不同时间频率光栅刺激引起的视觉诱发电位(VEP)方位效应的差异

以人视觉诱发电位(VEP)反应为指标,在不同的时间频率下测定了 VEP 对方波光栅刺激的反应幅度与光栅方位的关系。当光栅方位固定时,光栅闪烁的时间频率不同,VEP 反应的波形、潜伏期和反应频率差别很大,但其反应幅度均呈现方位选择性。当光栅的时间频率为9.1Hz时,光栅为垂直和水平方位时引起的 VEP 反应幅度比倾斜方位时都大,对任何光栅方位,VEP反应幅度与光栅对比度的对数呈线性关系;与此相反,当光栅时间频率为0.4Hz 时,光栅为倾斜方位时引起的 VEP 反应幅度比垂直和水平方位时更大。     

用脑光学成像精确测定猫初级视皮层视野拓扑投射关系

利用基于脑内源信号的光学成像和二维互相关分析的方法,对猫初级视皮层17区的视野拓扑离心度(即视网膜-皮层拓扑关系)进行了精确测量。当采用在同一屏幕内处于上下视野的、方位互相垂直的两个相邻光栅刺激时,皮层中一部分区域的绝大部分细胞因同时兴奋而导致方位功能图模糊不清。将这种方位功能图和用单一方位(水平或垂直)全屏光栅刺激所得到的功能图进行比较,通过计算每一像素的互相关系数,从而获得皮层的精确视野拓扑离心度。同时用电生理的方法测量了同一视皮层内的单细胞的感受野位置,证明这种方法得到的视野离心度和光学记录方法得到的相同。因此,本研究为大面积地确定视皮层细胞感受野在视野中的位置提供了一种快速和较准确的方法。     

特定方位的光栅识别学习不改变猫外膝体背核神经元的方位敏感性

视觉信号识别训练可改变视觉通路神经元的可塑性, 其神经机制尚不清楚。已有少数研究显示, 动物(猴) 长时间进行特定方位的光栅识别学习后, 视皮层部分神经元对视觉刺激的反应表现出与学习任务相关的敏感性变化。这种敏感性变化是否亦存在于皮层下结构尚无报道。本实验训练两只成年猫分别进行水平和垂直方位的条形静止正弦光栅的识别以获得食物奖赏, 两只猫的行为识别能力逐渐提高, 4 个多月后识别的正确率达85%以上, 用与训练方位垂直的正弦光栅检测发现, 识别正确率明显下降。细胞外记录外膝体背核(Dorsal lat eral geniculate nucleus, dLGN) 神经元对不同方位正弦光栅刺激的反应显示, 与正常猫相比, 训练猫外膝体细胞的最优方位并未向着训练方位发生明显改变, 对于感受野位于中央区15度视角以内的细胞来说, 其方位选择性强度以及在训练方位的发放强度与正常猫无明显差异。以上结果表明, 猫对特定方位的光栅识别学习不改变外膝体神经元的方位敏感性, 其行为上方位识别特异性的提高可能与视皮层细胞的方位编码可塑性有关。     

猫外膝体神经元对光栅刺激方位倾向性的一种分布特性

我们检测了猫外膝体(LGN)神经元对闪烁方波光栅的反应与光栅方位的关系。对一定对比度和空间频率的光栅,26个记录到的神经元的反应均随方位不同而变化,其最大反应和最小反应的比值平均为3.0±0.3(S.E.)。神经元的最优方位(即引起最大反应的光栅方位)随其感受野中心在视网膜上的位置而异,具有平行于其各自感受野中心与视网膜中央区(area cen-sralis)的连接线的倾向。     

脑光学成像技术揭示的猫初级视皮层方位倾斜效应

方位倾斜效应（ｏｂｌｉｑｕｅ ｅｆｆｅｃｔ）是人类普遍存在的视觉心理效应。为了检测其神经基础,我们采用脑光学成像方法,对猫初级视觉皮层较大范围内的水平－垂直方位光栅刺激敏感区和倾斜方位光栅刺激敏感区的大小及其反应强度进行了定量分析。结果表明：水平－垂直敏感区比倾斜角敏感区面积大,平均差异为４．７％;水平－垂直方位刺激引起的反应强度整体上比倾斜角方位刺激大。以上结果澄清了以往一些电生理研究结果的不同     

乌拉坦对青、老年猫视皮层神经元反应特性的影响(英文)

以前的电生理研究结果显示, 老年哺乳动物视皮层细胞的自发反应及对视觉刺激的诱发反应比青年动物的显著增加, 而对光栅刺激的方位和运动方向选择性却显著下降。然而, 这种视皮层细胞功能的老年性改变是否因青、老年猫细胞对不同麻醉水平的敏感性差异引起尚不清楚。为探讨该问题, 以常用的麻醉药——乌拉坦(Urethane)为实验对象, 通过改变其麻醉剂量分别记录青、老年猫初级视皮层细胞对不同方位和运动方向光栅刺激的调谐反应。研究结果显示, 在基础麻醉量的基础上, 累积增加 50 mg 和 100 mg 乌拉坦对青、老年猫视皮层细胞的自发反应和诱发反应以及对光栅刺激方位和运动方向的选择性不产生显著影响, 累积增加 150 mg 乌拉坦会导致青、老年猫视皮层细胞对视觉刺激的反应性下降, 但下降的幅度相似。以上研究结果表明, 不同剂量的乌拉坦对青、老年动物视皮层细胞的反应性具有相似的影响。     

猫视皮层神经元对光栅反应最优方位在视网膜上分布特性的研究

用金属微电极记录了114个猫皮层17、18区细胞对不同方位光栅图象刺激的反应。细胞最优方位与其感受野中心在视网膜的位置间有系统性关系,即最优方位总是倾向于垂直于各感受野中心与视网膜中心区(area centralis)的连线。这一规律对在18区或17、18区全体记录到的细胞而言,有统计意义。 在17、18区内,仅对于感受野位于视网膜离心度(eccentricity)大于9°视角的细胞、具有较窄感受野(宽度小于2.5°)的细胞以及感受野处于视网膜垂直经线附近的细胞,上述规律才有统计意义,而对感受野离心度小于9°的细胞、感受野宽度大于2.5°的细胞以及感受野在倾斜经线附近的细胞,上述规律不明显。     

用脑光学成像术研究不同空间拓扑位置猫初级视皮层的空间频率反应特性

采用基于内源信号的脑光学成像方法,在大范围视皮层研究了不同空间拓扑位置对应的皮层区的对光栅刺激空间频率反应特性。结果表明,周边视野对应区对高空间频率刺激反应极弱或没有反应,中心视野对应区对较宽的空间频率范围内的刺激均有反应,但对高频刺激反应更强;无论在周边对应区还是中心对应区,其视野越靠近中心,其空间频率调谐曲线和截止空间频率越靠近高频,而且这种过渡是平缓的。以上结果说明,猫初级视皮层空间频率反应     

猫外膝体神经元非寻常的方位调谐特性——Ⅰ、在正常猫的研究

在九只成年猫上用玻璃电极记录了单个外膝体神经元对不同方位的移动正弦光栅刺激的反应共详细测定了４００个细胞的方位调谐特性。少数外膝体神经元具有非寻常的方位调谐特性,包括：具蝴蝶状调谐曲线的方位调谐特性;双调谐的方位调谐特性和最优方位随刺激光栅空间频率的改变而变化的方位调谐特性。这些细胞非寻常的方位调谐特性往往伴随着非寻常的空间频率调谐特性。空们的方位调谐特性和空间频率调谐特性都不能用Ｓｏｏｄａｋ等提     

猫视皮层17,18区神经元对错觉轮廓的反应

研究了轻度麻醉下猫视皮层17, 18区细胞对错觉轮廓刺激的反应特性, 比较了对错觉轮廓有明显反应的细胞对真实轮廓和错觉轮廓刺激的感受野特性的异同. 共记录了猫视皮层17, 18区200个方位/方向选择性细胞, 其中有42%的细胞是错觉轮廓反应细胞. 将这些细胞对真实轮廓和错觉轮廓的反应进行比较, 尽管错觉轮廓反应细胞对移动光棒和错觉轮廓光棒的方位/方向调制曲线十分相似, 但对移动错觉棒和移动光棒的反应模式(潜伏期和反应时程)不同. 对由光栅组成的错觉轮廓而言, 细胞的反应大小与组成光栅的相位无关, 并且细胞对组成错觉轮廓光栅的最优空间频率比对普通移动光栅的最优空间频率要高得多, 说明细胞确实是对轮廓本身反应, 而不是对组成轮廓的光栅的末端反应. 某些速度调制类型的细胞对移动错觉棒反应的最优速度比对移动光棒的最优速度要低得多. 进一步验证了猫视皮层17, 18区部分细胞能对错觉轮廓反应, 并且观察到这些细胞对错觉轮廓和真实轮廓有不同的感受野反应特性, 提示视觉系统对两种刺激图形的检测机制可能存在着差异.     

Adaptation to contingencies in macaque primary visual cortex.

We tested the hypothesis that neurons in the primary visual cortex (V1) adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus. In a first series of experiments, the two gratings differed in orientation. One grating had optimal orientation and the other was orthogonal to it, and therefore did not activate the neuron under study. These experiments provided evidence in favour of our hypothesis. In most cells adaptation to the compound stimulus reduced responses to the compound stimulus more than it reduced responses to the optimal grating, and the responses to the compound stimulus were reduced more by adaptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation was specific to (and caused by) the simultaneous presence of the two orientations in the compound stimulus. To test whether V1 neurons could adapt to other contingencies in the stimulus attributes, we performed a second series of experiments, in which the component gratings were parallel but differed in spatial frequency, and were both effective in activating the neuron under study. These experiments failed to reveal convincing contingent effects of adaptation, suggesting that neurons cannot adapt equally well to all types of contingency.     

The Detection of Orientation Continuity and Discontinuity by Cat V1 Neurons

The orientation tuning properties of the non-classical receptive field (nCRF or “surround”) relative to that of the classical receptive field (CRF or “center”) were tested for 119 neurons in the cat primary visual cortex (V1). The stimuli were concentric sinusoidal gratings generated on a computer screen with the center grating presented at an optimal orientation to stimulate the CRF and the surround grating with variable orientations stimulating the nCRF. Based on the presence or absence of surround suppression, measured by the suppression index at the optimal orientation of the cells, we subdivided the neurons into two categories: surround-suppressive (SS) cells and surround-non-suppressive (SN) cells. When stimulated with an optimally oriented grating centered at CRF, the SS cells showed increasing surround suppression when the stimulus grating was expanded beyond the boundary of the CRF, whereas for the SN cells, expanding the stimulus grating beyond the CRF caused no suppression of the center response. For the SS cells, strength of surround suppression was dependent on the relative orientation between CRF and nCRF: an iso-orientation grating over center and surround at the optimal orientation evoked strongest suppression and a surround grating orthogonal to the optimal center grating evoked the weakest or no suppression. By contrast, the SN cells showed slightly increased responses to an iso-orientation stimulus and weak suppression to orthogonal surround gratings. This iso-/orthogonal orientation selectivity between center and surround was analyzed in 22 SN and 97 SS cells, and for the two types of cells, the different center-surround orientation selectivity was dependent on the suppressive strength of the cells. We conclude that SN cells are suitable to detect orientation continuity or similarity between CRF and nCRF, whereas the SS cells are adapted to the detection of discontinuity or differences in orientation between CRF and nCRF.     

对刺激朝向改变的自动加工:事件相关电位的证据

利用事件相关电位（ＥＲＰ）技术,探讨非注意状态的刺激朝向改变是否引起自动加工。刺激为具有一定朝向（垂直和水平各５０％）和一定空间频率（低频９０％,高频１０％）的光栅。要求被试忽略光栅朝向,对高频光栅作反应。刺激呈现时间为５０ｍｓ,刺激间隔在２５０至４５０ｍｓ之间随机变化。低频光栅刺激被分为两类,“匹配”（与前一刺激朝向相同）和“失匹配”（与前一刺激朝向不同）。结果发现,失匹配刺激比匹配刺激诱发出更大的枕区Ｐ１、更大的前额－中央区Ｎ１以及更大的前部与顶区Ｐ２,但前部与顶区的Ｎ２却更小。这些ＥＲＰｓ变化提示,视觉对非注意的刺激朝向变化进行了一定程度的自动加工;视觉通道可能存在类似听觉失匹配负波（ＭＭＮ）的、然而机制不同的自动加工成分     

A rapid evoked potential index of cortical adaptation

Contrast thresholds and acuity limits were measured in 4 observers with the swept visual evoked potential (VEP) technique. In this technique, grating contrast or grating spatial frequency is electronically varied while the subject's evoked response is retrieved in real time (without averaging). Contrast or spatial frequency variation make the stimulus vary in intensity; zero VEP response amplitude indicates the threshold intensity.Large shifts occur in the indicated threshold when stimulus sweep direction is reversed. Thresholds are always relatively elevated when the run begins with the strongest stimulus value. These shifts do not have a technical origin in the delay of the instrument (Nelson et al. 1984b). Here, it is shown that the shifts are due to orientation and spatial frequency selective adaptation, probably of cortical origin.Measurable adaptation is produced by momentary exposure to contrasts as low as 1.25%; nearly maximum adaptation (0.6 log units) is reached with 20% contrast. These findings support the concept of a contrast gain control mechanism in visual cortex, and pose practical problems for visual assessment with the evoked potential.     

Touch Influences Visual Perception with a Tight Orientation-Tuning

Stimuli from different sensory modalities are thought to be processed initially in distinct unisensory brain areas prior to convergence in multisensory areas. However, signals in one modality can influence the processing of signals from other modalities and recent studies suggest this cross-modal influence may occur early on, even in ‘unisensory’ areas. Some recent psychophysical studies have shown specific cross-modal effects between touch and vision during binocular rivalry, but these cannot completely rule out a response bias. To test for genuine cross-modal integration of haptic and visual signals, we investigated whether congruent haptic input could influence visual contrast sensitivity compared to incongruent haptic input in three psychophysical experiments using a two-interval, two-alternative forced-choice method to eliminate response bias. The initial experiment demonstrated that contrast thresholds for a visual grating were lower when exploring a haptic grating that shared the same orientation compared to an orthogonal orientation. Two subsequent experiments mapped the orientation and spatial frequency tunings for the congruent haptic facilitation of vision, finding a clear orientation tuning effect but not a spatial frequency tuning. In addition to an increased contrast sensitivity for iso-oriented visual-haptic gratings, we found a significant loss of sensitivity for orthogonally oriented visual-haptic gratings. We conclude that the tactile influence on vision is a result of a tactile input to orientation-tuned visual areas.     

A Window into brain development: hdEEG methods to track visual development in nonhuman primates

Electroencephalography (EEG) is widely used to study human brain activity, and is a useful tool for bridging the gap between invasive neural recording assays and behavioral data. High‐density EEG (hdEEG) methods currently used for human subjects for use with infant macaque monkeys, a species that exhibits similar visual development to humans over a shorter time course was adapted. Unlike monkeys, human subjects were difficult to study longitudinally and were not appropriate for direct within‐species comparison to neuronal data. About 27‐channel electrode caps, which allowed collection of hdEEG data from infant monkeys across development were designed. Acuity and contrast sweep VEP responses to grating stimuli was obtained and a new method for objective threshold estimation based on response signal‐to‐noise ratios at different stimulus levels was established. The developmental trajectories of VEP‐measured contrast sensitivity and acuity to previously collected behavioral and neuronal data were compared. The VEP measures showed similar rates of development to behavioral measures, both of which were slower than direct neuronal measures; VEP thresholds were higher than other measures. This is the first usage of non‐invasive technology in non‐human primates. Other means to assess neural sensitivity in infants were all invasive. Use of hdEEG with infant monkeys opens many possibilities for tracking development of vision and other functions in non‐human primates, and can expand our understanding of the relationship between neuronal activity and behavioral capabilities across various sensory and cognitive domains. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1342–1359, 2016     

Spatial frequency response functions obtained from cat visual evoked potentials

Visual evoked potentials (VEPs) were obtained from the surface of teh cat visual cortex in response to contrast reversing sinusoidal gratings. Gratings of different spatial frequency were presented either separately, using signal averaging to increase the signal-to-noise ratio, or as a spatial frequency sweep, in which spatial frequency was sequentially increased every 5 sec during a 40 sec trial (3.99 Hz) or every 3 sec during a 24 sec trial (6.65 Hz). The second harmonic amplitude- and phase-spatial frequency functions derived from averaging or from sweep trials were similar, indicating that the swept stimulus method can be used to provide a rapid and reliable measure of the VEP-spatial frequency function. Intravenous administration of physostigmine, an acetylcholinesterase inhibitor, evoked a spatial frequency-dependent change in VEP amplitude. At 3.99 Hz, responses to low spatial frequencies were enhanced to a greater extent than were responses to high spatial frequency stimuli. At 6.65 Hz, responses to mid-range spatial frequencies were enhanced to a greater extent than were responses to low and high spatial frequency stimuli. VEP phase at both 3.99 and 6.65 Hz was advanced to a greater degree at the higher spatial frequencies. These results indicate that the swept spatial frequency method may be useful in studying spatial frequency-dependent pharmacological effects on the VEP and support the possibility that pharmacological disruption of the cholinergic visual system can produce such changes.     

Patterns in the discharge of simple and complex visual cortical cells

The activity of visual cortical neurons (area 17) was recorded in anaesthetized cats in response to sinusoidal drifting gratings. The statistical structure of the discharge of simple and complex cells has been studied as a function of the various parameters of a drifting grating: spatial frequency, orientation, drifting velocity and contrast. For simple cells it has been found that the interspike interval distributions in response to drifting gratings of various spatial frequencies differ only by a time scale factor. They can be reduced to a unique distribution by a linear time transformation. Variations in the spatial frequency of the grating induce variations in the mean firing rate of the cell but leave unchanged the statistical structure of the discharge. On the contrary, the statistical structure of the simple cell activity changes when the contrast or the velocity of the stimulus is varied. For complex cells it has been found that the invariance property described above for simple cells is not valid. Complex cells present in their activity in response to visual stimuli two different firing patterns: spikes organized in clusters and spikes that do not show this organization ('isolated spikes'). The clustered component is the only component of the complex cell discharge that is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.     

Localization of areas of the cat visual cortex giving an invariant response to changes in pattern size

Regions of the visual cortex forming a code invariant to the transformation of pattern size were investigated by the averaged evoked potentials method. The response was assessed by amplitude of the negative wave, whose peak latency was 130±20 msec. A set of strips of light forming a grating was used as the stimulus. The gratings differed from each other in the number of strips or in area. With an increase in stimulus area, the response in area 17 increased, but the responses were identical to gratings of equal area but different orientation of the strips. In area 7 (middle part of the suprasylvian gyrus) response size was unchanged with an increase in area of the grating, whereas an increase in the number of orientations of the strips forming the grating led to an increased response. Since response magnitude is independent of the area of the grating, it is postulated that responses to pattern size invariant to transformation are located in area 7.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 115–121, March–April, 1973.     

Suppressed patterns alter vision during binocular rivalry

Binocular rivalry occurs when incongruent patterns are presented to corresponding regions of the retinas, leading to fluctuations of awareness between the patterns . One attribute of a stimulus may rival whereas another may combine between the eyes , but it is typically assumed that the dominant features are perceived veridically. Here, we show this is not necessarily the case and that a suppressed visual feature can alter dominant perception. The cortical representations of oriented gratings can interact even when one of them is perceptually suppressed, such that the perceived orientation of the dominant grating is systematically biased depending on the orientation of the suppressed grating. A suppressed inducing pattern has the same qualitative effect as a visible one, but suppression reduces effective contrast by a factor of around six. A simple neural model quantifies and helps explain these illusions. These results demonstrate that binocular rivalry suppression operates in a graded fashion across multiple sites in the visual hierarchy rather than truncating processing at a single site and that suppressed visual information can alter dominant vision in real-time.