Jurjut Ovidiu, Georgieva Petya, Busse Laura, Katzner Steffen
Werner Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen 72076, Germany, and.
Division of Neurobiology, Department Biology II, LMU Munich, Munich 82151, Germany.
J Neurosci. 2017 Jul 5;37(27):6460-6474. doi: 10.1523/JNEUROSCI.3485-16.2017. Epub 2017 May 30.
A fundamental property of visual cortex is to enhance the representation of those stimuli that are relevant for behavior, but it remains poorly understood how such enhanced representations arise during learning. Using classical conditioning in adult mice of either sex, we show that orientation discrimination is learned in a sequence of distinct behavioral stages, in which animals first rely on stimulus appearance before exploiting its orientation to guide behavior. After confirming that orientation discrimination under classical conditioning requires primary visual cortex (V1), we measured, during learning, response properties of V1 neurons. Learning improved neural discriminability, sharpened orientation tuning, and led to higher contrast sensitivity. Remarkably, these learning-related improvements in the V1 representation were fully expressed before successful orientation discrimination was evident in the animals' behavior. We propose that V1 plays a key role early in discrimination learning to enhance behaviorally relevant sensory information. Decades of research have documented that responses of neurons in visual cortex can reflect the behavioral relevance of visual information. The behavioral relevance of any stimulus needs to be learned, though, and little is known how visual sensory processing changes, as the significance of a stimulus becomes clear. Here, we trained mice to discriminate two visual stimuli, precisely quantified when learning happened, and measured, during learning, the neural representation of these stimuli in V1. We observed learning-related improvements in V1 processing, which were fully expressed before discrimination was evident in the animals' behavior. These findings indicate that sensory and behavioral improvements can follow different time courses and point toward a key role of V1 at early stages in discrimination learning.
视觉皮层的一个基本特性是增强对与行为相关的那些刺激的表征，但对于这种增强的表征在学习过程中是如何产生的，我们仍然知之甚少。通过对成年雌雄小鼠进行经典条件反射实验，我们发现方向辨别是在一系列不同的行为阶段中习得的，在这些阶段中，动物首先依赖刺激的外观，然后利用其方向来指导行为。在确认经典条件反射下的方向辨别需要初级视觉皮层（V1）之后，我们在学习过程中测量了V1神经元的反应特性。学习提高了神经辨别能力，锐化了方向调谐，并导致更高的对比度敏感性。值得注意的是，在动物行为中成功的方向辨别明显之前，V1表征中这些与学习相关的改善就已经完全表现出来了。我们提出，V1在辨别学习的早期阶段起着关键作用，以增强与行为相关的感觉信息。数十年的研究表明，视觉皮层中神经元的反应可以反映视觉信息的行为相关性。然而，任何刺激的行为相关性都需要学习，而且当刺激的重要性变得清晰时，视觉感觉处理如何变化却知之甚少。在这里，我们训练小鼠辨别两种视觉刺激，精确量化学习发生的时间，并在学习过程中测量V1中这些刺激的神经表征。我们观察到V1处理中与学习相关的改善，这些改善在动物行为中的辨别明显之前就已经完全表现出来了。这些发现表明，感觉和行为的改善可能遵循不同的时间进程，并指向V1在辨别学习早期阶段的关键作用。
