Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
Exp Brain Res. 2011 Jan;208(1):127-38. doi: 10.1007/s00221-010-2483-0. Epub 2010 Nov 11.
Simulations of orientation selectivity in visual cortex have shown that layer 4 complex cells lacking orientation tuning are ideal for providing global inhibition that scales with contrast in order to produce simple cells with contrast-invariant orientation tuning (Lauritzen and Miller in J Neurosci 23:10201-10213, 2003). Inhibitory cortical cells have been shown to be electrically coupled by gap junctions (Fukuda and Kosaka in J Neurosci 120:5-20, 2003). Such coupling promotes, among other effects, spike synchronization and coordination of postsynaptic IPSPs (Beierlein et al. in Nat Neurosci 3:904-910, 2000; Galarreta and Hestrin in Nat Rev Neurosci 2:425-433, 2001). Consequently, it was expected (Miller in Cereb Cortex 13:73-82, 2003) that electrical coupling would promote nonspecific functional responses consistent with the complex inhibitory cells seen in layer 4 which provide broad inhibition in response to stimuli of all orientations (Miller et al. in Curr Opin Neurobiol 11:488-497, 2001). This was tested using a mechanistic modeling approach. The orientation selectivity model of Lauritzen and Miller (J Neurosci 23:10201-10213, 2003) was reproduced with and without electrical coupling between complex inhibitory neurons. Although extensive coupling promotes uniform firing in complex cells, there were no detectable improvements in contrast-invariant orientation selectivity unless there were coincident changes in complex cell firing rates to offset the untuned excitatory component that grows with contrast. Thus, changes in firing rates alone (with or without coupling) could improve contrast-invariant orientation tuning of simple cells but not synchronization of complex inhibitory neurons alone.
视觉皮层方向选择性的模拟表明，缺乏方向调谐的 4 层复杂细胞是提供与对比度成比例的全局抑制的理想选择，以便产生具有对比度不变方向调谐的简单细胞（Lauritzen 和 Miller 在 J Neurosci 23:10201-10213, 2003）。已经表明抑制性皮质细胞通过缝隙连接电耦合（Fukuda 和 Kosaka 在 J Neurosci 120:5-20, 2003）。这种耦合促进了除其他影响外的尖峰同步和突触后 IPSP 的协调（Beierlein 等人在 Nat Neurosci 3:904-910, 2000；Galarreta 和 Hestrin 在 Nat Rev Neurosci 2:425-433, 2001）。因此，人们预计（Miller 在 Cereb Cortex 13:73-82, 2003），电耦合将促进与在 4 层中观察到的提供对所有方向刺激的广泛抑制的复杂抑制细胞一致的非特异性功能响应（Miller 等人在 Curr Opin Neurobiol 11:488-497, 2001）。这是使用机械建模方法进行测试的。Lauritzen 和 Miller 的方向选择性模型（J Neurosci 23:10201-10213, 2003）在有和没有复杂抑制神经元之间的电耦合的情况下进行了复制。虽然广泛的耦合促进了复杂细胞的均匀放电，但除非复杂细胞放电率发生协同变化以抵消随对比度增长的未调谐兴奋成分，否则对比度不变的方向选择性不会有任何改善。因此，单独改变放电率（有或没有耦合）可以改善简单细胞的对比度不变方向调谐，但不能单独改善复杂抑制神经元的同步。
