University of California, Los Angeles, California 90095
Columbia University, New York, New York 10027.
J Neurosci. 2021 Feb 24;41(8):1738-1754. doi: 10.1523/JNEUROSCI.1738-20.2020. Epub 2020 Dec 18.
Episodic memory is critical to human functioning. In adults, episodic memory involves a distributed neural circuit in which the hippocampus plays a central role. As episodic memory abilities continue to develop across childhood and into adolescence, studying episodic memory maturation can provide insight into the development and construction of these hippocampal networks, and ultimately clues to their function in adulthood. While past developmental studies have shown that the hippocampus helps to support memory in middle childhood and adolescence, the extent to which ongoing maturation within the hippocampus contributes to developmental change in episodic memory abilities remains unclear. In contrast, slower maturing regions, such as the PFC, have been suggested to be the neurobiological locus of memory improvements into adolescence. However, it is also possible that the methods used to detect hippocampal development during middle childhood and adolescence are not sensitive enough. Here, we examine how temporal covariance (or differentiation) in voxel representations within anterior and posterior hippocampus change with age to support the development of detailed recollection in male and female developing humans. We find age-related increases in the distinctiveness of temporal activation profiles in the posterior, but not anterior, hippocampus. Second, we show that this measure of granularity, when present during postencoding rest periods, correlates with the recall of detailed memories of preceding stimuli several weeks postencoding, suggesting that granularity may promote memory stabilization. Studying hippocampal maturation can provide insight into episodic memory development, as well as clues to episodic functioning in adulthood. Past work has shown evidence both for and against hippocampal contributions to age-related improvements in memory performance, but has relied heavily on univariate approaches (averaging activity across hippocampal voxels), which may not be sensitive to nuanced developmental change. Here we use a novel approach, examining time signatures in individual hippocampal voxels to reveal regionally specific (anterior vs posterior hippocampus) differences in the distinctiveness (granularity) of temporal activation profiles across development. Importantly, posterior hippocampus granularity during windows of putative memory stabilization was associated with long-term memory specificity. This suggests that the posterior hippocampus gradually builds the capacity to support detailed episodic recall.
情景记忆对于人类的正常机能至关重要。在成年人中，情景记忆涉及一个分布式的神经回路，其中海马体起着核心作用。随着情景记忆能力在儿童期和青春期不断发展，研究情景记忆成熟可以深入了解这些海马网络的发展和构建，并最终揭示它们在成年期的功能。虽然过去的发展研究表明，海马体有助于支持儿童中期和青春期的记忆，但海马体内部持续成熟对情景记忆能力发展变化的贡献程度仍不清楚。相比之下，成熟较慢的区域，如前额叶皮层，被认为是青春期记忆改善的神经生物学基础。然而，也有可能用于检测儿童中期和青春期海马体发育的方法不够敏感。在这里，我们研究了前后海马体中体素表示的时间协方差（或分化）如何随年龄变化，以支持男性和女性发育中的人类详细回忆能力的发展。我们发现，后海马体的时间激活模式的独特性随年龄增加而增加，但前海马体则没有。其次，我们表明，这种粒度度量，当在编码后休息期间存在时，与几周后编码前刺激的详细记忆回忆相关，这表明粒度可能促进记忆稳定。研究海马体成熟可以深入了解情景记忆的发展，以及情景记忆在成年期的功能线索。过去的工作已经证明了海马体对记忆表现的年龄相关改善有贡献的证据，但很大程度上依赖于单变量方法（平均海马体体素的活动），这些方法可能对细微的发展变化不敏感。在这里，我们使用一种新方法，通过检查单个海马体体素的时间签名，来揭示在整个发育过程中时间激活模式的独特性（粒度）在区域上的差异（前海马体与后海马体）。重要的是，在假定的记忆稳定窗口期间后海马体的粒度与长期记忆特异性相关。这表明后海马体逐渐建立了支持详细情景回忆的能力。
