Hardware computation of conductance-based neuron models

A Systematic Method for Configuring VLSI Networks of Spiking Neurons

An increasing number of research groups are developing custom hybrid analog/digital very large scale integration (VLSI) chips and systems that implement hundreds to thousands of spiking neurons with biophysically realistic dynamics, with the intention of emulating brainlike real-world behavior in hardware and robotic systems rather than simply simulating their performance on general-purpose digital computers. Although the electronic engineering aspects of these emulation systems is proceeding well, progress toward the actual emulation of brainlike tasks is restricted by the lack of suitable high-level configuration methods of the kind that have already been developed over many decades for simulations on general-purpose computers. The key difficulty is that the dynamics of the CMOS electronic analogs are determined by transistor biases that do not map simply to the parameter types and values used in typical abstract mathematical models of neurons and their networks. Here we provide a general method for resolving this difficulty. We describe a parameter mapping technique that permits an automatic configuration of VLSI neural networks so that their electronic emulation conforms to a higher-level neuronal simulation. We show that the neurons configured by our method exhibit spike timing statistics and temporal dynamics that are the same as those observed in the software simulated neurons and, in particular, that the key parameters of recurrent VLSI neural networks (e.g., implementing soft winner-take-all) can be precisely tuned. The proposed method permits a seamless integration between software simulations with hardware emulations and intertranslatability between the parameters of abstract neuronal models and their emulation counterparts. Most important, our method offers a route toward a high-level task configuration language for neuromorphic VLSI systems.

An analog circuit implementation of a quadratic integrate and fire neuron

Silicon neurons are of importance both to implement hybrid electronic-biological system as well as to develop fundamental understanding of the neurobiological systems they emulate. We have implemented a hardware version of the quadratic integrate and fire neural model. The quadratic integrate and fire neuron differs from the more common integrate and fire neuron in that the model, and thus the hardware, intrinsically generate spikes. Readily available discrete surface mount components are used to make the hardware available to a wider audience and facilitate experimentation.