Neural basis of aging and implicit learning

这项拟议的研究的主要目标是确定年轻人和老年人在内隐学习的神经过程中的差异。内隐学习是在没有意图或意识到所学内容的情况下无意识地获取信息。关于衰老的研究大多集中在外显学习上，因此，与年龄相关的健康大脑变化对内隐学习的影响在很大程度上被忽视了，限制了认知神经科学对衰老的范围。这是不幸的，因为对环境规律的敏感性使其能够更有效地预测和处理未来的事件，而这种能力在整个生命周期中是必不可少的。内隐学习是否会随着健康年龄的增长而下降尚不清楚，尽管当要学习的刺激很复杂，以及当人们接受延长训练时，可以观察到与年龄相关的缺陷。在这里，24名年轻人和24名老年人将接受功能磁共振成像(FMRI)，同时他们将学习和练习一种复杂的、概率顺序的内隐技能。据预测，老年人在早期的训练中会像年轻人一样学习得很好，但随着更多的练习，与年龄相关的缺陷将会出现(具体目标1)，这使得这项拟议的研究成为第一个评估内隐学习期间大脑活动的研究，当时行为既没有受到影响，也受到了损害。早期内隐学习和练习内隐学习之间的分离对认知神经科学来说很重要，原因有两个。首先，以前的成像研究表明，随着学习的进展，技能学习涉及不同的大脑区域；早期学习涉及内侧颞叶(即海马体)，后来的练习学习涉及纹状体(即尾状核)。这项拟议的研究将通过使用一种可以排除外显学习的范式来检验这些相同的学习-激活关系是否内隐学习(具体目标2)的特征。其次，早期学习和习惯性学习背后的大脑区域不同，它们受到衰老的影响程度不同。在拟议的研究中，功能连通性分析将检查大脑活动和早期学习与练习学习之间的关系，以评估神经招募中与年龄相关的差异如何随练习水平的不同而变化(具体目标3)。据预测，早期内隐学习将激活两个年龄组的海马区或MTL网络，反映了健康衰老中相对保留的MTL。在实践学习中，年轻人将在尾部或纹状体网络中表现出激活。由于与衰老相关的衰退，尾状核的激活在老年人中将不再占主导地位；老年人将依赖于他们完整的学习相关大脑区域，包括海马体和周围的MTL。这些发现将与健康衰老对纹状体的影响比MTL更大的观点一致。

The primary goal of the proposed research is to identify differences between young and old adults in the neural processes underlying implicit learning. Implicit learning is the non-conscious acquisition of information that occurs without intent or awareness of what has been learned. Research in aging has mostly focused on explicit learning, and thus, the effects of healthy age-related brain changes on implicit learning have remained largely ignored, limiting the scope of the cognitive neuroscience of aging. This is unfortunate because sensitivity to regularities in the environment makes it possible to anticipate and process future events more effectively and this ability is essential throughout the lifespan. Whether implicit learning declines with healthy aging is unclear, though age-related deficits are observed when the stimuli to be learned are complex and when people are given extended training. Here, 24 young and 24 old adults will undergo functional magnetic resonance imaging (fMRI) while they learn and practice a complex, probabilistic sequential implicit skill. It is predicted that old adults will learn as well as the young early in training, but with more practice, age-related deficits will emerge (Specific Aim 1), making this proposed study the first to assess brain activity during implicit learning when behavior is both spared and impaired. The dissociation between early and practiced implicit learning is important to cognitive neuroscience for two reasons. First, previous imaging studies suggest that skill learning involves different brain regions as learning progresses; early learning involves the medial temporal lobes (i.e. hippocampus) and later, practiced learning involves the striatum (i.e. caudate). The proposed study will be among the first to examine whether these same learning-activation relationships are characteristic of implicit learning (Specific Aim 2), by using a paradigm in which explicit learning can be ruled out. Second, the brain regions underlying early and practiced learning differ in the extent to which they are compromised by aging. In the proposed study, functional connectivity analyses will examine relationships between brain activity and early versus practiced learning to assess how age-related differences in neural recruitment vary with the level of practice (Specific Aim 3). It is predicted that early implicit learning will activate the hippocampus or MTL networks in both age groups, reflecting the relatively preserved MTL in healthy aging. In practiced learning, younger adults will demonstrate activation in caudal or striatal networks. Due to aging- related declines, caudate activation will not be as dominant in older adults; older adults will rely on their intact learning-related brain regions, including the hippocampus and surrounding MTL. These findings would be consistent with the view that healthy aging affects the striatum more than the MTL.