A thorough description of cognitive functioning in individuals with dementia and those at risk of developing dementia is essential for early and accurate diagnosis. Executive functioning is one cognitive domain in which deficits have been reported in various types of dementia, including mild cognitive impairment (MCI, often a transitional stage between normal aging and Alzheimer's disease), frontotemporal dementia (FTD), and Lewy body dementia (LBD). This thesis contains two papers addressing executive functioning in these patient groups, the first comparing MCI patients to normal controls and the second comparing FTD and LBD patients. In each study, we examined executive functioning across multiple domains (working memory, inhibitory control, verbal fluency, and planning), and compared groups in terms of statistical differences, the pattern of the severity of clinical impairment, and the frequency of impairment. Results indicated that MCI patients performed worse than controls on all of the tests administered, were clinically impaired in all 4 domains, and that clinical impairment was frequent in each of the domains. FTD and LBD patients performed remarkably similarly across all domains in group comparisons, pattern of clinical impairment, and frequency of impairment, with only one test producing results that could potentially differentiate the groups. All three patient groups were disproportionately impaired on measures of inhibitory control in comparison to other tests of executive functioning. Implications of these results are discussed
