Mechanisms of long-term adaptation in visual cortex

大脑有一种非凡的能力来改变自己的功能。在视觉系统中，当儿童学习阅读时，当老年人适应视力受损时，当新司机掌握导航交通时，这种可塑性是显而易见的。然而，在视觉大脑中产生长期可塑性的机制仍然不清楚。在国家科学基金会的支持下，明尼苏达大学的斯蒂芬·恩格尔博士正在进行研究，以阐明长期视觉可塑性的机制。这项工作建立在相对较好理解的短期可塑性影响的基础上。例如，当观察者看到明亮的条纹图案几分钟后，他们的视觉系统就会适应，结果可能会产生相当戏剧性的后果：以前明显的类似条纹的模糊图案可能会短暂地完全看不见。但很少有实验室研究长期考察知觉适应，这主要是由于方法上的限制。该项目使用最近开发的技术来克服这些障碍。参与者在头盔显示器上观看视频，该显示器源于头盔摄像头，并由笔记本电脑进行图像处理。该系统允许参与者生活在一个经过数字改变的视觉世界中。有四个实验使用这个系统来测试视觉系统中关于长期可塑性的假说。第一个假设是，持续时间更长的适应将产生更持久的可塑性。参与者被安排在类似于产生短期知觉适应效果的环境中长达五天的时间。适应的持久性是通过传统的知觉能力测试来衡量的。第二个假设是，正如初步结果所表明的那样，视觉系统适应于不考虑有噪音的、没有信息的视觉输入。这个项目中的实验测量了这种新的适应形式在长期内的强度。第三种假设认为，这两种适应效应都发生在早期的视觉大脑皮层。为了验证这一点，用功能磁共振成像(FMRI)测量了长期适应的神经基础。总而言之，这些实验可以强烈地约束对长期视觉可塑性的经验和理论描述。这项研究正在推进对人类视觉系统如何修改自身操作的理解。这种能力，即视觉可塑性，是获得一系列人类技能的基础，从学习阅读，到学习击球，再到学习看到卫星图像中的模式。该项目使用新技术将观察者放置在一个数字改变的世界中长达5天，并测量他们的视觉感知和视觉皮质如何适应这一挑战。结果可以帮助确定特定的因素，例如视觉刺激的长度和种类，这些因素会导致视觉表现的长期变化。反过来，在视觉可塑性至关重要的各种领域，从教育到军事再到公共卫生，这些技术都应该有重要的应用。

The brain has a remarkable ability to change its own function. In the visual system, such plasticity is evident when children learn to read, when the elderly adjust to impaired vision, and when new drivers master navigating traffic. The mechanisms that produce long-lasting plasticity in the visual brain remain unclear, however. With support from the National Science Foundation, Dr. Stephen Engel of the University of Minnesota is carrying out research to elucidate mechanisms of long-term visual plasticity. The work builds upon effects of short-term plasticity that are relatively well-understood. For example, when observers view a bright pattern of stripes for a few minutes, their visual systems adapt, and fairly dramatic consequences can result: Faint patterns of similar stripes that were previously apparent can be briefly rendered completely invisible. But few laboratory studies have examined perceptual adaptation over the long term, primarily due to methodological limitations. This project uses recently developed technology to overcome those roadblocks. Participants view video on a head-mounted display that originates in a head-mounted camera and is image-processed by a lap-top computer. The system allows participants to live in a visual world that has been digitally altered. Four experiments use this system to test hypotheses about long-lasting plasticity in the visual system. The first hypothesis is that longer duration adaptation will produce longer lasting plasticity. Participants are placed for up to five days in environments similar to those that produce short-term perceptual adaptation effects. The persistence of adaptation is measured using traditional tests of perceptual abilities. The second hypothesis is that the visual system adapts to discount noisy, uninformative visual input, as suggested by preliminary results. Experiments in this project measure the strength of this novel form of adaptation over the long term. The third hypothesis is that both kinds of adaptation effects arise in early visual cerebral cortex. To test this, the neural bases of long-term adaptation is measured with functional magnetic resonance imaging (fMRI). Together, these experiments can strongly constrain both empirical and theoretical accounts of long-lasting visual plasticity.This research is advancing understanding of how the human visual system can modify its own operation. This ability, visual plasticity, underlies the acquisition a wide array of human skills, from learning to read, to learning to hit a baseball, to learning to see patterns in satellite imagery. The project uses novel technology to place observers in a digitally altered world for up to 5 days, and measures how their visual perception and their visual cortex adapt to this challenge. Results can help identify specific factors, for example the length and kind of visual stimulation, which lead to long-lasting changes in visual performance. These in turn should have important applications in a diverse array of fields where visual plasticity is critical, from education to the military to public health.