The primary aim of this thesis is to investigate the physiological effects of transcranial direct current stimulation (tDCS) as applied to the primary motor cortex (M1). This research was largely motivated by the need to understand the basic physiological changes of tDCS, in order to evaluate its use as a potential tool in recovery after stroke, as well as its more general applicability as a tool to modulate plasticity. The experiments in this thesis assess the ability of tDCS to modulate the primary motor cortex in healthy controls. The effects of tDCS on cortical GABA and motor resting state functional connectivity were measured with magnetic resonance spectroscopy (MRS) and resting functional MRI (fMRI). Anodal stimulation reduced GABA concentration and increased functional connectivity in the stimulated M1. Testing these changes within the same individuals demonstrated that the magnitude of changes do not correlate across subjects. Novel evidence on the timecourse of GABA change demonstrated that the reduction in GABA is most prominent in the 30-minute period after stimulation. To determine whether the tDCS-induced modulations in inhibition is restricted to the stimulated hemisphere or whether inhibitory changes could be observed in the nonstimulated M1, or in the interhemispheric connections between the M1s, transcranial magnetic stimulation (TMS) was used to measure intracortical inhibition in each M1 and interhemispheric inhibition and facilitation in the contralateral M1. There were no polarity-specifc effects on intracortical inhibition within either M1, and no changes in interhemispheric excitability from the stimulated to non-stimulated M1. Development of a two-voxel MRS method at ultra high field (7 Tesla) allowed for concurrent measurements of cortical neurotransmitters from both M1s with excellent spectral quality and GABA quantifcation. This method was used to demonstrate the timecourse of tDCS-induced changes in neurochemicals concurrently from both M1s. Anodal stimulation reduced GABA in both the anode-targeted and non-stimulated M1. Cathodal stimulation decreased GABA and glutamate in the non-stimulated M1, with no concurrent changes in the cathode-targeted M1. Bilateral stimulation reduced glutamate in both M1 with no change in GABA.

Made available in DSpace on 2016-06-02T20:18:25Z (GMT). No. of bitstreams: 1 TeseFA.pdf: 2564005 bytes, checksum: c7d0312a5d5f573290646bf260f4b9c2 (MD5) Previous issue date: 2005-07-08 / Universidade Federal de Minas Gerais / Several are the pathologies that induce functional Inbalance, leading to a constant for search for different rehabilitation techniques. One of the most common sequels is the hemiparesia that causes a functional damage, turning the stroke patients one of the principal focuses for the rehabilitation in the area. Therefore the aim of the present research was evaluate the motor control and analyze the increase of the frequency of sessions in the gait training treadmill with body weight support (BWS) in chronic hemiparesis stroke patients. Patients followed an A-B-A design with treadmill training with BWS five times for three weeks (stage A) and treadmill training with BWS three times for three weeks (stage B). The recordings were accomplished in the beginning and in the end of each stage. The collected data were temporal-spatial variables, functional activities through Rivermead test, electromyographics signs of the dorsiflexion and plantar flexion muscular groups of the ankle and electrogoniometry of the dorsiflexion and plantar flexion of the ankle. Eight subjects concluded the experiment. Three patients had better outcomes after 5 times a week treatment, two patients showed improvement only when the treatment was performed 3 times a week, two patients improved gait variables independent of the training frequency and one not improved at all. The analysis of the electromyographics signs and of the data electrogonimetrics didn't allow any relationship with the performance level of the patients. Based on the reslts of the present studies we suggest that, the treadmill training with BWS comes as an effective method for the functional recovery and that it reflects in motor activities that improved activities of daily living. The increase of the frequency of sessions not necessarily reflects in an increase of the motor control, in the largest part of the patients. / Várias são as patologias que acarretam em desequilíbrio funcional, tornando a busca por diferentes técnicas de reabilitação uma constante na pesquisa clínica. Em neurologia, uma das seqüelas mais comum é a hemiparesia, seqüela esta que causa um grande prejuízo funcional, tornando as pessoas acometidas um dos principais focos para a reabilitação na área. Portanto os objetivos desse trabalho foram: avaliar o controle motor após treino da marcha em esteira com suporte parcial de peso corporal e analisar a influência do aumento da freqüência das sessões no treinamento da marcha em pacientes com hemiplegia crônica após acidente vascular encefálico. O método escolhido foi o sistema A-B-A de treinamento. As fases A foram realizadas com uma freqüência de 5 sessões por semana e a fase B com uma freqüência de 3 sessões por semana. Cada fase teve duração de três semanas e os dados foram coletados ao início e final de cada fase. Os dados coletados foram variáveis espaço-temporais da marcha, atividades funcionais, via teste de funções motoras Rivermead, sinais eletromiográficos dos grupos musculares dorsiflexores e flexores plantares do tornozelo e eletrogoniometria da dorsiflexão e plantiflexão do tornozelo. Oito sujeitos finalizaram o experimento. Três sujeitos, em relação as variáveis espaçotemporais e atividades funcionais, apresentaram um melhor desempenho nas fases A, dois sujeitos apresentaram um melhor desempenho durante a fase B, outros dois sujeitos apresentaram um bom desempenho perante o treinamento como um todo e apenas um não obteve um bom desempenho nesse tipo de treinamento. A análise dos sinais eletromiográficos e dos dados eletrogoniométricos não permitiu nenhum tipo de relação com o nível de desempenho dos pacientes. Baseado nos achados do presente trabalho, concluímos que: 1. O treino da marcha em esteira com SPP apresenta-se como um método efetivo para a recuperação funcional dos padrões cíclicos da marcha e que essa recuperação funcional se reflete em atividades motoras que envolvem atividades de vida diária melhorando a funcionalidade através do aumento do controle motor; 2. Que o aumento da freqüência das sessões não se traduz necessariamente em um aumento do controle motor, na maioria dos pacientes. Revelando assim a necessidade de se modular cada tratamento em relação às características individuais de cada paciente.