Department of Computational Biology, University of Tokyo, Kashiwa 277-8561, Japan.
J Neurosci. 2011 Jan 26;31(4):1516-27. doi: 10.1523/JNEUROSCI.3811-10.2011.
The development of direction selectivity in the visual system depends on visual experience. In the developing Xenopus retinotectal system, tectal neurons (TNs) become direction selective through spike timing-dependent plasticity (STDP) after repetitive retinal exposure to a moving bar in a specific direction. We investigated the mechanism responsible for the development of direction selectivity in the Xenopus retinotectal system using a neural circuit model with STDP. In this retinotectal circuit model, a moving bar stimulated the retinal ganglion cells (RGCs), which provided feedforward excitation to the TNs and interneurons (INs). The INs provided delayed feedforward inhibition to the TNs. The TNs also received feedback excitation from neighboring TNs. As a synaptic learning rule, a molecular STDP model was used for synapses between the RGCs and TNs. The retinotectal circuit model reproduced experimentally observed features of the development of direction selectivity, such as increase in input to the TN. The peak of feedforward excitation from RGCs to TNs shifted earlier as a result of STDP. Together with the delayed feedforward inhibition, a stronger earlier transient feedforward signal was generated, which exceeded the threshold of the feedback excitation from the neighboring TNs and resulted in amplification of input to the TN. The suppression of the delayed feedforward inhibition resulted in the development of orientation selectivity rather than direction selectivity, indicating the pivotal role of the delayed feedforward inhibition in direction selectivity. We propose a mechanism for the development of direction selectivity involving a delayed feedforward inhibition with STDP and the amplification of feedback excitation.
视觉系统的方向选择性的发展依赖于视觉经验。在发育中的非洲爪蟾视网膜-顶盖系统中，顶盖神经元（TNs）通过重复暴露于特定方向的移动条刺激视网膜神经节细胞（RGCs），产生时程依赖的可塑性（STDP）而变得具有方向选择性。我们使用具有 STDP 的神经网络模型研究了非洲爪蟾视网膜-顶盖系统中方向选择性发展的机制。在这个视网膜-顶盖回路模型中，一个移动的条带刺激视网膜神经节细胞（RGCs），它们对 TNs 和中间神经元（INs）提供前馈兴奋。中间神经元对 TNs 提供延迟的前馈抑制。TNs 还从相邻的 TNs 接收反馈兴奋。作为突触学习规则，使用分子 STDP 模型来模拟 RGCs 和 TNs 之间的突触。视网膜-顶盖回路模型再现了方向选择性发展的实验观察到的特征，例如 TN 的输入增加。由于 STDP，来自 RGCs 到 TNs 的前馈兴奋的峰值更早地转移。与延迟的前馈抑制一起，产生了更强的早期瞬态前馈信号，该信号超过了来自相邻 TNs 的反馈兴奋的阈值，导致 TN 的输入放大。延迟的前馈抑制的抑制导致了方向选择性的发展，而不是方向选择性，表明延迟的前馈抑制在方向选择性中起着关键作用。我们提出了一种涉及具有 STDP 的延迟前馈抑制和反馈兴奋放大的方向选择性发展的机制。
