Space and time are both essential features of episodic memory, for which the hippocampus is critical (Howard & Eichenbaum, 2015). Spatial tasks have been used effectively to study the behavioral relevance of place cells. However, the behavioral paradigms utilized for the study of time cells have not used time duration as a variable that animals need to be aware of to solve the task. Therefore, the behavioral relevance of this cell firing is unclear. In order to directly study the role of the hippocampus in processing elapsed time, we created a novel time duration discrimination task. Rats learned to make a decision to turn left or right depending on the preceding tone duration (10 s, left turn; 20 s, right turn). Once the rats reached criterion performance of 90% correct on two out of three consecutive days, they received either an excitotoxic hippocampal lesion or a sham‐lesion surgery. After recovery, rats were tested to determine hippocampal involvement in discriminating time duration. Rats with hippocampal lesions performed at chance level on their first testing day postlesion, and they were impaired relative to the sham‐lesioned rats. Although the hippocampal‐lesioned rats began discriminating at above chance level, their performance never returned to criterion even with 50 days of postoperative testing. Furthermore, while sham rats showed no difference in the number of errors they made on 10‐ versus 20‐s delay trials, hippocampal lesion rats similarly improved their performance under the 10‐s delay condition, but not under the 20‐s delay condition. Results indicate that hippocampal lesions resulted in a selective impairment in discriminating elapsed time only during the longer delay trials. The implications of these results are discussed in relation to the limits of working‐memory capacity and to the role of sustained hippocampal time cell activity in memory performance depending on the perceived relevance of the delay period.

中文翻译：

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在情景记忆的时间组织中，海马体支持经过时间的体验。

空间和时间都是情景记忆的基本特征，海马体对此至关重要（Howard & Eichenbaum, 2015）。空间任务已被有效地用于研究位置细胞的行为相关性。然而，用于时间细胞研究的行为范式并未将持续时间用作动物解决任务需要注意的变量。因此，这种细胞放电的行为相关性尚不清楚。为了直接研究海马体在处理经过时间方面的作用，我们创建了一个新的持续时间辨别任务。大鼠学会了根据前一音持续时间（10 秒，左转；20 秒，右转）来决定向左还是向右转。一旦大鼠在连续三天中的两天内达到 90% 正确的标准表现，他们接受了兴奋性毒性海马病变或假手术。恢复后，对大鼠进行测试以确定海马参与区分持续时间。海马损伤大鼠在损伤后的第一个测试日表现出偶然水平，并且与假损伤大鼠相比，它们受损。尽管海马体损伤的大鼠开始以高于偶然的水平进行区分，但即使经过 50 天的术后测试，它们的表现也从未恢复到标准水平。此外，虽然假大鼠在 10 秒和 20 秒延迟试验中犯的错误数量没有差异，但海马损伤大鼠在 10 秒延迟条件下的表现同样提高，但在 20 秒延迟条件下则不然。结果表明，仅在较长延迟试验期间，海马病变导致在区分经过时间方面的选择性损伤。这些结果的含义与工作记忆容量的限制以及持续的海马时间细胞活动在记忆性能中的作用有关，这取决于延迟期的感知相关性。