1 Nexus : a Neural Simulator for Integrating Top - down and Bottom - up Modeling

We have developed the NEXUS simulation environment as a tool for modeling largescale neural systems. The software is written in C and runs under UNIX. A unique aspect of NEXUS is that it is particularly suited for simulating hybrid neural models (i.e. systems integrating di erent modeling paradigms and/or architectures.) NEXUS is designed for large-scale simulations, and to facilitate model development, testing and analysis it incorporates several major features: network architectures based on topographic maps, programmable neural units, scalable and modular simulation, support for common learning paradigms including the generalized Hebb rule and backpropagation, and a user-friendly interface. These features make NEXUS a useful environment in which to study the \perceptual" properties of various network architectures.