Changes in plasticity and cognition as a result of neurovascular disease and non-invasive brain stimulation
Year: 2015
Type: dissertation
Abstract: Plasticity is a milestone in neuroscientific investigations into the biological mechanisms of learning. Plasticity is critically reduced in older adults and in individuals with neurovascular disorders that encompass changes in cerebral blood supply. Mechanisms underlying this altered plasticity are important to understand in order to develop future preventive and therapeutic strategies. Pathological and interventional changes in plasticity are thus the focus of the current thesis. In three interrelated studies, this thesis explores the underpinning of cognitive deterioration and the neural changes accompanying cognitive enhancement. The first study tested the associations between cerebral autoregulation (vasomotor reactivity, VMR), magnetic resonance imaging (MRI) measurements of structural and functional connectivity, and cognitive performance in patients with unilateral occlusive processes of the internal cerebral artery (ICA, n=14) and matched controls (n=11). Patients revealed lower VMR in the affected hemisphere (AH), decrease in whole-brain microstructure and in inter- and intra-hemispheric functional connections. Moreover, reduced VMR in the AH correlated with reduced microstructure in frontal areas and connectivity in the default-mode network (DMN). This suggests that disconnections within critical brain networks might mediate the effects of impaired VMR on cognition. The second study tested the short-term changes induced by transcranial direct current stimulation (tDCS) on language performance and the underlying neuronal mechanisms of these behavioral gains. Blood-oxygen level dependent (BOLD) activity and functional networks under real and sham tDCS were measured in 24 young healthy subjects. Here, tDCS over a core language area improved semantic fluency, decreased activity in the stimulated region and facilitated connections within the language network. The results point to a critical link between enhanced network connectivity and increased neural efficiency which might be necessary for improved task performance. The third study investigated long-lasting behavioral gains induced by training in combination with tDCS during language learning. In this study, 40 young healthy subjects acquired a novel vocabulary during 5 consecutive days under real or sham tDCS and were tested in two memory tasks on a daily basis. The results indicate that tDCS facilitated language acquisition and retention of the learned vocabulary. Findings from the three interconnected studies thus lead to the suggestion that tDCS could assist patients with occlusion / stenosis of the ICA, in which loss of cognition might be mediated by structural and functional changes in connectivity. A potential preventive therapy with tDCS could target these regions in frontal and parietal cortices, with the aim to improve cognition in these patients.
Author: Avirame, Keren
Language: English
Subfield: Neurology
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2239813188