Contribution du cortex moteur et des afferences cutanees dans le controle et la plasticite de la locomotion chez le chat

Locomotion is generated by a spinal interneuronal network that is influenced both by peripheral afferent feed-back and supraspinal descending pathways. In this thesis, we investigated the contribution of the motor cortex to the control of the hindlimb during locomotion and to the cortical modulation of hindlimb cutaneous reflexes in the intact cat. We also investigated the role of the motor cortex in the functional recovery of locomotion following a cutaneous denervation of the hindpaw.; To determine the contribution of the motor cortex to locomotor control, we recorded the responses evoked in hindlimb muscles by intracortical microstimulation applied throughout the hindlimb representation of the motor cortex. This stimulation modified the amplitude and duration of electromyographic activity as a function of the phase of the step cycle, suggesting that the cortex influences the structure of the locomotor pattern.; To study the interactions between cortical and cutaneous inputs during locomotion, cutaneous stimulation was delayed (0--50 ms) with respect to that of the motor cortex or the pyramid. Stimulation of the motor cortex, as well as of the pyramid, produced a mixture of facilitation and depression of the amplitude of the reflexes evoked by cutaneous stimulation. The nature of this modulation was different according to the cortical site, the cutaneous nerve and to the recorded muscle, suggesting a convergence of inputs onto subpopulations of spinal interneuronal networks.; Finally, we investigated the contribution of the motor cortex to the recovery of locomotion following a unilateral cutaneous denervation. Responses evoked in hindlimb muscles by stimulation of the motor cortex, via chronically implanted microwire electrodes, were recorded over a period of several months to ensure stability in the responses before denervation. After denervation, the amplitude of the cortically evoked responses increased, suggesting an increased corticospinal efficacy. This increase is suggested to contribute to the functional recovery, because it had similar time course to the changes observed in the background locomotor activity and the recovery was abolished after a pyramidotomy. (Abstract shortened by UMI.)...