Mechanisms of long-term adaptation in visual cortex

大脑具有改变自身功能的非凡能力。在视觉系统中，这种可塑性在儿童学习阅读、老年人适应视力受损以及新司机掌握交通导航时都很明显。然而，在视觉大脑中产生持久可塑性的机制仍然不清楚。在美国国家科学基金会的支持下，明尼苏达大学的Stephen Engel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的影响之上。例如，当观察者看到一个明亮的条纹图案几分钟时，他们的视觉系统会适应，并产生相当戏剧性的后果：以前明显的类似条纹的微弱图案可以短暂地完全不可见。但是，很少有实验室研究长期考察知觉适应，主要是由于方法的局限性。该项目使用最近开发的技术来克服这些障碍。参与者在头戴式显示器上观看视频，该视频来自头戴式摄像机，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化修改的视觉世界中。四个实验使用该系统来测试视觉系统中持久可塑性的假设。第一个假设是，较长时间的适应将产生更持久的可塑性。参与者被放置在类似于产生短期感知适应效应的环境中长达五天。适应的持久性是用传统的感知能力测试来衡量的。第二个假设是，视觉系统适应折扣嘈杂，无信息的视觉输入，如初步结果所示。该项目的实验测量了这种新的适应形式在长期内的强度。第三个假设是，这两种适应效应都出现在早期的视觉大脑皮层。为了验证这一点，长期适应的神经基础是用功能性磁共振成像（fMRI）来测量的。总之，这些实验可以强烈地限制长期视觉可塑性的经验和理论帐户。这项研究正在推进人类视觉系统如何修改自己的操作的理解。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，到学习打棒球，再到学习在卫星图像中看到图案。该项目使用新技术将观察者置于数字化改变的世界中长达5天，并测量他们的视觉感知和视觉皮层如何适应这一挑战。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。这些反过来应该在视觉可塑性至关重要的各种领域中有重要的应用，从教育到军事再到公共卫生。

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.