Chino Y M, Smith E L, Yoshida K, Cheng H, Hamamoto J
College of Optometry, University of Houston, Texas 77204-6052.
J Neurosci. 1994 Aug;14(8):5050-67. doi: 10.1523/JNEUROSCI.14-08-05050.1994.
The postnatal development of cortical binocularity is known to be adversely affected by early abnormal visual experience. However, little information exists on how the signals from the two eyes are combined in individual cortical neurons of animals reared with early discordant binocular visual experience. Since this is a fundamental issue in understanding visual cortical development, we used extracellular single-unit recording methods to study binocular integration in striate cortical neurons of strabismic cats. Specifically, we measured the sensitivity of individual cells to the relative interocular spatial phase of dichoptically presented drifting sinusoidal gratings (i.e., to binocular retinal image disparity). Clear alterations in ocular dominance were observed in all strabismic subjects. Nevertheless, the majority of cortical neurons exhibited some form of binocular interactions when both eyes were stimulated together. The most prominent aspect of cortical physiology in the strabismic animals was the relatively high prevalence of suppressive binocular interactions. Suppression was most frequently found in kittens reared with 2 weeks of early optical dissociation and among adult cats that received 2 weeks of early optical dissociation and a prolonged recovery period. However, substantial excitatory binocular interactions were also maintained in these animals. With an extended period of interocular misalignment (3 or 8 months), all forms of binocular interactions, excitatory and suppressive, were drastically reduced and a greater number of neurons were truly monocular. Although the reduction in the strength of binocular interactions occurred in all units irrespective of their monocular spatial properties, the effect was more pronounced among those units tuned to higher spatial frequencies and this spatial-frequency-dependent effect was larger in the subjects receiving longer periods of binocular dissociation. The results suggest that the "breakdown" of cortical binocular properties in strabismic subjects is not an all-or-none process, and that suppressive binocular interactions may be closely associated with the abnormal binocular interactions exhibited by strabismic humans. Furthermore, our findings are consistent with the notion that cortical disparity-detecting mechanisms are spatial-frequency dependent and, thus, can be selectively altered depending on an animal's early visual experience.
已知早期异常视觉经验会对皮质双眼视觉的产后发育产生不利影响。然而，对于早期双眼视觉经验不一致的动物，其单个皮质神经元中来自双眼的信号是如何整合的，目前了解甚少。由于这是理解视觉皮质发育的一个基本问题，我们采用细胞外单单位记录方法，研究斜视猫纹状皮质神经元中的双眼整合。具体而言，我们测量了单个细胞对双眼分别呈现的漂移正弦光栅的相对眼间空间相位的敏感性（即对双眼视网膜图像视差的敏感性）。在所有斜视实验对象中均观察到眼优势的明显改变。尽管如此，当双眼同时受到刺激时，大多数皮质神经元仍表现出某种形式的双眼相互作用。斜视动物皮质生理学最显著的方面是抑制性双眼相互作用的相对高发生率。抑制现象最常出现在早期经历2周光学分离饲养的小猫以及接受2周早期光学分离和较长恢复期的成年猫中。然而，这些动物中也保留了大量兴奋性双眼相互作用。随着眼间错位时间延长（3或8个月），兴奋性和抑制性的所有形式的双眼相互作用都大幅减少，更多神经元真正变为单眼。尽管双眼相互作用强度的降低在所有单位中都会发生，与它们的单眼空间特性无关，但在那些调谐到更高空间频率的单位中，这种效应更为明显；并且在接受更长时间双眼分离的实验对象中，这种空间频率依赖性效应更大。结果表明，斜视实验对象中皮质双眼特性的“破坏”并非全或无的过程，抑制性双眼相互作用可能与斜视人类表现出的异常双眼相互作用密切相关。此外，我们的研究结果与以下观点一致，即皮质视差检测机制是空间频率依赖性的，因此可以根据动物的早期视觉经验而选择性地改变。
