Some physicians from southern Europe
have been using the expression: «Fine Postural Control System»
without giving well defined limits for the meaning of this new
concept. Wise way of doing, indeed, that lets a great flexibility
for the expression of ideas at work! But nowadays the notion of
Fine Postural Control System is being critizised, then to avoid
fighting windmills it is necessary to adopt a definite position,
to take time writing - or reading - what does this expression
mean.
Using the expression:
«Fine Postural Control System» we simply want to say
that postural control adapts itself to the various behaviors of
man: if he is walking or quiet standing, mechanisms implied in
his postural control are not the same.
Man, indeed,
controls his position in his environment according to a fundamental
operational scheme, common to all behaviors:
But this global scheme may be modulated. Adaptation
of postural control to quiet standing, specified by this behavior,
is characterized by:
Dominance of tonic muscles activity
It
is almost a tautology saying that tonic muscles activity is predominant
in the course of a behavior that is not accompanied by movement!
But clinical corollary of this tonic dominance is not as evident
and deserves being told. When the system that controls tonic activity
for quiet standing is unsettled, then one can expect not only
difficulties for standing upright - as instability, dizzinesss,
vertigo - but also abnormal mechanical constraints at various
joints of the body axis, due to an abnormally asymmetrical distribution
of the tone, and bringing about pain of this body axis.
Discontinuity of the functioning of inputs of the postural
control system
Three
inputs of the postural control system present discontinuities
of their functioning between rest and movement behaviors: the
vestibular input, the proprioceptive input and the plantar exteroceptive
input.
The silence of the semicircular canals
Theoretically,
if there was absolutely no movement, accelerations that act on
the vestibular apparatus would be reduced to the acceleration
of gravitation alone, perceived by the otoliths, solely. Thus
between behaviors associated with movement and the behavior of
quiet standing there is a possible major discontinuity of the
functioning of vestibular input of the postural control system:
semicircular canals hush. And this theoretical discontinuity is
confirmed by experience: postural sway during quiet standing produces
accelerations lower than semicircular canal threshold.
Canals functional
examination does not allow to predict capacity for quiet standing.
The spindles gain
Discharge
frequency of neuromuscular spindles is not a linear function of
their stretching. Ratio of this discharge frequency to stretching
- the «gain» of the spindles - is discontinuous, much
more higher - up to ten times - for stretching of about one tenth
of millimeter than for stretching of about one millimeter. And
biomechanic measurements show that displacements of the center
of pressure during quiet standing normally bring about muscular
stretching closer to the tenth of millimeter than to the millimeter
as during walking. This discontinuity of the neuromuscular spindles
gain confers a particular importance to proprioceptive inputs
in the course of quiet standing.
The duration of exteroceptive plantar information
The duration
of exteroceptive plantar information is modulated by the behavior
adopted by the subject. One knows pretty well the rolling of plantar
support in the course of a step, it is not a simple left foot
right foot alternation, but it goes from the heel to the external
edge of the foot before it returns to internal side, finishing
on the first row. Nothing such in the course of quiet standing,
instead of the discontinuous duration of plantar exteroceptive
information, characteristic of walking, succeeds a relative continuity
in the duration of plantar information. Due to this discontinuity
of plantar information during walking it can be thought that the
postural system seeks its landmarks from the «inertial guidance
platform» according to the pretty term used by Berthoz to
designate the set of cephalic inputs. But during quiet standing
the postural system can also trust continuous plantar exteroceptive
informations and apparently it does so.
The predominance of feedback loops
When
he is walking and mostly when he is running, man must look ahead
to see possible obstacles and anticipate his avoiding reactions.
Thus, according to this image, in a dynamic behavior it is necessary
to anticipate, more than in a resting behavior. We do not know
if it is mathematically possible to formalize this need of anticipation
for controlling balance of human body in dynamic situations. But
we do know that stabilizing the body mass of a quiet standing
man is a far more simple mechanical problem, largely resoluble
by the feedback loops of a second order system.
This predominance
of feeback loops in quiet standing behavior accounts for the prevalence
of «chaotic pathologies» when this behavior is unsettled,
because recursive systems are submitted to chaotic risk. Solutions
of a recursive equation can be straight, periodic or chaotic according
to the values of its coefficients and a minimal modification of
a coefficient suffices to switch from a straight solution to a
chaotic one (Lorentz's butterfly effect).
Therefore
the model of the Fine Postural Control System introduces a new
etiology that completes the topologic etiology of the Charcot's
anatomo-clinic model. Beside the «lesions pathologies»
of the end of the XIXe century it is necessary to put the «chaotic
pathologies» of the end of the XXe century. Functions of
the central nervous system are not built according to infallible
logic, their logical structures, in some cases, can fail and entail
appearance of nervous illnesses without lesions.
History of the Fine Postural Control System
The dialectic of Charcot's model
History
of the Fine Postural Control System begins with Charcot. When
in 1860-70, indeed, this physician decided using the correspondence
between the topology of a lesion and a symptomatology to describe
illnesses of the central nervous system, on account of his decision,
he excluded illnesses without lesions from his nosology.
The reducing
aspect of this decision probably escaped neither Charcot himself,
nor his students. At least ulterior debates or documents on hysteria,
pithiatism, reflex nervous disorders, etc. can be interpreted
as attempts, unfruitful, to answer the irritating question raised
by these illnesses without lesions, rebels to the Charcot anatomo-clinic
model.
The Intersubjectivity base for objectivity
The
first world War 1914/1918 unlocked the reflection of Charcot's
followers, a little bit embarrassed in futile and ill-timed discussions,
by asking them a question, precise, concrete and heavy of human
consequences: What is to be done with soldiers who suffer from
head trauma? Do they want to escape trenches - or firing squad
- by alleging all their unreal complaints? The question was serious
enough to put it on the program of the 6 and 7 April 1916 meeting
of the Société de Neurologie with the Minister of
Armies. During this meeting a consensus came out of speeches from
all participants, and what participants: Pierre Marie - the reporter
- Babinski, Froment, Villaret, Sicard, Guillain, Lortat-Jacob,
Clovis Vincent, Roussy, Laignel-Lavastine, André Thomas,
Grasset and other fathers of the neurology. They explicitly said
that «descriptions by all subjects were absolutely identical,
made with the same expressions». This sameness between speeches
of patients bred intuition that «something is going wrong»
after a head trauma, something that physicians are not able to
call, then, but that is not hysteria or pithiatism.
Unanimously,
intersubjectivity is accepted as the base for objectivity of the
«subjective syndrome of head trauma», as they said
at this time.
Objective bases of the Post-Concussional Syndrome
This
meeting of the Société de Neurologie laid the foundations
for researches on objective bases of the Post-Concussional syndrome.
Effectively, during the next months after this meeting, were published
many papers on the relationship between canalicular function and
Post-Concussional syndrome. But this track turned out to be unfruitful
and it was necessary waiting for years and multiplication of researches
in fields as different as biomechanics, anatomo-pathology, histo-pathology,
stabilometry and postural clinical examination before it becomes
obvious that the Post-Concussional syndrome is the prototype of
Fine Postural Control System illnesses (See on this site: Articles
anciens / Le Syndrome Post-Commotionnel, cinquante ans d'évolution
des idées).
The prototype of Fine Postural Control System illnesses
Works
on the Post-Concussional Syndrome have been the crucible where
the notion of Fine Postural Control System has been forged, for
two reasons:
On one hand,
they have shown that the Post-Concussional Syndrome, clinically
very different from disorders of dynamic balance, is in fact an
unsettled state of quiet standing,
On the other
hand, they have revealed the «butterfly effect», characteristic
of «chaotic pathology», on the basis of the Post-Concussional
Syndrome and of its treatments.
Vestibular Neuritis and Post-Concussional Syndrome
Well
before stabilometric studies on the Post-Concussional Syndrome,
NeuroOtologists identified and described disorders of dynamic
balance as Vestibular Neuritis, for instance. And as early as
in 1935, Rademaker noticed that these patients, after the initial
tornado, were unable to walk on a rail but entirely able to execute
normally a Romberg's test. From this early stage of neurootology,
one could have thought already that vestibular functional tests
do not allow to predict the capacity of a patient for quiet standing.
Reciprocally
studies on the canalicular function in the course of Post-Concussional
Syndrome have always shown that it was normal but, before stabilometry,
physicians were unable to know that the behavior of quiet standing
is statistically abnormal after minor closed head traumas.
Physicians
have always understood that the Post-Concussional syndrome is
not a Vestibular Neuritis, there is no need of a great clinical
sens to distinguish them! But today, owing to the extension of
our observation capacities, we cannot prevent us from designating
disorders of different behaviors behind each of these different
illnesses.
The «Lorentz Butterfly Effect»
On one
hand this difference seems obvious yet, on the other hand, it
seems difficult to admit, why? Is it because physicians, reasonably
convinced of the power of Charcot's model, would want to see a
tangible proof, a true «lesion» of the Post-Concussional
syndrome, a real basis for this disorder of quiet standing behavior?
It is not shown, indeed. The only histopathologic documents presented
do not weigh enough: how to accept that the destruction of some
neurons, here and there in some brainstem structures, bring about
this tornado of symptoms that characterizes the Post-Concussional
syndrome? And doubt redoubles when postural therapeutic processes
are evoked: the wearing of optic prisms as weak as only one or
two prismatic diopters, the wearing of a bite as thin as a few
tenth of millimeters between teeth, putting of reliefs not thicker
than a few millimeters under the plant of the feet Everywhere
in the Post-Concussional Syndrome, as in the other postural pathologies,
you find this lack of proportionality between causes and effects;
lack of proportionality that is called «non-linearity»
in mathematics, «chaos» in some cases.
Accepting,
recognizing what has been observed is heavy of theoretical consequences,
here. Not only one accepts that the postural system that controls
the quiet standing behaviour is a non linear dynamic system, but
also one postulates that could exist another etiology than the
anatomo-clinic one for illnesses of the central nervous system.
A cause hidden in the faults of recursive systems. The logic of
these systems, indeed, makes that a minor modification of one
of their parameters could bring about consequences without proportionality
between causes and effects. «A butterfly beats his wings
in Brazil and a tornado is released to Texas» said Lorentz.
Conclusion
Charcot
was right using his anatomo-clinic model to put some order between
illnesses of the central nervous system. By separating illnesses
with and without lesions, he implicitly raised questions that
ended to the birth of psychoanalysis and of posturology.
The model
of the Fine Postural Control System gives structure to clinical
posturology by formalizing physicians discoveries: the postural
control adapts itself to the various behaviors of man; it is very
particularly specified by its object during the behavior of quiet
standing that considerably develops tonic and recursive aspects.