人脑初级视皮层内事件相关型视觉刺激fMRI BOLD响应特性初步研究

基于脑血氧水平依赖(BOLD)对比的功能磁共振成像（fMRI）方法是研究脑功能活动的一种重要的无损伤探测手段，BOLD的机制及它与脑神经活动关系一直是国际上十分活跃的研究领域，尤其是在实验研究方面. 视觉刺激所引起的脑的初级视皮层(V1) 的BOLD响应的时间特性已有较多的研究，但是在这些研究中，有的结论认为BOLD对视觉刺激的响应是线性的，有的结论却是相反的. 我们采用事件关联型核磁共振功能成像（ER-fMRI）方法，研究不同的短暂视觉刺激持续时间下的BOLD响应，得到了视觉刺激下的脑激活图. 同时找出了视觉刺激时间分别是1、2、3、4、5和6 s的V1区的BOLD响应曲线，并初步显示出BOLD响应与刺激持续时间的线性关系.     

视觉非随意注意的近红外脑功能成像技术与事件相关脑电位检测技术研究

近红外脑功能成像技术(fNIRI)是近年来发展起来的新技术,与心理学研究常用的事件相关脑电位检测技术(ERP)相比,能提供电生理信号之外的与脑功能活动相关的血液动力学信息。设计了非随意注意的经典范式,对同一组被试者分别使用近红外脑功能成像技术和事件相关脑电位检测技术检测其在实验过程中脑活动变化,然后对两种技术检测的结果进行处理和比较分析。结果发现近红外脑功能成像技术测出的非随意注意源定位在前额叶,与其相关P3a脑电皮层分布一致,甚至近红外脑功能成像技术测出的源定位范围可以缩小到Brodmann46区;血液激活先于P3a并在P3a完成后显著增强的现象支持深入研究脑机理的可能性。因此,近红外脑功能成像技术可有效地应用于脑的高级功能研究。     

两个非耦合Hindmarsh-Rose神经元同步的非线性特征研究

利用Hindmarsh-Rose(HR)神经元输出的膜电压作为刺激调整两个具有不同初始条件的非耦合HR神经元的电流输入，通过分析神经元放电峰峰间期(ISI)的分布揭示了两个神经元同步过程轨道演化的机理.在周期信号刺激下，两个具有相同参数原处于混沌状态的神经元可以 实现完全同步，且可以同步到不同于刺激信号频率的周期响应上；两个具有不同参数的神经 元可以实现相位同步，参数差别较小的两个神经元可以相位同步到与刺激信号不同频率的周 期响应上，参数差别较大的两个神经元只可能相位同步到与刺激信号相同频率的周期响应上 .混沌信号刺激两个神经元只可能同步到产生混沌信号神经元的放电模式上，可见混沌刺激 更有利于神经元信息编码与解码.分析两个被调整神经元系统的最大条件Lyapunov 指数(Lmc )与刺激强度k的关系表明当k达到某一阈值时两个系统的Lmc均为负值是两个系统实现同 步的必要条件.平均发放率相同的混沌刺激和周期刺激相比较混沌刺激更容易使两个神经元 实现同步，表明混沌刺激产生的效应更强，该结论与实验结果相符合. 关键词： 放电峰峰间期 同步 相位同步 条件Lyapunov 指数     

光学多普勒层析三维矢量测速方法研究

光学多普勒层析术(ODT)是一种高分辨、非侵入的生物医学成像手段,能同时得到组织的结构信息和组织内血管的流速信息.提出了一种新型的基于相位分辨技术的ODT三维矢量测速方法.在ODT系统样品臂的准直镜和聚焦透镜之间加入窄带相位片,形成三个不同的相位延迟,通过计算多普勒频移和不同相位延迟下的多普勒展宽,可得到毛细管内的三维矢量流场分布.对已知浓度的聚苯乙烯溶液进行了一系列不同角度和不同流速的实验,结果证明这种新型的ODT矢量测速方法可以较精确的实现三维矢量流速的测量.     

计算相位响应曲线的方波扰动直接算法

通过相位响应曲线可对具有极限环周期运动的动力系统的性质有更为深入的理解.神经元是一个典型的动力系统,因此相位响应曲线提供了一种研究神经元重复周期放电行为的新思路.本文提出一种求解相位响应曲线的方法,即方波扰动的直接算法,通过Hodgkin-Huxley,Fitz Hugh-Nagumo,Morris-Lecar和Hindmarsh-Rose神经元模型验证该算法可计算周期峰放电、周期簇放电的相位响应曲线.该算法克服了其他算法在运用过程中的局限性.利用该算法计算结果表明:周期峰放电的相位响应曲线类型是由其分岔类型所决定;在Morris-Lecar模型中发现一种开始于Hopf分岔终止于鞍点同宿轨道分岔的阈上周期振荡,其相位响应曲线属于第二类型.通过大量的相位响应曲线的计算发现相位响应的相对大小及正负性仅取决于扰动所施加的时间,而且周期簇放电的相位响应曲线比周期峰放电的相位响应曲线更为复杂.     

一种高性能液晶透镜的设计方法

提出了一种高性能液晶透镜的设计方法。该方法结合了电极结构的设计并利用了液晶材料线性响应区。所设计的电极结构用于产生抛物线的电压分布,将驱动电压控制在液晶材料的线性响应区内可以实现抛物线的相位分布。通过该方法设计的液晶透镜,其孔径可以是任意大小,且不依赖高阻膜。所设计的电极结构简单,加工只需要一次光刻。透镜由两个低电压驱动,驱动方法简单,其焦距可通过两个驱动电压进行调节。理论上这种液晶透镜的相位分布在变焦过程中保持理想的抛物线分布,且光焦度正比于两个驱动电压的差值。实验上,通过光刻法加工了所设计的电极结构,测量了液晶材料的线性响应区,制作了液晶层厚度为50μm的液晶透镜。通过偏振干涉原理采集了干涉条纹,并从中提取了相位信息。实验结果表明,透镜的相位服从抛物线分布,且光焦度与驱动电压的差值成正比。实验结果与理论分析一致。     

光纤型宽带可调连续波差频产生中红外激光器

报道一种新型光纤化宽带可调连续波中红外激光器系统,该激光系统采用准相位匹配(QPM)的差频产生(DFG)技术,非线性晶体为多周期的周期性极化掺镁铌酸锂晶体(PPMgLN),掺镱光纤激光器(YDFL)用作抽运光源,可调激光器经掺铒光纤放大器(EDFA)功率提升后作为信号光源。利用建立的准相位匹配-差频产生系统,获得了连续波中红外差频光输出;实验发现,温度导致相位失谐的半峰全宽(FWHM)为4.5℃;通过优化选择晶体周期,并结合调节信号光波长和控制温度,该准相位匹配-差频产生系统可在3.1~3.6μm内连续调谐。     

利用fNIRS研究情绪状态下的脑力负荷评估

为研究采用功能性近红外光谱(fNIRS)技术评估不同情绪状态下操作者脑力负荷(MWL)的可行性,为开展以MWL评估为基础的操作者功能状态(OFS)评估提供技术支持,进行了多种情绪刺激下的图片n-back任务实验,包括负性、积极和中性三组情绪.采用任务绩效、主观量表和fNIRS生理测量等方法采集16名参试者的实验数据.任务绩效和主观状态评分均表明参试者MWL在外部因素影响下发生变化.从fNIRS信息中提取了时域、频域和非线性域共380个生理特征作为OFS评估模型输入,采用支持向量机作为分类器,建立了MWL评估模型.评估模型采用中性情绪刺激下的任务数据作为训练数据,积极情绪和负性情绪刺激下的实验数据作为测试数据,分别取得了92.49%、75.90%和79.99%的平均分类正确率.通过实验数据分析,验证了任务负荷和情绪刺激能够有效影响操作者MWL的实验假设,证明了采用fNIRS技术建立多种情绪状态下MWL评估模型的可行性,为开展复杂任务情况下以MWL为基础的OFS评估提供依据.     

基于物体像的干涉条纹图像中散斑噪声的识别方法

散斑噪声是激光干涉时的普遍现象,其覆盖被测表面对应区域的形状信息,造成测量误差。针对斜入式激光干涉测量中散斑噪声的特点,提出一种基于物体像的散斑噪声的识别方法。该方法通过统计物体像中有效测量区域和背景区域内灰度分布的特点,自动计算出判定散斑噪声的上下阈值。基于物体像与干涉条纹图像间微米级的映射关系,得到干涉条纹图像中散斑噪声的位置。设计了相关实验,对干涉条纹图像中识别出的散斑噪声区域进行修补,消除了包裹相位图中一个条纹周期内相邻像素点间大于π的相位突变。     

利用功能性近红外光谱法研究大脑皮层血氧情况随任务特征变化规律

功能性近红外光谱(f NIRS)成像是一种新兴的光学脑成像技术。已有大量基于f NIRS简单任务脑力负荷评估方面的研究,但当实验任务从单一简单任务变化为复杂综合任务时,相应方法不能直接简单套用。借助于f NIRS技术,通过复杂任务特征分解的思路进行尝试,研究大脑皮层血氧情况随复杂任务各任务特征的变化规律,为f NIRS评估复杂任务脑力负荷等研究提供思路和基础。结果发现:前额叶大脑皮层(PFC)区域的含氧血红蛋白(Hb O)对复杂度、时间压力和有无控制三种任务特征的变化均有较高的激活程度响应;视觉皮层(VC)区域的Hb O对不同时间压力任务特征导致的任务难度变化有较高的激活程度响应,但对不同复杂度和有无控制特征的激活程度响应较低;运动皮层(MC)区域Hb O对有无控制输出特征有较高的激活程度响应,对不同时间压力特征的激活程度响应较弱。     

Biophysical and neural basis of resting state functional connectivity: Evidence from non-human primates

Functional MRI (fMRI) has evolved from simple observations of regional changes in MRI signals caused by cortical activity induced by a task or stimulus, to task-free acquisitions of images in a resting state. Such resting state signals contain low frequency fluctuations which may be correlated between voxels, and strongly correlated regions are deemed to reflect functional connectivity within synchronized circuits. Resting state functional connectivity (rsFC) measures have been widely adopted by the neuroscience community, and are being used and interpreted as indicators of intrinsic neural circuits and their functional states in a broad range of applications, both basic and clinical. However, there has been relatively little work reported that validates whether inter-regional correlations in resting state fluctuations of fMRI (rsfMRI) signals actually measure functional connectivity between brain regions, or to establish how MRI data correlate with other metrics of functional connectivity. In this mini-review, we summarize recent studies of rsFC within mesoscopic scale cortical networks (100 μm–10 mm) within a well defined functional region of primary somatosensory cortex (S1), as well as spinal cord and brain white matter in non-human primates, in which we have measured spatial patterns of resting state correlations and validated their interpretation with electrophysiological signals and anatomic connections. Moreover, we emphasize that low frequency correlations are a general feature of neural systems, as evidenced by their presence in the spinal cord as well as white matter. These studies demonstrate the valuable role of high field MRI and invasive measurements in an animal model to inform the interpretation of human imaging studies.     

Long-duration transcutaneous electric acupoint stimulation alters small-world brain functional networks

Acupuncture, which is recognized as an alternative and complementary treatment in Western medicine, has long shown efficiencies in chronic pain relief, drug addiction treatment, stroke rehabilitation and other clinical practices. The neural mechanism underlying acupuncture, however, is still unclear. Many studies have focused on the sustained effects of acupuncture on healthy subjects, yet there are very few on the topological organization of functional networks in the whole brain in response to long-duration acupuncture (longer than 20 min). This paper presents a novel study on the effects of long-duration transcutaneous electric acupoint stimulation (TEAS) on the small-world properties of brain functional networks. Functional magnetic resonance imaging was used to construct brain functional networks of 18 healthy subjects (9 males and 9 females) during the resting state. All subjects received both TEAS and minimal TEAS (MTEAS) and were scanned before and after each stimulation. An altered functional network was found with lower local efficiency and no significant change in global efficiency for healthy subjects after TEAS, while no significant difference was observed after MTEAS. The experiments also showed that the nodal efficiencies in several paralimbic/limbic regions were altered by TEAS, and those in middle frontal gyrus and other regions by MTEAS. To remove the psychological effects and the baseline, we compared the difference between diffTEAS (difference between after and before TEAS) and diffMTEAS (difference between after and before MTEAS). The results showed that the local efficiency was decreased and that the nodal efficiencies in frontal gyrus, orbitofrontal cortex, anterior cingulate gyrus and hippocampus gyrus were changed. Based on those observations, we conclude that long-duration TEAS may modulate the short-range connections of brain functional networks and also the limbic system.     

Analysis of a phase synchronized functional network based on the rhythm of brain activities

Rhythm of brain activities represents oscillations of postsynaptic potentials in neocortex, therefore it can serve as an indicator of the brain activity state. In order to check the connectivity of brain rhythm, this paper develops a new method of constructing functional network based on phase synchronization. Electroencephalogram (EEG) data were collected while subjects looking at a green cross in two states, performing an attention task and relaxing with eyes-open. The EEG from these two states was filtered by three band-pass filters to obtain signals of theta (4--7 Hz), alpha (8--13 Hz) and beta (14--30 Hz) bands. Mean resultant length was used to estimate strength of phase synchronization in three bands to construct networks of both states, and mean degree K and cluster coefficient C of networks were calculated as a function of threshold. The result shows higher cluster coefficient in the attention state than in the eyes-open state in all three bands, suggesting that cluster coefficient reflects brain state. In addition, an obvious fronto-parietal network is found in the attention state, which is a well-known attention network. These results indicate that attention modulates the fronto-parietal connectivity in different modes as compared with the eyes-open state. Taken together this method is an objective and important tool to study the properties of neural networks of brain rhythm.     

磁刺激穴位复杂脑功能网络构建与分析

本文采用互信息方法对磁刺激内关穴过程中的脑电信 号进行了两两通道间非线性时域关联特性分析, 构建了不同频率刺激前、刺激中、刺激后的脑功能网络, 并基于复杂网络理论对脑功能网络的特征进行了深入研究. 结果表明, 磁刺激频率为3 Hz 时, 大脑功能网络的平均度、平均聚类系数和全局效率与刺激前相比均有显著升高, 平均路径长度显著降低, 并且相应脑功能网络的"小世界"属性有所增强, 信息在大脑各区域间的传递更加高效. 本研究首次开展了磁刺激穴位复杂脑功能网络的构建与分析, 为探索磁刺激穴位对大脑神经调节的作用和机理提供新思路和新方法. 关键词： 复杂网络 磁刺激 脑功能网络 互信息     

人脑默认模式网络的动力学行为

大脑具有自适应、自组织、多稳态等重要特征,是典型的复杂系统.人脑在静息态下的关键功能子网络--默认模式网络(DMN)的激活处于多状态间持续跳转的非平衡过程,揭示该过程背后的动力学机制具有重要的科学意义和临床应用前景.本文基于功能磁共振获得的血氧水平依赖(BOLD)信号,建立了DMN吸引子跳转非平衡过程的能量图景、吸引子非联通图、跳转关系网络等;以高级视觉皮层和听觉等皮层活动为例,通过对应激活DMN状态空间的分布,以及XGBoost、深度神经网络等算法验证了DMN状态变化与外部脑区状态的密切依赖关系;通过偏相关、收敛交叉映射等方法分析了DMN内各个脑区之间的相互作用.本文结果有助于理解静息态下大脑内在非平衡过程的动力学机制,以及从动力学的角度探索具有临床意义的脑功能障碍生物标志物.     

Density Functional Approach Based on Numerically Obtained Bridge Functional

The Ornstein Zernike equation is solved with the Rogers Young approximation for bulk hard sphere fluidand Lennard-Jones fluid for several state points. Then the resulted bulk fluid radial distribution function combinedwith the test particle method is employed to determine numerically the function relationship of bridge functional as afunction of indirect correlation function. It is found that all of the calculated points from different phase space statepoints for a same type of fluid collapse onto a same smooth curve. Then the numerically obtained curve is used tosubstitute the analytic expression of the bridge functional as a function of indirect correlation function required in themethodology [J. Chem. Phys. 112 (2000) 8079] to deterrnine the density distribution of non-uniform hard spherefluid and Lennard Jones fluid. The good agreement of theoretical predictions with the computer simulation data isobtained. The present numerical procedure incorporates the knowledge of bulk fluid radial distribution function intothe constructing of the density functional approximation and makes the original methodology more accurate and moreflexible for various interaction potential fluid.     

静息状态下脑功能连接的磁共振成像研究

静息状态下脑功能连接的磁共振成像研究近年来取得了迅猛发展. 通过对fMRI信号低频涨落成分的同步性分析,可以得到大脑静息态任意脑区的功能连接和多套网络系统,其中“默认网络”的发现可能为人脑固有网络的研究提供新的思路. 而静息态网络与解剖连接之间可能存在的对应,以及在神经精神疾病患者脑中性质和连接的异常改变,使其具有重要的研究和临床应用价值. 该文总结了静息状态功能磁共振成像的主要研究成果,对静息状态脑功能网络的发现和发展、研究方法、各网络及其特点以及在临床方面的应用进行简单的介绍和分析.     

基于复杂度的针刺脑电信号特征提取

为探究针灸刺激对大脑活动产生的影响,文章设计了4种针刺频率针刺右腿足三里穴获取脑电的实验.首次采用排序递归图和关联维数方法提取针刺脑电信号的复杂度参数来反映针刺大脑的功能状态,并基于这些方法研究了针刺作用对大脑功能区域的影响以及不同针刺频率与脑电复杂度的相关性.发现针刺时脑电的复杂度高于针刺前,尤以频率为100次/min的针刺影响最为明显;从FP2, F7, T3导联脑电中提取的确定性指标(DET)可作为区分针刺状态与针刺前状态的一种特征参数. 关键词： 针灸 脑电 排序递归图 关联维数     

A new quantitative analysis of significant timing differences between externally cued and self-initiated motor tasks in an fMRI study

It is generally accepted that the temporal resolution of blood oxygenation level dependent functional MRI is limited due to the inherent latency and longevity of the haemodynamic response. However, in this study we introduce a technique for measurement of timing differences from within the same brain region in two (or more) separate tasks that allows accurate determination of cortical timing differences 200 ms. Our technique, based on a novel use of linear regression analysis, is shown to yield accurate results both in simulated and experimental data. We show that cortical timing differences measured using fMRI are consistent with published electrophysiological results. Measurement of timing differences using this technique could prove a useful strategy for identifying neural network components in a wide range of cognitive paradigms.     

Frequency Switches at Transition Temperature in Voltage-Gated Ion Channel Dynamics of Neural Oscillators

Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.