The Effects of Attention on Cortical Reinstatement in the Aging Brain

情景记忆的一个定义性特征是对先前经历的事件的生动回忆。情景记忆模型提出，编码时存在的相同神经表征在记忆检索过程中也会参与，这一过程称为皮质恢复。海马体在稳定记忆痕迹和促进检索方面起着至关重要的作用，它通过重新激活编码时存在的特定感觉皮层区域中的相同神经模式来实现。研究表明，感觉特异性皮层区域（如早期视觉皮层）的神经恢复模式与编码相关海马活动的程度相关[1]，并与更高的记忆准确性相对应[2]。这些发现表明，支持事件编码时复杂表征结合的海马-皮层连接是“重现”先前事件的经验的基础。正常衰老的特征是情景记忆下降，这被认为与海马和周围内侧颞叶结构中与年龄相关的结构和功能改变有关[3]。目前的文献主要集中在年龄相关的记忆衰退是否出现在特定的感觉皮层激活支持记忆检索的变化。研究发现，老年人在参与感觉处理的后皮质区域表现出活动减少和特异性降低，同时额叶区域的活动增加[4]。这种神经模式被认为是一种补偿机制，由减少神经专业化。这种领域一般的神经模式可能会导致难以区分存储在记忆中的类似项目[5]。此外，它也可能反映注意力控制的缺陷，这可能导致额叶而不是后感觉区域的过度招募[6]。事实上，老年人通常在行为范式中表现出注意力控制的缺陷[6]，并且额叶区域的过度招募与注意力控制的更大损伤有关[7]。一种可能性是，老年人更依赖于额叶而不是后部感觉区域，这可能反映了将注意力引导到感觉信息方面的障碍，从而降低了海马体将感觉表征绑定到情景记忆痕迹的程度，以及随后在提取时皮层表征的重新激活。我建议研究老年人在记忆过程中是否会招募感觉处理脑区如果注意力控制和编码策略的变化影响了感官信息编码的性质，那么提取的效果就不如年轻的成年人。要做到这一点，我建议使用一个任务，旨在操纵的视觉和语义信息的注意力在记忆编码的方向。目的是确定相对于语义刺激的视觉注意是否会减少提取时皮层恢复的年龄差异。为了测量神经活动，我打算使用功能磁共振成像，特别关注使用表征相似性分析（RSA）[8]。RSA利用代表性相异性矩阵来评估感兴趣区域中的神经激活对于编码和检索条件是否相似或不相似。因此，两种情况下神经模式的相似性越大，表明恢复越好，情景记忆回忆越好。应用概述的神经成像技术可以比较年轻人和老年人之间的编码-检索模式的相似性，我预计这项研究的发现将促进我们对衰老大脑中记忆缺陷的神经认知机制的理解。它将有助于当前的情景记忆模型，通过检查注意力分配是否可以促进老年人的皮质恢复效应，以及这与改善先前编码信息的回忆有何关系。

A defining feature of episodic memory is the vivid recollection of previously experienced events. Models of episodic memory propose that the same neural representations present at encoding are engaged during memory retrieval, a process termed cortical reinstatement. The hippocampus plays a crucial role in stabilising memory traces and facilitating retrieval by reactivating the same neural patterns in sensory-specific cortical regions that were present at encoding. Studies show that neural patterns of reinstatement in sensory-specific cortical regions such as early visual cortex are associated with the degree of encoding related hippocampal activity [1] and corresponds with higher memory accuracy [2]. These findings indicate that the hippocampal-cortical connections supporting the binding of complex representations at event encoding underlie the experience of 're-living' a previous event.Normal aging is marked by episodic memory decline, which is thought to be related to age-related structural and functional alterations in the hippocampus and surrounding medial temporal lobe structures [3]. Current literature has focused on whether age-related memory decline emerges from changes in sensory-specific cortical reactivation supporting memory retrieval. Older adults are found to exhibit reduced activity and decreased specificity in posterior cortical regions involved in sensory processing, combined with increased activity in frontal regions [4]. This neural pattern is believed to be a compensatory mechanism resulting from reduced neural specialisation. Such domain-general neural patterns may contribute to the difficulty in distinguishing between similar items stored in memory [5]. Additionally, it could also reflect deficits in attentional control that may lead to an over-recruitment of frontal rather than posterior-sensory regions [6].Indeed, older adults commonly display deficits in attentional control in behavioural paradigms [6] and over-recruitment of frontal regions has been linked to greater impairments in attentional control [7]. One possibility is that the greater reliance on frontal rather than posterior sensory regions in older adults may reflect impairments in directing attention to sensory information, thus reducing the extent to which sensory representations are bound into an episodic memory trace by the hippocampus, and the subsequent reactivation of cortical representations at retrieval.I propose to examine whether older adults recruit sensory processing brain regions during memory retrieval less effectively than younger adults, or if changes in attentional control and encoding strategies affect the nature of encoding sensory information. To do this, I propose to use a task designed to manipulate the orientation of attention of visual and semantic information during memory encoding. The aim is to determine whether orienting attention to visual relative to semantic stimuli will reduce age differences in cortical reinstatement at retrieval.To measure neural activity, I intend to use fMRI with a particular focus on using representational similarity analysis (RSA) [8]. RSA utilises representational dissimilarity matrices to assess whether neural activation in a region of interest is similar or dissimilar for encoding and retrieval conditions. Thus, greater similarity of neural patterns for both conditions indicates greater reinstatement and better episodic memory recollection. Applying the outlined neuroimaging technique allows the comparison of encoding-retrieval pattern similarity between young and older adults.I anticipate that the study findings will advance our understanding of the neurocognitive mechanisms underlying memory deficits in the aging brain. It will contribute to the current models of episodic memory by examining whether attentional allocation can facilitate cortical reinstatement effects in older adults and how this relates to improved recollection for previously encoded information.