Abstract
The scientific literature shows that cognitive dysfunction is a common feature in neurodevelopmental and aging-related disorders. Furthermore, several decades of research have pointed to a pressing need for identifying cognitive markers for neurodevelopmental disorders and neurological conditions associated with aging. The current thesis provides a comprehensive overview of cognitive domains deemed critical in attention-deficit/hyperactivity disorder (ADHD), Parkinson’s disease (PD), and Alzheimer’s disease (AD), with a particular focus on working memory (WM) in ADHD and PD. The four main chapters encompass the following studies: (1) an updated meta-analysis on verbal WM in children and adolescents with Attention-Deficit/Hyperactivity Disorder (https://doi.org/10.1080/13854046.2019.1604998); (2) a large-scale meta-analytic review that explored in-depth short-term memory (STM) and WM dysfunction in PD (https://doi.org/10.1007/s11065-021-09480-w); (3) a 1-year follow-up study on visuospatial STM and WM dysfunction in PD; and (4) a systematic review with meta-analysis summarizing statistical data on the cognitive profile of unaffected first-degree relatives of individuals with late-onset AD. Overall, results from the current thesis reinforce the understanding that WM dysfunction is a core neurocognitive feature of ADHD. In addition, patients with PD exhibit domain-general dysfunction (verbal and visuospatial), such that disease duration, larger daily levodopa equivalent dose, and years of education seemed to be associated with, respectively, visuospatial STM, verbal/visuospatial WM, and verbal STM dysfunctions in PD. Finally, we found compelling evidence that first-degree relatives of individuals with late-onset AD show a mild but robust amount of overall cognitive dysfunction compared to controls without a family history of AD. To sum up, this thesis adds to the literature by investigating cognitive domains that may contribute towards identifying cognitive markers in ADHD, PD and AD. Cognitive markers assist in implementing cognitive-based interventions that minimize the impact of cognitive dysfunction in daily life (e.g., academic underachievement in ADHD) and delay progression to advanced stages of neurological disorders (including the development of dementia). Thus, utilizing the findings presented in this thesis, future research can work towards developing effective therapies to optimize cognitive functioning and stave off decline in these populations