Plasticity of development of vision and of the mammalian visual pathways

我的研究目的是了解大脑中处理视觉的路径以及视觉本身的发展如何受到动物早期所见的影响，即所谓的与视觉有关的自然-营养问题。从动物物种的研究中得知，在发育过程中，异常的视觉输入会影响导致视觉障碍的视觉通路的发展，这些动物物种的视觉系统与我们的视觉系统一样，具有精确的双眼深度感知(立体视觉)。最近的研究表明，在出生之前，视觉系统的解剖组织根据一系列遗传指令发育到一个相当复杂的水平。由遗传指令建立的蓝图提供了一个模板，既允许也限制出生后视觉体验进一步影响发育的程度。几年前，我引入了一种新的方法来检验经验在开发中的作用，方法是每天让两个视觉输入相互竞争。在一天的部分时间里，动物接受正常的视觉输入，而在其余的时间里，它们接受严重异常的输入，形式是只有一只眼睛的视觉输入。第一个视觉输入与出生时遗传指令建立的解剖模板匹配，而另一个输入不匹配。我们推断，与出生时的模板匹配的视觉输入会比另一种更受欢迎。结果显然支持这种可能性；仅占总暴露时间30%的双眼视觉输入超过或保护了不受更长时间的每日单眼暴露的影响，以允许双眼正常视力的发展以及视觉皮质的正常外观。同样的策略将被用来建立对正常立体视觉发展的更严格的要求，即使用来自两只眼睛的信息来提供3D电影中生动的深度印象的能力。另一项研究将考察在双眼间歇性错位的情况下，正常视力和立体视觉的发育要求，就像用棱镜模拟的斜视(转眼)。我们将跟进最近一项出人意料的发现，即11周大之前被置于完全黑暗中10天的小猫会遭受严重但暂时的视力丧失，方法是确定一些条件，如发生这种影响的黑暗时间长度。和我之前的研究一样，在这些不同的研究中，每只眼睛的视力是通过使用跳台来评估的，在跳台上，小猫被要求跳跃以获得食物奖励，并抚摸下面并排放置的两个刺激中的一个。********

The objective of my research is to understand how the development of the pathways in the brain that process vision, and vision itself, is influenced by what an animal sees early in life, the so-called nature-nuture issue with respect to vision. From studies on animal species that have visual systems organized like ours for accurate binocular depth perception (stereoscopic vision), it is known that there are so called "critical periods" in development during which abnormal visual input can effect the development of the visual pathways that result in visual impairments. More recently it has been shown that prior to birth the anatomical organization of the visual system develops according to a series of genetic instructions to a level that can be quite sophisticated. The blueprint established by genetic instructions provides the template that both allows and constrains the extent to which visual experience after birth can further influence development. A few years ago I introduced a new method to examine the role of experience in development by sequentially pitting two visual inputs against each other each day. For part of the day animals receive normal visual input while for the remainder they receive grossly abnormal input, in the form of visual input to just one eye. The first visual input matches the anatomical template established by genetic instruction at birth, while the other input does not. We reasoned that visual input that matches the template at birth would be favoured over the other. The results clearly favour this possibility; binocular visual input that amounted to just 30% of the total exposure outweighed or protected against much longer daily periods of monocular exposure to permit the development of normal visual acuity in both eyes as well normal appearance of the visual cortex. The same strategy will be used to establish the far more strict requirements for development of normal stereoscopic vision, the ability to use information from the two eyes to provide a vivid impression of depth as in 3-D movies. Another study will examine the requirements for development of normal visual acuity and stereoscopic vision in the presence of intermittent misalignment of the two eyes as occurs in strabismus (a" turned eye") that will be simulated with prisms. We will follow-up to a recent unexpected finding of ours, that kittens placed in total darkness for 10 days before the age of 11 weeks suffer a severe but temporary loss of vision by determining some of the conditions such as the length of darkness under which this effects occur. As in my past studies, the vision of each eye for these various studies is evaluated by use of a jumping stand where kittens are required to jump for a food reward and petting to one of two stimuli placed side by side below them. ********