Il est classiquement admis que le cortex moteur des primates est organisé topographiquement en lien avec le contrôle des différentes parties du corps. Il a également été suggéré que différentes zones de cette aires corticales pourraient être impliquées dans différents processus de préparation motrice. Suivant cette dernière hypothèse, cette thèse a pour objectif d’étudier les modulations spatiales et temporelles de l’activité neuronale du cortex moteur au cours de la préparation et de l’exécution de mouvements de saisie manuelle. Trois singes ont été entraînés à réaliser une tâche pré-indicée de saisie manuelle. Chez chaque animal, une matrice d’électrodes a été implantée chroniquement dans le cortex moteur. Dans une première étude, nous avons démontré que les modulations d’activité associées à différents processus préparatoires sont localisées dans différentes zones du cortex moteur. Ces zones seraient activées séquentiellement au cours de la préparation motrice suivant une alternance de phases de traitement stationnaire et de propagation dynamique. Dans une seconde étude, nous avons exploré les interactions neuronales par l’utilisation de la mesure de corrélation de variabilité (rsc) entre paires de neurones. Cette deuxième étude a fait ressortir 3 résultats principaux. Les valeurs de rsc sont plus élevées au cours de la préparation du mouvement que lors de son exécution. Elles diminuent avec la distance qui sépare les neurones. Elles sont plus importantes entre interneurones qu’entre neurones supposés pyramidaux. L’ensemble de ces observations ont été discutées en lien avec différentes modèles d’organisation spatiale des aires motrices corticales. / The motor cortex follows a somatotopic organization in which the different body parts are controlled by distinct cortical zones. It has also been proposed that different spatial zones of this cortical area could be involed in distinct processes of motor preparation. Following this latter hypothesis, the objective of this thesis is to study the spatio-temporal modulations of motor cortex activity during movement preparation and execution. Three monkeys have been trained in an instructed delayed reach-to-grasp task. In each animal, a multielectrode Utah array was chronically implanted in the motor cortex to explore the dynamic modulations of neural activity during task performance. In a first study, we demonstrated that the modulations of neural activity related to distinct processes of motor preparation occur at different cortical locations. These locations are activated sequentially during motor preparation through alternating phases of stationary processing and dynamic propagation. In a second study, we analysed the neural interactions using a measure of spike count correlation (rsc) between pair of neurons. We reported 3 main results. Correlations are higher during movement preparation than during execution. They decrease with the distance between neurons. Finally, they are higher bewteen putative interneurons than bewteen putative pyramidal neurones. All these observations are discussed in relation to several models of the spatial organization the motor cortex.

Thesis (Ph.D.)--Boston University / Several investigators have reported on the fine structure of the normal adrenal gland of the rat using electron microscopy, and many have described the changes which occur during the processes of regeneration of both enucleated and transplanted adrenal glands, using a variety of histochemical techniques for subsequent analysis by optical microscopy. Since the larger inclusions, such as intracellular lipid droplets, have been followed through the stages of regeneration (Brenner, et al, 1953), an attempt was made in this investigation to analyze the changes in cytoplasmic organelles during the process of regeneration, utilizing the electron microscope, and to correlate the observations with those of the regenerating adrenal gland that have been reported using optical microscopy. Experimental Procedure Male albino rats of the Wistar strain, weighing between ninety-five and one hundred fifty grams were bilaterally adrenalectomized by the dorsal approach under ether anesthesia. The right adrenal glands were either used for control purposes or discarded. The left adrenal gland was bisected and autotransplanted into pockets made in the dorsal musculature. All animals were given Purina Laboratory Chow ad libitum and a one percent saline drinking water for a period of seven days post-operatively, after which tap water was given. These animals were sacrificed and their transplants removed after two, four, seven, fourteen, twenty-one, and sixty days of regeneration. Tissue specimens of one cubic millimeter size were fixed for two hours in cold one percent osmium tetroxide buffered to pH 7.2 with veronal-acetate buffer, after which they were dehydrated and embedded in either methacrylate monomers or epoxy resin. After curing the plastic in an oven, sections of three hundred to eight hundred Angstrom units thickness were cut on a Porter-Blum microtome, placed on carbon coated copper grids, which has previously been covered with a thin layer of Formvar, and observed in an RCA EMU Microscope, Model 3B, at fifty kilovolts. Normal control animals were sacrificed and their left adrenals processed in the same manner as above [TRUNCATED]

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Abstracted in Dissertation abstracts, v. 15 (1955) no. 12, p. 2608. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 85-93).

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The sensorimotor network receives a rich variety of somesthetic afferents and outputs considerable motor efferents, both of which drive experience-dependent plasticity in the system. It remains unclear to what extent subtle changes in somaesthesis and motor function extrinsic to the brain drive plasticity in the functional organisation and anatomy of the sensorimotor network. This thesis contains a series of multimodal MRI experiments to investigate how altered-use and disuse can induce plastic changes in the sensorimotor network of the human brain. In Chapter 3, a method of mapping digit somatotopy in primary somatosensory cortex at the single-subject level using 7.0 tesla fMRI was developed and applied for a study of healthy participants. Using a phase-encoding paradigm, digit representations were accurately mapped in under 10 minutes. These maps were reproducible over time and comparable to a standard block design. In Chapter 4, a further fMRI study assessed the potential for short-term reorganisation of digit representations in primary somatosensory cortex following a manipulation whereby the right index and right middle fingers were glued together for 24 hours. There was a marked shift in the cortical overlap of adjacent digits after the glued manipulation, not seen across an equivalent control period, providing strong evidence for short-term remapping of primary somatosensory cortex. In Chapter 5, a patient study investigated plasticity associated with chronic unilateral disuse of the upper limb. A cross-sectional comparison with control participants showed reduced grey matter density in the posterior right temporoparietal junction, and increased radial diffusivity in the white matter of the right superior longitudinal fasciculus, consistent with change in the right ventral attention network. A complementary longitudinal study in Chapter 6 investigated structural plasticity associated with rehabilitation of the disused limb. There were localised increases in grey matter density, notably in the right temporoparietal junction, further implicating a potential role for regions responsible for egocentric attention in regaining upper limb use. In Chapter 7, a further patient study investigated candidate predictive biomarkers at the sub-acute stage of stroke recovery, identifying CST-lesion cross-section and sensorimotor network strength as correlates of motor function, which warrant further study. The results of the studies presented in this thesis provide a novel insight into the nature and time frame of functional and structural plasticity associated with altered use and disuse. Further study of how subtle changes in our sensory and motor use shape the sensorimotor network is warranted, particularly in the context of disuse in non-neurological clinical populations.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 153 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 107-135).

Diss. (sammanfattning) Uppsala : Univ., 2004. / Härtill 4 uppsatser.