A role of afferent activity in the maturation of thalamocortical connections of visual system

猫、猴和包括人类在内的其他哺乳动物的视皮层神经元的双目视觉反应可以在出生后发育的关键期被单眼视觉剥夺改变，这是最著名的经验依赖性脑功能改变的例子之一。假设来自每只眼的传入细胞相互竞争与皮质神经元的突触连接，来自被剥夺眼的不太活跃的传入无法维持这种联系，即两种传入细胞的活动之间的平衡对决定每条眼特定通路的命运是重要的。这一突触竞争假说已经在猫的各种类型的剥夺实验中得到了支持。如果这样的竞争假说成立，那么来自一只眼睛的输入的增加而不是由于剥夺而导致的减少也应该改变皮层神经元的双眼反应。否则，这种由剥夺引起的变化可能是由于“废弃”的反应能力减弱所致。然而，这一假说从未用这种单眼激活范式进行过检验。在本项目中，我们通过电刺激行为猫2天来激活其中一条视神经，发现这种慢性的单眼激活导致皮层神经元视觉反应的眼睛优势转移。

Binocular visual responsiveness of neurons in visual cortex of cats, monkeys and other mammals including humans can be changed by monocular visual deprivation in the critical period of postnatal development, one of the best-known examples of experience-dependent modification of brain function.It is hypothesized that afferents from each eye compete with one another for synaptic connections with cortical neurons so that less active afferents from the deprived eye fail to maintain the connections, i.e., balance between activities of both afferents is important to determine the fate of each eye-specific pathway.This synaptic competition hypothesis has been supported by various types of deprivation experiments in kittens. If such a competition hypothesis is valid, then an increase in inputs from one eye instead of decrease due to deprivation should also change binocular responsiveness of cortical neurons. Otherwise the deprivation-induced change might be due to "disuse" weakening of responsiveness.However, the hypothesis has never been tested with such a monocular activation paradigm. In the present project, we activated one of the optic nerves by electrical stimulation in behaving kittens for 2 days, and found that such a chronic, monocular activation induced a shift in ocular dominance of visual responses of cortical neurons.