Analysis of cultured neuronal networks using intraburst firing characteristics

It is an open question whether neuronal networks, cultured on multielectrode arrays, retain any capability to usefully process information (learning and memory). A necessary prerequisite for learning is that stimulation can induce lasting changes in the network. To observe these changes, one needs a method to describe the network in sufficient detail, while stable in normal circumstances. We analyzed the spontaneous bursting activity that is encountered in dissociated cultures of rat neocortical cells. Burst profiles (BPs) were made by estimating the instantaneous array-wide firing frequency. The shape of the BPs was found to be stable on a time scale of hours. Spatiotemporal detail is provided by analyzing the instantaneous firing frequency per electrode. The resulting phase profiles (PPs) were estimated by aligning BPs to their peak spiking rate over a period of 15 min. The PPs reveal a stable spatiotemporal pattern of activity during bursts over a period of several hours, making them useful for plasticity and learning studies. We also show that PPs can be used to estimate conditional firing probabilities. Doing so, yields an approach in which network bursting behavior and functional connectivity can be studied.     

Bursting Hodgkin–Huxley model-based ultra-low-power neuromimetic silicon neuron

This paper presents a compact, ultra-low-power implementation of the bursting Hodgkin?CHuxley model-based silicon neuron. The Hodgkin?CHuxley model is a neuron imitation that consists of two calcium current channels, a potassium current channel and a leakage current channel. In the proposed architecture, the calcium and the potassium current channels have been implemented using a sigmoid-function structure, a log-domain filter, and a linear transconductor. Different neuronal signals can be generated by changing the value of the capacitor in the log-domain filter. The proposed silicon neuron is capable of generating four different outputs, namely, spiking, spiking with latency, bursting, and chaotic signals. Ultra-low-power consumption is achieved by current-reuse technique and subthreshold region operation of MOSFETs. The circuit is designed using 0.13???m standard CMOS process. The entire design uses 43 transistors, with a total power consumption of only 43?nW.     

Broad range of neural dynamics from a time-varying FitzHugh-Nagumo model and its spiking threshold estimation

We study the use of the FitzHugh-Nagumo (FHN) model for capturing neural spiking. The FHN model is a widely used approximation of the Hodgkin-Huxley model that has significant limitations. In particular, it cannot produce the key spiking behavior of bursting. We illustrate that by allowing time-varying parameters for the FHN model, these limitations can be overcome while retaining its low-order complexity. This extension has applications in modeling neural spiking behaviors in the thalamus and the respiratory center. We demonstrate the use of the FHN model from an estimation perspective by presenting a novel parameter estimation method that exploits its multiple time-scale properties, and compare the performance of this method with the extended Kalman filter in several illustrative examples. We demonstrate that the dynamics of the spiking threshold can be recovered even in the absence of complete specifications for the system.     

Emergent spiking in non-ideal memristor networks

Memristors have uses as artificial synapses and perform well in this role in simulations with artificial spiking neurons. Our experiments show that memristor networks natively spike and can exhibit emergent oscillations and bursting spikes. Networks of near-ideal memristors exhibit behaviour similar to a single memristor and combine in circuits like resistors do. Spiking is more likely when filamentary memristors are used or the circuits have a higher degree of compositional complexity (i.e. a larger number of anti-series or anti-parallel interactions). 3-memristor circuits with the same memristor polarity (low compositional complexity) are stabilised and do not show spiking behaviour. 3-memristor circuits with anti-series and/or anti-parallel compositions show richer and more complex dynamics than 2-memristor spiking circuits. We show that the complexity of these dynamics can be quantified by calculating (using partial auto-correlation functions) the minimum order auto-regression function that could fit it. We propose that these oscillations and spikes may have similar phenomena to brainwaves and neural spike trains and suggest that these behaviours can be used to perform neuromorphic computation.     

多频激励忆阻型Shimizu-Morioka系统的簇发振荡及机理分析

为了研究忆阻系统的簇发振荡及其形成机理,该文在Shimizu-Morioka(S-M)系统的基础上引入忆阻器件和两个慢变化的周期激励项,建立了一种多时间尺度的忆阻型S-M系统。首先研究了单一激励下S-M系统的簇发行为及分岔机制,得到一种对称型“sub-Hopf/sub-Hopf”簇发模式。然后借助De Moivre公式将多频激励系统转化为单频激励系统,结合快慢分析法重点分析了附加激励幅度对“sub-Hopf/sub-Hopf”簇发模式的影响。对应于不同附加激励幅度该文发现了两种新的簇发模式,即扭曲型“sub-Hopf/sub-Hopf”簇发和嵌套级联型sub-Hopf/sub-Hopf”簇发。借助时序图、分岔图和转换相图分析了相应的簇发机制。最后,采用Multisim软件搭建电路模型并进行仿真实验,得到的实验结果与理论分析结果相吻合,从而实验证明了忆阻型S-M系统的簇发模式。     

Manipulating epileptiform bursting in the rat hippocampus using chaos control and adaptive techniques

Epilepsy is a relatively common disease, afflicting 1%-2% of the population, yet many epileptic patients are not sufficiently helped by current pharmacological therapies. Recent reports have suggested that chaos control techniques may be useful for electrically manipulating epileptiform bursting behavior in vitro and could possibly lead to an alternative method for preventing seizures. We implemented chaos control of spontaneous bursting in the rat hippocampal slice using robust control techniques: stable manifold placement (SMP) and an adaptive tracking (AT) algorithm designed to overcome nonstationarity. We examined the effect of several factors, including control radius size and synaptic plasticity, on control efficacy. AT improved control efficacy over basic SMP control, but relatively frequent stimulation was still necessary and very tight control was only achieved for brief stretches. A novel technique was developed for validating period-1 orbit detection in noisy systems by forcing the system directly onto the period-1 orbit. This forcing analysis suggested that period-1 orbits were indeed present but that control would be difficult because of high noise levels and nonstationarity. Noise might actually be lower in vivo, where regulatory inputs to the hippocampus are still intact. Thus, it may still be feasible to use chaos control algorithms for preventing epileptic seizures.     

Synchronization and Small-Signal Analysis of Nonlinear Periodic Circuits

Common approaches to simulate the steady-state behavior of nonlinear periodic circuits forced by a periodic signal of small amplitude assume that the forcing signal effects are additive to the steady-state solution of the unperturbed circuit. This assumption leads to the adoption of the variational model of the nonlinear unperturbed circuit. The variational model does not pose any particular problem when dealing with nonautonomous circuits, but must be suitably formulated when autonomous circuits are considered and the frequency of the forcing signal is close to the working frequency of the unperturbed nonlinear circuit. We show that, in this case, synchronization effects must be accounted for, and, as synchronization phenomena are intrinsically nonlinear, it is impossible to take them into account using a variational model. In fact, conventional variational models are derived from the unperturbed nonlinear circuit working at steady state and with a fixed relative phase between perturbation and system, i.e., without any possibility of phase shifts (that is, of any dynamics leading to possible synchronization). In general, this yields inaccurate or even wrong results. In this paper, we investigate this limitation of the approaches based on the variational model. Some simulation results are reported that show the transition between the nonsynchronization region to the synchronization one of well-known simple oscillators, such as the Van der Pol one when the parameters of the small-signal perturbation are varied.     

A kinematic model for the oligo-mode action of a CW dye laser

Several stable oligo-mode spectra of a CW dye laser were recorded with the aid of an optical spectrum analyzer (scannable Fabry-Perot) giving Fourier transforms of the light field. Simultaneously the total intensity was measured with a fast photodiode and analyzed for beat signals with an RF spectrum analyzer. The spectra observed can be explained consistently in terms of a kinematic model postulating that competing modes cannot exist simultaneously and therefore show a "spiking" behavior. The repetition frequency of the spiking was found to be the frequency difference of the competing modes, a mechanism known from mode-locking. For the spectra observed experimentally, analytic expressions for the time development of the field amplitudes are given which are in good agreement with the experimental results.     

Response of a CW Nd3+:YAG laser to sinusoidal cavity perturbations

Sinusoidal perturbations are applied to the resonator of a CW Nd³⁺:YAG laser to study the response of the system. Two kinds of resonances are observed. The resonant AM mode exhibits a sinusoidal modulation in the output and its frequency is determined by the pumping power and cavity losses. The spiking mode shows a train of regular pulses and its frequency is constant. Nonlinear coupled rate equations are solved to show solutions in good agreement with the experimental observations. The effect of nonresonant perturbation on the output is also presented.     

BCD工艺中的NMOS管结漏电问题的研究

针对BCD工艺中出现的NMOS管结漏电问题进行研究,通过失效分析的方法发现有结穿刺现象,怀疑为金属阻挡层工艺窗口较小。为进一步调查金属阻挡层的工艺容宽,尝试采用了苛刻的多次合金的方法对当前使用的阻挡层进行考察,发现经过多次合金处理的产品成品率大幅下降,从而确认金属阻挡层的工艺容宽较小。为了改进工艺进行准直溅射阻挡层、不同的金属阻挡层厚度、RTP、小应力阻挡层等试验,并结合多次合金的方法对阻挡层进行了考核。实验结果表明,应力过大是NMOS管漏电的根本原因。最后研发出一种优化的小应力阻挡层菜单,并成功应用于BCD工艺量产中。     

A multiconductance silicon neuron with biologically matched dynamics

We have designed, fabricated, and tested an analog integrated-circuit architecture to implement the conductance-based dynamics that model the electrical activity of neurons. The dynamics of this architecture are in accordance with the Hodgkin-Huxley formalism, a widely exploited, biophysically plausible model of the dynamics of living neurons. Furthermore the architecture is modular and compact in size so that we can implement networks of silicon neurons, each of desired complexity, on a single integrated circuit. We present in this paper a six-conductance silicon-neuron implementation, and characterize it in relation to the Hodgkin-Huxley formalism. This silicon neuron incorporates both fast and slow ionic conductances, which are required to model complex oscillatory behaviors (spiking, bursting, subthreshold oscillations).     

Microwave self-modulation of a diode laser coupled to an external cavity

An external cavity coupled to a conventional Fabry-Perot GaAs diode laser operating continuously has been found to cause modulation of the light output at a frequency within the range 0.5 to several GHz. The modulation depth is close to 100 percent and the linewidth can be made as narrow as 180 kHz. The modulation is thought to be stimulated by the intensity noise fluctuations, which peak at the well-known spiking frequency fr. The oscillations are strongly enhanced by a frequency locking action of the external cavity, being efficient when the external cavity round-trip time2L/c, or a multiple thereof, corresponds to the inverse of the spiking frequency. Since the latter is dependent on both pump current and temperature, the system can simply be tuned by adjusting the pump current. For a fixed resonator length, the narrow-band oscillations occur in a small current range, in which an increase in frequency with increasing current at a rate of 400 kHz/mA is observed. A small-signal analysis based on simple rate equations shows the influence of the external cavity on the intrinsic resonance frequency fr. It demonstrates that self-modulation can only occur for small values of the coupling coefficient ε between the laser diode and the external cavity.     

面向神经形态感知的人工脉冲神经元的研究进展

近年来,随着人工智能技术和脉冲神经网络(SNN)的迅猛发展,人工脉冲神经元的研究逐渐兴起。人工脉冲神经元的研究对于开发具有人类智能水平的机器人、实现自主学习和自适应控制等领域具有重要的应用前景。传统的电子器件由于缺乏神经元的非线性特性,需要复杂的电路结构和大量的器件才能模拟简单的生物神经元功能,同时功耗也较高。因此,最近研究者们借鉴生物神经元的工作机制,提出了多种基于忆阻器等新型器件的人工脉冲神经元方案。这些方案具有功耗低、结构简单、制备工艺成熟等优点,并且在模拟生物神经元的多种功能等方面取得了显著进展。文章将从人工脉冲神经元的基本原理出发,综述和分析目前已有的各种实现方案。具体来说,将分别介绍基于传统电子器件和基于新型器件的人工脉冲神经元的实现方案,并对其优缺点进行比较。此外,还将介绍不同类型的人工脉冲神经元在实现触觉、视觉、嗅觉、味觉、听觉和温度等神经形态感知方面的应用,并对未来的发展进行展望。希望能够为人工脉冲神经元的研究和应用提供有益的参考和启示。     

ALSI或ALSICU刻蚀后硅渣残留去除方式的研究

半导体器件制造中会用到ALSI或ALSICU做金属连线,ALSI或ALSICU里一般含有0.5%¹%的Si,目的是防止ALSI互融造成PN junction spiking,但引入Si、金属连线刻蚀后会有硅渣析出,刻开区分布不规则的小黑点,影响表观。比较和分析了目前半导体制造行业几种去硅渣方式的机理和优缺点,同时提出一种新的高效的干法去硅渣方式。在上述分析的基础上,标准化了去硅渣工艺,提出的去硅渣标准流程,对半导体制造具有广泛的指导作用。     

Dependency of the highest harmonic oscillation frequency on junction diameter of IMPATT diodes

The effect of series resistance and junction capacitance on the high-frequency limit of IMPATT diode operation is studied with a Read-type small-signal theory, and is confirmed experimentally. Oscillation frequencies from 30 to 400 GHz have been measured with Si p⁺-n-n⁺abrupt junction diodes with a depletion layer width of 0.2 µm. The highest oscillation frequency increases as the junction diameter is decreased, owing to reduced junction capacitance and increased bias-current density. The highest oscillation frequency observed is 423 GHz, which is obtained in the fifth harmonic mode with a diode of 16-µm junction diameter. Fundamental oscillation frequency is found to depend strongly on dc bias-current density, and to be close to the avalanche frequency of the small-signal theory.     

Spiking in light pulses from GaAs Q-switched junction lasers

Using a detection system with 150-ps resolution, a spiking behavior has been detected in theQ-switched light output from GaAs junction lasers. At the lower currents in theQ-switching region, a single light spike, whose width is about 300 ps, is observed. At higher currents, additional light spikes appear whose widths and spacings decrease as the current is increased. At the highest pumping levels, only the initial spike is clearly resolved and its width has decreased to less than 200 ps. Qualitative agreement is obtained from a simple theory based on the standard rate equations. The necessary modifications to the theory are discussed and results of computer calculations are presented which predict that the width of the initial spike can be much less than 100 ps at sufficiently high pumping levels.     

Resonant modes of GaAs junction lasers

The resonant modes of GaAs junction lasers are obtained from a proposed model and compared with experimental results. Theoretical results are based on an assumed laser medium whose dielectric constant varies both along and perpendicular to the junction plane. The frequency separations of the transverse modes are found to be in very good agreement with presented high-resolution spectral measurements of stripe-geometry laser radiation. Furthermore, the theoretical field distributions are also in good agreement with observed transverse field variations reported previously. The laser output spectrum usually shows a number of "satellites" located adjacent to each longitudinal (Fabry-Perot) resonance. It is shown that each satellite represents the frequency of a transverse resonance having a different mode number along the junction plane and a corresponding Hermite-Gaussian intensity profile along the plane. Theory shows that the frequency separation of two adjacent satellites is related to the falloff rate of the dielectric constant along the junction plane. This focusing is measured from the intensity profile of a far-field pattern. From this information, the theoretical frequency separation is calculated and found to agree well with the measured separation of 6.4 GHz (0.15 Å).     

Spikes in the light output of room temperature GaAs junction lasers

Observations of the light intensity of pulsed, GaAs injection lasers at room temperature have revealed a regular, damped spiking behavior. The lasers were made by diffusing Zn into ann-type substrate. A stripe contact permits the excitation of only a very narrow region of the junction. The spiking was most clearly observed with a rectangular current pulse of 50 ns in width and a 0.5-ns risetime. Because of the long delays inherent in these diodes, the laser light appears at the very end of the current pulse, as the threshold value of the current is crossed. With increased pumping, the emission starts at earlier times and extends to the end of the current pulse. Only three or four spikes can be seen clearly because of the fast damping. The decay time is of the order of 2 ns and the interval between the spikes is about 1 to 1.4 ns. The spiking theory advanced by Statz and Tang to explain the time behavior of ruby has been applied to GaAs lasers. The rate equations in this formulation are derived under the assumption that the standing-wave nature of the field in the cavity creates a spatially inhomogeneous inversion along the resonator. Numerical solutions to these equations have been obtained for the cases of one and three longitudinal modes. The approximations used are first, that the pump power is kept near threshold, second, that there is no diffusions of carriers, third, that the gain curve is Lorentzian in shape, and last, that the modes are located symmetrically with respect to the line center. The two parameters that are needed to solve the equations are the cavityQand the spontaneous recombination lifetime. Using the values available in the literature, good agreement has been found between theory and experiment.     

EEG signal modeling using adaptive Markov process amplitude

In this paper, an adaptive Markov process amplitude algorithm is used to model and simulate electroencephalogram (EEG) signals. EEG signal modeling is used as a tool to identify pathophysiological EEG changes potentially useful in clinical diagnosis. The least mean square algorithm is adopted to continuously estimate the parameters of a first-order Markov process model. EEG signals recorded from rodent brains during injury and recovery following global cerebral ischemia are utilized as input signals to the model. The EEG was recorded in a controlled experimental brain injury model of hypoxic-ischemic cardiac arrest. The signals from the injured brain during various phases of injury and recovery were modeled. Results show that the adaptive model is accurate in simulating EEG signal variations following brain injury. The dynamics of the model coefficients successfully capture the presence of spiking and bursting in EEG.     

On the integration of unstable linear systems

An efficient approach to the problem of numerically computing the solution to a system of ordinary autonomous differential equations has been proposed by Davison and Maki. In this letter, their algorithm is modified to effectively treat the problem of integrating in unstable system whose forcing function is a constant.