[en] Parkinson's disease (PD) is a neurodegenerative disease characterized by a set of motor and non-motor symptoms. Gait disorders are among the most disabling motor impairments in PD patients, as they severely affect their quality of life. In recent decades, the treadmill has been explored as a tool for improving gait in PD. Understanding the mechanisms underlying these improvements will ameliorate the efficacy and prescription of physical therapy in PD. However, in spite of the growing body of evidence that links gait to cognitive function, the role played by attention in the gait improvements associated to treadmill walking in PD is still unknown. In the same way, the possible associated neurophysiological mechanisms have never been explored. However, transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has been explored recently in order to improve gait in PD, and offers a promising tool in increasing the efficacy of rehabilitative interventions. It could also enhance our understanding of PD-pathophysiology. Nevertheless, the combined use of tDCS and the treadmill in PD has not yet been investigated. The work presented here consists of three studies. The first explores the attentional demands involved in gait improvements associated with the treadmill in PD. The second investigates the immediate kinematics and neurophysiological effects of a single treadmill walking session on PD. The third study investigates the kinematic and neurophysiological effects of the combined use of tDCS and treadmill walking in patients with PD. The results of this thesis do not support attentional resources as a possible mechanism for treadmill-associated gait improvements in PD. Likewise, a specific therapeutic effect of a single treadmill walking session on gait in PD was observed, with no associated neurophysiological changes in the outcomes measured. However, the combination of tDCS and treadmill resulted in a specific spinal excitability modulation. Further studies would be recommended to explore the role of belt displacement and constant speed as main underlying mechanisms. Additional studies are also needed to investigate the functional significance of the interaction of tDCS and treadmill walking in PD.

[gl] A enfermidade de Parkinson (EP) é unha enfermidade neurodexenerativa, caracterizada por un conxunto de síntomas motores e non motores. Os trastornos da marcha considéranse entre os síntomas motores máis incapacitantes que afectan severamente á calidade de vida dos pacientes con EP. Nas últimas décadas, o tapiz rodante foi explorado como unha ferramenta que mellora a marcha na EP. Coñecer os mecanismos subxacentes a estas melloras, incrementará a eficacia e a prescrición da fisioterapia na EP. Con todo, a pesar do crecente corpo de evidencia que vincula a marcha á función cognitiva, aínda non se sabe se a atención xoga aquí un papel primordial. Da mesma maneira, os posibles mecanismos neurofisiolóxicos asociados nunca foron explorados. Doutra banda, explorouse recentemente a estimulación cerebral transcraneal de corrente contínua directa (tDCS), unha modalidade de estimulación cerebral non invasiva, para mellorar a marcha na EP, ofrecendo unha ferramenta prometedora para potenciar a eficacia das intervencións de rehabilitación, ademais de mellorar a nosa comprensión da fisiopatoloxía na EP. Con todo, aínda non investigou a combinación de tDCS co tapiz rodante na EP. O traballo presentado aquí consta de tres estudos. O primeiro explora se as demandas atencionais están involucradas nas melloras da marcha asociadas co tapiz rodante na EP. O segundo investiga os efectos cinemáticos e neurofisiolóxicos inmediatos dunha sesión de tapiz rodante na EP. O terceiro estudo explora os efectos cinemáticos e neurofisiolóxicos da combinación de tDCS e tapiz rodante na EP. Os resultados desta tese indican que os recursos atencionais non explican as melloras da marcha asociadas sobre o tapiz rodante na EP. Do mesmo xeito, observouse un efecto terapéutico específico de soa sesión de tapiz rodante sobre a marcha na EP, sen cambios neurofisiolóxicos asociados. Con todo, a combinación de tDCS e tapiz rodante resultou nunha modulación específica a nivel espinal. Recomendamos máis estudos que exploren o papel do desprazamento da banda rodante e a velocidade constante como principais mecanismos subxacentes, así como, necesítanse máis estudos para investigar a importancia funcional da combinación da tDCS e o tapiz rodante na EP.