Adesnik Hillel
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 USA; Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720 USA.
Neuron. 2017 Aug 30;95(5):1147-1159.e4. doi: 10.1016/j.neuron.2017.08.014.
The synaptic mechanisms of feature coding in the visual cortex are poorly understood, particularly in awake animals. The ratio between excitation (E) and inhibition (I) might be constant across stimulus space, controlling only the gain and timing of neuronal responses, or it might change, directly contributing to feature coding. Whole-cell recordings in L2/3 of awake mice revealed that the E/I ratio systematically declines with increasing stimulus contrast or size. Suppressing somatostatin (SOM) neurons enhanced the E and I underlying size tuning, explaining SOM neurons' role in surround suppression. These data imply that contrast and size tuning result from a combination of a changing E/I ratio and the tuning of total synaptic input. Furthermore, they provide experimental support in awake animals for the "Stabilized Supralinear Network," a model that explains diverse cortical phenomena, and suggest that a decreasing E/I ratio with increasing cortical drive could contribute to many different cortical computations.
视觉皮层中特征编码的突触机制目前仍知之甚少，尤其是在清醒动物中。兴奋（E）与抑制（I）的比例在整个刺激空间中可能是恒定的，仅控制神经元反应的增益和时间，也可能发生变化，直接参与特征编码。对清醒小鼠L2/3层进行的全细胞记录显示，随着刺激对比度或大小的增加，E/I比例会系统性下降。抑制生长抑素（SOM）神经元可增强与大小调谐相关的E和I，这解释了SOM神经元在周围抑制中的作用。这些数据表明，对比度和大小调谐是由变化的E/I比例与总突触输入的调谐共同作用的结果。此外，它们为“稳定超线性网络”这一解释多种皮层现象的模型在清醒动物中提供了实验支持，并表明随着皮层驱动增加E/I比例降低可能有助于许多不同的皮层计算。
