Spikelets are small spike-like depolarizations that are found in somatic recordings of many neuron types. Spikelets have been assigned important functions, ranging from neuronal synchronization to the regulation of synaptic plasticity, which are specific to the particular mechanism of spikelet generation. As spikelets reflect spiking activity in neuronal compartments that are electrotonically distinct from the soma, four modes of spikelet generation can be envisaged: (1) dendritic spikes or (2) axonal action potentials occurring in a single cell as well as action potentials transmitted via (3) gap junctions or (4) ephaptic coupling in pairs of neurons. In one of the best studied neuron type, cortical pyramidal neurons, the origins and functions of spikelets are still unresolved; all four potential mechanisms have been proposed, but the experimental evidence remains ambiguous. Here we attempt to reconcile the scattered experimental findings in a coherent theoretical framework. We review in detail the various mechanisms that can give rise to spikelets. For each mechanism, we present the biophysical underpinnings as well as the resulting properties of spikelets and compare these predictions to experimental data from pyramidal neurons. We also discuss the functional implications of each mechanism. On the example of pyramidal neurons, we illustrate that several independent spikelet-generating mechanisms fulfilling vastly different functions might be operating in a single cell.

中文翻译：

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锥体神经元中的小穗：产生机制、区分特性和功能意义

小穗是在许多神经元类型的体细胞记录中发现的小尖峰状去极化。小穗被赋予了重要的功能，从神经元同步到突触可塑性的调节，这些都是特定于小穗产生的特定机制的。由于小穗反映了与体细胞不同的神经元隔室中的尖峰活动，因此可以设想四种小穗产生模式：（1）树突状尖峰或（2）发生在单个细胞中的轴突动作电位以及通过（ 3) 间隙连接或 (4) 神经元对中的 ephaptic 耦合。在研究最好的神经元类型之一，即皮质锥体神经元中，小穗的起源和功能仍未得到解决；已提出所有四种潜在机制，但实验证据仍然模棱两可。在这里，我们试图在一个连贯的理论框架中协调分散的实验结果。我们详细回顾了可以产生小穗的各种机制。对于每种机制，我们介绍了小穗的生物物理基础以及由此产生的特性，并将这些预测与锥体神经元的实验数据进行了比较。我们还讨论了每种机制的功能含义。在锥体神经元的例子中，我们说明了几个独立的小穗产生机制，实现了截然不同的功能，可能在单个细胞中运行。我们详细回顾了可以产生小穗的各种机制。对于每种机制，我们介绍了小穗的生物物理基础以及由此产生的特性，并将这些预测与锥体神经元的实验数据进行了比较。我们还讨论了每种机制的功能含义。在锥体神经元的例子中，我们说明了几个独立的小穗产生机制，实现了截然不同的功能，可能在单个细胞中运行。我们详细回顾了可以产生小穗的各种机制。对于每种机制，我们介绍了小穗的生物物理基础以及由此产生的特性，并将这些预测与锥体神经元的实验数据进行了比较。我们还讨论了每种机制的功能含义。在锥体神经元的例子中，我们说明了几个独立的小穗产生机制，实现了截然不同的功能，可能在单个细胞中运行。