Medical Scientist Training Program and Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA.
J Neurosci. 2010 Apr 7;30(14):5071-7. doi: 10.1523/JNEUROSCI.2193-09.2010.
Adaptive processes over many timescales endow neurons with sensitivity to stimulus changes over a similarly wide range of scales. Although spike timing of single neurons can precisely signal rapid fluctuations in their inputs, the mean firing rate can convey information about slower-varying properties of the stimulus. Here, we investigate the firing rate response to a slowly varying envelope of whisker motion in two processing stages of the rat vibrissa pathway. The whiskers of anesthetized rats were moved through a noise trajectory with an amplitude that was sinusoidally modulated at one of several frequencies. In thalamic neurons, we found that the rate response to the stimulus envelope was also sinusoidal, with an approximately frequency-independent phase advance with respect to the input. Responses in cortex were similar but with a phase shift that was about three times larger, consistent with a larger amount of rate adaptation. These response properties can be described as a linear transformation of the input for which a single parameter quantifies the phase shift as well as the degree of adaptation. These results are reproduced by a model of adapting neurons connected by synapses with short-term plasticity, showing that the observed linear response and phase lead can be built up from a network that includes a sequence of nonlinear adapting elements. Our study elucidates how slowly varying envelope information under passive stimulation is preserved and transformed through the vibrissa processing pathway.
自适应过程在多个时间尺度上赋予神经元对刺激变化的敏感性，其范围同样广泛。虽然单个神经元的尖峰时间可以精确地反映其输入的快速波动，但平均发放率可以传递关于刺激较慢变化特征的信息。在这里，我们研究了在大鼠触须通路的两个处理阶段中，对缓慢变化的触须运动包络的发放率响应。在麻醉大鼠的触须上，通过噪声轨迹进行移动，其幅度以几个频率之一的正弦波调制。在丘脑神经元中，我们发现刺激包络的率响应也是正弦波，相对于输入有一个近似频率独立的相位提前。皮层中的反应相似，但相位偏移大约大三倍，与更大的发放率适应相一致。这些响应特性可以被描述为输入的线性变换，其中一个参数可以量化相位偏移以及适应程度。通过具有短期可塑性的突触连接的适应神经元模型可以再现这些结果，表明观察到的线性响应和相位超前可以由一个包含一系列非线性适应元件的网络构建。我们的研究阐明了在被动刺激下，如何通过触须处理通路来保存和转换缓慢变化的包络信息。
