Center for Perceptual Systems, Section of Neurobiology, School of Biological Sciences, College of Natural Sciences, The University of Texas at Austin, Austin, Texas 78705, USA.
J Neurosci. 2011 Aug 24;31(34):12339-50. doi: 10.1523/JNEUROSCI.2039-11.2011.
Primary visual cortex (V1) is the site at which orientation selectivity emerges in mammals: visual thalamus afferents to V1 respond equally to all stimulus orientations, whereas their target V1 neurons respond selectively to stimulus orientation. The emergence of orientation selectivity in V1 has long served as a model for investigating cortical computation. Recent evidence for orientation selectivity in mouse V1 opens cortical computation to dissection by genetic and imaging tools, but also raises two essential questions: (1) How does orientation selectivity in mouse V1 neurons compare with that in previously described species? (2) What is the synaptic basis for orientation selectivity in mouse V1? A comparison of orientation selectivity in mouse and in cat, where such measures have traditionally been made, reveals that orientation selectivity in mouse V1 is weaker than in cat V1, but that spike threshold plays a similar role in narrowing selectivity between membrane potential and spike rate. To uncover the synaptic basis for orientation selectivity, we made whole-cell recordings in vivo from mouse V1 neurons, comparing neuronal input selectivity-based on membrane potential, synaptic excitation, and synaptic inhibition-to output selectivity based on spiking. We found that a neuron's excitatory and inhibitory inputs are selective for the same stimulus orientations as is its membrane potential response, and that inhibitory selectivity is not broader than excitatory selectivity. Inhibition has different dynamics than excitation, adapting more rapidly. In neurons with temporally modulated responses, the timing of excitation and inhibition was different in mice and cats.
初级视皮层（V1）是哺乳动物中出现朝向选择性的部位：视丘脑传入 V1 的纤维对所有刺激朝向的反应相等，而其靶 V1 神经元则对刺激朝向选择性地反应。V1 中朝向选择性的出现长期以来一直是研究皮层计算的模型。最近在小鼠 V1 中出现朝向选择性的证据为通过遗传和成像工具来剖析皮层计算提供了可能性，但也提出了两个基本问题：（1）小鼠 V1 神经元中的朝向选择性与以前描述的物种中的朝向选择性相比如何？（2）小鼠 V1 中朝向选择性的突触基础是什么？将小鼠和传统上已进行此类测量的猫的 V1 中的朝向选择性进行比较，结果表明，小鼠 V1 中的朝向选择性比猫 V1 中的弱，但在膜电位和尖峰率之间缩小选择性方面，尖峰阈值起着相似的作用。为了揭示朝向选择性的突触基础，我们在体内从小鼠 V1 神经元中进行了全细胞膜片钳记录，比较了基于膜电位、突触兴奋和突触抑制的神经元输入选择性与基于尖峰的输出选择性。我们发现，一个神经元的兴奋性和抑制性输入与膜电位反应的刺激朝向选择性相同，并且抑制选择性不比兴奋选择性宽。抑制的动力学与兴奋不同，适应更快。在具有时间调制反应的神经元中，兴奋和抑制在小鼠和猫中的时间不同。
