The Cartridge: A Canonical Neural Circuit Abstraction of the Lamina Neuropil - Construction and Composition Rules

The Lamina is a neuropil that  resides in the optic lobe of the early visual system of the fruit fly. Its neural circuit consists of some 700~800 cartridges. A cartridge is an atomic neural circuit abstraction whose I/O behavior can be studied in isolation. The anatomy of the neurons, neurotransmitter types and connectivity patterns of the neurons in the cartridge are briefly reviewed. A circuit-level model of a cartridge suitable for implementation on a GPU platform is presented in detail. Cartridge interconnects create neural circuits with different I/O characteristics. A number of cartridge composition rules for building neural circuits with different spatial I/O characteristics are discussed. We present a model neural circuit for initial functional evaluations and scaling of the Lamina and its interconnection with the Medulla. Implementation considerations of the Lamina neural circuit are discussed.