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Contrôle cortico-spinal à partir des aires motrices et pré-motrices impliquant le système propriospinal cervical chez l'Homme

Abstract : The C3-C4 propriospinal neurons, located at the C3-C4 spinal levels, has excitatory and inhibitory connections to arm motoneurons. They receive descending and peripheral inputs, communicate with multiple spinal interneurons and send an efferent copy to the cerebellum. The excitatory propriospinal neurons are under the control of spinal inhibitory interneurons. The propriospinal neurons could assist the motor command displayed by suprasegmental structures and could also assist the beginning and the ending of movement. Behavior studies in animals, have shown that reaching movement and precision grip are influenced by this system. The aim of this thesis is to confirm the function of the propriospinal system into arm motor command transmission in human. This work has been divided in two parts. In the first part, we have studied in human the effects of an activation of the propriospinal system on the wrist flexor (FCR) muscle contraction during reach to grasp and reach to point. In order to see the effect of the propriospinal neurons on muscular contraction during different tasks, propriospinal neurons were activated with transcranial magnetic stimulations (TMS) and ulnar nerve electrical stimulation. We have shown that FCR muscular contraction was facilitated during reach to grasp but not during reach to point. We have also shown that during reach to grasp, the reaching phase was facilitated by propriospinal neurons, but not the grasping phase. By increasing the intensity of the median nerve stimulation, propriospinal facilitation disappeared. We hypothesized that this difference in propriospinal facilitation between the different tasks and movement phases, originated from a difference of propriosceptive feedbacks and descending inputs. We have also suggested that propriospinal neurons control was different depending on whether the task is static (feedback inhibition removal) or dynamic (reinforcement of the descending inputs on propriospinal neurons). We suggest that the propriospinal system could assist dexterity by stabilizing the arm. In the second part, we have shown that inhibitor propriospinal neurons and ventral premotor cortex (vPM) or primary motor cortex (M1) interact.We made descending and peripheral volleys to converge on the inhibitor propriospinal neurons by using TMS and median nerve electrical stimulation. According to our results, there is an interaction between inhibitor propriospinal neurons and the vPM but not between propriospinal neurons and M1. This interaction may imply cortico-spinal inputs from vPM or by passing through M1. Thus, we have inhibited transitorily M1 synaptic transmissions by using paired continuous theta burst while testing interaction between inhibitor propriospinal neurons and vPM. Preliminary data have shown that despite inhibition of M1, interaction between vPM and inhibitor propriospinal neurons still exists : it might be that cortico-spinal inputs projects (directly or not) from vPM onto inhibitor propriospinal neurons
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Louis-Solal Giboin. Contrôle cortico-spinal à partir des aires motrices et pré-motrices impliquant le système propriospinal cervical chez l'Homme. Neurobiologie. Université Pierre et Marie Curie - Paris VI, 2012. Français. ⟨NNT : 2012PAO66395⟩. ⟨tel-00829414⟩



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