Richard
Belli, D.C., D.A.C.N.B.
Primitive
positions consist primarily of gait, stance, and lateral swim line. These are remnants of our evolutionary
change from swimming to crawling to standing, and finally to walking in the
upright position. These movements
require the orderly and progressive activation of many muscle groups, which
consist of alternate contractions of flexors and extensors.
Oscillatory
circuits exist in the brain stem and spinal cord that provide the essential
timing for the sequential activation of the muscles needed to produce the
desired, repetitive movement; these circuits are termed “central pattern
generators”. Central pattern generators
are defined as circuits that can produce rhythmic motor patterns in the absence
of phasic drive, either from a sensory input or a descending control
pathway. In other words, a central
pattern generator is present when the existence of a rhythm does not depend on
specific timing cues from peripheral or higher centers in the animal, although
these inputs will certainly alter the motor patterns produced. With bipedal movement requiring even greater
descending control than quadruped locomotion.
Primitive
cerebellar and pontine nuclei are intimately associated with the hypothalamus
and reticular formation to modulate movement mediated metabolic function. Therefore, any structural or chemical factor
that alters the function of these nuclei will be expressed by aberration of the
normal inhibition and facilitation patterns of these primitive movements. Since these nuclei are associated to the
hypothalamic, vagal-motor, and reticulospinal function, it is reasonable to
believe that alterations of these normal patterns are indicators of dysfunction
in one or more of these areas.
The
existence of central oscillatory circuits does not mean that reflexes and
sensory feedback are unimportant for movement.
On the contrary, sensory input is clearly important in shaping
rhythmically generated movements so that they are appropriate to what is going
on at the time. Although the movement is initiated by cerebral cortex and
determined by the generator, it is modified by feedback from sensory input.
Walking
and swimming call into play neurons found in many brain regions, as well as the
spinal cord circuits and peripheral sensor neurons. The generators are subject to command centers in the
supplementary motor areas and/or the premotor areas in the case of striated
muscle and the hypothalamus in the case of smooth muscle. In walking the pontine and medullary
reticulospinal tracts are both active.
The pontine reticulospinal tract facilitates anti-gravity muscles and
the medullary reticulospinal tract modulates inhibition and facilitation of
gait muscles.
The
reticular formation is the primitive control center of the brain stem gray
matter. The term reticular formation is
used only with midbrain, pons and medulla, however the polysynaptic net extends
rosturally into the thalamus and hypothalamus and caudally into the
propriospinal network of the spinal cord.
The reticular formation receives extensive modulation and regulation
through collaterals from sensory and motor pathways and cerebellum efferent
fibers as well as direct descending cortical reticular pathways. The reticular formation has roles in many
neurological functions, including somatic motor modulation, modulation of
autonomic function, cortical arousal mechanisms and sensory input.
In
addition to mechanical modulation, all central-pattern-generating circuits are
subject to modulation by neurotransmitters and hormones, which can alter the
frequency and intensity of the motor patterns.
Therefore, any deviation from normal of either will disrupt the normal
inhibition and facilitation of the primitive pattern. Variations from normal can either be intrinsic, due to chemical
or mechanical dysfunction, or induced by the practitioner performing the
test. When the gait system is
intrinsically disrupted, tests can be performed with mechanical or chemical
input that brings the system back to homeostasis, thus normalizing gait
function. For example, if the central
pattern generators of gait are disrupted from decreased mechanical input, the
practitioner can temporarily increase mechanical input into the system from a
suspect motion segment and test gait for normalization. If the central pattern generators are
dysfunctional due to a chemical imbalance such as endocrine dysfunction, the
practitioner can temporarily stimulate the endocrine system and observe
normalization of the gait pattern.
Walking
is nearly automatic and probably calls into play more central pattern generator
circuits than any other movement, making the primitive gait position an
excellent tool for central nervous system investigation. Testing of central pattern generators
through the gait mechanism can be used to ascertain dysfunction as well as
correction modalities of nearly any chemical or structural abnormality. When a patient is placed in the supine
position on the treatment table with one leg advanced, the contra lateral
latissimus and the ipsilateral pectoralis, amongst other muscles, should be
normally inhibited. When the patient is
lying supine in the gait position and inhibition is not normal, it indicates
that there is systemic dysfunction that needs correction. Furthermore if the patient is supine in the
gait position and inhibition is normal, provocative testing such as structural
or chemical challenge can be used to determine whether any of the modalities
tested will move the system away from homeostasis and disrupt the normal gait
pattern. For example, therapy
localization to an acupuncture point that needs treatment will disrupt gait;
insalivation of a nutrient that is of already adequate quantity in the system
will disrupt gait; mechanically challenging a joint into greater fixation will
disrupt gait. These are just a few of a
multitude of factors that can disrupt a normal gait pattern. In other words, any factor of the triad of
health that moves the system out of homeostasis will disrupt the normal gait
pattern of inhibition and facilitation.
As
can be seen from the information presented here, the primitive positions such
as gait, stance, and lateral swim line are intimately associated with the
primitive control centers of the nervous system such as the reticular formation,
hypothalamus and cerebellum. Therefore,
because it is testing the primitive nuclei associated with the central pattern
generators, gait testing is an extremely sensitive testing tool for determining
neurophysiological dysfunction.