不同时程的前掩蔽声对小鼠下丘神经元声反应的掩蔽效应

自由声场条件下,以强度为神经元最佳频率阈上5dB,时程分别为40、60、80和100ms的纯音作为前掩蔽声,观察和记录了不同时程掩蔽声对小鼠(MusmusculusKm)下丘神经元发放和声强处理的影响.结果发现:随掩蔽声时程的增加,神经元发放抑制率逐渐增大(P<0.0001,n=41),反应潜伏期延长(P<0.01,n=41);其中受掩蔽声抑制的41个神经元中,绝大部分的(90.2%,37/41)反应动力学范围随掩蔽声时程的增加而逐渐变窄(P<0.0001),另有4个神经元的反应动力学范围则出现增加(9.8%,4/41).推测前掩蔽声的时程效应与掩蔽声激活的抑制性输入强度以及持续时间相关.     

兔内膝体神经元声反应的观察

实验在10只三碘季胺酚麻痹的新西兰兔上进行.采用记录单个神经元放电的方法,观察了短纯音引起的内膝体(MGB)神经元的声反应.实验结果表明:兔MGB神经元的声反应类型与猫、鼠等类似;并且声反应型式随纯音刺激频率、强度、时程的变化而变化.     

GABA能抑制参与弱噪声对下丘频率调谐的前掩蔽

在自由声场条件下，选用强度相当于纯音阈上5dB SPL、80ms的弱包络白噪声作为前掩蔽声，观察加入掩蔽声后神经元频率调谐的变化．对发生锐化的神经元导入荷包牡丹碱（Bicuculline，BIC），观察去GABA能抑制后前掩蔽效应的变化．结果显示：弱噪声前掩蔽使大部分神经元的频率调谐曲线（frequency tuning curve，FTC）锐化（P〈0．01），导入BIC后，弱噪声的抑制率下降．研究结果证实GABA能抑制参与了弱噪声所致的下丘神经元前掩蔽．     

调频声频率变化率对大鼠听皮层神经元声反应的影响

采用在体细胞外单细胞记录方法,研究调频声频率变化率及时程对调频声所诱发的听皮层神经元反应的影响.实验在34只乌拉坦麻醉的SD大鼠上进行,在皮层41区记录了113个对调频声有反应的细胞电活动.观察发现,调频声刺激的时程和频率变化率发生改变,可对诱发的听皮层神经元反应的反应型式和放电频数产生影响.这种影响表明,听皮层在复杂声上传信息的处理过程中可能存在复杂的编码机制.     

罗非鱼对低频声刺激的听觉行为

用行为定量解析法,对罗非鱼在低频区(100～1000Hz)由计算机分别以 1s和5s给声和撒声,用4个不同频率声为刺激,以速度、方向、间距和重心变化以及它们的个体间平均值作行为量,统计分析,研究罗非鱼的听觉反应行为。结果表明,罗非鱼对低频各频率声刺激皆有明显反应,其最敏感频率在 400Hz,与有关鱼类听觉文献以及有关罗非鱼电生理学研究结果一致。     

小鼠下丘神经元对不同调制范围的调频声的扫频方向选择性

在自由声场刺激条件下,固定调频(frequency-modulated,FM)声的幅度和时程,改变调制范围(modulation range,MR)和扫频方向,记录和测定了小鼠下丘神经元对FM声上、下扫频方向的选择性,探讨了MR对神经元扫频方向选择性的影响.实验共记录到102个神经元,其中45个(44.1%)神经元表现...     

一种基于心理声学模型的小波包域音频数字水印算法

首先根据心理声学模型,计算载体音频信号的掩蔽门限,并利用人耳听觉的临界频率与小波包子带间的相似特性,将DFT域掩蔽门限映射到小波包域;然后将水印信号嵌入到中低频小波包系数中,嵌入强度由掩蔽门限自适应控制。由于该方案是基于人类听觉系统的,在最大限度上挖掘了水印嵌入强度,使鲁棒性和不可感知性得到了很好的平衡。实验结果表明,利用这种水印算法,嵌入的水印信号是不可察觉的,并且对数据压缩、加噪、去噪、重采样(D／A、A／D转换)、低通滤波等常用音频信号处理技术具有很好的鲁棒性。     

一种基于心理声学模型的小波包域音频数字水印算法

首先根据心理声学模型 ,计算载体音频信号的掩蔽门限 ,并利用人耳听觉的临界频率与小波包子带间的相似特性 ,将DFT域掩蔽门限映射到小波包域 ;然后将水印信号嵌入到中低频小波包系数中 ,嵌入强度由掩蔽门限自适应控制。由于该方案是基于人类听觉系统的 ,在最大限度上挖掘了水印嵌入强度 ,使鲁棒性和不可感知性得到了很好的平衡。实验结果表明 ,利用这种水印算法 ,嵌入的水印信号是不可察觉的 ,并且对数据压缩、加噪、去噪、重采样 (D/A、A/D转换 )、低通滤波等常用音频信号处理技术具有很好的鲁棒性     

基于心理声学模型数字音频水印算法

提出了一种将心理声学模型和小波变换、离散余弦变换相结合的数字音频水印算法,根据人耳听觉系统的掩蔽效应,计算载体音频信号的掩蔽阈值.为了消除图像水印的像素相关性,首先对水印图像进行置乱,以增强水印信号的安全性.然后将水印信号嵌入到小波变换近似分量的DCT变换域中,嵌入强度由掩蔽阈值自适应控制.仿真实验结果表明:该算法隐藏水印具有很强的不可感知性;叠加了水印的音频信号对数据压缩、加噪、重新采样、重新量化、低通滤波等常用的音频信号处理技术具有很好的鲁棒性.     

不同最佳频率的下丘神经元的声反应特性和方位敏感性

在自由声场刺激条件下 ,从 2 0只昆明小鼠 (Kunming Mus Musculus)下丘 (Inferior Col-liculus,IC)记录到 1 93个神经元 .将这些神经元按其最佳频率 (best frequency,BF) (k Hz)分为(5 ,1 0 ],(1 0 ,1 5 ],(1 5 ,2 0 ]和 (2 0 ,3 1 ]4个频率段 ,观察和分析它们的声反应特性 ,并用最小阈值(minimum threshold,MT)和放电率 (firing rate)标准对这些神经元前听空间俯仰方位(Elevation) 0平面的 7个水平方位 (Azimuth)角 (同侧 90°、60°、3 0°,0°,对侧 3 0°、60°、90°)的敏感性进行了研究 .结果表明 :1、IC神经元的放电率和潜伏期基本随刺激强度的增加而增加和缩短 ,其函数表现为三种基本不同的形式 :单调型、非单调型以及放电率函数的不规则型和潜伏期函数的饱和单调型 .非单调函数神经元数目高于单调函数神经元 .三种函数形式的神经元数目分布与 BF之间无明显相关 ;2、BF较高的 IC神经元的潜伏期与 BF较低的神经元的潜伏期之间未发现显著性差异 ;3、用低 MT和最大放电率指标检测 IC神经元的方位特性发现 ,在神经元的最敏感角度展现出低 MT和高放电率 ,虽然最佳敏感角度的分布随频率段而不同 ,但绝大部分神经元的最敏感角度位于对侧 ,其中以对侧 60°所占比例最大 .用低 MT指标所确定的最佳敏感角度     

Effects of forward masking on the responses of the inferior collicular neurons in the big brown bats, Eptesicus fuscus

The present study explores the forward masking of the two-tone stimuli in sequence that evoked responses in the inferior colliculns (IC) of the echolocating bats. The results indicate that forward masking is obvious in the acoustic responses of the IC neurons to the two-tone stimuli.Meanwhile the intensity sensitivity of the neurons responding to the probe increases with the inter-tone interval decreasing. The effects of forward masking are correlated with the relative intensity and the interval between the masker and probe. That is, the effects of forward masking are reduced with the masker intensity decreasing and enhanced with the probe intensity decreasing and the inter-tone interval shortened. The present study suggests that there is a correlation between the characteristics of the response to the probe and the dynamic conditions of the postsynaptic currents in the IC neurons.     

Temporal dynamics of a neural solution to the aperture problem in visual area MT of macaque brain

A critical step in the interpretation of the visual world is the integration of the various local motion signals generated by moving objects. This process is complicated by the fact that local velocity measurements can differ depending on contour orientation and spatial position. Specifically, any local motion detector can measure only the component of motion perpendicular to a contour that extends beyond its field of view. This "aperture problem" is particularly relevant to direction-selective neurons early in the visual pathways, where small receptive fields permit only a limited view of a moving object. Here we show that neurons in the middle temporal visual area (known as MT or V5) of the macaque brain reveal a dynamic solution to the aperture problem. MT neurons initially respond primarily to the component of motion perpendicular to a contour's orientation, but over a period of approximately 60 ms the responses gradually shift to encode the true stimulus direction, regardless of orientation. We also report a behavioural correlate of these neural responses: the initial velocity of pursuit eye movements deviates in a direction perpendicular to local contour orientation, suggesting that the earliest neural responses influence the oculomotor response.     

Receptive field plasticity of neurons in rat auditory cortex

Using conventional electrophysiological technique, we investigated the plasticity of the frequency receptive fields (RF) of auditory cortex (AC) neurons in rats. In the AC, when the frequency difference between conditioning stimulus frequency (CSF) and the best frequency (BF) was in the range of 1--4 kHz, the frequency RF of AC neurons shifted. The smaller the differences between CSF and BF, the higher the probability of the RF shift and the greater the degree of the RF shift. To some extent, the plasticity of RF was dependent on the duration of the session of conditioning stimulus (CS). When the frequency difference between CSF and BF was bigger, the duration of the CS session needed to induce the plasticity was longer. The recovery time course of the frequency RF showed opposite changes after CS cessation.The RF shift could be induced by the frequency that was either higher or lower than the control BF, demonstrating no clear directional preference. The frequency RF of some neurons showed bidirectional shift, and the RF of other neurons showed single directional shift. The results suggest that the frequency RF plasticity of AC neurons could be considered asan ideal model for studying plasticity mechanism. The present study also provides important evidence for further study of learning and memory in auditory system.     

Dynamic properties of neurons in cortical area MT in alert and anaesthetized macaque monkeys.

In order to see the world with high spatial acuity, an animal must sample the visual image with many detectors that restrict their analyses to extremely small regions of space. The visual cortex must then integrate the information from these localized receptive fields to obtain a more global picture of the surrounding environment. We studied this process in single neurons within the middle temporal visual area (MT) of macaques using stimuli that produced conflicting local and global information about stimulus motion. Neuronal responses in alert animals initially reflected predominantly the ambiguous local motion features, but gradually converged to an unambiguous global representation. When the same animals were anaesthetized, the integration of local motion signals was markedly impaired even though neuronal responses remained vigorous and directional tuning characteristics were intact. Our results suggest that anaesthesia preferentially affects the visual processing responsible for integrating local signals into a global visual representation.     

Network model of shape-from-shading: neural function arises from both receptive and projective fields

It is not known how the visual system is organized to extract information about shape from the continuous gradations of light and dark found on shaded surfaces of three-dimensional objects. To investigate this question, we used a learning algorithm to construct a neural network model which determines surface curvatures from images of simple geometrical surfaces. The receptive fields developed by units in the network were surprisingly similar to the actual receptive fields of neurons observed in the visual cortex which are commonly believed to be 'edge' or 'bar' detectors, but have never previously been associated with shading. Thus, our study illustrates the difficulty of trying to deduce neuronal function solely from determination of their receptive fields. It is also important to consider the connections a neuron makes with other neurons in subsequent stages of processing, which we call its 'projective field'.     

Topography of acoustic response characteristics in the midbrain inferior colliculus of Kunming mouse

Topography of acoustic response characteristics of the midbrain inferior colliculus(IC)of the Kunming mouse was studied by using extracellular recording techniques.The characteristic frequency(CF)range represented in the different divisions of the IC differed markedly:4-15 kHz in the dorsal cortex(DC),10-70 kHz in the central nucleus(CN),and 4-35kHz in the external cortex(EC).The CF in the CN increased from dorsal and lateral to ventral and medial,higher CFs represented at its ventromedial part and lower CFs at its dorsal part.The isofrequency contours of CFs were incurvate.Minimum thresholds(MT)of the auditory neurons in DC and the central part of CN were lower(about 10dB SPL),but considerably higher in the dorsal and ventral region of EC.Results suggest that each of the divisions in the mouse IC may have different auditory functions.     

刺激呈现率影响小鼠下丘神经元声反应特性

自由声场条件下,以强度为特征频率阈上5dBSPL、时程为40ms的短纯音为声刺激,记录了小鼠下丘神经元对不同呈现率（0．5～20Hz）的声刺激反应．结果显示,随呈现率的增高,绝大多数神经元（87．3％,103／118）的冲动发放数单调下降,少数（12．7％,15／118）神经元的冲动发放数呈非单调变化,冲动发放数与刺激呈现率之间有显著相关性．即使在低范围内改变呈现率也能显著影响多数神经元的声反应特性,其临界呈现率及最大呈现率低于3．3Hz的神经元分别超过70％（75．4％,89／118）和40％（44．9％,53／118）．此外,提高刺激呈现率,部分神经元（17．8％,21／118）的发放模式发生改变,主要是由紧张型或相位爆发型向相位型转变．可见,下丘神经元声反应特性与声刺激呈现率密切相关．     

Dynamic receptive field plasticity in rat spinal cord dorsal horn following C-primary afferent input

The central terminals of cutaneous primary afferent neurons are spatially ordered in the dorsal horn in a highly organized fashion such that a point-to-point map represents the body surface. This afferent terminal somatotopic map correlates with the map of the receptive fields of the cells on which they terminate. The location, size and modality of the cutaneous receptive fields of dorsal horn neurons necessarily depend upon the anatomical presence of afferent nerve fibres which deliver information from the periphery, directly or indirectly, to the cells. However the receptive field size and modality of a cell do not depend only on anatomical connections. Excitatory and inhibitory interneurons, descending influences and facilitations or depressions of synaptic contacts can alter receptive field properties. Here we show that prolonged and substantial cutaneous receptive field changes can be produced by brief inputs from peripheral unmyelinated afferent fibres.     

Non-classical receptive field mediates switch in a sensory neuron's frequency tuning

Animals have developed stereotyped communication calls to which specific sensory neurons are well tuned. These communication calls must be discriminated from environmental signals such as those produced by prey. Sensory systems might have evolved neural circuitry to encode both categories. In weakly electric fish, prey and communication signals differ in their spatial extent and frequency content. Here we show that stimuli of different spatial extents mimicking prey and communication signals cause a switch in the frequency tuning and spike-timing precision of electrosensory pyramidal neurons, resulting in the selective and optimal encoding of both stimulus categories. As in other sensory systems, pyramidal neurons respond only to stimuli located within a restricted region of space known as the classical receptive field (CRF). In some systems, stimulation outside the CRF but within a non-classical receptive field (nCRF) can modulate the neural response to CRF stimulation even though nCRF stimulation alone fails to elicit responses. We show that pyramidal neurons possess a nCRF and that it can modulate the response to CRF stimuli to induce this neurobiological switch in frequency tuning.