Testing and surpassing limits of 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，这种神经可塑性经常发生，例如当我们从室内移动到室外时。不断变化的环境会极大地影响视觉输入，皮层神经元会改变它们的反应方式，以保持我们的视力。这种类型的神经可塑性，被称为视觉适应，在成年人的大脑中很容易发生。然而，它的影响往往是短期的，限制了它在教育、培训和卫生方面的潜在应用。为了理解和克服这一障碍，明尼苏达大学的斯蒂芬·恩格尔博士和他的同事们将通过延长实验室研究时间的一个数量级来测试适应的极限。参与者将连续适应长达一周的时间，通过虚拟现实护目镜观察世界，该护目镜显示头戴式摄像头的修改输出。这些实验将测量适应的影响能持续多久，并测试几个可能限制这种神经可塑性增长的因素。这包括大脑中受益于神经可塑性的部分和可能受到神经可塑性伤害的部分之间的竞争，因为它们依赖于提供神经可塑性输入的大脑区域的稳定性。理解适应应该允许它产生有益的神经可塑性，这有许多应用。它可以成为培训视觉专家的一部分，如行李扫描仪操作员或图像分析师。它可能会成为重建弱视等视觉疾病患者大脑的一部分。这项工作还将检验适用于许多领域的神经可塑性理论。它将为认知神经科学的教学提供教材，并将直接支持对各种研究生和本科生进行尖端方法的培训。成年人的视觉皮层可以根据环境的变化显著改变其功能，使其在输入大量变化的情况下仍能发挥最佳功能。关键的是，视觉体验环境的时间越长，适应能力就越强，持续时间也就越长。这表明长期接触改变的视觉输入可能会在大脑皮层产生持久的变化。技术问题阻碍了在受控条件下长时间适应持续时间的研究，然而仍然不知道是否有一些因素“刹车”，限制了它的强度和耐久性。PI开发了克服这一障碍的方法，并检查了连续4天的适应效果，发现了明显的局限性。拨款的总体目标是了解产生这些限制的制动器。从整体上看，适应既会带来收益，也会带来成本，而这一提议将检验观察到的限制是否源于它们。第一组实验将测试成本是否限制了早期视觉区域的适应，检查文献中的特定成本，删除它们，并观察适应的限制是否仍然存在。第二组实验将检验长期适应。他们将测试一个假设，即长期适应可以克服限制，通过纠正后期视觉区域的“编码灾难”来降低成本。这项工作将区分主要的适应理论，使用行为和功能磁共振成像（fMRI）数据的定量分析。它也代表着一个重大的经验进步；数十项研究已经检查了视觉皮层的适应性，但之前的工作没有测量或测试适应的极限。从教育到军事再到公共卫生，这项研究的结果可能会影响到视觉可塑性很重要的各种领域的工作。工作的结果将被纳入教育材料（一个介绍功能磁共振成像课程和文本），将免费分发。赠款还将为不同群体的学生提供培训机会。

The brain has a remarkable ability to modify its own function. In the visual system such neuroplasticity occurs routinely, for example when we move from indoors to outside. Changing environments affects visual input dramatically, and cortical neurons alter how they respond in order to keep us seeing well. This type of neuroplasticity, called visual adaptation, occurs readily in the adult brain. Its effects tend to be short-lasting, however, limiting its potential applications in education, training, and health. To understand and overcome this roadblock, Dr. Stephen Engel and colleagues at The University of Minnesota will test the limits of adaptation, by extending laboratory studies an order of magnitude in duration. Participants will adapt for up to a week continuously, by viewing the world through virtual reality goggles that display modified output of a head-mounted camera. The experiments will measure how long-lasting the effects of adaptation can become, and test several factors that could be limiting the growth of this type of neuroplasticity. These include competition between the parts of the brain that benefit from neuroplasticity and the parts that could be hurt by it, since they depend upon stability of the brain regions that provide their input. Understanding adaptation should allow it to produce beneficial neuroplasticity, which has many applications. It could become part of training visual experts such as baggage scanner operators or imagery analysts. It could become part of efforts to rewire the brains of patients suffering from visual diseases, such as amblyopia ("lazy eye"). The work will also test theories of neuroplasticity that are applicable in many domains. It will produce educational materials for teaching of cognitive neuroscience, and will directly support the training of a diverse set of graduate and undergraduate students in cutting edge methods.Adult visual cortex can alter its function dramatically in response to changes in the environment, allowing it to function optimally, despite large changes in input. Critically, the longer vision experiences an environment, the stronger and longer lasting adaptation becomes. This suggests that long-term exposure to altered visual input may produce long-lasting changes in cortex. Technical issues have prevented the study of long adapting durations under controlled conditions, however leaving it unknown whether some factors 'put on the brakes', restricting its strength and durability. The PI developed methods to overcome this roadblock, and examined effects of a 4-days of continuous adaptation, revealing significant limits. The general goal of the grant is to understand the brakes producing those limits. For vision as a whole, adaptation can produce costs, as well as benefits, and this proposal will test whether observed limits are due to them. A first set of experiments will test whether costs limit adaptation in early visual areas, examining specific costs from the literature, removing them, and observing whether limits on adaptation remain present. A second set of experiments will examine longer-term adaptation. They will test the hypothesis that long-term adaptation can overcome limits, reducing costs by correcting for a "coding catastrophe" in later visual areas. The work will distinguish between major theories of adaptation, using quantitative analysis of behavioral and functional MRI (fMRI) data. It also represents a major empirical step forward; dozens of studies have examined adaptation in visual cortex, but no previous work has measured or tested adaptation's limits. Results of this research could influence work in a diverse array of fields where visual plasticity is important, from education to the military to public health. Results of the work will be incorporated into educational materials (an introductory fMRI course and text) that will be freely distributed. The grant will also provide training opportunities for a diverse group of students.