Berry M J, Meister M
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
J Neurosci. 1998 Mar 15;18(6):2200-11. doi: 10.1523/JNEUROSCI.18-06-02200.1998.
The response of a spiking neuron to a stimulus is often characterized by its time-varying firing rate, estimated from a histogram of spike times. If the cell's firing probability in each small time interval depends only on this firing rate, one predicts a highly variable response to repeated trials, whereas many neurons show much greater fidelity. Furthermore, the neuronal membrane is refractory immediately after a spike, so that the firing probability depends not only on the stimulus but also on the preceding spike train. To connect these observations, we investigated the relationship between the refractory period of a neuron and its firing precision. The light response of retinal ganglion cells was modeled as probabilistic firing combined with a refractory period: the instantaneous firing rate is the product of a "free firing rate, " which depends only on the stimulus, and a "recovery function," which depends only on the time since the last spike. This recovery function vanishes for an absolute refractory period and then gradually increases to unity. In simulations, longer refractory periods were found to make the response more reproducible, eventually matching the precision of measured spike trains. Refractoriness, although often thought to limit the performance of neurons, may in fact benefit neuronal reliability. The underlying free firing rate derived by allowing for the refractory period often exceeded the observed firing rate by an order of magnitude and was found to convey information about the stimulus over a much wider dynamic range. Thus, the free firing rate may be the preferred variable for describing the response of a spiking neuron.
一个发放脉冲的神经元对刺激的反应通常由其随时间变化的发放率来表征，该发放率可根据脉冲时间的直方图估算得出。如果细胞在每个小时间间隔内的发放概率仅取决于该发放率，那么可以预测其对重复试验的反应具有高度变异性，然而许多神经元表现出更高的保真度。此外，神经元膜在一次脉冲之后会立即进入不应期，因此发放概率不仅取决于刺激，还取决于先前的脉冲序列。为了将这些观察结果联系起来，我们研究了神经元的不应期与其发放精度之间的关系。视网膜神经节细胞的光反应被建模为概率发放并结合不应期：瞬时发放率是一个“自由发放率”（仅取决于刺激）与一个“恢复函数”（仅取决于自上次脉冲以来的时间）的乘积。对于绝对不应期，该恢复函数为零，然后逐渐增加至1。在模拟中，发现较长的不应期会使反应更具可重复性，最终与测量到的脉冲序列的精度相匹配。不应期虽然通常被认为会限制神经元的性能，但实际上可能有益于神经元的可靠性。考虑不应期后得出的潜在自由发放率通常比观察到的发放率高出一个数量级，并且发现在更宽的动态范围内传递有关刺激的信息。因此，自由发放率可能是描述发放脉冲的神经元反应的首选变量。
