musical tones lies another related area, which
may be called the musical overflow. In this area the memories of tunes
probably are stored and coordinated. No uncomplicated lesions are described
for the area concerned in the consciousness of musical tones or the memories
of tunes, but lesions involving these areas seem to affect the power of
appreciating tones and tunes. Persons so affected become “tone deaf,” and
this condition may occur without any loss of hearing as a primary sensation.
It is in harmony with the facts of physiological
action elsewhere in the nervous system if it should be found that people
who “have no ear for music” have the neurons of this area either undeveloped
or of faulty structure. The study of the brains of musicians is also needed
in order that such relationships may be determined.
The areas for the appreciation of musical tones extend
toward the olfactory areas. No associations are recognized between these
senses, as is the case between the visual overflow and the auditory overflow,
or between the visual overflow and the sensory overflow, but both are intimately
associated with the lower centers. The appreciation of noises does not
affect the emotional centers or the affective states, but musical tones
are very efficient in arousing emotional reactions. For this reason music
is employed as it is in social affairs, in churches, and under all conditions
in which it is desired to bring feelings into play.
No direct association path exists between the anterior
temporal area, the musical area, and the motor areas. The consciousness
of musical tones, the memories of tunes and the appreciation of the significance
of music arouse no marked motor reactions, but appear, on the other hand,
to inhibit whatever motor reactions might be aroused by the activity of
other cortical area. It is recognized that music exerts a restful influence
upon the body, that it is preeminently adapted to the quieting of those
who are inclined to listen with pleasure to it. The physiological basis
of this fact is to be found in the absence of direct paths for the transmission
of the impulses from the centers for musical tones and memories to the
Origin of Auditory Impulses
The auditory impulses originate in the cochlea. The
various structures which transmit the vibrations to the fibrillae of the
dendrites of the auditory neurons of the first order appear to modify the
amplitude and perhaps the force of the vibrations, but not to modify the
essential qualities of vibrations; that is, the vibrations remain as such,
and no structure appears to have for its function the translating of vibrations
into any other sort of reaction quality, as is the case with certain other
sensations. Sound waves are recognized as sound waves in physics, and the
physical phenomena of sound coincide with the auditory sensations in consciousness
sufficiently for us to realize the relationship between sounds as heard
and sounds as subject to the laws governing the vibrations which produce
The cells of the cochlea send axons as acustic nerves
to the acustic nuclei; these in turn send axons to the nuclei of the trapezoid
body and the superior olive, the inferior quadrigeminates and the internal
geniculate body. The axons of the acustic radiations transfer the impulses
thus carried to the first and perhaps the second temporal convolutions.
It is not known whether the impulses are transferred by means of all of
the nuclei mentioned or not. There is reason to believe that at least a
part of the lateral fillet fibers pass without relay from the acustic nuclei
of insertion to the internal geniculate body. There is no reason to suppose
that the medial fillet fibers, or at any rate more than a very few fillet
fibers, pass into the acustic radiations directly.
The Auditory Cortex
The auditory cortex differs slightly from that of
other cortical areas. Perhaps the most conspicuous difference is found
in the length of the radiations. These fibers extend into the external
layer of cells, instead of stopping in the neighborhood of the line of
Bailarger. The stratum zonale is rather less pronounced in the primary
auditory areas than in the auditory overflow. This structure resembles
that of the visual cortex and visual overflow.
The pyramids of the auditory area are not so large
as those of the motor area, nor as those of the internal layer of large
pyramids of the visual area. The external layer of large pyramids is well
represented; the pyramids are not so typical in outline as those of the
motor area, but the stellate cells of the corresponding layer of the visual
area are not found.
The length of the radiations, permitting the impulses
to be carried without relay to the cells of the stratum zonale, is the
basis for the fact that consciousness is so quickly affected by auditory
stimuli. It is a matter of common experience that a noise arouses attention
much more quickly than do other sensory stimulations. A flash of light
or an odor fail to attract the attention in so great a degree as do sounds,
and even when such stimuli are pronounced enough to arouse forced attention,
the reaction is less rapid than in the case of the sounds.
The same condition exists in the area for the appreciation
of musical tones. The enjoyment of music seems to be more directly primary
in its nature than is the enjoyment of the activities of other sensations,
except those of the body itself. Doubtless this depends in part upon the
length of the radiating fibers.
The primary auditory areas and the auditory overflow
which lies posterior to the primary area are closely associated with the
motor areas by the long tracts. Incoming auditory impulses affect the motor
areas quickly, as is evident in the phenomenon of attention and in the
relationships underlying the speech functions.
The locality where the visual overflow meets the auditory overflow
is concerned in the speech mechanism. Injury of this area may be so limited
as to interfere with the relationships of the auditory speech are and the
visual speech area without affecting in any very serious manner the activities
of either center acting alone or in connection with the motor speech area.
In such cases the power to read aloud is lost, and the power to write from
dictation. But the patient is able to copy from the printed page into writing,
or to repeat aloud the sentences spoken to him.
The biological value of the auditory impulses lies
chiefly in the facts, first, that the auditory radiations reach the stratum
zonale, and thus are able to arouse consciousness and motor reactions very
speedily, and, second, in the fact that the environment of the individual
is so greatly increased by the auditory impulses. The overflow areas are
less extensive than they are in the case of the visual cortex, and the
association tracts from the temporal lobes to other parts of the brain
are less complicated and widespread than in the case of the visual cortex;
yet the auditory are and its connections are of considerable importance
from a biological standpoint, as well as from the standpoint of their relationships
in the control of human life. The development of the auditory cortex depends
upon the stimulation of the cortical neurons by impulses from the lower
centers. The stimulation of the primary auditory area affects the cells
of the auditory overflow, including the cortical areas for musical tones.
The activities of the cells of the overflow area are associated with memories
of sounds and with the simpler coordinations of the significance of things
The activities of the cells of the overflow areas are associated,
in turn, with increased activity of the cells of the adjacent intermediate areas.
These are functional in the coordination of the impulses initiated by the overflow
activities, and are associated in consciousness with the correlation of the
memories and the abstract ideas built upon the auditory memories and the significances
of things heard.