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Modelação numérica em polarização neuronal transcraniana:aplicação clínica à epilepsia
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A polarização neuronal transcraniana (PN) é uma técnica não-invasiva, indolor, económicae portátil que permite modular a excitabilidade cortical. Recentemente, a investigação e aplicabilidadeda PN para o tratamento de várias doenças tem vindo a crescer. Contudo, de modo aoptimizar as aplicações clínicas deste método, é imprescindível conhecer a distribuição da densidadede corrente no cérebro.Primeiro, usando o Método de Elementos Finitos, mostramos que não existe uma relaçãolinear entre a intensidade de corrente, a área do eléctrodo e a densidade de corrente num pontofixo no cérebro. Em segundo lugar, comparamos a performance de modelos de PN através damedição da focalidade e distribuição da densidade de corrente (à superfície do cérebro e em profundidade)para várias montagens de eléctrodos esponja e eléctrodos EEG colocados no SistemaInternacional 10 ¡ 10.O nosso estudo introduz o uso de eléctrodos EEG na PN. Estes eléctrodos aumentam a focalidadedesta técnica, sobretudo quando um cátodo é usado em combinação com vários ânodos.Adicionalmente, a sua utilização requer menos corrente injectada, facilita a associação dasposições no escalpe com as zonas de representação do cérebro e permite a aplicação da PN concomitantementecom o registo do EEG.Por último, introduzimos um sistema experimental inédito, que combina o registo contínuodo EEG com a PN. Este sistema é mais seguro que os existentes, permitindo uma avaliação detalhadada actividade interictal na epilepsia humana durante a aplicação da PN. Permite tambémuma escolha optimizada da montagem de eléctrodos para diferentes focos epileptogénicos. Estesistema foi testado em dois pacientes com epilepsia focal refractária à terapia farmacológica.Notavelmente, a actividade paroxística interictal diminuiu em todos os casos estudados. Os resultadosencontrados são encorajadores e abrem perspectivas promissoras para o uso desta técnicana terapia da epilepsia humana.
Transcranial direct current stimulation (tDCS) is a non invasive, painless, economic andportable technique that has been shown to modulate cortical excitability. Recently, research intDCS and its applications to the treatment of several pathologies have been expanding. However,to optimize the clinical applications of tDCS a reliable estimate of the current density in the brainis of outmost importance.First, using the Finite Element Method, we show that a non-linear relationship exists betweenthe injected current, the electrode area and the current density at a fixed target point in the brain.Second, we investigate the performance of tDCS models by studying the focality and the distributionof the current density (at the surface of the brain and in depth) using sponge and EEGelectrodes in the 10-10 international system coordinates.Our study introduces the use of EEG electrodes in tDCS. These electrodes increase the focalityof this technique, particularly when one cathode and several anodes are used in combination. Inaddition, we show that this montage requires less injected current, can be placed at scalp positionswith known relationship with the underlying cerebral cortex and further allows the use of tDCSand EEG recording concomitantly.We propose the first experimental system that combines continuous recording of the EEGsimultaneously with tDCS. This system improves safety and allows a detailed evaluation of theinterictal events. Furthermore, it permits the optimization of the montages of the electrodes fordifferent locations of the epileptogenic foci. To date, this system was tested in two epilepticpatients and we demonstrate that their interictal activity was reduced in all cases studied. Ourresults are encouraging and open doors for the application of tDCS in human epilepsy therapy.
Transcranial direct current stimulation (tDCS) is a non invasive, painless, economic andportable technique that has been shown to modulate cortical excitability. Recently, research intDCS and its applications to the treatment of several pathologies have been expanding. However,to optimize the clinical applications of tDCS a reliable estimate of the current density in the brainis of outmost importance.First, using the Finite Element Method, we show that a non-linear relationship exists betweenthe injected current, the electrode area and the current density at a fixed target point in the brain.Second, we investigate the performance of tDCS models by studying the focality and the distributionof the current density (at the surface of the brain and in depth) using sponge and EEGelectrodes in the 10-10 international system coordinates.Our study introduces the use of EEG electrodes in tDCS. These electrodes increase the focalityof this technique, particularly when one cathode and several anodes are used in combination. Inaddition, we show that this montage requires less injected current, can be placed at scalp positionswith known relationship with the underlying cerebral cortex and further allows the use of tDCSand EEG recording concomitantly.We propose the first experimental system that combines continuous recording of the EEGsimultaneously with tDCS. This system improves safety and allows a detailed evaluation of theinterictal events. Furthermore, it permits the optimization of the montages of the electrodes fordifferent locations of the epileptogenic foci. To date, this system was tested in two epilepticpatients and we demonstrate that their interictal activity was reduced in all cases studied. Ourresults are encouraging and open doors for the application of tDCS in human epilepsy therapy.
Descrição
Tese de doutoramento, Engenharia Biomédica e Biofísica, 2009, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Estimulação transcraniana Epilepsia Engenharia biomédica Teses de doutoramento