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    Which intellectual activities are related to cognitive reserve? Introduction and testing a three-dimensional model
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    Abstract A common assertion is that semantic memory emerges from episodic memory, shedding the distinctive contexts associated with episodes over time and/or repeated instances. Some semantic concepts, however, may retain their episodic origins or acquire episodic information during life experiences. The current study examined this hypothesis by investigating the ERP correlates of autobiographically significant (AS) concepts, that is, semantic concepts that are associated with vivid episodic memories. We inferred the contribution of semantic and episodic memory to AS concepts using the amplitudes of the N400 and late positive component, respectively. We compared famous names that easily brought to mind episodic memories (high AS names) against equally famous names that did not bring such recollections to mind (low AS names) on a semantic task (fame judgment) and an episodic task (recognition memory). Compared with low AS names, high AS names were associated with increased amplitude of the late positive component in both tasks. Moreover, in the recognition task, this effect of AS was highly correlated with recognition confidence. In contrast, the N400 component did not differentiate the high versus low AS names but, instead, was related to the amount of general knowledge participants had regarding each name. These results suggest that semantic concepts high in AS, such as famous names, have an episodic component and are associated with similar brain processes to those that are engaged by episodic memory. Studying AS concepts may provide unique insights into how episodic and semantic memory interact.
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    OBJECTIVE: To assess the neuropsychological domains modulated by cognitive reserve (CR) in patients with MCI and AD. BACKGROUND: CR has been shown to modulate cognition in patients with AD, but the mechanism of this effect remains unknown. We aimed to test whether CR modulates all cognitive domains, as would be expected with neural reserve, or performance on cognitive domains involved in fluid intelligence, as would be expected with neural compensation. DESIGN/METHODS: 470 subjects (138 with AD, 332 with MCI) were selected from the ADNI database, with years of education used as a proxy for CR. We assessed the effects of CR on performance in memory related tasks (familiarity, episodic memory, semantic memory, working memory) after controlling for age, gender, and regional atrophy. To test more specifically that semantic memory, and not episodic memory, is modulated by CR, we compared episodic memory tasks varying in semantic richness. Finally, we tested the effects of CR on additional cognitive tasks in domains expected to be part of (executive function, semantic memory) or not part of (visuospatial processing, attention) neural compensation. RESULTS: CR modulated performance on semantic memory (p<.0001), but not episodic memory, familiarity, or working memory. CR did not have an effect on encoding or delayed recall on the AVLT, which tests memory of semantically unrelated word lists, but did have an effect on the LMT, where patients are asked to remember details of a semantically rich story (p<.0001). Finally, CR modulated performance on category naming (p=.002), trails part B (p<.0001), and digit span backwards (p<.001), additional tasks which rely heavily on semantic memory or executive function, but not tests of basic attention or visuospatial function. CONCLUSIONS: CR improves performance in executive functioning and semantic memory, lending support to neural compensation as a mechanism for CR. Study Supported by: R21-NS077059, P50-AG005134
    Cognitive reserve