In the neural circuits as well as other excitable cell systems, cells are occasionally coupled by electrical synapses and constitute an electrically continual laminar structure, refered to as a syncytium. The neural syncytium is often found in the developing neocortex and hippocampus, but is also prevalent in a number of nuclei in the mature mammalian brain and especially in the retina. The vertebrate retina is a good model for syncytial integration, i.e. information processing in neural syncytia. Figure 10.1 is a schematic illustration showing a gross structure of the vertebrate retina. The principal cell types are shown with different colors. Each of these principal cell types can be classified into several subtypes, which are not shown in the figure to avoid confusion. In Figure 10.1, the bottom side corresponds to the frontal surface of the retina from which the light comes in through the optical apparatus of the eye. The light passes through the transparent retina to reach the photoreceptor array (gray), where the light signal is transduced to the voltage signal. The voltage signal is transmitted to the horizontal cell (purple) and the bipolar cell (red). The photoreceptors, horizontal cells and bipolar cells interact with each other in the outer plexiform layer (OPL). The bipolar cell transmits the output of the outer retinal circuit to the amacrine cell (white) and the ganglion cell (orange). The bipolar cells, amacrine cells and ganglion cells interact in the inner plexiform layer (IPL). The interplexiform cell (light green) is a unique neuron which provides a feedback pathway from IPL to OPL. Schematic illustration of the vertebrate retina. The principal cell types are distinguished by different colours. See for details. Inset: Cross section of the retina. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780203746899/334cf3a0-50b8-4727-8b6b-8ee80fc7e0dc/content/fig10_1.tif"/> (Reprinted with permission from Matsumoto, T., Kobayashi, H. and Yagi, T. Proceedings of IEICE, 76(7), 783–791.) (Color plate I)