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A critique of posturology: towards an alternative neuroanatomy?

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Abstract

Conclusions Is posturology, then critical? This was never its intention, it is solely its success which challenges and questions. All that has been said is so obvious that the only wonder is why it has not been said sooner. But since there appears to be a problem, why not survey it? And one is finally confronted with a project that is incapable of further division, the requirement to understand sensory integration in the certainty that anatomic thought must play a leading role therein.
Surg Radiol Anat (1991) 13 : 255-257
Editorial
Surgical'''
Radiologie
Anatomy
Journal of Clinical Anatomy
© Springer-Verlag 1991
A critique of posturology: towards an alternative neuroanatomy?
PM Gagey
Institut Médical de Posturologie, 4, avenue Corbera, F-75012-Paris, France
Posturology replies to the
question of Charles Bell
Offprint requests: PM Gagey
'
through which he is aware of the
inclination of his body and that he
possesses the capacity of adjusting it
and of correcting any departure from
the vertical. But what then is this
sense?'.
The desire to respond to this
question, so marvelously formulated
by Charles Bell, consituted the
attractive force that gave birth to
posturology: a slow birth since it
involved the abandonment of inap!
propriate questioning, a slow birth
since it was a long wait for the
necessary technological advances. But
since the 19th century men have
sought passionately for the sense that
stabilises us in our environment and
have found it a plurality. There is
vision, since Romberg's patients fell
only when they closed their eyes;
there is sensation in the lower limbs,
again Romberg; there is the vestibular
sensation of Flourens but also
'muscular sensation': in 1850, Longet,
a pupil of Claude Bernard, showed
that section of the nuchal muscles
destabilised his animaIs as much as
the labyrinthectomies of Flourens'
pupils. Finally, there is oculomotor
information, for weIl before the end of
the last century Cyon demonstrated
the destabilising
effects of his spectacles with pris!
matie lenses placed before the eyes of
pigeons!
The quest for a postural sense was
fruitful in the 19th century, perhaps
too fruitful. The researchers sought
one sense and found several, and this
seems to have disconcerted them since
there was no sign of an attempt at
synthesis.
One man, however, in the middle
of the 19th century, opened a way to
the answer by changing the problem:
instead of seeking too hasty an
explanation of the mechanism that
keeps a man upright, he simply began
by seeking to observe and describe
this upright position itself.
Unfortunately, Vierordt, in the Ber!
lin of the 1840s, had available only a
pen attached to the spikes of his
soldiers' helmets, which scratched a
sheet of smoked paper. The signal
recorded, a mere scrawl, was very
difficult to interpret and, what was
worse, this technique modified the
phenomenon observed by adding
cephalic interference. AlI Vierordt's
rivaIs, and they were many : Mitchell
SW 1886, Hinsdale R 1887, Bullard
WN 1903, Hancock JA 1894, Bolton
JW 1903, Miles WR 1922, Fearing FS
1924,
256
Latmanizova LV 1931, Hellebrandt
FA 1938, Edwards AS 1924, Gold!
berg L 1943, to mention only the
more important, encountered the
same difficulties however ingenious
their apparatus, until the day when
progress in electronic and computer
technique made it possible to record
the phenomenon without modifying
it and to analyse the signal. We now
know how to investigate the control
of orthostatic posture and its varia!
tions under the influence of various
factors. Today, posturology is able
to answer Charles
Bell's
question
by supplying a simple and coherent
model validated by a satisfactory
series of experiments : the model of
the fine postural system.
The fine-tuned postural system
It is impossible for a man in the
standing position to control small
variations in position in relation to
the environment without the aid of
sensory organs related to that envi!
ronment: the retinae, the utricular
and saccular maculae, and the baro!
receptors of the soles of the feet are
the 'exoceptors' of the fine postural
system. At the moment we do not
know of any others.
But the eye moves in the orbit
whereas the vestibule is enclosed in
the petrous block, and the informa!
tion supplied by these two organs
can only he used conjointly by the
system if it has available comple!
mentary information as to the reci!
procal position of these exoceptors.
The position of the retina in relation
to the macula of the utricle can be
supplied only by the oculomotor
system. There thus appears the
concept of a particular captor of the
fine-tuned postural system, the
'endocaptor', without direct rela!
tionship with the environment and
yet essential to monitoring of the
orthostatie posture. The same reaso-
'
ning applies to the plantar exocep!
tors in relation to the cephalic exo!
ceptors. The feet enjoy a great
many degrees of freedom in
relation to the head, and the
position of the various parts of the
skeleton from the occiput to the
bones of the tarsus and metatarsus
must he relayed to the system by
the other, proprioceptive,
endoceptors to provide awareness
of the reciprocal position of the
cephalic and plantar exoceptors.
The mass of information sup!
plied by these exo- and endoceptors
is considerable and yet aIl this
information must he integrated and,
what is more, in real time or else
the man will become unsteady. The
quality of postural control depends
not only on good functioning of the
different receptors and of their cen!
tripetal routes, but also - even espe!
cially - on sensory integration. The
most evident quality of the control
of orthostatic posture is the fineness
of its precision, which is demons!
trated by posturographic recordings.
Every normal standing motionless
man maintains his line of gravit y
within a cylinder of barely a square
cm in section. Such fineness of pre!
cision postulates discrimination of a
particularly high acuity, the attribu!
te of low-amplitude movements, as
has been known for the neuromus!
cular spindles since the studies of
PBC Matthews and, for the oculo!
motor muscles, since the work of
lB
Baron. Movements of high
amplitude are not controlled with
the same fineness. Only the organi!
sation that presides over the control
of orthostatic posture and of mini!
mal postural oscillations deserves to
be characterised as a fine-tuned
postural system. Beyond a certain
limit of destabilisation, return to the
position of equilibrium is gover!
ned by another system: the semicir!
cular canals then come into play,
the bonds of muscular thixotropy
are broken according to EG Walsh,
PM Gagey: A critique of posturology
and the neuromuscular spindles
respond more feebly.
The posturographic study of uns!
table subjects confirms this distinc!
tion by isolating two populations of
patients: one that functions by its
fine-tuned postural system, howe!
ver deranged it may be, the other
not.
There should be no confusion in
this matter. The behavior control!
ling orthostatic posture is a particu!
lar hehavior specified by identified
neurophysiologie responses, and
deserves a name: it is the behavior
of the fine-tuned postural system.
Naive posturology
The fine-tuned postural system is a
model on the route pursued by pos!
turology, one constructed over the
years to express its research, quite
simple and sincerely, without taking
account of when it hecame a' threat
to other medical disciplines such as
anatomy and clinieal neuro!
anatomy. For when posturology
speaks of a 'system', it is really uti!
lising the concept of the theory of
compulsion, ie of the 'black box'
which contains no-one knows what,
which can be as complicated as it is
possible to imagine, of which one
knows only what goes in and what
comes out, and whose transference
functions can be studied. That the
central nervous system should be
regarded as a black box is to make a
mockery of the remarkable studies
of generations of anatomists!
It
means a break with the most funda!
mental bases of clinieal neuroanato!
my, in opposition to a long, respec!
table and effective tradition.
It may still he accepted that, in
this sense, posturology is 'non-neu!
rological' - everyone is entitIed to
pursue his fantasies - but it is clear
enough that the epistemologic bases
of posturology are serious and
PM Gagey: A critique of posturology
undeniable, that what it has to say
also falls within a long cultural tra!
dition, and it even seems to display
a clinical and therapeutie effective!
ness. Posturology is working well!
It is a naive posturology that allows
itself to appear so critical.
Possibilities for a critique
On this basis there would be no
possibility of reestablishing a dia!
logue between clinical neuroanato!
my and posturology unless each
contained its faults.
It is unacceptable to renounce
altogether any understanding of the
'black box'. Hence, posturology
necessarily appears to be marked
out as of historical nature, to be
only a stage. Even if this stage is
presently essential, we should not
bluff and disguise our ignorance of
the anatomy of the central nervous
system. Sooner or later posturology
will rejoin the royal road of anato!
mo-clinical neurology, provided
only that the latter also corrects its
inexactitudes, For neurology takes
as the foundation of its principles
the concept of the 'lesion', yet in the
era of the electron mieroscope and
stereochemistry it may weil be
asked what a lesion is. How are we
entitled to refuse the term 'lesion' to
a disorder that decimates only one
part of the population of the
neurones of the brainstem nuclei:
,
.
the nuclei of III, the red nuclei as
regularly seen in animals subjected
to craniocervical injury , or the ves!
tibular nuclei as has been described
in man in post-concuscional syn!
dromes? And suppose only the
mitochondria have disappeared? Or
if
it
is a neuromediator that has
been deprived of a radical? Where
are the bounds of the concept of the
lesion? The dichotomy we still per!
ceive between functional and lesio!
nal disorders is based on habits of
thought rather th an on critical
thought. We must agree to a change
of scale in our view of the central
nervous system: what was an enor!
mous advance in the 19th century
should not block our present pro!
gress. We need another dimension
for the anatomy of the central ner!
vous system.
Towards an alternative
neuroanatomy
Current studies in posturology
underline the importance of sensory
integration, and particularly of its
derangements in postural disorders.
This means that attention is no lon!
ger focussed on the nervous path!
ways and centers but on the neu!
rones and their dendrites, the sites
of nervous integration. And we no
longer need the histology of Ramon
y Cajal but a new study of the neu!
rone, fertilised by the essential
257
concepts of anatomy: cranial and
caudal, ventral and dorsal, right and
left, and the Euclidean dimensions,
the patient geometrie application to
measure the neurone in its relational
space. For the temporal series of
events which take place at dendritie
level are surely dependent on these
geometrie conditions. The waves of
depolarisation progress here and
there on the dendrites and encounter
each other or not at their bran!
chings for strictly spatio-temporal
reasons. An awareness of the geo!
metric anatomy of the neurones is
necessary even if, as we may sus!
pect, the evolution of the temporal
series hold surprises for us in their
caprices. No doubt, this anatomy
will usher us into the fractal domain.
Conclusions
Is posturology, then critical? This
was never its intention, it is solely
its success which challenges and
questions. All that has been said is
so obvious that the only wonder is
why it has not been said sooner. But
since there appears to be a pro!
blem, why not survey it? And one is
finally confronted with a project
that is incapable of further division,
the requirement to understand sen!
sory integration in the certainty that
anatomic thought must play a lea!
ding role therein.
... Conversely, knowing the properties of non-linear dynamic systems, it can be assumed that changes in the temporal series of chained events affecting the central nervous system have consequences for the individual, especially if these changes are minimal [1] . ...
Article
If I place an orthoses beneath a limited area of the plantar sole, I must accept the idea that this limited area of the plantar sole comes into contact with the ground before the neighboring areas. It is then possible to accept the hypothesis that this time lag between the ground contacts of the different zones of the foot sole introduces a temporal shift of the sensory messages emitted by the plantar sole. If this temporal shift of sensory messages does exist, which is not proven, then the placement of an orthoses beneath a limited area of the plantar sole alters the time series of events affecting the central nervous system. This modification may — must (?) — vary according to the height of the orthoses, which of course changes the time difference it causes.If I place an optical prism in front of an eye, I change around the direction of the visual space perceived by that eye. Whatever the mechanisms used by the central nervous system to compensate for the sensitive and sensory incoherencies produced by this displacement of the visual space, one is entitled to logically attribute them a temporal component since it is a displacement (sooner or later my foot touches the marks of this new visual space).It can be assumed that these changes in the temporal series of events affecting the central nervous system have no consequences for the individual, especially if these changes are minimal.Conversely, knowing the properties of non-linear dynamic systems, it can be assumed that changes in the temporal series of chained events affecting the central nervous system have consequences for the individual, especially if these changes are minimal [1].Until now, as far as we know, only a few researchers have tested this latter hypothesis, among human beings [2 - 6] or animals [7]. The conclusions of their works make it possible to propose this statement to criticism: « The regulation of the postural tonic activity of a subject can be modified by a minimal modification of his interface with the environment. »As this statement implies therapeutic potentialities, so long as it is not falsified it will represent a certain irruption of time in the neurological therapeutic thought, traditionally a little frileux and stuck within its spatial representations
... instruction donnée au sujet (Zok et al. 2008), position des pieds, distance de la cible visuelle (Gagey 1991a)), signalant le manque de normes internationales qui faciliteraient la comparaison des valeurs entre les études (Visser et al. 2008). ...
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