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Functional multisensory integration and plasticity of vestibular reflexes

Abstract : The aim of this thesis was to specify the role of the vestibular system in the orientation-related homeostasis. We evaluated vestibular responses to changes in orientation in space (1) in normal population to reveal in what proportion different sensory systems are implicated in the generation of the cardio-vascular and respiratory responses, and (2) in populations with altered vestibular afference: bilateral vestibular loss patients and aerobatic pilots.The results indicated that the vestibular system cooperates with trunk graviceptors to evoke respiratory response to changes in orientation during Off-Vertical Axis Rotation protocol (OVAR). The contribution of each sensory source was found to vary between individuals. Another study tested the hypothesis that the vestibular modulation of cardio-vascular parameters can be influenced by visual input during OVAR. Preliminary results from this study have demonstrated that the OVAR stimulation has an effect on the mean cardio-vascular parameters. The modulatory effect of OVAR on the arterial pressure has also been shown. The phases of modulation were varying between individuals which can indicate the neural nature of the observed modulation. The effect of visual stimulation on modulation has been detected, however further analysis is required. In another study, subjects presenting bilateral vestibular loss were shown to have the same cardio-vascular response to changes in the position of the head during Head-Down-Neck-Flexion protocol (HDNF) as normals. This reconstruction of the vestibulo-sympathetic reflex in human seems to originate from the sensory sources other than labyrinthine. Finally, we studied aerobatic pilots as humans experiencing intense and unusual vestibular stimulations. We have not revealed the expected vestibular habituation in the study using the OVAR and EVAR (Earth-Vertical Axis Rotation) stimulations, but were significantly less susceptible to motion sickness. We suggest that the pilots do not develop habituation, as they require unsuppressed responses for a better performance.We conclude that to generate the orientation-related responses, the Central Nervous System integrates the vestibular and non-vestibular signals and is subject to plastic changes in altered sensory conditions, if the response needs to be changed or restored. This multisensory processing is individually tuned, with the variable portion of vestibular impact in this processing, depending on activities, sensory state and the requirements to the response.
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Olga Kuldavletova. Functional multisensory integration and plasticity of vestibular reflexes. Human health and pathology. Normandie Université, 2020. English. ⟨NNT : 2020NORMC405⟩. ⟨tel-02900414⟩

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