Combining Transcranial Electrical Stimulation With Magnetic Resonance Imaging In Behavioural Measurements In Health And Disease

The ability of the brain to rearrange its circuitry and adapt its functioning is termed neuroplasticity and underlies early brain development and complex brain functions, such as learning and memory formation. Furthermore, mechanisms responsible for neuroplasticity are of fundamental importance for recovery from brain injury and malfunctioning of such mechanisms plays a relevant role in the development of several neuropsychiatric diseases. The cellular mechanisms associated with neuroplasticity have been a subject of extensive research and multiple methods have been developed to induce neuroplasticity in cell cultures and brain slices. Manipulation of human neuroplasticity in vivo can be achieved by invasive electric stimulation of the brain or with pharmacological interventions, which are often developed in an attempt to prevent, cure or delay the progression of diseases related to neuroplasticity alterations. However, pharmacological interventions affect the whole brain and are often accompanied by undesirable side-effects, consequently having limited application. Non-invasive brain stimulation (NIBS) techniques have received increased attention in the last decades as methods for the research of plasticity in the intact human brain. Transcranial magnetic stimulation (TMS) is a well established technique while transcranial electric current stimulation (tES) methods have more recently gained popularity and demonstrated growing potential in basic neuroscience research as well as in numerous clinical applications. This thesis addresses the effects of tES techniques on aspects of human healthy and pathologic cognitive functioning, using behavioural measurements and functional imaging methods. The first section presents the basic concepts concerning neuroplasticity and techniques of non-invasive brain stimulation, which are necessary for the understanding of the studies presented in the thesis. The second and the third sections describe the research projects that were performed, presenting and discussing the obtained results. Finally, the last section summarizes and discusses the overall findings and offers a perspective on future research directions.