Plasticity of development of vision and of the mammalian visual pathways

我研究的目的是了解处理视觉的大脑通路的发展，以及视觉本身，是如何受到动物早期所看到的东西的影响的，这就是所谓的关于视觉的自然-自然问题。从对具有像我们这样具有精确双目深度感知（立体视觉）的视觉系统的动物物种的研究中，我们知道，在发育过程中存在所谓的“关键时期”，在此期间，异常的视觉输入会影响视觉通路的发育，从而导致视觉障碍。最近有研究表明，在出生前，视觉系统的解剖组织根据一系列遗传指令发展到相当复杂的水平。由遗传指令建立的蓝图提供了一个模板，既允许也限制了出生后视觉体验对发育的进一步影响程度。几年前，我介绍了一种新的方法，通过每天连续地将两种视觉输入相互对照，来检验经验在发展中的作用。在一天中的一部分时间里，动物接受正常的视觉输入，而在其余时间里，它们只接受一只眼睛的视觉输入。第一种视觉输入与出生时由遗传指令建立的解剖模板相匹配，而另一种输入则不匹配。我们推断，与出生时的模板相匹配的视觉输入会比其他的更受青睐。研究结果显然支持这种可能性；双眼的视觉输入仅占总暴露量的30%，超过了或保护了更长的单眼暴露时间，从而使双眼的正常视力和视觉皮层的正常外观得以发展。同样的策略将被用于建立对正常立体视觉发展的更严格的要求，即利用两只眼睛的信息提供像3d电影中那样生动的深度印象的能力。另一项研究将检查在斜视（一种“转动的眼睛”）中出现的两眼间歇性错位的情况下，正常视力和立体视觉发展的要求，这将用棱镜模拟。我们将跟进我们最近的一个意想不到的发现，即在11周之前将小猫放在完全黑暗的环境中10天，通过确定一些条件，如黑暗的长度，这种影响会发生，从而导致严重但暂时的视力丧失。就像我过去的研究一样，在这些不同的研究中，每只眼睛的视力都是通过使用跳跃架来评估的，在跳跃架中，小猫被要求跳跃以获得食物奖励，并抚摸它们下面并排放置的两个刺激物中的一个。* * * * * * * *

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. ********