局部场电位和微分特性影响下神经元网络发放锋电位的检测

在利用多电极阵列(multielectrode arrays,MEA)记录离体培养海马神经元网络的电生理研究中,发现电极附近神经元群体同步放电形成了局部场电位(local field potential,LFP),同时细胞外记录信号为跨膜电压信号的微分,这些因素使检测网络发放的锋电位遇到困难。为正确检测锋电位(spike),在综合比较多种检测方法的基础上,提出一种改进的峰值检测法,以0.6ms为判决阈值,有效解决了原峰值检测法因滑动窗分界导致的重复检测。通过该方法检测发育成熟的网络发放的锋电位,虚警率和漏报率分别为:5%±1%和2%±1%,效果优于传统的阈值检测法。上述结果表明,改进的方法适合于神经元网络电活动的研究。     

MEA信号锋电位的小波变换分类

小波变换是信号处理领域最近若干年发展起来的先进方法，对信号的时域信息和频域信息都有很好的表现。我们利用小波变换对MEA信号的锋电位数据矩阵进行小波分解，将各锋电位变换后的最后一个尺度的逼近信号和各尺度上的细节信号的方差对波形非相似性测度的贡献率的大小作为依据，鉴别波形的不同。找出贡献率和大于90％的8个数据进行系统聚类，大大地降低了数据的维数和计算机的机时，并得到了很好的分类结果。     

超声特征信号评价金属蜂窝构件钎焊质量

金属蜂窝构件钎焊质量通常以钎着率（单位面积内检测到的焊合面积占比）为指标进行评价。实际生产中采用超声C扫幅值成像无损检测,以GH4099高温合金薄壁窄筋蜂窝板件为研究对象,提出基于超声A扫信号特征值参数的无监督机器学习分类方法。首先在数字超声信号提取时域、功率谱上各8个特征值;其次对数据进行标准化处理、主成分分析 （Principal components analysis,PCA）降维,得到各自贡献率为95%以上的前3组共6个主成分值;然后以这些值为特征值作为输入进行K均值、高斯混合模型聚类、模糊C均值聚;最后采用多分类器融合算法提高模型准确率,将分类结果可视化与超声C扫图像比对,验证分类评价效果。12组数据实验结果表明：3种聚类算法成像结果与超声C扫结果一致,其中融合投票计算比于单分类器更为准确,为非监督机器学习方法在超声信号评价蜂窝构件钎焊质量中的应用提供了新思路。     

用于形状特征提取的spike函数

形状特征是图像的一种重要视觉特征，其提取方法是形状识别、图像检索以及图像匹配等领域的研究热点。Spike参数用来反映磨粒轮廓角度的变化，spike参数越大，磨粒越尖锐，磨粒的磨损作用越大。在spike参数的基础上，提出了4种用于形状特征提取的spike函数，分别为用于表征形状轮廓细节特征的spike-angle函数和spike-height函数，以及用于表征形状轮廓整体特征的spike-area函数和spike-distance函数。根据spike函数提取形状特征时，采用多个步长的spike-angle函数和spike-height函数，同时采用单个步长的spike-area函数和spike-distance函数。为了消除起始点对spike函数计算的影响，以多尺度spike函数的归一化傅里叶变换系数的幅值作为形状特征。分别在MPEG-7和Swedish leaf数据集进行实验验证，与其他方法的对比结果表明采用spike函数提取形状特征，用于形状识别时，识别准确率高，抗噪声能力强。     

基于改进KNN-DPC算法的科技创新人才分类研究

为了提高科技创新人才培养过程中人才层次分类的效果,提出了一种结合主成分的改进K近邻优化的密度峰值聚类算法(IKDPC).首先,论文将主成分分析思想及流程融入到K近邻优化的密度峰值聚类算法(KNN-DPC)中来提高对高维数据的处理能力;进而,为了克服复杂数据集和噪声点对KNN-DPC算法的影响,对局部密度度量方法进行了改进,并设计了全新的两种样本数据点的分配策略,从而有效提高了聚类效率和聚类质量;最后,将IKDPC算法针对科技创新人才样本指标数据进行实例研究,实证结果表明该算法能有效地对科技创新人才进行分类,并为科学合理地探究科技创新人才培养过程中的分类问题提供科学量化参考.     

电子舌对不同储藏期鸡蛋识别的研究

本文基于伏安法电子舌原理,模拟人类味觉对熟鸡蛋蛋黄味道进行识别的研究。本研究采用金(Au),镉(Cd),铂(Pt),钯(Pd)四个工作个电极,铂辅助电极,AgCl参比电极,幅值1伏(v),周期1秒(s)的方波为激励信号,通过脉冲伏安法采集信号,并对采集信号提取的特征包括脉冲的最大值、最小值、平均值、相对积分值和始末点斜率。用主成分分析(PCA)方法成功地对两个不同储藏期鸡蛋进行分类识别,为检测鸡蛋新鲜度提供了新方法。     

一种有效的分类型数据聚类方法

鉴于传统的K-means聚类算法只限于处理数值型数据,将K-means算法扩展到分类型数据域,提出一种分类型数据聚类方法.根据与每个分类属性的每个值相关的数据分布信息,同时结合数据的纵向与横向分布来评价数据对象与类之间的差异性,定义了一种新的距离度量.该方法能发现同一属性不同值间的内在关系,并能有效地度量对象间的差异性.用UCI中的数据集对所提算法进行验证,实验结果表明了该算法具有较好的聚类效果.     

一个高效的多变量时间序列聚类算法

时间序列聚类分析是数据挖掘研究的一个重要内容。已有的聚类算法大多采用k均值对低维数据进行聚类,不能对高维多变量时间序列（MTS）数据进行有效聚类。提出一种高效的多变量时间序列聚类算法PCA-CLUSTER,首先利用主成分分析对MTS数据降维;选取MTS数据的主成分序列进行K近邻聚类分析。理论分析和实验结果表明算法可以有效解决MTS数据聚类问题。     

基于主元分析与模糊C均值聚类的丙烯腈反应器优化

鉴于主元分析法的降维特性和模糊C均值聚类算法良好的分类性能，本文在丙烯腈反应器操作参数的优化中，结合这两种方法，将主元分析处理后的数据作为新的样本输入，利用模糊C均值聚类算法进行优化操作。在保留原有信息的基础上，去除了冗余数据，加快了聚类速度。实验表明，混合算法的聚类结果比单纯的基于聚类优化的方法能较好地对操作参数的优化起指导作用。     

基于K-means的朴素贝叶斯分类算法的研究

将K-means算法引入到朴素贝叶斯分类研究中，提出一种基于K-means的朴素贝叶斯分类算法。首先用K-means算法对原始数据集中的完整数据子集进行聚类，计算缺失数据子集中的每条记录与k个簇重心之间的相似度，把记录赋给距离最近的一个簇，并用该簇相应的属性均值来填充记录的缺失值，然后用朴素贝叶斯分类算法对处理后的数据集进行分类。实验结果表明，与朴素贝叶斯相比，基于K-means思想的朴素贝叶斯算法具有较高的分类准确率。     

针对锋电位的启发式阈值检测算法

作为植入式脑电信号处理的关键环节,锋电位检测的精确度将直接影响后续脑电信号的解码与分析.提出了一种基于启发式阈值的锋电位自动检测算法.通过对椭圆滤波器参数的优化,降低了原始信号中有用信号衰减程度,实现了较低幅值锋电位的有效保留.并且启发式阈值的设定大大降低了采集环境引入的混杂噪声干扰,实现了具有鲁棒性的锋电位自动阈值检...     

Spike sorting based on radial basis function network with overlap decomposition

Spike sorting is the essential step in analyzing recording spike signals for studying information processing mechanisms within the nervous system. Overlapping is one of the most serious problems in the spike sorting for multi-channel recordings. In this paper, a modified radial basis function (RBF) network is proposed to decompose the overlapping signals and separate spikes within the same RBF network. A modified radial basis function based on the Gaussian function is employed in the method to improve the accuracy of overlap decomposition. In addition, the improved constructing algorithm reduces the calculation cost by taking advantage of the symmetry of the RBF network. The performance of the presented method is tested at various signal-to-noise ratio levels based on simulated data coming from the University of Leicester and Wave-clus software. Experiment results show that our method successfully solves the fully overlapping problem and has higher accuracy comparing with the Gaussian function.     

2DPCA在脑磁图棘波信号检测中的应用

棘波是癫痫疾病诊断和癫痫灶评估的重要标志，脑磁图设备能更精确地捕捉到癫痫患者在发作间期的棘波信号。然而，目前临床医生仍依赖于手动方法标记棘波信号，缺少便捷离线的多通道棘波检测方法。提出一种脑磁图的多通道棘波检测方法，针对给定时间宽度的多通道脑磁图信号的时间序列可以看作为一个二维矩阵，利用二维主成分分析（2DPCA）方法提取该矩阵的本征特征，再结合最近邻分类器实现离线的多通道棘波信号检测。通过临床癫痫患者的脑磁图信号验证表明，提出的方法棘波信号检测率高达93.23%，且该方法是有效的。     

Spike train decoding without spike sorting

We propose a novel paradigm for spike train decoding, which avoids entirely spike sorting based on waveform measurements. This paradigm directly uses the spike train collected at recording electrodes from thresholding the bandpassed voltage signal. Our approach is a paradigm, not an algorithm, since it can be used with any of the current decoding algorithms, such as population vector or likelihood-based algorithms. Based on analytical results and an extensive simulation study, we show that our paradigm is comparable to, and sometimes more efficient than, the traditional approach based on well-isolated neurons and that it remains efficient even when all electrodes are severely corrupted by noise, a situation that would render spike sorting particularly difficult. Our paradigm will also save time and computational effort, both of which are crucially important for successful operation of real-time brain-machine interfaces. Indeed, in place of the lengthy spike-sorting task of the traditional approach, it involves an exact expectation EM algorithm that is fast enough that it could also be left to run during decoding to capture potential slow changes in the states of the neurons.     

Unsupervised spike detection and sorting with wavelets and superparamagnetic clustering

This study introduces a new method for detecting and sorting spikes from multiunit recordings. The method combines the wavelet transform, which localizes distinctive spike features, with superparamagnetic clustering, which allows automatic classification of the data without assumptions such as low variance or gaussian distributions. Moreover, an improved method for setting amplitude thresholds for spike detection is proposed. We describe several criteria for implementation that render the algorithm unsupervised and fast. The algorithm is compared to other conventional methods using several simulated data sets whose characteristics closely resemble those of in vivo recordings. For these data sets, we found that the proposed algorithm outperformed conventional methods.     

Supervised Learning of Logical Operations in Layered Spiking Neural Networks with Spike Train Encoding

Few algorithms for supervised training of spiking neural networks exist that can deal with patterns of multiple spikes, and their computational properties are largely unexplored. We demonstrate in a set of simulations that the ReSuMe learning algorithm can successfully be applied to layered neural networks. Input and output patterns are encoded as spike trains of multiple precisely timed spikes, and the network learns to transform the input trains into target output trains. This is done by combining the ReSuMe learning algorithm with multiplicative scaling of the connections of downstream neurons. We show in particular that layered networks with one hidden layer can learn the basic logical operations, including Exclusive-Or, while networks without hidden layer cannot, mirroring an analogous result for layered networks of rate neurons. While supervised learning in spiking neural networks is not yet fit for technical purposes, exploring computational properties of spiking neural networks advances our understanding of how computations can be done with spike trains.     

Performance evaluation of PCA-based spike sorting algorithms

Deciphering the electrical activity of individual neurons from multi-unit noisy recordings is critical for understanding complex neural systems. A widely used spike sorting algorithm is being evaluated for single-electrode nerve trunk recordings. The algorithm is based on principal component analysis (PCA) for spike feature extraction. In the neuroscience literature it is generally assumed that the use of the first two or most commonly three principal components is sufficient. We estimate the optimum PCA-based feature space by evaluating the algorithm's performance on simulated series of action potentials. A number of modifications are made to the open source nev2lkit software to enable systematic investigation of the parameter space. We introduce a new metric to define clustering error considering over-clustering more favorable than under-clustering as proposed by experimentalists for our data. Both the program patch and the metric are available online. Correlated and white Gaussian noise processes are superimposed to account for biological and artificial jitter in the recordings. We report that the employment of more than three principal components is in general beneficial for all noise cases considered. Finally, we apply our results to experimental data and verify that the sorting process with four principal components is in agreement with a panel of electrophysiology experts.     

Sorting of neural spikes: When wavelet based methods outperform principal component analysis

Sorting of the extracellularly recorded spikes is a basic prerequisite for analysis of the cooperative neural behavior and neural code. Fundamentally the sorting performance is defined by the quality of discriminative features extracted from spike waveforms. Here we discuss two features extraction approaches: principal component analysis (PCA), and wavelet transform (WT). We show that only when properly tuned to the data, the WT technique may outperform PCA. We present a novel method for extraction of spike features based on a combination of PCA and continuous WT. The method automatically tunes its WT part to the data structure making use of knowledge obtained by PCA. We demonstrate the method on simulated and experimental data sets.     

Spike timing precision and neural error correction: local behavior

The effects of spike timing precision and dynamical behavior on error correction in spiking neurons were investigated. Stationary discharges-phase locked, quasiperiodic, or chaotic-were induced in a simulated neuron by presenting pacemaker presynaptic spike trains across a model of a prototypical inhibitory synapse. Reduced timing precision was modeled by jittering presynaptic spike times. Aftereffects of errors-in this communication, missed presynaptic spikes-were determined by comparing postsynaptic spike times between simulations identical except for the presence or absence of errors. Results show that the effects of an error vary greatly depending on the ongoing dynamical behavior. In the case of phase lockings, a high degree of presynaptic spike timing precision can provide significantly faster error recovery. For nonlocked behaviors, isolated missed spikes can have little or no discernible aftereffects (or even serve to paradoxically reduce uncertainty in postsynaptic spike timing), regardless of presynaptic imprecision. This suggests two possible categories of error correction: high-precision locking with rapid recovery and low-precision nonlocked with error immunity.