Neuroscience Graduate Program, Department of Neuroscience, Peter O'Donnell Jr. Brain Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390
J Neurosci. 2022 May 11;42(19):3975-3988. doi: 10.1523/JNEUROSCI.2479-21.2022. Epub 2022 Apr 8.
The hippocampus is critical for rapid acquisition of many forms of memory, although the circuit-level mechanisms through which the hippocampus rapidly consolidates novel information are unknown. Here, the activity of large ensembles of hippocampal neurons in adult male Long-Evans rats was monitored across a period of rapid spatial learning to assess how the network changes during the initial phases of memory formation and retrieval. In contrast to several reports, the hippocampal network did not display enhanced representation of the goal location via accumulation of place fields or elevated firing rates at the goal. Rather, population activity rates increased globally as a function of experience. These alterations in activity were mirrored in the power of the theta oscillation and in the quality of theta sequences, without preferential encoding of paths to the learned goal location. In contrast, during brief "offline" pauses in movement, representation of a novel goal location emerged rapidly in ripples, preceding other changes in network activity. These data demonstrate that the hippocampal network can facilitate active navigation without enhanced goal representation during periods of active movement, and further indicate that goal representation in hippocampal ripples before movement onset supports subsequent navigation, possibly through activation of downstream cortical networks. Understanding the mechanisms through which the networks of the brain rapidly assimilate information and use previously learned knowledge are fundamental areas of focus in neuroscience. In particular, the hippocampal circuit is a critical region for rapid formation and use of spatial memory. In this study, several circuit-level features of hippocampal function were quantified while rats performed a spatial navigation task requiring rapid memory formation and use. During periods of active navigation, a general increase in overall network activity is observed during memory acquisition, which plateaus during memory retrieval periods, without specific enhanced representation of the goal location. During pauses in navigation, rapid representation of the distant goal well emerges before either behavioral improvement or changes in online activity.
海马体对于快速获取多种形式的记忆至关重要，尽管海马体快速巩固新信息的回路级机制尚不清楚。在这里，通过监测成年雄性 Long-Evans 大鼠在快速空间学习过程中大量海马神经元的活动，评估了网络在记忆形成和检索的初始阶段如何变化。与几项报道相反，海马网络并没有通过积累位置场或在目标位置提高放电率来显示目标位置的增强表示。相反，群体活动率随着经验的增加而全局增加。这些活动的改变反映在θ振荡的功率和θ序列的质量上，而不是对学习目标位置的路径进行优先编码。相比之下，在运动的短暂“离线”暂停期间，新目标位置的表示迅速出现在涟漪中，先于网络活动的其他变化。这些数据表明，海马网络可以在主动运动期间没有增强的目标表示的情况下促进主动导航，并且进一步表明，在运动开始之前，海马体涟漪中的目标表示支持随后的导航，可能通过激活下游皮质网络。理解大脑网络快速吸收信息并利用先前学习的知识的机制是神经科学的核心关注领域。特别是，海马体回路是快速形成和使用空间记忆的关键区域。在这项研究中，当大鼠执行需要快速记忆形成和使用的空间导航任务时，量化了海马体功能的几个回路级特征。在主动导航期间，观察到记忆获取过程中整体网络活动的普遍增加，在记忆检索期间达到平台期，而目标位置没有特定的增强表示。在导航暂停期间，遥远目标的快速表示在行为改善或在线活动变化之前就已经出现。
