| الوصف: |
Clinicians including rehabilitation professionals use a variety of evidence-based behavioural techniques to help improve functioning for adults affected by cognitive and language disorders. In recent years, the use of non-invasive brain stimulation has been studied as a method to augment behavioural therapies; transcranial direct current stimulation (tDCS) is one such approach that is proposed to increase neural efficiency which can potentially improve cognitive processing. Although tDCS has been implemented with different groups of participants across several studies, questions remain about its effects on cognitive processing, particularly among older adults. Additionally, the effects of tDCS on the interaction between cognitive processing and cerebral hemodynamics remain poorly understood. Thus, the purpose of this thesis was to examine the effects of tDCS on cognition in older adults and to develop a fuller understanding of the interaction between cognitive processing and cerebral oxygenation hemodynamics, measured with functional near-infrared spectroscopy (fNIRS). Three studies were conducted: a scoping review, and two small sample randomized controlled trials. In the first study, a scoping review and meta-analysis were conducted to investigate the effects of tDCS on the brain-cognition interaction in the context of aging. Findings revealed that tDCS has the greatest effect in healthy younger adults in both cognition and cerebral oxygenation hemodynamics. The second study, which was amended from an older adult sample to a healthy younger adult sample due to COVID-19, investigated the effects of tDCS on the interaction between cerebral oxygenation hemodynamics measured with fNIRS and working memory performance. Consistent with the previously mentioned scoping review and meta-analysis, anodal tDCS increased working memory performance and blood-oxygen concentrations, however, only during higher cognitive load demands. In the third study, the effects of tDCS on a clinical geriatric inpatient sample with depression and/or anxiety were investigated. In this study, it was found that tDCS selectively modulated executive functioning subprocesses, notably inhibition processing, complex planning, and processing speeds. Together, these results contribute to the ecological validity and feasibility of using tDCS in clinical care settings, while adding clinical and aging-specific considerations on the effect of tDCS between the brain and cognition interaction. Importantly, this series of studies adds to the literature on the use of tDCS, and the interaction with individualized resting-state cerebral oxygen hemodynamics, which helps to better control for variability across aging and disease status. Although COVID-19 impacted the sample recruited for both the second and the third studies presented, the results provided a foundation for future tDCS-fNIRS studies with healthy older adults and those with cognitive impairment from neurological diseases and disorders. |