Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts.
Neuroscience Program, Brandeis University, Waltham, Massachusetts.
Hippocampus. 2019 Feb;29(2):111-127. doi: 10.1002/hipo.23020. Epub 2018 Nov 22.
Hippocampal place cells represent nonspatial information through a process called rate remapping, which involves a change in the firing rate of a place cell without changes in its spatial specificity. However, many hippocampal phenomena occur on very short time scales over which long-term average firing rates are not an appropriate description of activity. To understand how rate remapping relates to fine-scale temporal firing phenomena, we asked how rate remapping affected burst firing and trial-to-trial spike count variability. In addition, we looked at how rate remapping relates to the theta-frequency oscillations of the hippocampus, which are thought to temporally organize firing on time scales faster than 100 ms. We found that theta phase coding was preserved through changes in firing rate due to rate remapping. Interestingly, rate remapping in CA1 in response to task demands preferentially occurred during the first half of the theta cycle. The other half of the theta cycle contained preferential expression of phase precession, a phenomenon associated with place cell sequences, in agreement with previous results. This difference of place cell coding during different halves of the theta cycle supports recent theoretical suggestions that different processes occur during the two halves of the theta cycle. The differentiation between the halves of the theta cycle was not clear in recordings from CA3 during rate remapping induced by task-irrelevant sensory changes. These findings provide new insight into the way that temporal coding is utilized in the hippocampus and how rate remapping is expressed through that temporal code.
海马体位置细胞通过称为频率重映射的过程来表示非空间信息，该过程涉及位置细胞的发射率发生变化，而其空间特异性不变。然而，许多海马体现象发生在非常短的时间尺度上，在这些时间尺度上，长期平均发射率不是活动的适当描述。为了了解频率重映射与精细时间发射现象之间的关系，我们询问了频率重映射如何影响爆发发射和试验间尖峰计数变异性。此外，我们还研究了频率重映射与海马体的 theta 频率振荡之间的关系，theta 频率振荡被认为在 100 毫秒以内的时间尺度上对发射进行时间组织。我们发现，由于频率重映射导致的发射率变化，theta 相位编码得以保留。有趣的是，由于任务需求导致的 CA1 中的频率重映射优先发生在 theta 周期的前半部分。theta 周期的后半部分优先表达相位超前，这是与位置细胞序列相关的现象，与先前的结果一致。theta 周期的不同半部分的位置细胞编码的这种差异支持了最近的理论假设，即在 theta 周期的两个半部分中发生不同的过程。在由与任务无关的感觉变化引起的频率重映射过程中，来自 CA3 的记录中并没有清楚地区分 theta 周期的两半部分。这些发现为我们提供了对海马体中时间编码的利用方式以及频率重映射如何通过该时间编码来表达的新见解。
