Mechanisms of Perceptual Learning in Primary Visual Cortex

描述：有许多类型的学习是在不同的大脑区域实现的，但不同学习形式背后的基本机制可能非常相似。最广泛研究的学习形式之一是视觉系统中的知觉学习，它被定义为通过对感觉任务的训练而在表现上永久提高。训练提高了感知简单和复杂视觉属性的能力，如用随机点立体图定义的深度，刺激的突出，以及通过X光机可视化的炸弹轮廓。研究视觉系统中的知觉学习有助于理解学习机制，因为它被认为涉及视觉加工的早期阶段，其中最了解单个单位和大脑皮层结构的属性。此外，知觉学习范式被用于治疗视觉障碍(如弱视)，并用于增强脑损伤后的重组和行为恢复，强调了解潜在机制的重要性。理解学习机制的一个先决条件是描述单个神经元的响应特性以及它们在学习过程中的相互作用是如何变化的。实现这一点的一个主要障碍是，在学习过程中，无法在体内从相同的单个神经元进行长期记录。现在，我们第一次绕过了这一限制，开发了一种使用长期植入的四极管阵列的方法，允许我们在清醒、行为正常的猕猴连续几天和几周内从相同的神经元进行记录。我们计划在一项方位辨别任务中研究知觉学习，这项任务与练习提高了对刺激方位的辨别成绩有关。在这种模式下的学习是特定于经过训练的视网膜位置的，因此被认为反映了早期视觉区域的可塑性，比如初级视觉皮质(V1)。我们将在猕猴的V1区研究这一过程。首先，我们将测量在不训练期间(特定目标1)在几天和几周内可变定向调节功能的情况。确定V1中基线方位图的稳定性是研究学习如何修改它们的重要第一步。此外，包含在一组神经元活动中的信息除了取决于这些神经元的个体属性外，还取决于这些神经元之间的成对相互作用。一个很好的类比是一个团队的表现，它不仅取决于其个别成员的能力，而且还取决于球员之间的互动方式。因此，为了量化学习前后神经回路的信息量，还必须测量神经元之间的相关性的强度(具体目标2)。在特定的目标3中，我们将在动物接受方位辨别任务的训练时，从V1中的相同神经元进行慢性记录。这是非常令人兴奋的，因为我们现在第一次能够记录学习过程中的单个神经元，并描述神经回路的相关变化。公共卫生相关性研究最广泛的学习形式之一是视觉系统中的知觉学习，其定义是由于大量感官任务的广泛训练而导致的性能的永久性改善。知觉学习范式用于弱视等视觉障碍的治疗，在促进脑损伤后的重组和行为恢复方面具有巨大的潜力，强调了了解学习机制的重要性。我们将研究知觉学习，同时在学习过程中长期记录相同神经元的信息。

DESCRIPTION: There are many types of learning realized in different brain areas but the basic mechanisms underlying different forms of learning may be quite similar. One of the most widely studied forms of learning is perceptual learning in the visual system, defined as the permanent improvement in performance as a result of training on a sensory task. Training improves the ability to perceive simple as well as complex visual attributes such as depth defined with a random-dot stereogram, pop-out of a stimulus, and bomb outlines visualized though x-ray machines. Studying perceptual learning in the visual system is advantageous for understanding mechanisms of learning since it is thought to involve early stages of visual processing where the most is known about the properties of single units and cortical architecture. In addition, perceptual learning paradigms are used in the treatment of visual disorders (such as amblyopia) and in the enhancement of reorganization and behavioral recovery after brain injury, underscoring the importance of understanding the underlying mechanisms. A prerequisite for understanding learning mechanisms is to characterize how the response properties of individual neurons as well as their interactions change during the course of learning. A major impediment for realizing this has been the inability to record from the same individual neurons chronically, in vivo, during the course of learning. We now, for the first time, bypassed this limitation by developing a method using chronically implanted tetrode arrays that allows us to record from the same neurons across multiple consecutive days and weeks in awake, behaving macaques. We plan to study perceptual learning in an orientation discrimination task associated with improved performance in the discrimination of the orientation of a stimulus as a result of practice. Learning in this paradigm is specific to the trained retinal position and is therefore thought to reflect plasticity in early visual areas like the primary visual cortex (V1). We will study this process in area V1 of the macaque. First, we will measure how variable orientation tuning functions are across days and weeks during periods of no training (Specific Aim 1). Determining the stability of baseline orientation maps in V1 is an essential first step for studying how learning can modify them. Moreover, the information contained in the activity of a population of neurons also depends on the pair wise interactions between these neurons in addition to their individual properties. A good analogy is the performance of a team which does not only depend on the capabilities of its individual members but also in the way players interact with each other. Therefore, in order to quantify the information content of neural circuits before and after learning it is essential to also measure the strength of correlations between the neurons (Specific Aim 2). In Specific Aim 3, we will record chronically from the same neurons in V1 while animals are being trained in an orientation discrimination task. This is very exciting since for the first time we are now able to record from individual neurons during the course of learning and characterize the associated changes in neural circuits. PUBLIC HEALTH RELEVANCE One of the most widely studied forms of learning is perceptual learning in the visual system, defined as the permanent improvement in performance as a result of extensive training on numerous sensory tasks. Perceptual learning paradigms are used in the treatment of visual disorders such as amblyopia and using learning paradigms has great potential in the enhancement of reorganization and behavioral recovery after brain injury, underscoring the importance of understanding learning mechanisms. We will study perceptual learning while recording from the same neurons chronically during the course of learning.