[Editor's note: These excerpts from Elie de Cyon's book represent, to our knowledge, the first emergence of the role of the neck muscles and of the oculomotor muscles in postural control]
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(...) When I started my experiments on the
motor deficiencies that, according to Flourens' data, generally
occur following lesions of the semi-circular canals, in the head
muscles as well as in the body ones, I felt it necessary to begin
by determining the nature of those motor deficiencies: co-ordination
disorders or innervation disorders? Following that line of thought,
I first had to answer the question concerning the measure in
which an abnormal attitude of the head is likely to disturb the
animal's sense of balance [Editor's note: our emphasis]
and induce motor anomalies.
We already had, on that subject,
Longet's very interesting experiments dating back to the forties,
but which have since almost fallen into oblivion. Longet showed
that the occurring motor deficiencies are not linked in any way
to the discharge of the cerebro-spinal liquid, but constitute
a secondary phenomenon, consecutive to the cutting of the nape
muscles during the operation. And indeed, whenever Longet merely
severed those nape muscles, without opening the vertebral canal,
he immediately observed the same phenomena. Furthermore, those
phenomena were completely absent whenever he let the cerebro-spinal
liquid discharge through a small opening made at the level of
the occipital ligaments without causing more or less significant
lesions to the nape muscles. Longet explained his experiments
by claiming that the unusual attitude of the head following the
cutting of the nape muscles had the immediate consequence of a
loss of the sense of balance, but that such loss would be the
cause of the ensuing motor deficiencies. To achieve the same
result, it is not even necessary to sever all nape muscles.
The cutting of the posterior right muscles is amply enough to
make the animal's gait insecure and unsteady.
When I reproduced Longet's experiments,
I easily observed the phenomena he had described. Right after
the cutting of the right muscles of the head, the big and the
small posterior ones, a sway on both sides appeared in most dogs.
When forced to walk, they spreaded their legs, most of them walked
very slowly, their head slightly bent down. Those animals put
their paws on the floor extremely cautiously and always in order
to spread the front paws as far as possible from one another.
When running, which was very hard for them, the animals often
fell, and they needed some efforts to rise to their paws again.
Such phenomena generally disappeared after five or six days -
the head, until then leaning on the chest by the chin, took back
its normal attitude, and at the same time the walking movements
became normal as well.
The fact observed by Longet, as well as the conclusions he drew
from it, have been fully confirmed and the importance of a normal
attitude of the head for keeping one's balance came into light.
If the observed balance disorders and the motor deficiencies are
not as important as after the cutting of the semi-circular canals,
neither should we forget that the changes brought to the attitude
of the head are far from reaching the same degree as in that last
operation.
A second series of experiments,
initiated by the same line of thought, had consisted in artificially
giving to pigeons, without causing any lesion of important parts,
an attitude of the head similar to that we observed most of the
time following the destruction of the semi-circular canals. That
fairly complicated attitude is characterised by the fact that
the beak is directed upwards and the occiput, on the contrary,
downwards, usually towards the ground. The animals can easily
be given that attitude of the head, by fixing the head to the
sternal region with a few cutaneous stitches. The animals whose
head is fixed that way behave exactly like those whose semi-circular
canals, horizontal as well as vertical, have been destroyed -
they cannot keep their balance, and as long as they are standing,
they keep staggering on both legs and try to find a third point
of support by leaning on their tail. But they mainly fail to and
fall backwards, often over the head, around the transversal axis
of the body. They also perform roundabout movements, mainly in
the same only way. In short: we observe in them very acute disorders
in the whole locomotion sphere. Once the stitches are removed
and the head has a normal attitude again, all disorders immediately
disappear and the locomotion goes back to normal. Those experiences
therefore show very clearly how much a normal attitude of the
head is important for the animal to be able to keep its balance
and to perform rational movements.
But during a shift of the head such
as the one occurring in such experiments, our judgement on the
origin of sound is not less wrong than that bearing on the position
and the distance of objects seen. Now, the following experiment
showed with all possible evidence that errors in visual perceptions,
at least when they happen suddenly, can have the effects of
an insecurity in the walk and disorders of the sense of balance.
I fastened in front of the eyes of a pigeon a pair of prismatic
glasses - the animal thus affected by an artificial strabismus
then showed a series of motor deficiencies that present very clear
analogies with the disorders observed following the cutting of
the semi-circular canals. In some cases of such strabismus, the
sway movements of the head correspond to those occurring after
the cutting of the two horizontal semi-circular canals. In one
of the pigeons affected by artificial strabismus, I observed,
during the first moments, roundabout movements. Errors in visual
and auditory perceptions therefore seem to be the most important
of all those here considered.
[Editor's note: The following excerpt may well explain why
Elie de Cyon's works have not been given the importance they deserved]
As may be concluded from the preceding
lines, my conception of the role of head movements in the physiological
functioning of the semi-circular canals completely diverged from
that of Goltz. Goltz saw the starting point of that functioning
in the alleged shifts of the endolymph of the canals
during the various head movements. Head movements would therefore
act as real excitation means. In my conception, on the contrary,
as I expressed it as early as 1873, those motor deficiencies would
be the direct consequence of errors in visual and auditory perceptions,
which are supposed, in normal conditions, to inform us on the
situation of objects in the exterior space and on the position
of our body in that space. Then if the attitudes of the head play
any role in the functioning of the semi-circular canals is concerned,
it is only as far as they help us avoid errors in those perceptions.
Carrying on with my experiments,
I developed that perspective even more and I supported it with
the important observation that we can observe the most acute balance
disorders in pigeons, in the absence of any sway movement of the
head. I will deal with that question more thoroughly in the following
paragraphs - let me just add here that many experiments carried
out later by Bornhardt, Spamer, Ewald and I have also shown the
inconsistency of Goltz's theory, concerning the currents of the
endolymph.
[Editor's note: The following excerpt represents a first sketch of clinical study of the neck reflex, fifty years before the publications of Tadashi FUKUDA who, before 1980, did not know this work by Elie de CYON]
(...) After a
few preliminary researches, I finally gave preference to the following,
very simple, method. A sheet of paper is carefully fixed on an
exactly vertical board, at level of the head of the person submitted
to the experiment. That person is standing, blindfold, and draws
horizontal and vertical lines with a pencil and a ruler. Even
if all the subjects were blindfold, all drawings have been executed
in a completely dark room. The subject begins by setting the ruler
in the direction he considers horizontal or vertical. We must
take care that the ruler and the hand that holds it are taken
off the paper as soon as a line has been drawn. The same goes
for the right hand and the pencil. That way, we are sure that
any new direction drawn is not under the influence, by mediation
of the hands, of the line previously drawn.
For the reproduction of sagittal or transversal directions, we
fixed the sheet on a table the surface of which was exactly horizontal
- the subject was sat, his head and the superior part of his body
upright. We will describe later (§ 6) the experiments performed
in order to know if the straight lines thus drawn really correspond
to the sagittal direction. A discussion on the mode of interpretation
of the drawings obtained will also be given then. Those drawings
allow us to measure exactly the changes that the imposed conditions
of the experiments bring to the three factors we have just evoked.
The mere aspect of the drawing already provides information on
the way of the error in each direction.
In order to measure that error,
we just have to draw on the sheet of paper, after each experiment,
the normal direction. The angles formed by the two verticals with
the two horizontals, etc., generally correspond to the intensity
of the error. Most of the time we know that intensity thanks to
the mere aspect of the intersection point between the vertical
and the horizontal lines, or the sagittal and transversal lines
drawn in the dark - we just have to measure the width of the angle
those lines respectively form with one another. However, the widths
of the angles that are systematically indicated on the drawings
must not be considered as the absolute measure of the intensity
of the errors. The first experiments have notably shown that the
intensity of the errors, in the same experimental conditions,
is not necessarily proportional to the widths of the angles. It
also happens that those widths do not always precisely indicate
the way of the error. But even in the case when the way of the
errors is identical and when their intensities are proportional
to one another, the widths of the intersection angles cannot always
help measure such intensities - the latter can stay equal to 90°
or slightly under 90°, whereas the error has been very important.
Those angles widths notably inform us on the relations existing
between the errors in the various directions, that is to say on
the most important factor and , for us, the most instructive.
The study of the errors of direction in man is of the utmost interest,
most of all because it can give us information on the mechanism
of the formation of our representations of time and space. The
fact to know in which way we make an error, under given circumstances,
on one direction or another, is certainly already interesting
in itself, but that does not tell us in which organ the sensations
of direction are formed, or how our representation of a tridimensional
space is created from the perception of the various directions.
[Editor's note: "Person C", whose test results de Cyon then presents, is no other than de Cyon himself, which accounts for certain incoherence between his results and those now described from statistical studies]
§ 4 - Errors of perceptions of the vertical and horizontal directions, during the rotations of the head around its sagittal axis.
The errors of
perception occurring in the oblique positions of the head, and
more particularly when it is bent on the right or left shoulder,
have already caught the scientists' attention.
(...) The study of the influences that the head rotations, and
consequently that of the two labyrinths, have on our perceptions
of direction, is of a particular interest. During the reproductions
of Aubert's experiments by Nagel, Sachs and Meller, etc., it already
appeared that the degree of inclination of the head on the right
or left shoulder is likely to have an undeniable influence on
the production of the error, as well as on the intensity of the
apparent obliqueness of the vertical line in the dark (fig. 1).
FIG. 1 - Person C
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§ 5 - Errors occurring during the rotations of the head around its vertical and horizontal axes.
We will first
reproduce a few figures showing the more frequent errors observed
during the rotations of the head around its vertical axis. As
we can see, the vertical lines but slightly deviate from the normal
direction, at least no more than in the dark and with an upright
position of the head - the deviation goes the same way for the
two rotations, and that way coincides with that of the error which
I generally make when drawing in darkness, even with my head upright.
As I have just said, I usually make the same deviation from the
vertical line, even if to a lesser degree, when drawing in the
light.
The horizontal lines suffer, mostly
during the rotation of the head to the right, a more considerable
deviation, but that deviation is still going, during the rotation
of the head to the left, the same way as when the head is held
upright. Figure 9 shows the deviations I make, when the body
turns around the vertical axis at the same time as the head,
that is to say in such a position that during the rotation to
the left, the right part of the body, and during the rotation
to the right, the left part of the body, is in front of the sheet
of paper designed to be drawn on. As we can see, the deviations
from the directions then go exactly the same way as when only
the head turns.
FIG. 9 - Person C. Rotation of the head and of the body around the vertical axis. During the rotation to the right the deviation of the angle is of 10°, the rotation to the left of 2°. |