Effects of Healthy Aging and Mild Cognitive Impairment on Memory Representations

阿尔茨海默病(AD)不仅会损害记忆等认知能力，还会损害视觉等感觉功能。目前的项目调查了AD早期称为遗忘性轻度认知障碍(AMCI)的记忆-视觉交互作用，以及健康老龄化。我们专注于视觉刺激的记忆，在AD患者中，视觉刺激的记忆能力大幅下降，在确诊前十多年预测痴呆症。我们提出了3项功能磁共振成像(FRMI)研究，每项研究包括3组参与者：aMCI、老年人和年轻人。虽然大多数关于记忆和aMCI的功能磁共振研究都是研究记忆过程，但我们关注的是这些过程或记忆表征所使用的信息的质量。据我们所知，还没有一项功能磁共振研究考察了MCI中记忆表征的质量。我们的第一个目标是研究健康衰老和aMCI对记忆表征的视觉和语义特征的影响。有证据表明，健康的衰老会损害后枕颞叶(OTC)和内侧颞叶(MTL)区域的视觉表征，但我们初步认为，它不影响OTC/MTL前部的语义表征。相比之下，AMCI在语义加工和前颞叶功能方面存在障碍。我们检验了这一假设，即在aMCI和健康老年人中，后部OTC/MTL的视觉表征都受到了损害，而在aMCI中，前部OTC/MTL的语义表征受到了损害，但在健康老年人中没有(假设1)。健康衰老和病理性衰老之间的这种分离对于AD的早期诊断具有重要意义。我们的第二个目标是考察语义支持对健康老年人和AMCI记忆表征的影响。语义支持效应指的是可靠的发现，即允许或促进使用先前存在的语义知识的条件往往会减弱与年龄相关的认知缺陷，包括记忆障碍。AMCI的语义支持效应较弱，与其语义加工缺陷相一致。三项研究中的每一项都考察了不同形式的语义支持效应(加工水平、图式一致性和概念注意)。我们检验了这一假设，即在健康的老年人中，语义支持效应比AMCI在更大程度上提高了视觉记忆表征和随后的视觉记忆的质量(假设2)。这一发现对语义支持在这些人群的记忆训练中的应用具有一定的指导意义。总之，建议的研究将系统地研究MCI和健康衰老中视觉记忆缺陷的神经机制。他们将使用新的表征相似性分析，这些分析还没有被用来研究aMCI中的记忆表征。预期的结果将有助于疾病早期诊断AD的方法，并有助于恢复aMCI和健康老龄化的记忆，因此，具有非常重要的意义。

Alzheimer’s Disease (AD) impairs not only cognitive abilities, such as memory, but also sensory functions, such as vision. The current project investigates memory-vision interactions in the early stage of AD known as amnestic Mild Cognitive Impairment (aMCI), as well as in healthy aging. We focus on memory for visual stimuli, which declines substantially in AD, predicting dementia more than a decade before diagnosis. We propose 3 functional MRI (fRMI) studies, each including 3 groups of participants: aMCI, older adults, and younger adults. Whereas most fMRI studies on memory and aMCI investigated memory processes, we focus on the quality of the information used by these processes or memory representations. To our knowledge, no fMRI study has examined the quality of memory representations in MCI. Our first aim is to investigate the effects of healthy aging and aMCI on visual vs. semantic features of memory representations. There is evidence that healthy aging impairs visual representations in posterior occipito-temporal cortex (OTC) and medial temporal lobe (MTL) regions, but we have preliminary that it spares semantic representations in anterior OTC/MTL. In contrast, aMCIs are impaired in semantic processing and anterior temporal function. We test the hypothesis that visual representations in posterior OTC/MTL are impaired in both aMCI and healthy older adults, whereas semantic representations in anterior OTC/MTL are impaired in aMCI but not in healthy older adults (Hypothesis 1). This dissociation between healthy and pathological aging has important implications for the early diagnosis of AD. Our second aim is to examine the semantic support effect on memory representations in healthy older adults and aMCIs. The semantic support effect refers to the reliable finding that conditions that allow or promote the use of preexistent semantic knowledge tend to attenuate age-related cognitive deficits, including memory deficits. The semantic support effect is weaker in aMCIs, consistent with their semantic processing deficits. Each of the 3 studies investigates a different form of the semantic support effect (levels of processing, schema congruency, and conceptual attention). We test the hypothesis that the semantic support effect enhances the quality of visual memory representations and subsequent visual memory to a greater extent in healthy older adults than in aMCIs (Hypothesis 2). This finding has implications for the use of the semantic support in memory training in these populations. In sum, the proposed studies will systematically examine the neural mechanisms of visual memory deficits in MCI and healthy aging. They will use novel representational similarity analyses that have not been used yet to investigate memory representations in aMCI. The expected results will contribute to methods for diagnosing AD early in the disease and to rehabilitating memory in aMCI and healthy aging, and are hence, highly significant.