Department of Psychology, University of Jyväskylä , Jyväskylä , Finland.
Faculty of Sport and Health Sciences, Health Sciences, University of Jyväskylä , Jyväskylä , Finland.
J Neurophysiol. 2019 Jan 1;121(1):131-139. doi: 10.1152/jn.00696.2018. Epub 2018 Nov 21.
Hippocampal dentate spikes (DSs) are short-duration, large-amplitude fluctuations in hilar local field potentials and take place while resting and sleeping. During DSs, dentate gyrus granule cells increase firing while CA1 pyramidal cells decrease firing. Recent findings suggest DSs play a significant role in memory consolidation after training on a hippocampus-dependent, nonspatial associative learning task. Here, we aimed to find out whether DSs are important in other types of hippocampus-dependent learning tasks as well. To this end, we trained adult male Sprague-Dawley rats in a spatial reference memory task, a fixed interval task, and a pattern separation task. During a rest period immediately after each training session, we either let neural activity to take place as usual, timed electrical stimulation of the ventral hippocampal commissure (vHC) to immediately follow DSs, or applied the vHC stimulation during a random neural state. We found no effect of vHC stimulation on performance in the spatial reference memory task or in the fixed interval task. Surprisingly, vHC stimulation, especially contingent on DSs, improved performance in the pattern separation task. In conclusion, the behavioral relevance of hippocampal processing and DSs seems to depend on the task at hand. It could be that in an intact brain, offline memory consolidation by default involves associating neural representations of temporally separate but related events. In some cases this might be beneficial for adaptive behavior in the future (associative learning), while in other cases it might not (pattern separation). NEW & NOTEWORTHY The behavioral relevance of dentate spikes seems to depend on the learning task at hand. We suggest that dentate spikes are related to associating neural representations of temporally separate but related events within the dentate gyrus. In some cases this might be beneficial for adaptive behavior in the future (associative learning), while in other cases it might not (pattern separation).
海马齿状回棘波（DSs）是短暂的、幅度大的电活动，在静息和睡眠时发生。在 DSs 期间，齿状回颗粒细胞增加放电，而 CA1 锥体神经元减少放电。最近的研究结果表明，DSs 在依赖海马的非空间联想学习任务的训练后，对记忆巩固起着重要作用。在这里，我们旨在了解 DSs 是否在其他类型的依赖海马的学习任务中也很重要。为此，我们在空间参考记忆任务、固定间隔任务和模式分离任务中训练成年雄性 Sprague-Dawley 大鼠。在每次训练后立即的休息期间，我们让神经活动像往常一样进行，对腹侧海马连合（vHC）进行定时电刺激以立即跟随 DSs，或者在随机神经状态下施加 vHC 刺激。我们发现 vHC 刺激对空间参考记忆任务或固定间隔任务的表现没有影响。令人惊讶的是，vHC 刺激，尤其是在 DSs 发生时，改善了模式分离任务的表现。总之，海马处理和 DSs 的行为相关性似乎取决于手头的任务。默认情况下，离线记忆巩固可能涉及将时间上分离但相关的事件的神经表示相关联。在某些情况下，这可能对未来的适应性行为有益（联想学习），而在其他情况下则不然（模式分离）。新的和值得注意的是，齿状回棘波的行为相关性似乎取决于手头的学习任务。我们认为，齿状回棘波与在齿状回内将时间上分离但相关的事件的神经表示相关联有关。在某些情况下，这可能对未来的适应性行为有益（联想学习），而在其他情况下则不然（模式分离）。
