Rôle des afférences plantaires dans le contrôle postural et oculomoteur de sujets sains et de sujets avec Inefficience des Afférences Plantaires non symptomatique

Abstract : This thesis aims at assessing the role of plantar cutaneous afferents in postural and oculomotor control by manipulating plantar exteroception with thin mechanical plantar stimulations. The 1st study showed that lateral, and even more medial mid-foot plantar inserts (LAS / MAS) improve stability in quiet stance and induce a backward shift of the CoP of young healthy subjects during eye movements. They also have a specific action upon vergence (not saccades): MAS increase the phasic amplitude of divergence and decrease its tonic part, in other words they mainly act on the pre-programmed component of the movement; whereas LAS act upon convergence, increasing its tonic amplitude, which is under the influence of visual retroaction. The inserts have a direct influence upon postural and oculomotor control through specific and independent paths. The 2nd study explained the variability of the subjects’ answers of the former. We measured their degree of reliance upon plantar cutaneous afferents with the Plantar Quotient method (PQ = Surface CoP foam / Surface CoP firm gorund X 100). A PQ<100 suggest a Plantar Extercoeptive Inefficency (PEI): PEI subjects do not show any improvement of their stability or any modification of vergence with the inserts. We propose that this situation is non-physiological and results from a non-noxious latent dysfunction of the sole receptors, opposing the PEI subjects to those who have a normal PQ. The 3rd study investigated the relationship between the use of plantar and visual afferents in young healthy subjects with the method of the PQ and Romberg Quotient (RQ). It has evidenced the existence of a synergic use of visual and plantar afferents in close-distance vision, only among normal PQ subjects. The PEI subjects have a significantly lower RQ than the others only at close distance on firm ground. On foam, their RQ increases; eyes closed, their PQ increases, which objectifies a visual-podal asynergy. The 4th study, on the same population, showed that a bilateral LAS increase esophoria only at far distance and among the PEI subjects. The 5th study revealed the influence of plantar exteroception upon the perception of verticality on the same population. It has brought out a decrease of the leftward error at near distance among the normal PQ subjects with a right LAS, and a decrease of the absolute error at far distance among the PEI subjects with a bilateral MAS. Taken together, these studies support, from a theoretical point of view, the importance of plantar afferents for postural control as well as vergence control, SVV estimation and eyes alignment (phorias). They demonstrate that the use of these afferents depends on the subjects and have multidisciplinary clinical implications.
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Arnaud Foisy. Rôle des afférences plantaires dans le contrôle postural et oculomoteur de sujets sains et de sujets avec Inefficience des Afférences Plantaires non symptomatique. Anatomie, Histologie, Anatomopathologie [q-bio.TO]. Université Sorbonne Paris Cité, 2016. Français. ⟨NNT : 2016USPCB036⟩. ⟨tel-02170516v2⟩

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