Modeling the L4 neuron of the fly (Musca domestica) vision system

Vision systems based on digital image processing techniques are limited in a variety of areas, particularly speed and memory. Contrast enhancement, image segmentation, object recognition, and object tracking require extensive processing. Biological vision systems drastically outperform computer based digital vision systems in these areas. The animal retina is composed of processing layers with specialized neural cells designed to enhance contrast, segment images, and even produce temporal information. In the vision system of the fly, Musca domestica, the L1, L2, and L4 monopolar cells are of particular interest. The photoreceptor terminals R1 through R6 and L1 and L2 form a cartridge with current shunting inhibition that enhances contrast at the first synaptic contact. L1 and L2 cells are thought to exaggerate contrast while also providing a data reduction encoding scheme to increase communication efficiency with L4 cells and the inner plexiform layer. Research conducted by the authors attempts to simulate the encoding scheme of L1, L2, and L4, and the interactions of these three monopolar cells. This paper proposes that L1 and L2 encode edge information and orientation related to a single cartridge via a sinusoidal modulation scheme. L4 mediates information processing between cartridges via three bi-directional dendritic communication with adjacent L4 cells. Finally, we propose that L4 also synthesizes and forwards the edge orientation information and image movement information to the medulla. A single cartridge simulation was conducted using Matlab. Simulation results will be compared to actual signals taken from the fly eye. Because the fly eye is modular, the goal of this research is to implement the L1, L2, and L4 cell function in analog hardware--the result being a real-time parallel analog vision system.