One limitation of our

study is that we did not have an action execution condition to compare our results with previous studies. A direct comparison of action execution with action observation using a source level analysis of brain responses will significantly advance our understanding of the fundamental mechanisms underlying the development of the perceptual-motor system. Acknowledgments We would like to thank J. Werker, L. Boyd and J. Garland for their support and mentorship in this project. This work is supported Inhibitors,research,lifescience,medical by the Natural Sciences and Engineering Research Council of Canada.
Alzheimer disease (AD) is a neurodegenerative disorder clinically characterized by progressive dementia. The cardinal pathologic features include accumulations of both extracellular Aβ peptide in neuritic Inhibitors,research,lifescience,medical plaques (NPs) and intracellular hyperphosphorylated tau in neurofibrillary tangles (NFTs). These two lesions form the basis of current diagnostic criteria of AD (CERAD, Braak), yet both have been demonstrated in cognitively normal (CN) elderly adults (Tomlinson et al. 1968; Crystal et al. 1988; Katzman et al. 1988; Braak and Braak 1991; Inhibitors,research,lifescience,medical Mirra et al. 1991; Mochizuki et al. 1996; Troncoso et al. 1996; Price and Morris 1999; Knopman et al. 2003). This state, which we have termed asymptomatic AD

(ASYMAD) (Riudavets et al. 2007; Iacono et al. 2008), and others have called preclinical AD (Schmitt et al. Inhibitors,research,lifescience,medical 2000), or high-pathology controls (Benzing et al. 1993), suggests that some individuals are resistant to the effects of AD pathology. Recent investigations of individuals with ASYMAD have begun to reveal possible underlying mechanisms responsible for this resilience. For example, ASYMAD subjects have neuronal hypertrophy in the CA1 region of the hippocampus and anterior cingulate cortex (Riudavets et

al. 2007; Iacono et al. 2009a). Neuronal nuclear and nucleolar hypertrophy has also been demonstrated in the hippocampus, anterior and posterior cingulate cortices, and primary visual cortex of these individuals (Iacono et al. 2008). The current Inhibitors,research,lifescience,medical study investigates differences in longitudinal changes in brain activity among groups of individuals who eventually follow divergent clinical and pathological trajectories. This study is unique in that cerebral blood flow (CBF) SB1518 mouse positron emission tomography (15O-PET) already scans were obtained on average 10.0 (SD 3.6) years prior to death when all participants were CN. Thus, we are able to assess antemortem brain changes in individuals who have AD pathology years later at autopsy yet maintained normal cognition (ASYMAD) and compare them to those with AD pathology and cognitive impairment (CI) as well as those who remained CN and histologically normal. By examining changes in brain activity demonstrated by the PET imaging, we can assess both similarities and differences in premorbid brain function across the groups.