Laure Buhry

A

Neuronal variability has been thought to play an important role in the brain. As the variability mainly comes from the uncertainty in biophysical mechanisms, stochastic neuron models have been proposed for studying how neurons compute with noise. However, most papers are limited to simulating stochastic neurons in a digital computer. The speed and the efficiency are thus limited especially when a large neuronal network is of concern. This brief explores the feasibility of simulating the stochastic behavior of biological neurons in a very large scale integrated (VLSI) system, which implements a programmable and configurable Hodgkin-Huxley model. By simply injecting noise to the VLSI neuron, various stochastic behaviors observed in biological neurons are reproduced realistically in VLSI. The noise-induced variability is further shown to enhance the signal modulation of a neuron. These results point toward the development of analog VLSI systems for exploring the stochastic behaviors of biological neuronal networks in large scale.Neuronal variability has been thought to play an important role in the brain. As the variability mainly comes from the uncertainty in biophysical mechanisms, stochastic neuron models have been proposed for studying how neurons compute with noise. However, most papers are limited to simulating stochastic neurons in a digital computer. The speed and the efficiency are thus limited especially when a large neuronal network is of concern. This brief explores the feasibility of simulating the stochastic behavior of biological neurons in a very large scale integrated (VLSI) system, which implements a programmable and configurable Hodgkin-Huxley model. By simply injecting noise to the VLSI neuron, various stochastic behaviors observed in biological neurons are reproduced realistically in VLSI. The noise-induced variability is further shown to enhance the signal modulation of a neuron. These results point toward the development of analog VLSI systems for exploring the stochastic behaviors of biological neuronal networks in large scale.

Q

Conductance-based models of biological neurons can accurately reproduce the waveform of the membrane voltage, as well as the spike timing in response to injected currents. Nevertheless, finding the good model parameter set to fit membrane voltage recordings is often a very time-consuming and complex task, difficult to achieve manually. We present a new variant of an optimization algorithm, the differential evolution. We specifically designed this technique for the automated tuning of neuro-mimetic analog integrated circuits based on an Hodgkin-Huxley formalism for a point-neuron model. It indeed enables us to estimate all the parameters of the model, while avoiding local minima. The method is first tested on three types of neuron models (fast spiking, regular spiking, and intrinsically bursting), and then applied to the automated tuning of a neuro-mimetic circuit from the reference membrane voltage of a fast spiking neuron model.

-Modification Neuroadaptive Control Architecture for Discrete-Time Systems

We propose a new estimation method for the characterization of the Hodgkin-Huxley formalism. This method is an alternative technique to the classical estimation methods associated with voltage clamp measurements. It uses voltage clamp type recordings, but is based on the differential evolution algorithm. The parameters of an ionic channel are estimated simultaneously, such that the usual approximations of classical methods are avoided and all the parameters of the model, including the time constant, can be correctly optimized. In a second step, this new estimation technique is applied to the automated tuning of neuromimetic analog integrated circuits designed by our research group. We present a tuning example of a fast spiking neuron, which reproduces the frequency-current characteristics of the reference data, as well as the membrane voltage behavior. The final goal of this tuning is to interconnect neuromimetic chips as neural networks, with specific cellular properties, for future theoretical studies in neuroscience.

Global parameter estimation of an Hodgkin-Huxley formalism using membrane voltage recordings: Application to neuro-mimetic analog integrated circuits

Nowadays, many software solutions are currently available for simulating neuron models. Less conventional than software-based systems, hardware-based solutions generally combine digital and analog forms of computation. In previous work, we designed several neuromimetic chips, including the Galway chip that we used for this paper. These silicon neurons are based on the Hodgkin–Huxley formalism and they are optimized for reproducing a large variety of neuron behaviors thanks to tunable parameters. Due to process variation and device mismatch in analog chips, we use a full-custom fitting method in voltage-clamp mode to tune our neuromimetic integrated circuits. By comparing them with experimental electrophysiological data of these cells, we show that the circuits can reproduce the main firing features of cortical cell types. In this paper, we present the experimental measurements of our system which mimic the four most prominent biological cells: fast spiking, regular spiking, intrinsically bursting, and low-threshold spiking neurons into analog neuromimetic integrated circuit dedicated to cortical neuron simulations. This hardware and software platform will allow to improve the hybrid technique, also called “dynamic-clamp,” that consists of connecting artificial and biological neurons to study the function of neuronal circuits.

Automated parameter estimation of the hodgkin-huxley model using the differential evolution algorithm: Application to neuromimetic analog integrated circuits

In 1952 Hodgkin and Huxley introduced the voltage-clamp technique to extract the parameters of the ionic channel model of a neuron. Although this method is widely used today, it has a lot of disadvantages. In this paper, we propose an alternative approach to the estimation method of the voltage-clamp technique using metaheuristics such as simulated annealing, genetic algorithms and differential evolution. This method avoids approximations of the original technique by simultaneously estimating all the parameters of a single ionic channel with a single fitness function. To compare the different methods, we apply them on measurements from a neuromimetic integrated circuit. This circuit, due to its analog behavior, provides us noisy data like a biological system. Therefore we can validate the efficiency of our method on experimental-like data.

Tunable neuromimetic integrated system for emulating cortical neuron models

Neuromorphic engineering often faces the adjusting of the neuromimetic systems. Indeed, adjusting the parameters of integrated circuits and systems is a shared issue to address for the designers of tunable systems. This paper presents an original method to automatically tune reconfigurable neuromimetic analog integrated circuits according to biological relevance. This method is based on an evolutionary optimization technique, the Differential Evolution (DE) algorithm that had never been used for biological neuron modeling. To illustrate the adjusting method, we show how to reproduce the behavior of two kinds of well-known neurons, inhibitory and excitatory, by an automated tuning of the parameters of neuromimetic circuits. The behavior of the hardware neurons is then compared to the model one.

Parameter estimation of the Hodgkin-Huxley model using metaheuristics: Application to neuromimetic analog integrated circuits

This paper presents an original method to adjust parameters for a neuromimetic IC based on neuron conductance-based models (Hodgkin-Huxley formalism). To adjust the chip, we use a Metaheuristic, the Differential Evolution algorithm (DE). We detail the DE for its implementation in our hardware neural simulator. The DE estimates in the same time all the parameters of one ionic channel. We discuss about the DE performance for each channel. We conclude by mentioning the future applications of this technique in chip design and neuron modeling.