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Optimizing the efficacy of transcranial direct current stimulation on cortical neuroplasticity based on a neurovascular coupling model

Asif Jamil
Doctoral thesis
Date of Examination: 2017-01-24
Date of issue: 2017-03-01
Advisor: Nitsche, Michael Prof. Dr.
Referee: Wilke, Melanie Prof. Dr.
Referee: Farina, Dario Prof. Dr. Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0023-3DBC-2

 

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Abstract

English

Transcranial direct current stimulation (tDCS) induces polarity-specific enduring alterations of cortical excitability, and activity. Cortical excitability can be monitored in a limited set of cortical areas in the human brain, to explore the effects of tDCS. For exploring tDCS-induced cortical activity alterations, only indirect measures, such as electroencephalography (EEG), and functional magnetic resonance tomography (fMRI) are available. As presented in the following dissertation, we aimed to explore the relationship between systematically varying stimulation intensities of tDCS with the respective physiological and functional effects in the human motor cortex, with the goal of obtaining stimulation parameters which yield greater and longer lasting neuroplastic effects. We devised a multi-modal experimental approach and set out to answer three questions. First, we investigated the relevance of intrinsic inter-individual variability in the response to tDCS, where baseline sensitivity to TMS was analyzed as a viable and useful predictor. In the second part of the study, we aimed to explore the association between tDCS-induced excitability and activity alterations, obtained by TMS and fMRI, to identify the physiological association between these parameters, as well as which technique may be optimally suited to monitor tDCS-induced cortical activity alterations for the model of the human motor cortex. The current intensity dose-reponse relationship of tDCS was systematically investigated with both techniques within a randomized, repeated-measures sham-controlled design. In the last part, we aimed to functionally validate our findings by combining tDCS with a bimanual motor learning task, and to see whether our findings could also be extended to also helping the aging population (65+ years). Obtaining an optimized model, which is more effective than currently available, is important because tDCS is increasingly applied to alter cognitive processes in healthy humans and clinical symptoms in neurodegenerative diseases.
Keywords: transcranial direct current stimulation; neurovascular coupling; motor cortex; inter-individual variability; bimanual motor learning
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