Nonlinear synchronization in EEG and whole-head MEG recordings of healthy subjects
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第14卷㊀第3期Vol.14No.3㊀㊀智㊀能㊀计㊀算㊀机㊀与㊀应㊀用IntelligentComputerandApplications㊀㊀2024年3月㊀Mar.2024㊀㊀㊀㊀㊀㊀文章编号:2095-2163(2024)03-0128-05中图分类号:TP18,TP399文献标志码:A基于平滑非线性能量算子划分的尖峰相关特征癫痫发作自动检测算法何雪兰,吴㊀江,蒋路茸(浙江理工大学信息科学与工程学院,杭州310018)摘㊀要:针对癫痫发作自动检测算法多集中于时域㊁频域等传统特征,无法全面表征癫痫脑电信号的信息等问题,本文结合癫痫脑电图中异常波振幅和频率提高的现象,提出一种基于平滑非线性能量算子划分的尖峰相关特征癫痫发作自动检测算法㊂该算法使用传统的时域㊁频域特征,结合尖峰相关性特征对脑电信号进行刻画,使用有监督的机器学习分类器,测试癫痫发作自动检测的有效性和可靠性㊂本文将提出的方法在开源数据集CHBMIT上进行了评估,获得了96.52%的准确率㊁95.65%的敏感性和97.09%的特异性㊂实验结果表明,基于平滑非线性能量算子划分的尖峰相关特征,能够作为癫痫脑电信息的补充,提高癫痫发作检测的性能㊂关键词:癫痫发作检测;机器学习;尖峰相关性;平滑非线性能量算子Automaticseizuredetectionalgorithmbasedonspike-relatedfeaturesofsmoothednonlinearenergyoperatordivisionHEXuelan,WUJiang,JIANGLurong(SchoolofInformationScienceandEngineering,ZhejiangSci-TechUniversity,Hangzhou310018,China)Abstract:Mostcurrentseizureautomaticdetectionalgorithmsfocusontraditionalfeaturessuchastimedomainandfrequencydomain,whichcannotfullycharacterizetheinformationofepilepticEEGsignals.Thispaperproposesanautomaticseizuredetectionalgorithmbasedonspikecorrelationfeaturesdividedbyasmoothnonlinearenergyoperator,takingintoaccountthephenomenonthattheamplitudeandfrequencyofabnormalwavesinepilepticEEGwillincrease.Thealgorithmusestraditionaltime-domainandfrequency-domainfeatures,combinedwithspikecorrelationfeaturestocharacterizetheEEGsignal,andusessupervisedmachinelearningclassifierstotestitseffectivenessandreliabilityforautomaticseizuredetection.TheresearchevaluatestheproposedmethodontheopensourcedatasetCHBMITandobtains96.52%onaccuracy,95.65%onsensitivityand97.09%onspecificity.Theexperimentalresultsshowthattheproposedspike-relatedfeaturesbasedonthesmoothednonlinearenergyoperatorsegmentationcanbeusedasacomplementtotheepilepticEEGinformationtoimprovetheperformanceofseizuredetection.Keywords:seizuredetection;machinelearning;spikecorrelation;smoothednonlinearenergyoperator基金项目:浙江省基础公益项目(LGF19F010008);北京邮电大学泛网无线通信教育部重点实验室(BUPT)(KFKT-2018101);浙江省重点研发计(2022C03136);国家自然科学基金(61602417)㊂作者简介:何雪兰(1999-),女,硕士研究生,主要研究方向:癫痫检测;吴㊀江(1978-),男,博士,高级工程师,主要研究方向:无线通信技术,工业物联网㊂通讯作者:蒋路茸(1982-),男,博士,教授,主要研究方向:生理电信号处理㊁复杂网络和无线传感器网络㊂Email:jianglurong@zstu.edu.cn收稿日期:2023-03-150㊀引㊀言癫痫是一种神经系统疾病,由大脑神经元异常放电引起[1],常常表现为突发性㊁反复性和复发性等特点㊂癫痫发作的临床症状复杂多样,如阵发性痉挛㊁意识丧失㊁认知功能障碍等[2]㊂这些发作事件对患者的认知水平及正常生活都产生了明显影响㊂因此,癫痫的诊断和治疗对于预防癫痫发作和改善生活质量至关重要㊂头皮脑电图是一种用于临床记录脑活动的无创信号采集方法[3],用于记录大脑活动时的电波变化㊂头皮脑电图包含丰富的生理㊁心理和病理信息,是评估癫痫和其他脑部疾病的有效工具[4]㊂在脑电图的记录中,癫痫发作和癫痫样放电(如棘波㊁尖波和棘慢波复合体)是癫痫的重要生物标志物[5],并被广泛应用于临床评价㊂目前,临床上基于脑电图的识别与分析是医生进行癫痫检测的黄金标准,但对海量的临床脑电数据进行人工筛查,不仅给医生带来沉重的负担,还存在较强的主观性㊁判断标准不统一等问题[6-7],影响分析的效率和准确性㊂因此,设计一种自动的癫痫发作检测方法是亟待解决的问题㊂为了克服传统诊断方法的局限性㊁提高医疗效率,伴随着机器学习的快速发展,癫痫发作的自动检测已成为行业内关注的重点㊂研究者们根据头皮脑电图的时域㊁频域或非线性特征建立了特征工程方法[8-10],并通过具有一个或多个特征的分类器检测癫痫发作㊂Mursalin等学者[11]从时域㊁频域和基于熵的特征中选择突出特征,使用随机森林分类器学习选定特征集合的特性,获得了更好的分类结果㊂杨舒涵等学者[12]使用时域和非线性特征对脑电信号进行表征,结合XGBoost分类器,实现了癫痫的自动检测㊂Zarei等学者[13]使用离散小波变换DWT和正交匹配追踪(OrthogonalMatchingPursuit,OMP)提取EEG中不同的系数,计算非线性特征和统计特征,使用SVM进行分类,获得了较好的检测性能㊂吴端波等学者[14]使用aEEG尖峰和cEEG棘波提取的方法计算棘波率,使用阈值法对癫痫进行发作检测㊂上述模型虽然都能取得较好的分类结果,但是也存在以下问题:(1)多数研究在特征提取阶段仅从时域㊁频域或时频域中表征脑电信号信息,这些特征所涵盖的信息量并不足以全面描述一段EEG信号㊂(2)在癫痫发作的自动检测中,强调周期性的信号转换对于有效㊁可靠地区分癫痫发作的重复特征至关重要,而互相关是时域上广泛用于表示信号周期性的方法㊂针对上述问题,本文提出一种基于平滑非线性能量算子划分的尖峰相关(SpikeCorrelation,SC)特征的癫痫发作自动检测算法㊂SC是关于自适应提取的脑电图尖峰信号段之间时间延迟的最大互相关㊂使用平滑非线性能量算子衡量癫痫脑电信号中出现的异常波,将脑电信号在癫痫发作期和非发作期的尖峰相关特征作为度量患者大脑活动的一个重要补充㊂本文提出的算法主要使用巴特沃斯滤波器对脑电信号进行滤波,去除外部伪迹的干扰,然后从传统特征角度出发,提取时域㊁频域特征,再结合提出的尖峰相关特征,进一步表征癫痫发作时的异常信息㊂最后结合有监督的机器学习分类模型,实现癫痫发作的自动检测㊂1㊀方法癫痫发作自动检测整体流程设计如图1所示,其中包含预处理㊁特征提取和分类等3个模块㊂脑电信号通道筛选滤波数据分割归一化预处理特征提取传统特征:时域、频域尖峰相关特征分类癫痫发作/非发作图1㊀癫痫发作自动检测流程图Fig.1㊀Flowchartofseizuredetection1.1㊀脑电信号预处理头皮脑电数据通过放置在头皮固定位置的电极采集得到㊂由于外置电极,这种采集方式很容易受到外部干扰,导致采集到的数据被噪声污染㊂此外,由于受试者在采集过程中生理活动产生的内部伪迹(如:眨眼㊁心脏跳动等)[15],也会对数据产生干扰,影响分类结果㊂因此,针对内部伪迹,本文首先对采集到的脑电信号进行通道筛选,剔除受眼部运动干扰严重的2个电极FT1和FT2;同时,由于左侧耳电磁极易受到心电伪迹的干扰,因此也剔除了靠近耳部的2个电极FT9和FT10㊂所以,在通道筛选阶段,共选择了脑电图中20个通道信号㊂㊀㊀滤波是一种常见的去除脑电信号外部伪迹的方法,本文采用1 48Hz的带通巴特沃斯滤波器进行滤波,抑制其他频率范围的信号[16]㊂根据数据集中标注的癫痫发作开始和结束时间,为了保证波形的完整性,设置重叠率为50%的滑动窗口,将脑电信号分割成4s的数据片段,最后对所有片段进行归一化处理㊂由于通道筛选和滤波后的脑电信号幅值的浮动一般是在可接受范围内,最大最小标准化能够较大程度地还原真实EEG信号波形㊂因此,本文采用最大最小标准化对原始EEG信号进行归一化操作,推得的公式为:Xmin-max=X-X-maxX()-minX()(1)1.2㊀特征提取原始脑电信号数据量庞大,且不具有代表性,而特征提取方法可以提炼出能够表征癫痫发作特征的数据,用于模型的建立㊂因此,本文主要使用传统时域㊁频域特征和基于平滑非线性能量算子的尖峰相关性特征,对脑电数据进行特征提取㊂1.2.1㊀传统特征提取研究主要从时域和频域两个角度对脑电信号进行传统特征提取㊂本文主要提取时域上每个通道的最大值㊁最小值㊁平均值㊁峰度(Kurtosis)㊁偏斜度921第3期何雪兰,等:基于平滑非线性能量算子划分的尖峰相关特征癫痫发作自动检测算法(Sknewness)和线长(LineLength);频域上主要提取每个信号频域分量的振幅㊂其中,峰度㊁偏斜度和线长的数学定义分别见式(2) (4):Kurtosis=E[(x-mean(x))4]{E[(x-mean(x))2]}2(2)Sknewness=E[(x-mean(x)std(x))3](3)LineLength=1nðni=1absxi+1-xi()(4)㊀㊀其中,x表示脑电信号片段;E表示对括号中数值求期望;xi表示采样点i的值;n表示片段x中采样点数㊂1.2.2㊀尖峰相关特征提取根据癫痫发作时脑电信号异常波的振幅和频率发生改变的特异性现象,本文提出将尖峰相关特征作为表征癫痫发作时异常特征的补充㊂非线性能量算子(NLEO)是一种对信号进行能量度量的方法[17],能够跟踪信号的瞬时能量㊂对于离散信号xn,其非线性能量算子表达如式(5)所示:φ[x(n)]=x(n-l)x(n-p)-x(n-q)x(n-s)(5)㊀㊀通常,当癫痫脑电信号中出现异常放电时,脑电波的振幅和频率会有所提高,可以更好地突出异常波在平稳状态下的放电波形,但非线性能量对脑电信号中可能存在的噪音信号也具有很高的敏感度㊂为了进一步提高NLEO对非平稳信号的表征能力和抗干扰能力,文献[18]提出了一种NLEO的改进方法,即平滑非线性能量算子(SNLEO),将计算所得的能量与一个窗函数进行卷积运算,在一定程度上减小低波幅噪音信号对输出结果的影响㊂SNLEO计算见式(6):φ[x(n)]=w(n)∗φ[x(n)](6)㊀㊀其中,w是一个矩形的窗函数, ∗ 表示卷积操作㊂在非线性能量算子的计算中,本文使用的参数值为l=1,p=2,q=0和s=3,并采用7个点的窗函数进行卷积计算㊂获得SNLEO后,需要设定一个合适的阈值,尽可能多地筛选出可能是尖峰的样本,同时最小化漏检率㊂本文使用自适应阈值,对SNLEO进行尖峰筛选识别㊂本文采用影响检测尖峰数量没有大范围变化的阈值作为最优阈值㊂最优阈值的搜索范围为SNLEO的10% 90%[19],相邻2个峰值的中间被确定为一个尖峰的起始点或结束点㊂由于数据在划分过程中导致波形的不连续问题,本文将检测到的第一个和最后一个尖峰丢弃,以确保每个片段具有完整的尖峰形态㊂如果检测出尖峰,则将每个划分好的尖峰与后续5个尖峰片段相关联㊂本文使用尖峰相关性(SpikeCorrelation,SC)来定义该矩阵,并将SC的平均值和标准差作为癫痫发作检测的特征㊂SC计算见式(7 8):SCi,j=maxmRxixj(m)(7)Rxixj(m;i,j)=E[xi(n)xj(n+m)]σxiσxj(8)㊀㊀其中,xi㊁xj是脑电EEG信号的片段,这里i=[2, ,S-6],j=[i+1, ,i+5];S表示在一个片段中检测到的峰值数;σ表示脑电图片段的标准差㊂估计SC特征的处理过程如图2所示㊂将一个片段的第一个和最后一个丢弃,而后根据得到的尖峰计算其与后面5个尖峰的相关性㊂根据图2(a)中样例计算出的尖峰相关矩阵如图3所示㊂10050-501234时间/s(a)癫痫发作片段样例EEG/μV400200SNLEO/μV23224168尖峰数/个1234时间/s(b)片段(a)对应的S N L E Ot h(c)基于(b)确定的自适应阈值t h阈值104.87710050-50EEG/μV1234时间/s(d)划分好的尖峰片段(“*”表示丢弃的片段)12345678910t h图2㊀使用自适应阈值的SNLEO计算尖峰相关性示意图Fig.2㊀SchematicdiagramofSNLEOcalculationofspikecorrelationsusingadaptivethreshold1234567892345678910图3㊀尖峰片段得到的最大相关矩阵Fig.3㊀Maximumcorrelationmatrixobtainedfromspikefragments031智㊀能㊀计㊀算㊀机㊀与㊀应㊀用㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第14卷㊀㊀㊀此外,计算了SNLEO的平均值㊁标准差和平均最大SNLEO值spikiness㊂其中,spikiness被定义为SNLEO中峰值的最大值除以SNLEO的平均值[20],以及检测到的峰值数量(snum)㊁平均持续时间(swidth)和平均峰值间间隔(sgap)㊂基于SNLEO划分的尖峰相关特征的具体描述见表1㊂表1㊀尖峰相关特征的描述Table1㊀Descriptionofspike-relatedcharacteristics特征描述mean(SC)尖峰相关性矩阵的平均值std(SC)尖峰相关性矩阵的标准差mean(SNLEO)SNLEO的平均值std(SNLEO)SNLEO的标准差spikiness平均最大SNLEO值snum峰值数量swidth平均持续时间sgap平均峰值间间距1.3㊀分类模型使用传统机器学习分类器RF和SVM来评估本文提出的方法,这些分类器经常被用于癫痫发作的自动检测㊂2㊀实验2.1㊀数据集本研究采用公开的头皮脑电数据集CHB-MIT㊂该数据集共记录了美国波士顿儿童医院的23名癫痫患者的头皮脑电数据,每个患者的数据都是由多个.edf文件组成,采样频率256Hz,共含有157次癫痫发作㊂大多数文件包含有23个EEG通道信号,并采用国际标准10-20系统使用的EEG电极位置命名这些通道记录㊂由于癫痫发作时间远小于发作间期的时间,为了保证数据集正负样本的均衡性,本文采用欠采样的方式在发作间期随机采样和癫痫发作样本数量相当的负样本㊂2.2㊀评价指标为了验证本文方法的有效性,采用准确率(Acc)㊁敏感性(Sen)㊁特异性(Spe)㊁F1值和AUC等指标进行实验评估㊂计算方法见式(9) 式(11):Acc=TP+TNTP+TN+FP+FN(9)Sen=TPTP+FN(10)Spe=TNTN+FP(11)㊀㊀其中,TP㊁FP㊁FN和TN分别为真阳性㊁假阳性㊁假阴性和真阴性㊂本文产生的所有实验结果都是在配置为Intel(R)Core(TM)i7-9700CPU@3.00GHz,16GBRAM的计算机上实现的㊂实验模型使用Python3.7和Scikit-learn构建㊂2.3㊀结果分析本文先对提取的传统时域㊁频域特征分别使用RF和SVM分类模型进行测试,所得实验结果见表2㊂由表2可知,SVM分类模型表现最佳㊂表2㊀基于传统特征的实验结果Table2㊀Experimentalresultsbasedontraditionalcharacteristics特征分类器AccSenSpe传统特征RF0.86210.75330.9339SVM0.95900.93850.9736㊀㊀在确定分类模型SVM的基础上,将传统特征和尖峰相关特征结合,探讨尖峰相关特征对癫痫脑电信号的表征能力㊂添加前后对比结果见表3㊂表3㊀尖峰相关特征对比的分类结果Table3㊀Classificationresultsofspike-relatedfeaturecomparison分类器特征AccSenSpeSVM传统特征0.95900.93850.9736传统特征+尖峰相关特征0.96520.95650.9709㊀㊀由表3可知,尖峰相关特征能够对癫痫脑电信号信息进行表征㊂加入尖峰相关特征后,检测结果在Acc上提升了0.62%,在Sen上提升了1.8%,在Spe上有所降低㊂在实际的临床应用中,正确识别发作样本比正确识别非发作样本更重要,因此Sen指标更能准确衡量方法的优劣㊂本文提出的方法虽然在Spe上略有降低,但Sen指标上有一定程度的提升㊂3㊀结束语本文提出了一种基于平滑非线性能量算子划分的尖峰相关特征的癫痫发作自动检测算法㊂该算法使用传统的时域㊁频域特征,结合尖峰相关性特征对脑电信号进行刻画,使用RF和SVM分类器来测试癫痫发作自动检测的有效性和可靠性㊂将所提方法在开源数据集CHB-MIT上进行了评估,SVM分类器获得了更好的结果,其准确率㊁敏感性和特异性分别为96.52%,95.65%和97.09%㊂此外,研究开展的特征消融实验结果表明,提出的基于平滑非线性能131第3期何雪兰,等:基于平滑非线性能量算子划分的尖峰相关特征癫痫发作自动检测算法量算子划分的尖峰相关特征,能够作为癫痫脑电信息的补充,进一步提高癫痫发作检测的性能㊂参考文献[1]PATELDC,TEWARIBP,CHAUNSALIL,etal.Neuron–gliainteractionsinthepathophysiologyofepilepsy[J].NatureReviewsNeuroscience,2019,20(5):282-297.[2]SPECCHION,WIRRELLEC,SCHEFFERIE,etal.InternationalLeagueAgainstEpilepsyclassificationanddefinitionofepilepsysyndromeswithonsetinchildhood:PositionpaperbytheILAETaskForceonNosologyandDefinitions[J].Epilepsia,2022,63(6):1398-1442.[3]SCHADA,SCHINDLERK,SCHELTERB,etal.Applicationofamultivariateseizuredetectionandpredictionmethodtonon-invasiveandintracraniallong-termEEGrecordings[J].ClinicalNeurophysiology,2008,119(1):197-211.[4]BENBADISSR,BENICZKYS,BERTRAME,etal.TheroleofEEGinpatientswithsuspectedepilepsy[J].EpilepticDisorders,2020,22(2):143-155.[5]王学峰.癫癎的脑电图:传统观点㊁新认识和新领域[J].中华神经科杂志,2004,37(3):7-9.[6]刘晓燕,黄珍妮,秦炯.不同类型小儿癫痫持续状态的临床及脑电图分析[J].中华神经科杂志,2000,33(2):73-73.[7]MATURANAMI,MEISELC,DELLK,etal.Criticalslowingdownasabiomarkerforseizuresusceptibility[J].NatureCommunications,2020,11(1):2172.[8]彭睿旻,江军,匡光涛,等.基于EEG的癫痫自动检测:综述与展望[J].自动化学报,2022,48(2):335-350.[9]HOSSEINIMP,HOSSEINIA,AHIK.AreviewonmachinelearningforEEGsignalprocessinginbioengineering[J].IEEEReviewsinBiomedicalEngineering,2020,14:204-218.[10]ACHARYAUR,HAGIWARAY,DESHPANDESN,etal.CharacterizationoffocalEEGsignals:Areview[J].FutureGenerationComputerSystems,2019,91:290-299.[11]MURSALINM,ZHANGY,CHENY,etal.Automatedepilepticseizuredetectionusingimprovedcorrelation-basedfeatureselectionwithrandomforestclassifier[J].Neurocomputing,2017,241:204-214.[12]杨舒涵,李博,周丰丰.基于机器学习的跨患者癫痫自动检测算法[J].吉林大学学报(理学版),2021,59(1):101-106.[13]ZAREIA,ASLBM.Automaticseizuredetectionusingorthogonalmatchingpursuit,discretewavelettransform,andentropybasedfeaturesofEEGsignals[J].ComputersinBiologyandMedicine,2021,131:104250.[14]吴端坡,王紫萌,董芳,等.基于aEEG尖峰和cEEG棘波提取的癫痫发作检测算法[J].实验技术与管理,2020,37(12):57-62.[15]骆睿鹏,冯铭科,黄鑫,等.脑电信号预处理方法研究综述[J].电子科技,2023,36(4):36-43.[16]OCBAGABIRHT,ABOALAYONKAI,FAEZIPOURM.EfficientEEGanalysisforseizuremonitoringinepilepticpatients[C]//2013IEEELongIslandSystems,ApplicationsandTechnologyConference(LISAT).Farmingdate,USA:IEEE,2013:1-6.[17]BOONYAKITANONTP,LEK-UTHAIA,CHOMTHOK,etal.AreviewoffeatureextractionandperformanceevaluationinepilepticseizuredetectionusingEEG[J].BiomedicalSignalProcessingandControl,2020,57:101702.[18]MUKHOPADHYAYS,RAYGC.Anewinterpretationofnonlinearenergyoperatoranditsefficacyinspikedetection[J].IEEETransactionsonBiomedicalEngineering,1998,45(2):180-187.[19]TAPANIKT,VANHATALOS,STEVENSONNJ.IncorporatingspikecorrelationsintoanSVM-basedneonatalseizuredetector[C]//EMBEC&NBC2017:JointConferenceoftheEuropeanMedicalandBiologicalEngineeringConference(EMBEC)andtheNordic-BalticConferenceonBiomedicalEngineeringandMedicalPhysics(NBC).Singapore:Springer,2018:322-325.[20]TAPANIKT,VANHATALOS,STEVENSONNJ.Time-varyingEEGcorrelationsimproveautomatedneonatalseizuredetection[J].InternationalJournalofNeuralSystems,2019,29(4):1850030.231智㊀能㊀计㊀算㊀机㊀与㊀应㊀用㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第14卷㊀。
Noise-Induced Synchronization among Sub-RF CMOS Neural Oscillators forSkew-Free Clock DistributionAkira Utagawa,Tetsuya Asai,Tetsuya Hirose,and Yoshihito AmemiyaGraduate School of Information Science and Technology,Hokkaido UniversityKita14,Nishi9,Kita-ku,Sapporo060-0814,JAPANEmail:**********************.hokudai.ac.jpAbstract—A possible idea is presented here for deal-ing with clock skew problems on synchronous digital sys-tems.Nakao et al.recently reported that independent neu-ral oscillators can be synchronized by applying temporal random impulses to the oscillators[1].We regard neural oscillators as independent clock sources on LSIs;i.e.,clock sources are distributed on LSIs,and they are forced to syn-chronize through the use of random noises.We designed neuron-based clock generators operating at sub-RF region (<1GHz)by modifying the original neuron model to a new model that is suitable for CMOS implementation with 0.25-µm CMOS parameters.Through circuit simulations, we demonstrate that the clock generators are certainly syn-chronized by pseudo-random noises.1.IntroductionSynchronous sequential circuits with global clock-distribution systems are the mainstream of implementation in present digital VLSI systems where the clock distribu-tion is the core of synchronous digital operations.Practical clocks given through external pads are distributed to se-quential circuits being synchronous to the same clocks via distributed clock networks.System clocks for synchronous digital circuits must arrive at all the registers simultane-ously.In practice,time mismatches of clock arrival which are called‘clock skew’occur in LSIs[2].The major rea-sons for these mismatches derive from the system clock distribution(wiring defects or asymmetric clock paths),the propagation delay of the clock chip,and the clock traces on the board.The propagation delay is dependent on the fab-rication process,voltage,temperature,and loading,which makes the clock skew even more complicated.Small clock skews prevent us from increasing the clock frequency,and large skews may result in severe malfunctions.Indeed clock-skew effects on the circuit performance rise as the in-tegration density(∼miniaturization)or the clock frequency increases.To resolve these clock-skew issues,various technolo-gies on clock distribution are widely used in present digi-tal systems such as zero-skew clock distribution[3],insert-ing buffers for skew compensation[4]and controlling the clock-wire length[5].In regular circuit structures,clock skews are effectively reduced by designing clock paths based on H trees(see[6]for details including statistical analysis).For large-scale complex clock networks,opti-mizing buffers in the clock distribution tree usually reduces clock skew.One possible way to cancel clock skew is to use asynchronous digital circuits where only local clocks are used instead of global system clocks[7].However, the functions of these circuits currently cannot satisfy var-ious sophisticated demands.Moreover,major LSI design-ers have recently started using advanced genetic algorithms in their post-manufacturing processes to calculate the re-quired margin[8].The present solutions for the skew problems may in-crease both the total length of clock distribution wires and the power consumption,as well as optimization and post-processing costs.In this paper,we propose another solution for the skew problems.Nakao et al.recently reported that independent neural oscillators can be synchronized by ap-plying appropriate noises to the oscillators[1].We here regard neural oscillators as independent clock sources on LSIs;i.e.,clock sources are distributed on LSIs,and they are forced to synchronize with the addition of artificial (or natural if possible)noises.In the following sections, we show a modified neuron-based model that are suitable for hardware implementation,neuron-based clock genera-tor for sub-RF operations(<1GHz),and circuit simulation results representing synchronous(or asynchronous)oscil-lations with(or without)external noises.2.The ModelIn the original model[1],FitzHugh-Nagumo neuron was used to demonstrate the noise-induced synchronization be-tween the time courses of N trials under different initial conditions.Instead we use N Wilson-Cowan oscillators in our model that are suitable for analog CMOS implementa-tion.The dynamics are given bydu idt=−u i+fβ(u i−v i),(1) dv idt=−v i+fβ(u i−θ)+I(t),(2)where u i and v i represent the system variables of the i-th os-cillator,θthe threshold,I(t)the common temporal random impulse and fβ(·)the sigmoid function with slopeβ.2007 International Symposium on Nonlinear Theory and its A pplications NOLTA'07, Vancouver, Canada, September 16-19, 20070.510.5 1vuu nullcline v nullcline trajectoryFigure 1:Nullclines and trajectories of single Wilson-Cowan type oscillator receiving random impulses.0 0.5 1 160170180 190200utime0 0.51 160170180 190200vtimeFigure 2:Time courses of system variables of single Wilson-Cowan type oscillator receiving random impulses.Figure 1shows numerical simulation results of a single Wilson-Cowan oscillator receiving temporal random im-pulses given by I (t )=α j δ(t −t (1)j )−δ(t −t (2)j )where δ(t )=Θ(t )−Θ(t −w )(Θ,w and t j represent the step func-tion,the pulse width and the positive random number witht (1)j t (2)j for all j s,respectively).The system parameters were θ=0.5,β=10,α=0.1,w =1,and the averaged inter-spike interval of |I (t )|was set at 100.We observed the limit-cycle oscillations,and confirmed that the trajectory was certainly fluctuated by I (t ).The time courses of u and v are shown in Fig.2.We conducted numerical simulations using 10oscillators (N =10).All the oscillators have the same parameters,and accept (or do not accept)the common random impulse I (t ).The initial condition of each oscillator was randomly chosen.Figure 3shows the raster plots of 10oscillators (vertical bars were plotted at which u i >0.5and du i /dt >0).When the oscillators did not accept I (t )(α=0),they exhibited independent oscillations as shown in Fig.3(a);1510 240024502500 25502600o s c i l l a t o r n o .time(b) with noise1510 240024502500 25502600o s c i l l a t o r n o .time(a) without noiseFigure 3:Raster plots of 10oscillators.(a)independent oscillations without random impulses,(b)synchronous os-cillations with random impulses.0 0.5 1 0100020003000 40005000R (t )time(b) with noise0 0.5 1 010002000300040005000R (t )time(a) without noiseFigure 4:Time courses of order parameter values (a)with-out random impulses and (b)with random impulses.however,all the oscillators were synchronized when α=0.1as shown in Fig.3(b).To evaluate the degree of the synchronization,we use the following order parameter:R (t )=1N j exp(i θj ) ,where N represents the number of oscillators,i the imagi-nary unit and θj =tan −1[(v j −v ∗)/(u j −u ∗)]((u ∗,v ∗)repre-sents the fixed point of the oscillator).When all the oscilla-tor are synchronized,R (t )equals 1because of the uniformθj s,while R (t )is less than 1if the oscillators are not syn-chronized.Figure 4shows the time courses of the order parameter values.When α=0,R (t )was unstable and was always less than 1[Fig.4(a)],whereas R (t )remained at 1after it became stable at t ≈2000when α=0.1[Fig.4(b)].These results indicate that if we implemented these oscilla-tors as clock generators on CMOS LSIs,applying common random pulses to the oscillators could synchronize them.Figure 5:Wilson-Cowan circuit for sub-RF operations.0.5 1 1.5 2 2.5 00.511.5 22.5v (V )u (V)u nullcline v nullcline trajectoryFigure 6:Nullclines and trajectories of oscillator circuit receiving pseudo-random impulse.3.The circuit and simulation resultsWe designed a Wilson-Cowan oscillator circuit for sub-RF operations (Fig.5).The circuit consists of a di fferen-tial pair (M1to M3)and a bu ffer circuit composed of two standard inverters.In the following simulations,we used TSMC’s 0.25-µm CMOS parameters with W /L =0.36µm /0.24µm except for M3’s channel length (L =2.4µm).Pseudo-random sequences (V mseq )were generated using a 4-bit M-sequence circuit,and were distributed to the circuit through a RC filter.The supply voltage was fixed at 2.5V .Figure 6shows SPICE results of the nullclines and tra-jectories receiving random impulses (C =10fF,R =100k Ω,the clock frequency of the M-sequence circuit was 50MHz,which resulted in a 300-ns pseudo-random se-quence).Time courses of u and v are shown in Fig.7.We observed qualitatively-equivalent nullclines and trajec-toriesto those of the Wilcon-Cowan oscillators.We con-firmed the limit-cycle oscillations where the trajectory was e ffectively fluctuated by the M-sequence circuit with the0 0.5 1 1.5 2 2.5 5051 52 5354 55 56 57 58 59 60u (V )time (ns)0 0.5 1 1.5 2 2.5 5051 52 5354 55 56 57 58 59 60v (V )time (ns)Figure 7:Time courses of system variables of oscillator circuit receiving pseudo-random impulses.1510 1.951.961.97 1.981.992o s c i l l a t o r n o .time (µs)(b) with noise1510 1.951.961.97 1.981.992o s c i l l a t o r n o .time (µs)(a) without noiseFigure 8:Raster plots of 10oscillator circuits.(a)in-dependent oscillations without random impulses,(b)syn-chronous oscillations with random impulses.RC filter.The oscillation frequency was about 1GHz when the reference voltage V ref was set at 1V .Figure 8shows the raster plots of 10oscillator circuits (vertical bars were plotted at which v i >1.25V and dv i /dt >0).All the cir-cuits exhibited independent oscillations when random se-quence V mseq was not given to them [Fig.8(a)],whereas they exhibited complete synchronization when V mseq was given [Fig.8(b)].Time courses of the order parameter val-ues were shown in Fig.9.When random impulse was not given to the circuit,R (t )was not stable and was always less than 1[Fig.9(a)],while R (t )remained at 1after it be-came stable at t ≈700µs when random impulse was given [Fig.9(b)].Our results indicate that if we distributed these circuits as ubiquitous clock sources on CMOS LSIs,they could be synchronized when common random impulses were given to the circuits.Although this may cancel out the present clock skew problems,device mismatches between0 0.5 1 012 345R (t )time (µs)(b) with noise0 0.5 1 012 345R (t )time (µs)(a) without noiseFigure 9:Time courses of order parameter values (a)with-out random impulses and (b)with random impulses.0.90.92 0.94 0.96 0.98 1 0 0.5 11.5 22.5 3〈 R (t ) 〉σ (mV)Figure 10:Synchrony dependence on parameter mismatch.the clock sources may prevent the sources from complete synchronization.Therefore,we investigated the device-mismatch dependence of the proposed circuits.For our dis-tributing purposes,local mismatches in a single oscillator circuit would be negligible;i.e.,mismatches in a di fferen-tial pair (M1and M2)and a current mirror.Mismatches in inverters corresponding to threshold θin Wilson-Cowan model would also be negligible because they only shift the fixed point,and do not vastly change the oscillation fre-quency.However,mismatches of M3between the oscilla-tors may drastically change each oscillator’s intrinsic fre-quency.Therefore,we distributed threshold voltages of M3s of all the oscillators.Zero-bias threshold voltages (VTO)of M3s were randomly chosen from the Gaussian distribution (mean:0.37V and standard deviation:σ).Fig-ure 10shows the dependence of averaged order-parameter values 〈R (t )〉(from 0to 1µs)on σ.We generated 10ran-dom VTO sets for each σ,and plotted the error bars and the mean values in the figure.We confirmed that 〈R (t )〉was gradually decreased when σwas increased.4.ConclusionWe designed CMOS sub-RF oscillators that could be synchronized using common random impulses,based on a theory in [1].We proposed a modified Wilson-Cowan model for implementing FitzHugh-Nagmo oscillators.We confirmed that the synchronization properties of the mod-ified model were qualitatively equivalent to those of the original model.We then designed sub-RF oscillator cir-cuits based on the modified model.Through circuit simula-tions,we demonstrated that the circuits exhibited the same synchronization properties as in the original and modified models.For our clock-distributing purposes,we investi-gated the synchrony dependence on device mismatches be-tween the distributed oscillator circuits.The result showed that the synchrony was gradually decreased when variance of the mismatch was linearly increased,which indicated that our ‘ubiquitous’clock sources with small device mis-matches would be synchronized by optimizing our param-eter sets.References[1]H.Nakao,K.Arai,and K.Nagai,“Synchrony oflimit-cycle oscillators induced by random external impulses,”Phys.Rev.E vol.72,026220,2005.[2]D.E.Brueske and S.H.K.Embabi,“A dynamic clocksynchronization technique for large systems,”IEEE p.,Packag.,Manufact.Technol.B ,vol.17,pp.350-361,1994.[3]R.S.Tsay,“An exact zero-skew clock routing algo-rithm,”IEEE Trans.on Comp.-Aided Design of Inte-grated Cir.Syst.,vol.12,no.2,pp.242-249,1993.[4]R.B.Watson,Jr.,and R.B.Iknaian,“Clock bu fferchip with multiple target automatic skew compensa-tion,”IEEE J.Solid-State Circuits ,vol.30,pp.1267-1276,1995.[5]T.-H.Chao,Y .-C.Hsu,J.-M.Ho,and A.B.Kahng,“Zero skew clock routing with minimum wirelength,”IEEE Trans.Circuits and Systems II ,vol.39,no.11,pp.799-814,1992.[6]M.Hashimoto,T.Yamamoto,and H.Onodera,“Sta-tistical analysis of clock skew variation in H-tree structure,”IEICE Trans.on Fundamentals of Elec-tronics,Communications and Computer Sciences ,vol.E88-A,no.12,pp.3375-3381,2005.[7]C.J.Myers,Asynchronous Circuit Design ,Wiley-Interscience,2001.[8]E.Takahashi,Y .Kasai,M.Murakawa and T.Higuchi,“Post-fabrication clock-timing adjustment using ge-netic algorithms,”IEEE J.Solid-State Circuits ,vol.39,no.4,pp.643-649,2004.。
257ISSN: 1749-3889 ( print ) 1749-3897 (online)BimonthlyVol.7 (2009) No.3JuneEngland, UK ***************************.uk International Journal ofN o n l i n e a r S c i e n c e Edited by International Committee for Nonlinear Science, WAUPublished by World Academic Union (World Academic Press)CONTENTS259.New Exact Travelling Wave Solutions for Some Nonlinear Evolution EquationsA. Hendi268.A New Hierarchy of Generalized Fisher Equations and Its Bi- Hamiltonian StructuresLu Sun274.New Exact Solutions of Nonlinear Variants of the RLW, the PHI-four and Boussinesq Equations Based on Modified Extended Direct Algebraic MethodA. A. Soliman, H. A. Abdo283. Monotone Methods in Nonlinear Elliptic Boundary Value ProblemG.A.Afrouzi, Z.Naghizadeh, S.Mahdavi290. Influence of Solvents Polarity on NLO Properties of Fluorone Dye Ahmad Y. Nooraldeen1, M. Palanichant, P. K. Palanisamy301.Projective Synchronization of Chaotic Systems with Different Dimensions via Backstepping DesignXuerong Shi, Zhongxian Wang307.Adaptive Control and Synchronization of a Four-Dimensional Energy Resources System of JiangSu ProvinceLin Jia , Huanchao Tang312.Optimal Control of the Viscous KdV-Burgers Equation Using an Equivalent Index MethodAnna Gao, Chunyu Shen,Xinghua Fan319.Adaptive Control of Generalized Viscous Burgers’ Equation Xiaoyan Deng, Wenxia Chen, Jianmei Zhang327. Wavelet Density Degree of a Class of Wiener Processes Xuewen Xia, Ting Dai332.Niches’ Similarity Degree Based on Type-2 Fuzzy Niches’ Model Jing Hua, Yimin Li340.Full Process Nonlinear Analysis the Fatigue Behavior of the Crane Beam Strengthened with CFRPHuaming Zhu, Peigang Gu, Jinlong Wang, Qiyin Shi345.The Infinite Propagation Speed and the Limit Behavior for the B-family Equation with Dispersive TermXiuming Li353.The Classification of all Single Traveling Wave Solutions to Fornberg-Whitham EquationChunxiang Feng, Changxing Wu360.New Jacobi Elliptic Functions Solutions for the Higher-orderNonlinear Schrodinger EquationBaojian Hong, Dianchen Lu368.A Counterexample on Gap Property of Bi-Lipschitz Constants Ying Xiong, Lifeng Xi371.A Method for Recovering the Shape for Inverse Scattering Problem of Acoustic WavesLihua Cheng, Tieyan Lian, Ping Li379.An Approach of Image Hiding and Encryption Based on a New Hyper-chaotic SystemHongxing Yao, Meng Li258International Journal of Nonlinear Science (IJNS)BibliographicISSN: 1749-3889 (print), 1749-3897 (online), BimonthlyEdited by International Editorial Committee of Nonlinear Science, WAUPublished by World Academic Union (World Academic Press)Publisher Contact:Academic House, 113 Mill LaneWavertree Technology Park, Liverpool L13 4AH, England, UKEmail:******************.uk,*********************************URL: www. World Academic Union .comContribution enquiries and submittingThe paper(s) could be submitted to the managing editor ***************************.uk. Author also can contact our editorial offices by mail or email at addresses below directly.For more detail to submit papers please visit Editorial BoardEditor in Chief: Boling Guo, Institute of Applied Physics and Computational Mathematics, Beijing, 100088, China;************.cnCo-Editor in Chief: Lixin Tian, Nonlinear Scientific Research Center, Faculty of Science, Jiangsu University, Zhenjiang, Jiangsu,212013;China;**************.cn,************.cnStanding Members of Editorial Board:Ghasem Alizahdeh Afrouzi, Department ofMathematics, Faculty of Basic Sciences, Mazandaran University,Babolsar,Iran;**************.ir Stephen Anco, Department of Mathematics, Brock University, 500 Glenridge Avenue St. Catharines, ON L2S3A1,Canada;***************Adrian Constantin ,Department of Mathematics, Lund University,22100Lund,****************.seSweden;*************************.se,Ying Fan, Department of Management Science, Institute of Policy and Management, ChineseAcademy of Sciences, Beijing 100080,China,**************.cn.Juergen Garloff, University of Applied Sciences/ HTWG Konstanz, Faculty of Computer Science, Postfach100543, D-78405 Konstanz, Germany;************************Tasawar Hayat, Department of mathematics,Quaid-I-AzamUniversity,Pakistan,*****************Y Jiang, William Lee Innovation Center, University of Manchester, Manchester, M60 1QD UK;*******************Zhujun Jing,Institute of Mathematics, Academy of Mathematics and Systems Sciences, ChineseAcademy of Science, Beijing, 100080,China;******************Yue Liu,Department of Mathematics, University of Texas, Arlington,TX76019,USA;************Zengrong Liu,Department of Mathematics, Shanghai University, Shanghai, 201800,China;******************.cnNorio Okada, Disaster Prevention Research Institute, KyotoUniversity,****************.kyoto-u.ac.jp Jacques Peyriere,Université Paris-Sud, Mathématique, bˆa t. 42591405 ORSAY Cedex , France;************************,****************************.frWeiyi Su, Department of Mathematics, NanjingUniversity, Nanjing,Jiangsu, 210093,China;*************.cnKonstantina Trivisa ,Department of Mathematics, University of Maryland College Park,MD20472-4015,USA;****************.eduYaguang Wang,Department of Mathematics, Shanghai Jiao Tong University, Shanghai, 200240,China;***************.cnAbdul-Majid Wazwaz, 3700 W. 103rd Street Department of Mathematics and Computer Science, Saint Xavier University, Chicago, IL 60655 ,USA;**************Yiming Wei, Institute of Policy and management, Chinese Academy of Science, Beijing, 100080,China;*****************Zhiying Wen,Department of Mathematics, Tsinghua University, Beijing, 100084, China;*******************Zhenyuan Xu, Faculty of Science, Southern Yangtze University, Wuxi , Jiangsu 214063 ,China;*********************Huicheng Yi n, Department of Mathematics, Nanjing University, Nanjing, Jiangsu, 210093, China;****************.cnPingwen Zhang, School of Mathematic Sciences, Peking University, Beijing, 100871, China;**************.cnSecretary: Xuedi Wang, Xinghua FanEditorial office:Academic House, 113 Mill Lane Wavertree Technology Park Liverpool L13 4AH, England, UK Email:***************************.uk **************************.uk ************.cn。
*国家自然科学基金资助项目(63,66);广东省自然科学基金资助项目(5)通信作者z y @y 基于近似熵的癫痫发作预测研究*刘治远1,解玲丽2,陈子怡3,黄瑞梅1,李小江1,周毅1(1.中山大学中山医学院生物医学工程系,广州510080;2.中山大学数学与计算科学学院,广州510275;3.中山大学附属第一医院神经内科,广州510080)摘要:临床采用诱发方法检测获得的失神发作患者EEG 信号,研究其发作前脑电信号的动力学变化的规律,寻找预测癫痫失神发作一般规律和方法。
我们选择合适的电极对,使用非线性动力学的方法,采用复杂度变化度量的近似熵指标,通过闪光刺激癫痫患者获得的EEG 信号进行动力学特征研究,根据EE G 信号表现出的同步情况实现对癫痫发作的预测。
结果表明,本研究可以实现对临床光刺激进行诱发的癫痫失神患者的发作进行预测。
研究中采用优化电极的方法优于采用固定电极对。
关键词:癫痫;脑电图;T 检验;近似熵;发作预测中图分类号:R318文献标识码:A 文章编号:1672-6278(2011)01-0020-04Prediction of Epileptic Seizure based on Approximate Entropy of EEGLIU Zhiyuan 1,XIE Lingli 2,CHEN Ziyi 3,HUA NG Ruimei 1,LI Xiao jiang 1,ZHOU Yi1(1.D epartment o f Biomedical Engineering ,Zhon gs han Schoo l o f M edicine,Sun Y at -s en U nive rsity,G uan gzho u 510080,China ;2.School o f Mathematics and Com putational Science,Sun Y at -s en U niv ersity,G uan gzho u 510275;3.De partment o f Neu r o lo gy,the F irs t A ff liate d Hos pital,Sun Y at -sen U niv ersity,G ua n gzhou 510080)Abstr act:In this study,we try to find out the general regularity and method to predict absences seizure by studying regularities of dynamics of spatiotemporal transitio ns of EEG during epilep tic seizures.With no nlinear dynamical method,using Appro ximate Entropy (A pEn),w e s tudied the dy namical features o f EEG signal w hich w as o btained fro m clinical data.The selection of cri tical cortical cites involved a model w hich could opti mize the pro bability to be best.Before epileptic absence seizure,the T-index of those critical cites will change to so me deg ree and will progressively conv erge.Then,a pro bably predictio n can be given.The prediction scheme o f opti ma electrode is better than using fi xed electrodeduring tw o seizures is considerable.Key wor ds:Epilepsy;Electroencephalog ram(EEG);T-test;Appro xi mate entropy;Prediction of seizures1引言癫痫患者一般有两种不同的状态:表现正常的发作间期和发作期,有些病例还含有明显的发作前期和发作后期。
Action ....................... 动作Animator .................. 原画者,动画设计Assista .................... 动画者Antic ....................... 预备动作Air Brushing …喷效Angle .............................. 角度Animated Zoom ……画面扩大或缩小Animation Film......................... ........ 动画片Animation Computer …电脑控制动画摄影Atmosphere Sketch .............. 气氛草图B.P.(Bot Pegs) ................... 下定位Bg(Background) ................... 背景Blurs ............................. 模糊Blk(Blink) ..................眨眼Brk Dn(B.D.)(Break-Down) …中割Bg Layout .............................. 背景设计稿Background Keys ................... ...背景样本Background Hookup ............. 衔接背景Background Pan ...................... 长背景Background Still 短背景Bar Sheets ............................ 音节表Beat................... 节拍Blank ..................空白Bloom ............................ 闪光Blow Up ..............................放大Camera Notes ................. 摄影注意事项C.U.(Close-Up) …特写Clean Up .............. 清稿,修形,作监Cut ............................ 镜头结束Cel=Celluloid ............................. 化学板Cycle ................................ 循环Cw(Clock-Wise) …顺时针转动Ccw(Counter Clock-Wise) …逆时针转动Continue(Cont ,Con‘D)…继续Cam(Camera) ................. 摄影机Cush(Cushion) ……缓冲C=Center ................ 中心点Camera Shake ……镜头振动Checker ................... ....... 检查员Constant .................... 等速持续Color Keys=Color Mark-Ups 色指定Color Model ................... 彩色造型Color Flash(Paint Flash) …跳色Camera Animation………动画摄影机Cel Level .......................化学板层次Character .................... 人物造型Dialog (Dialogue ............... 双重曝光Multi Runs ............. 多重曝光1st Run .................. 第一次曝光2nd Run........................ 地二次曝光Dry Brushing ……干刷Diag Pan(Diagonal) .................. 斜移Dwf(Drawing) .......................... 画,动画纸Double Image ............... 双重影像Dailies (Rushes) ……样片Director ................................. 导演Dissolve(X. D) .................... ......溶景,叠化Distortion ............................................. 变形Double Frame ......................................... 双(画)格Drawing Disc .................................... 动画圆盘E.C. U = Extreme Close Up 大特写Ext(Exterior) ................ ... 外面;室外景Eft(Effect) .......................... 特效Editing ......................... 剪辑Exit(Moves Out, O. S. ) …出去Enter(In) ................. 入画Ease-In....................... ... 渐快Ease-Out .................. 渐慢Editor...................... 剪辑师Episode ……片集Field(Fld) .............................. 安全框Fade(In/On) ……画面淡入Fade(Out/Off) ……画面淡出Fin(Finish) ..................... 完成Folos(Follows) …跟随,跟着Fast; Quickly ……快速Field Guide ……安全框指示Finial Check ........... ...... 总检Footage .................... 尺数(英尺)F.G. (Foreground)…前景Focal Length ……焦距Frame …格数Freeze Frame ..................... 停格Gain In ……移入Head Up ............... 抬头Hook Up ...................... 接景;衔接Hold ...............画面停格Halo ............................... 光圈Int(Interior) ......................... 里面;室内景Inb(In Between) .................................. 动画In-Betweener ……动画员I&P(Ink & Paint) …描线和着色Inking ..................描线In Sync .................... 同步Intermittent ..................... 间歇Iris Out ..................... 画面旋逝Jiggle .................. 摇动Jump …跳Jitter ................ 跳动Lip Sync(Synchronization) 口形Level ........................... 层Look ……看Listen ........................ 听Layout .......................... 设计稿;构图Laughs(Laffs) ……笑L/S(Light Source) ……光源Line Test(Pencil Test) …铅笔稿试拍;线拍M. S. (Medium Shot) ..................... 中景M. C. U. (Mediium Close Up) …近景Moves Out(Exit; O. S. ) ...... ........... 出去Moves In ................................... 进入Match Line ......................... 组合线Multi Runs ................. 多重拍摄Mouth ............................. 嘴Mouth Charts ........................ 口形图Mag T rack(Magnetic S ound T rack) 音轨Multicel Levels …多层次化学板Multiplane ....................... 多层设计N/S Pegs ...................... 南北定位器N.G.(No Good) ..................... 不好的,作废Narration ……旁白叙述Ol(Overlay) ...................... .. 前层景Out Of Scene ................. 到画外面O.S.(Off Stage Off Scene) …出景Off Model .......................... 走型Ol/Ul(Underlay) 前层与中层间的景Overlap Action …重叠动作Ones ...................... 一格;单格Pose ...................... 姿势Pos(Position) ……位置;定点Pan ........................... 移动Pops In /On ..................... 突然出现Pause ....................... 停顿;暂停Perspective ……透视Peg Bar ...................... 定位尺P.T.(Painting) ...... ........... 着色Paint Flashes(Color Flashes) 跳色Papercut ................... ...... 剪纸片Pencil Test ............. 铅笔稿试拍Persistence Of Vision 视觉暂留Post-Synchronized Sound后期同步录音Puppet .......................... ...... 木偶片Ripple Glass ................... 水纹玻璃Re-Peg ............................ 重新定位Ruff(Rough-Drawing) …草稿Run ...................... 跑Reg(Register) ..................... .组合Rpt(Repeat) ................................. 重复Retakes ...................... 重拍;修改Registration Pegs ……定位器Registration Holes ……定位洞Silhouette(Silo) .................... 剪影Speed Line ................... 流线Storm Out ............................. 速转出Sparkle ....................... 火花;闪光Shadow ................ 阴影Smile ....................... 微笑Smoke ……烟Stop .............................. 停止Slow ...................... ..... 慢慢的Sc(Scene) .......................... 镜号S/A(SameAs)............................... 兼用S.S(Screen Shake) …画面振动Size Comparison ……大小比例Storyboard(Sab) …分镜头台本Sfx(Sound Effect) …声效;音效Settle ..................................... 定姿;定置Self-Line(Self-Trace Line) 色线Sound Chart(Bar Sheeets) 音节表Special Effect ....................... 特效Spin ................................. 旋转T.A.(Top Aux) .............. 上辅助定位T.P.(Top Pegs) .............. 上定位Track ........................................................ 声带Turns ........................................................ 转向Take …………拍摄(一般指拍摄顺序) Truck I n................................................ 镜头推人Truck Out ................................ 镜头拉出Tr(Trace) .................同描Tapers ................................. 渐Taper-Up ......................... 渐快Taper-Down .................... 渐慢Tight Field .......................... 小安全框Tap(Beat) ...................节拍Tittle ..................... 片名;字幕Ul(Underlay) ............................ 中景;后景Up .................... 上面Use ....................... 用Vert Up ................... 垂直上移V.O. (V oice Over) …旁白;画外音Value .................................... 明暗度Wipe .........................转(换)景方式Work Print …工作样片X(X-Diss) (X. D. ) ……两景交融Xerox Down ................ .. 缩小Xerox Up(Xerox Paste-Ups) 放大X-Sheet ...................... 摄影表Zoom Out ........................... 拉出Zoon Chart.................镜头推拉轨迹Zoom In ……推进Zoom Lens …变焦距镜头MMagnetic Tape 磁性录音带Makeup A rtist 美容师Manipulation 操纵Markup 固定利润Matte 影像形板Maysles Films 梅思利电影公司Memory-Hook 回马枪Memory-Jogger 回马枪Merrill Lynch 美林动画Metamorphic A nimation 变形动画Metamorphosis 变形Micro-Markets 微众市场Mixer 混音师Modeling 模型制作Montage 蒙太奇Morph 型变Mos 不需要现场收音的无声取景Motion Board 活动脚本或动作脚本Motion Capture 动作资料截取Motion Cintrol 电脑控制拍摄系统Motion Picture Film 动画影片Motion Tests 动作测试Motor Home 移动居住车Mouse 滑鼠Mouthpiece 发言人Multi-City Bidding 多城市竟标Music Bookends 音乐书签Music First 以音乐为优先Musical Instrument Digital Interface Midi电子乐器一的数位介面NNational Association O f Broadc国家广播电子技师协会National Cash Register 国家收银机公司Nbc 国家广播公司Negative Conformer 底片组合员Ng 不好的镜头Nonlinear Editing 非线性剪辑OOfff-Camera 镜外表演Off-Key 走调Offline System 线外系统Offline System 线外剪辑系统One-Stop Operation 一贯作业On Camera 镜内表演On-Camera Sag Rates 演员同业公会规定的上镜费On Location 出外景Online Editing 线上剪辑One-Light 单一光度One-Light Film Print 单光影片洗印One-Stop Operation 一次作业Opaquer 著色人员Open Camera 公开摄影Optical House 视觉效果工作室Optical Printer 光学印片室Original Arrangment 编曲著作Original Recording 录音著作Original Score 总谱制作Out-Of-Pocket 现款支付Outside Props 棚外道具师Outtakes 借用镜头PPacific Data Images 太平洋影像公司Pegs 过场用之画面Pencil Test 铅笔测试稿Perceived Value 知觉价值Personalities 知名人士Personality Testimonials 名人见证Petsuasion 说服Photo Cd 影像光碟Pickup Footage 从旧有的广告借凑而来的影片Pictures First 以画面为优先Pixels 像素Playback 播放Playback Person 录影机播放员Post-Scoring 后制配乐Posttesting 后测Pre-Lite 预先排演Pre-Production Meeting 拍制前会议Pre-Production Stage 制前阶段Prescoring Music 拍摄前配乐Pretesting 前测Price-Quote 报价或喊价Printed Circuiry 印刷电路Producer 广告公司的制片,制作人Product Shot 商品展示镜头Production Assistant P .A 制作助理Production Boutique 制片工作室Production Notes 制作住记Production Package 制作议价组合Production Specification Sheets 制作分工明细表Promotions 促销Prop People 道具师Peoperties 舞台道具Props 道具Public-Domain Music大众共有或版权公有的音乐Publisher's Fee 发行费用Pulldowm 抓片RRanddom A ccess 随机存取Random Access Memory Ra随m机存取记忆体Raster 屏面Read Only Memory Rom 唯读记忆体Real Opinions 真实反应的意见Real People 消费大众或一般人Real People Reactions And Opinions消费大众的真实反应及意见Recordist 录音师Reebok 锐跑Reflections 反光Rendering 算图Rental Facilities 出租公司Residual 后续付款Rhapsody In Blue 《蓝色狂想曲》Rhythm And Hues 莱休电脑动画公司Right-To-Work 自由工作权Ripomatic/Stealomatic Storyboard 借境脚本Roll Camera 开动摄影机Rotoscope 逐格帖合的重覆动画动作Rough Cut 粗剪SSample Reels 作品集Scencs 场景Scenics A rtist 布景设计师Scratch Track 临时音轨Screen Actors Guild Sag 电影演员同业公会Screen Extra's Guild Sag 电影临时演员同业公会Scripts 剧本Script Clerk 场记Set Construction Costs 搭景费用Set Designer 布景设计师Set Dresser 布影装饰师Shadows 阴影Shape Library 清晰对焦Shooting Board 模型资料库Shooting Day 制作脚本拍片日Shooting In Two 一次两画格的方式拍摄Shot List 拍摄程序表Shutter 快门Sides 台词表Silent Scenes 无声场景Silent Takes 无声取景Slate 开拍板Slice-Of-Life Episodes 生活片段式对白Snapshot 快照拍摄Solid State Screensound 数位录音工作站Song-And-Dance 歌舞片Sound People 音效人员Sound Stage 隔音场Sound Take 有声摄影Special Effects Person 特殊效果人员Special-Effects 特效Specification Sheet 职责明细表Speed 运转正常Splice 捻接Sprint斯布林特电话公司Stand-In 替身Stand-Up Presenters 播报员推荐Standing Sets 常备的布景配置Star Personality 知名人物Stereo-Mixing 立体声混音Sticks 排字手托Stills 剧照Still Photos 静态照片Stock Footage 底片材料、库存影片Stop-Motion 单格拍制Story Line 故事情节Storyboard 故事脚本Strobe-Lighe Photography 频闪闪光灯摄影法Subaru Autombile 速霸陆汽车Super 16mm Format 超16 厘米底片规格Sync Sound 同步收音Synchronized 同步TThe Screening Room 试播室Takes 取景镜头Talent Reports 劳务报价单Teamsters 卡车驾驶员Teamsters Union 卡车驾驶员工会Telepromrter 读稿机Test Commercial 测试性广告Testimonial Release Print 电影院放映片Three-Dimensional 3d 三度空间Ight Close-Up 大特写Time-Code 时码Tissue S heets 薄绵纸Top Light 顶光Trim 剪修Trims 修剪下来的片头尾Tracing Paper 扫图纸Track Left 摄影机左移Track R ight 摄影机右移Track Time 音轨时限Trade 通路Tri-X 柯打tri-X 底片Turnarounds 转场Unique Selling Proposition 独特的销售主张VVideo 视觉或影像部分Video Master 影像母带Video Tape Recording Person 录音带录制员Vignetters 集锦式快接画面处理Virtual Reality 虚拟实境Visual Timeline 视觉时间尺Visually Oriented 视觉导向Voiceover Announcer 旁白播音员WWardrobe Attendant 服装师West And Brady 威布广告公司Wild Wall 活动墙板Window Burn-In 叠印框Wire-Frame 立体线稿Words-And-Music 旁白加音乐Words First 以文案为优先Zoom 变焦Zoom In 镜头向前推进。
专业英语Specialized English一、将词组译成英语信道容量Channel capacity信息量Amount of information信号功率Signal power噪声功率Noise power噪声谱密度Noise spectral density通信保真Fidelity of communication光波系统Optical system中继距离Distance spacing半导体激光器Semiconductor laser光纤放大器Fiber amplifier波分复用Wavelength-division multiplexing 光纤损耗Fiber loss光纤色散Fiber dispersion掺饵光纤放大器Erbium-doped fiber amplifier同步数字系列Synchronous digital hierarchy 支路信号Tributary signals数字交叉连接Digital cross connect网络维护Network maintenance支路映射Tributary mapping同步传输帧Transmission frame线路终端复用器Line Terminal Multiplexer灵敏度Sensitivity虚容器Virtual container成帧字节framing bytes段开销Section overhead端到端传输End of transmission误码监视Error monitoring信号处理节点Signal processing node净负荷Net load指针Pointer离线率The rate of off-time软交换Soft switching功率谱密度Power spectral density开环功率控制Open loop power control抗干扰能力Anti jamming ability拦截Blocking rate虚电路Virtual circuit时隙Time slot时分复用Time division multiplexing局域网Local area network服务质量Service quality广域网Wide area network公众交换电话网Public switched telephone network分组交换Packet switching蓝牙规范Bluetooth specification免提电话 A hands-free phone通用接入框架Universal access framework接入控制协议Access control protocol业务发现协议Service Discovery Protocol立体声耳机Stereo headset网络电视Network television数字用户线接入复用器Digital subscriber line access multiplexer 视频点播Video on demandIP组员协议IP crew agreement机顶盒The set-top box前向纠错Forward error correction高清电视High definition television实时流协议Real time streaming protocol通信信道Communication channel光发送机Optical transmitter光接收机Optical receiver光脉冲Optical pulse光源Light source非线性效应Nonlinear effect信噪比Signal to noise ratio误码率Bit error rate强度调制直接检验Intensity modulation direct inspection嵌入式系统Embedded system特定用途集成电路Application specific integrated circuit数字助理Digital assistant通信协议Communication protocol微控制器Micro controller实时系统Real time system二、将词组译成应为pulse code modulation 脉冲编码调制the highest frequency component 最高频率分量signaling and synchronization information 信号和同步信息per-channel codec system 每个信道编解码系统two-to-four wire conversion 两到四线转换the lower-frequency portion of the spectrum 低频部分的频谱nonlinear A/D converter 非线性模数转换器amplitude distortion振幅失真to prevent power-line frequency noise from being transmitted防止电力线频率噪声的传播resolution of the resulting digital signal解决由此产生的数字信号the resulting serial bit stream由此产生的串行位流line-to-line crosstalk 线间串扰in a fully integrated form 在一个完全集成的形式coaxial systems同轴系统multimode fiber多模光纤single-mode fiber单模光纤fiber losses 光纤损耗fiber dispersion光纤色散coherent lightwave systems 相干光通信系统fiber amplifiers光纤放大器wavelength-division multiplexing 波分复用erbium-doped fiber amplifier 掺铒光纤放大器propagation mode传播模式refractive index profile折射率剖面optical receiver光接收机dielectric介质destructive interference破坏性干涉stepped-index fiber加强指数纤维synchronous transmission system同步传输系统the equipment supplied by different manufacturers不同厂商提供的设备terminal multiplexer 终端复用器synchronous DXC 同步数字交叉连接设备individual tributary signals各支路信号section overhead段开销central processing unit中央处理单元Local area network 局部区域网络Network topology 网络拓扑Token ring network 令牌环网络reed relay簧片继电器electromechanical switching device机电开关装置crosstalk串扰labour-intensive 劳动密集型semiconductor lasers 半导体激光器light-emitting diode 发光二极管semiconductor photodiodes 半导体光电二极管intensity modulation with direct detection 强度调制直接检测error-correction codes 纠错码receiver sensitivity 接收机灵敏度三、简写PCM (Pulse-code modulation) 脉冲编码调制CDMA (Code division multiple access)码分多址PAM (Pulse amplitude modulation) 脉冲振幅调制ATM (Asynchronous Transfer Mode) 异步传输模式GPRS(General Packet Radio Service)通用分组无线服务USB (Universal serial Bus)通用串行总线AON (Active optical network) 有源光纤网FTTC (fiber to the curb) 光纤到路边WWW ( world wide web ) 全球资讯网LAN (Local Side Band) 局域网WAN (wide area network)广域网WLAN 无线局域网SSB (single side band) 单边带DSP ( digital signal processing) 数字信号处理LASER ( light amplification by stimulated emission of radiation )受激辐射的光放大CCITT(Telephone Consultative Committee)国际电话与电报顾问委员会SLIC (subscriber-line interface circuit)用户线接口电路EDFA (erbium-doped fiber amplifier)掺饵光纤放大器DSF (Dispersion shifted fiber)色散位移光纤ADM (Add and drop multiplexer)分插复用IEEE (Institute of Electrical and Electronic Engineers)电气与电子工程师学会ITU (International Telecommunications Union) 国际电信联盟CATV (Cable Television)有线电视ISDN (Integrated Services Digital Network) 综合数字业务网AGC 自动增益控制器TDM (time-division multiplexer)时分复用SDH(Asynchronous Digital Hierarchy)同步数字系列CCS (Common-Channel Signaling)公共信道信令WDM (wavelength-division multiplexing) 波分复用NNI (Network Node Interface) 网络节点接口LTM (Line Terminal Multiplexer) 线路终端复用器MEMS (Micro Electro Mechanical switching) 微机电开关CPU (central processing unit)中央处理单元CSMA/CD (Multiple Access with collision detection)多路存取/碰撞检测PDCP (Personal Digital cellular packet) 分组数据聚合协议PN 伪码GSM 全球移动通信系统CELP (Code Excited Linear Predictive) 线性预测HDSL (High-bit-rate Digital Subscriber Line) 高比特率数字用户线ADSL (Asymmetrical Digital Subscriber Line) 非对称数字用户线CAP ( Carrierless amplitude modulation) 无载波振幅调制DMT (Discrete multi-tone modulation) 离散多音调制FTTC (Fiber to the curb) 路用光纤FTTH (Fiber to the home) 家用光纤IDN (integrated digital network) 集成数字网络PSTN (public telephone switched network) 公共交换电话网WiFi 无线上网。
脑机接口技术的无创性脑电刺激The field of brain-computer interface (BCI) technology has witnessed remarkable advancements in recent years, particularly in the realm of noninvasive brain stimulation through electroencephalography (EEG). This technique allows for direct communication between the human brain and external devices, opening up new horizons in the treatment of neurological disorders, rehabilitation, and even cognitive enhancement.近年来,脑机接口(BCI)技术领域取得了显著进展,特别是在通过脑电图(EEG)进行的无创性脑刺激方面。
这种技术实现了人脑与外部设备之间的直接交流,为神经系统疾病的治疗、康复甚至认知增强开辟了新的领域。
Noninvasive brain stimulation using EEG-based BCI involves the recording of electrical activity in the brain through electrodes placed on the scalp. These electrodes capture the brain's neural signals, which are then processed and translated into commands that can control external devices. This process allows for the precise targeting of specific brain regions, enabling the delivery of tailored stimuli to modulate neural activity.基于EEG的BCI无创性脑刺激技术涉及通过放置在头皮上的电极记录大脑的电活动。
Nonlinear synchronization in EEG and whole-head MEGrecordings of healthy subjectsCornelis J.Stam1,Michael.Breakspear2,Anne-Marie van Cappellen van Walsum3,Bob W. van Dijk31Department of clinical neurophysiology,VU University Medical Centre2Brain Dynamics centre,Westmead Hospital,Sydney,Australia and School of Physics, University of Sydney,Australia.3MEG centre,VU University Medical CentreAddress for correspondence:C.J.Stam,Department of Clinical Neurophysiology,VU University Medical Centre,P.O.Box7057 1007MB Amsterdamphone:+31(20)4440727fax:+31(20)4444816e-mail:cj.stam@Vumc.nlshort title:nonlinear synchronization in EEG/MEGAbstractObjectiveAccording to Friston,brain dynamics can be modelled as a large ensemble of coupled nonlinear dynamical subsystems with unstable and transient dynamics.In the present study two predictions from this model(the existence of nonlinear synchronization between macroscopic field potentials and itinerant nonlinear dynamics)were investigated.The dependence of nonlinearity on the method of measuring brain activity(EEG versus MEG) was also investigated.MethodsDataset I consisted of10MEG recordings in10healthy subjects.Dataset II consisted of simultaneously recorded MEG(126channels)and EEG(19channels)in5healthy subjects. Nonlinear coupling was assessed with the synchronization likelihood and dynamic itinerancy with the synchronization entropy.Significance was assessed with surrogate data testing (ensembles of20surrogates).ResultsSignificant nonlinear synchronization was detected in14out of15subjects.The nonlinear dynamics were associated with a high index of itinerant behaviour.Nonlinear interdependence was significantly more apparent in MEG data than EEG.ConclusionSynchronous oscillations in MEG and EEG recordings contain a significant nonlinear component which exhibits characteristics of unstable and itinerant behaviour.These findings are in line with Friston’s proposal that the brain can be conceived as a large ensemble of coupled nonlinear dynamical subsystems with labile and unstable dynamics.The spatial scale and physical properties of MEG acquisition may increase the sensitivity of the data to underlying nonlinear structure.Key wordsMEG EEG synchronization non-linear oscillations dynamics entropy1.IntroductionSynchronization of activity within and between neuronal networks in the brain is currently the focus of intense research efforts(Fries et al.,1997;Bhattacharya2001;Tallon-Baudry et al., 2001;Varela et al.,2001).This interest is due to the idea that synchronous oscillations may be an important mechanism by which specialized cortical and subcortical regions integrate their activity into a functional whole(Singer,2001).Thus they are an important candidate solution for the so called“binding problem”.Synchronous oscillations in different frequency bands may correspond to different functions and different spatial scales of integration(Basar et al., 2001).By and large,low frequencies in particular in the theta band,are hypothesized to play a role in coupling between distant brain regions(for instance prefrontal and post rolandic association cortices)whereas high frequencies are thought to be more important for short ranges interactions(von Stein and Sarnthein,2000).The importance of synchronous gamma band activity for object representation was first reported in animal studies in the early nineties(Eckhorn et al.,1988;Gray et al.,1989;Engel et al.,1991).This basic result has now been replicated many times,also in awake human subjects using EEG(Rodriguez et al.,1999;Tallon Baudry et al.,2001).Synchronous gamma oscillations may provide a mechanism whereby complex objects are temporarily represented in working memory(Bertrand and Tallon-Baudry,2000)or a way to bind brain regions involved in associative learning into Hebbian cell assemblies(Miltner et al.,1999).Local synchronization in the theta band has been associated with encoding and retrieval of information in episodic memory(Klimesch et al.,1994;Klimesch1996;1999;Burgess and Gruzelier1997;2000).Theta band coupling between frontal and post rolandic cortical regions has been reported during the retention interval of visual working memory tasks(Anokhin et al.,1999;Sarnthein et al.,1998;Stam2000)as well as during an N-back working memory task(Ross and Segalowitz,2000).According to Anokhin et al.stronger theta band coherence is associated with a higher intelligence(Anokhin et al.,1999).Local desynchronization in the lower alpha band has been associated with attentional processes and upper alpha band desynchronization with semantic memory in a number of studies by Klimesch and coworkers (reviewed in Klimesch1996;1999).The functional meaning of long distance coupling in the alpha band is less clear.Despite the fact that the importance of synchronous oscillations at different spatial scales and in different frequency bands for integrating brain activity is increasingly accepted,several questions need to be addressed.These questions relate to the origin and nature of synchronous oscillations and their relationship to optimal information processing in the brain.We discuss two ambitious models of brain dynamics that have attempted to deal with these issues.In a series of papers,Edelman and co workers stressed that optimal information processing in the brain requires a delicate balance between local specialization and global integration/ synchronization of brain activity(Tononi et al.,1994;1998a,b).They introduced a measure, the neural complexity or C N,which quantifies how optimal the balance between local specialization and global integration is(Tononi et al.,1994).This measure was applied to fMRI data in Friston et al.(1995).According to the model of Tononi et al the neural complexity is expected to decrease during states of lower consciousness and impaired brain function.However increased rather than decreased neural complexity has been reported during epileptic seizures and in Alzheimer’s dementia,which is in disagreement with the predictions of the model(Van Putten and Stam,2001;Van Cappellen van Walsum et al., submitted).A different concept of integrative brain dynamics has been put forward by Friston(2000a,b, c).Friston models the brain as a large number of interacting nonlinear dynamical systems. The elementary states of such a system are designated“neural transients”,which can bethought of as brief spatiotemporal patterns of synchronous brain activity.Friston stresses the ’labile’nature of normal brain dynamics,which consists of a rapid succession of neural transients and itinerant jumping between different marginally stable dynamical states(The terms‘nonstationary’,‘transient,’unstable’and‘itinerant’may have different meanings in different contexts.To clarify the present use of these terms,we include a short list of definitions in Appendix I.).In this model interactions between subsystems can be linear(as in the case of synchronous oscillations)as well as nonlinear.Nonlinear interactions between brain regions may reflect the unstable nature of brain dynamics including the changing modulatory influences of one frequency band on another(‘asynchronous coupling’).In a modeling and experimental study Breakspear(2002)demonstrated how interactions between coupled nonlinear dynamical systems can give rise to some of the phenomena described by Friston,and how such activity may contribute to the varying waveform of the alpha rhythm. In the model of Friston optimal information processing is not obtained by a static balance between specialization and integration,but rather by unstable,nonlinear dynamics with rapidly fluctuating interactions(Friston2000b).The model of Friston thus predicts that at least some of the interactions between brain regions will be nonlinear and transient.In contrast,the theory of Tononi et al.is compatable with linear and stationary dynamics. There is some empirical evidence for(nonlinear)coupling between theta and gamma frequencies in EEG(Schack et al.,2001;2002)and MEG recordings(Friston,2000a). Several studies have attempted to demonstrate nonlinear dynamics in normal EEG recordings. In most cases nonlinearity was studied with measures that characterize local dynamics (Pritchard et al.,1995;Stam et al.,1999)or global dynamics(Rombouts et al.,1995).The convergent finding of these studies is that nonlinear activity is present in scalp EEG data,at strong levels of significance,albeit only weakly and/or intermittently.Recent investigations of nonlinear interdependence between scalp EEG channels similarly report robust statistical evidence for nonlinear effects in approximately5%of windowed epochs(Breakspear and Terry2002).There is some evidence for nonlinear structure in MEG data(Kowalik et al., 2001)but nonlinear interactions between channels have not been studied.To test the predictions of Friston a measure is needed that is sensitive to nonlinear interdependencies between time series and can deal with transient dynamics.Measures based upon the concept of generalized synchronization seem to be suited for this goal(Rulkov et al., 1995;Schiff et al.,1996;Le van Quyen et al.,1998).In the pathological case of epileptic seizure activity nonlinear coupling between EEG signals has been demonstrated with this class of synchronization measures(Le van Quyen et al.,1998).Recently we introduced the synchronization likelihood,which is also based upon the concept of generalized synchronization but avoids some of the shortcoming of the other methods(Stam and van Dijk, 2002).The synchronization likelihood characterizes linear as well as nonlinear synchronization between time series and can be computed with a high temporal resolution. From the synchronization likelihood a second measure,the synchronization entropy,can be computed.This measures the spatio-temporal variability of synchronization,and thus reflects the presence of unstable dynamics.The present study was undertaken to further explore the nature of synchronous activity in the brain and to test some of the predictions of the model proposed by Friston(2000a,b,c).Three questions were addressed:(1)Is there evidence for nonlinear interactions between different neural networks in the brain?(2)If there is evidence for nonlinearity,to what extent is this related to transient or itinerant brain dynamics with rapidly fluctuating synchronization levels?3.Are MEG recordings better able to detect nonlinear interactions than EEG recordings?To examine these questions MEGs and EEGs recorded in10elderly and5young healthy subjects during a no–task,eyes–closed condition were studied with the synchronization likelihood and the synchronization entropy.The presence of nonlinearstructure was tested statistically with phase randomised,multichannel surrogate data(Prichard and Theiler,1994;Rombouts et al.,1995).2.Methods2.1.SubjectsIn this study recordings of two groups of healthy subjects were investigated.The first group (dataset I)consisted of ten healthy subjects(control subjects taken from a study on MEG changes in Alzheimer’s disease).Mean age was64.5year(range:53-74year);3subjects were male.Three subjects were left handed(1male).All subjects disavowed a history of cognitive dysfunction,and were screened for signs of cognitive decline/dementia.The protocol of this study was approved by the medical ethical Review Board of the Vrije Universiteit Medical Centre.All subjects or their relatives gave written informed consent after the nature of the procedure was explained..The second group(dataset II)consisted of five healthy subjects,all co workers of the MEG centre at the VU University medical centre(2females;mean age30.5 year,range25–38year;all right-handed).2.2.MEG and EEG recordingsMagnetic fields were recorded while subjects were seated inside a magnetically shielded room (Vacuumschmelze GmbH,Germany)using a151channel whole-head MEG system(CTF Systems Inc.,Canada).A third order software gradient(Vrba,1996)was used with a recording passband of0.25-125Hz.Fields were measured during a no-task,eyes-closed condition.At the beginning and conclusion of each recording the head position relative to the co-ordinate system of the helmet was recorded by leading small AC currents through3head position coils attached to the left and right pre-auricular points and the nasion on the subjects head.Head position changes during a recording condition up to approximately1.5cm were accepted.In the case of dataset I,16second artefact-free epochs(sample frequency250Hz;4096 samples)of MEG data were chosen for analysis.Of the original151channels34were excluded either because their locations were too inferior for the registration of neural activity or because they contained significant artefact in at least one of the subjects.This exclusion criteria permitted analysis of the same117channels in all subjects.The MEG data were band-pass filtered off line between0.5and40Hz.For dataset II,the MEG was recorded with the same system and the same settings as dataset I,except for a higher sample frequency of625Hz.These recordings were down-sampled to 313Hz and artefact-free epochs of13seconds(4096samples)were selected.In the case of dataset II a larger number of channels(126)were artefact free in all subjects and hence were included in the analysis.For this dataset,EEG data were acquired simultaneously with the MEG.The EEG was recorded with Ag/AgCl electrodes from the following19positions of the international10-20system:Fp1,F7,F3,T7,C3,P7,P3,)P1,Fz,Cz,Pz,Fp2,F8,F4,T8,C4, P8,P4,O2.The EEG was re-referenced off line against an average reference electrode and digitally filtered between0.5and40Hz.The EEG epoch used for analysis coincided exactly with the MEG epoch.For both datasets a subset of19MEG channels corresponding roughly with the location of the19EEG electrodes was also analysed.2.3.Synchronization likelihoodThe synchronization likelihood is a measure of the degree of synchronization or coupling between two or more time series(Stam and van Dijk,2002).The measure is based upon the concept of generalized synchronization as introduced by Rulkov et al.(1995).Generalized synchronization is said to exist between two dynamical systems X and Y if there exists acontinuous one-to-one function F such that the state of one of the systems (the response system)is mapped onto the state of the other system (the driver system):Y =F(X)(Rulkov et al,1995,Kocarev and Parlitz 1996,Abarbanel et al.1996).To make this concept operational we assume time series of measurements x i and y i (i =1…N)recorded from X and Y.From these time series we reconstruct vectors in the state space of X and Y with the method of time-delay embedding (Takens,1981):X i =(x i ,x i+l ,x i+2l ,…,x i+(m-1)l )[1]Here l is the time lag and m the embedding dimension.In a similar way vectors Y i are reconstructed from the time series y i .Now if the state of Y is a function of the state of X,each X i will be associated with a unique Y i .Also if two vectors X i and X j are almost identical (the distance between X i and X j is very small)then,because of the continuity of F,Y i and Y j will also be almost identical.The synchronization likelihood expresses the chance that this will be the case.For this we need a small critical distance εx ,such that when the distance between X i and X j is smaller than εx ,X will be considered to be in the same state at times i and j.εx is chosen such that the likelihood of two randomly chosen vectors from X (or Y)will be closer than εx (or εy )equals a small fixed number p ref .It is important to note that p ref is the same for X and Y,but εx need not be equal to εy .Now the synchronization likelihood S between X and Y at time i is defined as follows:∑−−=j j i y i Y Y N S )('1εϑ[2]Here we only sum over those j satisfying w1<│i-j │<w2,and │X i -X j │<εx .N’is number of j fulfilling these conditions.The value of w1is the Theiler correction for autocorrelation and w2is used to create a window (w1<w2<N)to sharpen the time resolution of S i (Theiler 1986).When no synchronization exists between X and Y,S i will be equal to the likelihood that random vectors Y i and Y j are closer than εy ;thus S i =p ref .In the case of complete synchronization S i =1.Intermediate coupling is reflected by p ref <S i <1.Because p ref is the same for X and Y,the synchronization likelihood is the same considering either X or Y as the driver system.Choosing p ref the same for X and Y is necessary to ensure that thesynchronization likelihood is not biased by the degrees of freedom or dimension of either X or Y (Stam and van Dijk,2002).From the basic definition of S i as given in [2]we can derive several variations by averaging over time,space or both.First,we can consider the average synchronization likelihood between X and two or more other systems.If we denote the index channel by k,S ki is the average synchronization between channel k and all other channel at time i.By averaging over all time points i we obtain S k .Averaging over all channels k gives S,the overall level of synchronization in a multi channel epoch.In the present study the synchronization likelihood was computed with the followingparameter settings:l =10;m =10;w1=100(product of lag and embedding dimension);w2=400;p ref =0.05.The length of w1and w2is expressed in samples.There is no unique way to choose these parameters;however the present parameter choices proved to be effective in distinguishing between MEG recordings of healthy controls and Alzheimer patients.2.4.Synchronization entropyThe strength of synchronization in an array of coupled nonlinear oscillators may be highly heterogeneous in both temporal and spatial domains,even if the coupling strength is constant.For example,in the setting of weakly coupled chaotic oscillators,the presence of intermittent bursts of desynchronization due to unstable periodic orbits has been the focus of much research (Pikovsky and Grassberger 1991,Rulkov and Suschik 1997,Heagy et al.1998,Pecora 1998).This phenomenon results in an irregular pattern of phase synchrony over a wide range of temporal scales (Breakspear 2002).To characterize the variability of thesynchronization likelihood S k,i as a function of space as well as time we introduce the synchronization entropy H s .The synchronization entropy is computed in a similar way as the Shannon information entropy.First the interval between p ref and 1is equipartitioned into N bins (in the present study we used N =100).Then we define p i as the likelihood that the value of S k,i will fall in the i th bin.The entropy H s is then obtained as,∑=−=N i ii s p p H 1log [3]When a logarithm with a base of 2is used,the unit of H s is bits.If there is no spatial and temporal variability in S k,i then p i will equal 1for one value of i,and 0for all other i.In this case the entropy H s will be zero.If there is maximal variability S k,i can take all values in the interval between p ref and 1with equal probability and p i will equal 1/N for all i .The entropy H s will then take its maximal value of log(N).2.5.Multivariate surrogate data testingThe basic idea of surrogate data testing is to compute a nonlinear statistic Q from the original data,as well as from an ensemble of surrogate data (Theiler et al.1992).The surrogate data have the same linear properties (in particular power spectrum and coherence)as the original data,but are otherwise random.This permits testing of the null hypothesis H 0that the original data are linearly filtered gaussian noise.This hypothesis is tested by computing a z-score:surrogates surrogates D S Q Q z ..)(−=[4]The z-score expresses the number of standard deviations Q is away from the mean Qs of the surrogate data.Assuming that Q is approximately normally distributed in the surrogate data ensemble,the null hypothesis can be rejected at the p<0.05level when z >1.96.In the present study we used two different nonlinear test statistics:the synchronization likelihood S(averaged over time and over all channels)and the synchronization entropy Hs.In both cases an ensemble of 20surrogate data was constructed from each original epoch.The surrogate data were constructed by applying a Fourier transform to all MEG channels,adding a random number to the phase of each frequency,and then applying an inverse Fourier transform.For each frequency the same random number was added to the phases of the different channels,thereby preserving exactly the coherence between the channels (Prichard and Theiler,1994;Rombouts et al.,1995).3.ResultsThe results of surrogate data testing using either the averaged synchronization likelihood S or the synchronization entropy Hs as a test statistic are shown in table I for dataset I and in table II for dataset II.In all ten subjects of dataset I the mean synchronization of the surrogate data was lower then the synchronization of the original data.The corresponding z-scores show that the null hypothesis could be rejected in all subjects,with z-scores ranging from2.770to9.163for the analysis with117channels and from2.794to9.404for the analysis with a subset of19 channels.Consequently,there is strong statistical evidence in all subjects that the interdependence in the MEG data cannot be fully described by a stationary linear/stochastic model,and hence may contain nonlinear parable results were obtained with the synchronization entropy Hs as test statistic:the mean entropy of the surrogate data was lower than the entropy of the original data in nine of the ten subjects for the analysis with117 channels,and in all subjects for the analysis with19channels.The null hypothesis could be rejected in seven out of the ten subjects for the analysis with117channels and in four out of ten for the analysis with19channels.Results of a more detailed analysis of a single representative subject(C98-16EC)are shown in figures1and2.In both figures,surrogate data testing was done using the S k(average synchronization likelihood between channel k and all other channels)of all117channels as test statistics.Figure1shows S k of the original MEG data(upper curve)and S k of each of the 20surrogate data sets.It is clear that for most channels S k of the original data lies outside and above the range of S k of the surrogate data.Note that this graphical comparison allows direct (non-parametric)testing of the null hypothesis.The parametric test(based on estimation of the Z-scores)is only necessary when adjusting for repeated comparisons.Figure2shows the significance of the difference between S k of the original data and S k of the surrogate data, expressed as z-scores.For a significance level of p<0.05the null hypothesis could be rejected in22out of117channels,which is much higher than expected by chance(6out of117).In the five subjects of dataset II the mean synchronization of the surrogate data was also lower than the synchronization of the original data,although the difference was only marginal in the case of subject JD.This pattern was obvious for the126channel and19channel MEG data as well as for the EEG data.In each subject the absolute synchronization likelihood was always higher in the EEG data than the MEG data,and higher for the126channel than for the 19channel analysis.However,the opposite is true of the z-scores.In the case of the126 channel MEG data the z-scores ranged from1.22to7.59(mean5.19)and the null hypothesis could be rejected in four of the five subjects.For the19channel MEG data z-scores ranged from0.317to6.195and the null hypothesis could be rejected in the same four subjects as for the126channel analysis.In the case of the EEG z-scores ranged from1.19to4.27(mean 3.15),and the null hypothesis could be rejected in the same four subjects who showed significant results with MEG.In these four subjects the z-scores for the126channel MEG data were always much higher than the z-scores for the corresponding EEG data;for the19 channel MEG this was the case in three of the four subjects(Fig.3).The apparent contradiction(between the synchronization strengths and the z-scores)is a result of the synchronization measures for the surrogate data sets,which were on average much higher in the EEG data.In all subjects of dataset II the synchronization entropy was lower for surrogate data compared to original data,and for MEG(for126as well as19channel analysis)compared to EEG.For MEG z-scores ranged from1.377to5.083for the126channels analysis,and from 1.339to3.043for the19channels analysis.The null hypothesis could be rejected in three out of five subjects at the95%confidence level for the126channel analysis and in four out offive subjects for the19channels analysis.For EEG the z-scores ranged from0.718to3.014, and the null hypothesis could be rejected in two of the five subjects.Mean results for MEG recordings in dataset I(bottom row of table I)and dataset II(second last row in table II)were generally in good agreement.The younger subjects of dataset II had a slightly higher synchronization and synchronization entropy,and slightly lower mean z-scores.For the subjects in dataset I the z-scores for the117and the19channel analysis were strongly correlated,although the19channel z-scores were slightly lower.This is illustrated in figure4.4.DiscussionThe present study was performed to answer the following three questions:(1)Is there evidence for significant nonlinear synchronization between brain regions in healthy subjects during a no-task eyes-closed state?(2)Does this nonlinearity have a stable or an unstable, itinerant character?(3)Are MEG recordings more suitable to detect nonlinear synchronization than EEG recordings?We will consider the results of the present study in relation to these three questions.The results obtained with both data sets strongly suggest the presence of nonlinear synchronization in multichannel MEG data ing the averaged synchronization S as a test statistic the null hypothesis that all couplings can be described with a linear model could be rejected in all ten subjects of dataset I,and in four of five subjects in data set II.The level of significance was usually very high,with z-scores>4(corresponding with p<0.00005)in 12of15subjects.We interpret these results as supporting the presence of nonlinear coupling across multiple cortical regions in healthy human subjects.However,to assess the validity of these results,three issues deserve mentioning:(1)the use of a parametric statistical test to reject the null hypothesis;(2)the possibility of type I statistical errors;(3)the reliability of phase-randomized surrogate data.First,we compared the S of the original MEG data with the mean S obtained from an ensemble of20surrogate data(S-surr)for each subject by computing a z-score;the z-score quantifies the distance between S and S-surr in terms of the standard deviations of S-surr.The tacit assumption is that S-surr is approximately normally distributed,which may not be true. In theory it is possible that a non gaussian distribution of S in the surrogate data ensemble will bias the test of the null hypothesis.To avoid this bias the null hypothesis can also be tested in a non-parametric manner(Rapp et al.,1994).When S of the original data is larger then S of each of the20surrogate data,then for a one-sided test the null hypothesis can be rejected at the p<0.05level.In figure1we show that this is the case for one representative subject:S k of the original data is always higher then S k of the surrogate data.In conclusion we think it is unlikely that our results are due to non gaussian distribution of S in the surrogate data sets. Also,assessment of very high significances with non parametric tests is problematic because it would require ensembles of hundreds to thousands of surrogate data for each subject which is computationally prohibitive.Second,to test the null hypothesis we used an alpha level of p<0.05in each individual subject.Because15subjects were investigated there is a chance of type I statistical error (spurious rejections of the null hypothesis due to multiple independent tests).However,if we apply a rigorous Bonferroni correction,and use an adjusted significance level of p<0.05/15or p<0.0033(z>2.12)the conclusions remain the same and we can still reject the null hypothesis in14of15subjects.Finally,the reliability of the procedure to generate surrogate data needs to be considered. Ideally surrogate data preserve only but exactly the linear properties(power spectrum; coherence)of the original data.Any differences between original and surrogate data can then be ascribed to nonlinear properties of the original data.Problems can arise in two circumstances:(1)When the amplitude distribution of the original data is non-gaussian;(2) When the basic frequencies of the original data do not match exactly with the frequencies of the discrete Fourier transform.The latter problem typically arises with(nearly)periodic time series In the case of univariate time series these problems are well known,and procedures to avoid them have been proposed(Theiler et al.,1992;Stam et al.,1998).Whether the same problems also affect surrogate data testing for nonlinear couplings between time series in multivariate data sets is unknown.To address this problem we considered a simple model system,consisting of two identical time series(4096samples).Each time series was the。