RELATIVE CONTRIBUTIONS OF BURST AND TONIC RESPONSES TO THE RECEPTIVE-FIELD PROPERTIES OF LATERAL GENICULATE NEURONS IN THE CAT
RELATIVE CONTRIBUTIONS OF BURST AND TONIC RESPONSES TO THE RECEPTIVE-FIELD PROPERTIES OF LATERAL GENICULATE NEURONS IN THE CAT
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DOI：
10.1152/jn.1992.68.6.2199
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发表时间：
1992-12-01
影响因子：
2.5
通讯作者：
SHERMAN, SM
中科院分区：
文献类型：
--
作者：
GUIDO, W;LU, SM;SHERMAN, SM
1. 在麻醉、瘫痪的体内制备中，我们记录了61个膝状神经元（2个W、25个X、33个Y和1个混合）对不同空间频率、时间频率和对比度的漂移正弦波光栅的细胞外反应。我们的目标是研究由电压依赖性低阈值（LT） Ca2+尖峰和与LT尖峰无关的纯张力反应引起的这些视觉反应的差异贡献。以LT尖峰反应的细胞被称为处于突发放电模式，而那些以纯强直方式反应的细胞则处于中继或强直放电模式。我们使用在之前的论文中描述的细胞内研究中提出的经验标准（Lu et al. 1992），将总视觉反应分为LT爆发和强直成分。如果一个反应成分的动作电位的峰间间隔小于或等于4ms，并且在爆发事件中的第一个峰发生在大于或等于100ms的沉默期之后（或者当神经元对视觉刺激的反应时间大于或等于8hz时大于或等于50ms），则该反应成分被认为是LT爆发。所有其他活动都被认为是强直反应的一部分。除了LT爆发外，我们还发现了另一种类型的爆发反应，即高阈值（HT）爆发。它们也有动作电位簇，其峰间间隔小于或等于4毫秒。然而，高温爆发，不像低温爆发，没有爆发前的沉默期。高温脉冲是强直反应成分的一部分，仅仅反映了当细胞变得更加去极化从而更加敏感时发生的峰间间隔的逐渐减少。因此，尖峰间间隔是必要但不充分的标准，以确定LT爆发。在W、X和Y细胞中记录视觉诱发的LT爆发。当被激发时，LT脉冲与漂移的正弦波光栅刺激同步发生，每个刺激周期的频率不超过一次。在对单个视觉刺激周期的反应中，LT爆发可以包含总反应，张力成分可以包含总反应，或者LT爆发和张力成分可以混合。当刺激同时诱发低电位爆发和强直反应时，低电位爆发总是第一反应。在用光栅刺激测试的61个细胞中，47个表现出LT爆发，14个没有。那些发生爆炸的人表现出不同程度的爆发力。我们偶尔对单个细胞进行长时间的记录，观察它们在爆发和强直放电模式之间的切换。我们得出的结论是，大多数细胞的膜电位接近LT尖峰失活所需的水平，膜电压的微小波动可以在这些响应模式之间切换。我们偶尔也会同时记录几个细胞，并注意到不同的细胞可能处于不同的模式。这意味着，无论控制反应模式的传入通路是什么，都不需要对所有膝状神经元起全局作用。用两个指标来表达LT爆发性的变化。对于第一个指标，通过将总视觉反应分为LT突发和强直分量，并计算每个细胞的基本（F1）傅立叶响应幅度，确定每个细胞的LT突发比。一旦分离，我们将LT爆发分量的F1振幅除以LT爆发分量和强音分量的F1振幅之和。另一个指标是刺激周期引起LT爆发的百分比。这个百分比是通过检查对每个刺激周期的反应和确定LT爆发的存在或不存在来计算的。这些指标是高度相关的（r = 0.93），两者都表明，LT爆发在总反应中所占的比例是可变的，从某些细胞几乎检测不到到其他细胞的绝大多数反应。Y细胞出现LT爆发的比例（88%）略高于X细胞（64%）。6. 对平均反应直方图的检查表明，LT爆发成分增加了视觉反应的实质性非线性。作为非线性的度量，我们使用了响应的第二次傅立叶谐波（F2）分量，并计算了F2与f1的比值。对于每一个被测试的神经元，这个比例在LT爆发时大于张力反应成分。因此，LT爆发似乎扭曲了视觉反应，使它们不那么线性。为了测试LT破裂量随刺激强度变化的可能性，我们为35个神经元生成了响应-空间频率函数，为15个神经元生成了响应-对比响应函数。细胞内LT破裂的程度随空间频率或对比无显著差异；也就是说，在一个空间频率或对比度下，LT爆发在总响应中的比例并不比另一个更普遍。因此，对于微弱或不太显著的刺激，低强度脉冲似乎不能提供选择性的非线性反应放大。为了测试LT爆发随时间频率变化的可能性，我们为17个神经元生成了响应-时间频率函数（在最佳空间频率下）。我们发现随着时间频率的增加，LT爆发率逐渐增加。如前所述，我们发现LT爆发在反应周期中比强直反应成分发生得更早。我们使用10个细胞的响应-时间频率函数来检查这些时间差异是否反映了相位和/或潜伏期差异。这两种成分的潜伏期几乎相同，但LT爆发是由刺激的早期阶段引起的，而不是紧张性反应成分。因此，我们得出结论，LT爆发和张力反应成分之间的时间差异主要是由于相位而不是潜伏期。我们得出的结论是，LT尖峰有助于视觉信号通过外侧膝状核转移到视觉皮层。它们并不代表丘脑中继细胞与它们的感觉输入的强制性断开。相反，它们可以提供一种非线性放大，允许超极化中继细胞向皮层发出显著刺激存在的信号。
1. In an anesthetized, paralyzed in vivo preparation, we recorded extracellular responses of 61 geniculate neurons (2 W, 25 X, 33 Y, and 1 mixed) to drifting sine-wave gratings of various spatial frequency, temporal frequency, and contrast. Our goal was to study the differential contributions to these visual responses of bursting caused by voltage dependent, low-threshold (LT) Ca2+ spikes and of purely tonic responses unrelated to LT spikes. Cells responding with LT spikes are said to be in the burst firing mode and those responding in a purely tonic fashion to be in the relay or tonic firing mode. We separated the total visual response into LT burst and tonic components by use of the empirical criteria set forth in our intracellular study described in the previous paper (Lu et al. 1992). A response component was considered to be an LT burst if its action potentials displayed interspike intervals less-than-or-equal-to 4 ms and if the first spike in the burst episode occurred after a silent period of greater-than-or-equal-to 100 ms (or greater-than-or-equal-to 50 ms when the neuron responds to visual stimuli at temporal rates greater-than-or-equal-to 8 Hz). All other activity is considered to be part of the tonic response.2. In addition to LT bursts, we recognized another type of burst response, the high-threshold (HT) burst. These also have clusters of action potentials with interspike intervals less-than-or-equal-to 4 ms. However, HT bursts, unlike LT bursts, lack a preburst silent period. HT bursts are part of the tonic response component and merely reflect the gradual decrease in interspike intervals that occurs as the cell becomes more depolarized and thus more responsive. Thus interspike interval is a necessary but insufficient criterion to identify LT bursts.3. Visually evoked LT bursts were recorded among W, X, and Y cells. When evoked, LT bursts occurred in phase with drifting sine-wave grating stimuli at a rate never exceeding one per stimulus cycle. In response to individual cycles of the visual stimulus, LT bursts could comprise the total response, a tonic component could comprise the total response, or an LT burst and tonic component could be mixed. When a stimulus evoked a mixture of LT bursts and tonic response components, LT bursts were always the first response.4. Of the 61 cells tested with grating stimuli, 47 exhibited LT bursts and 14 did not. Those that did exhibited varying amounts of burstiness. We occasionally recorded individual cells for a sufficiently lengthy period to observe them switch between the burst and tonic firing modes. We conclude that most cells have membrane potentials close to the level needed for LT spike deinactivation and that small fluctuations in membrane voltage can switch them between these response modes. We also occasionally recorded several cells simultaneously and noted that different cells could be in different modes. This implies that whatever afferent pathways control response modes need not act globally on all geniculate neurons.5. Two indexes were used to express the variation of LT burstiness. For the first index, an LT burst ratio was determined for each cell by separating the total visual response into LT burst and tonic components and calculating the fundamental (F1) Fourier response amplitude for each. Once separated, we divided the F1 amplitude of the LT burst component by the sum of F1 amplitudes of the LT burst and tonic components. The other index was the percentage of stimulus cycles that elicit LT bursts. This percentage was computed by inspecting the response to each stimulus cycle and determining the presence or absence of an LT burst. The indexes were highly correlated (r = 0.93), and both showed that LT bursts represent a variable proportion of the total response from barely detectable for some cells to the vast majority of the response for others. The proportion of cells exhibiting LT bursts was slightly higher for Y cells (88%) than for X cells (64%). 6. Inspection of average response histograms indicated that the LT burst component added a substantial nonlinearity to the visual response. Is a measure of nonlinearity, we used the second Fourier harmonic (F2) component of the response and computed an F2-to-F1 ratio. For every neuron tested, this ratio was larger for the LT burst than the tonic response component. Thus LT bursts seem to distort visual responses by making them less linear.7. To test for the possibility that the amount of LT bursting may vary with stimulus strength, we generated response-versus-spatial frequency functions for 35 neurons and response-versus-contrast response functions for 15 neurons. The extent of LT bursting seen in cells did not vary significantly with spatial frequency or contrast; that is, the proportion of LT bursting in the total response was no more prevalent at one spatial frequency or contrast than another. Thus LT bursts do not appear to provide a selective nonlinear response amplification for weak or less salient stimuli.8. To test for the possibility that LT bursting may vary with temporal frequency, we generated response-versus-temporal frequency functions (at optimal spatial frequency) for 17 neurons. We found a progressive increase in the LT burst ratio with increasing temporal frequency.9. As noted, we found that LT bursts occurred earlier in the response cycle than did the tonic response components. We used the response-versus-temporal frequency functions of 10 cells to examine whether these temporal differences reflect phase and/or latency differences. The latencies of the two components were virtually identical, but the LT bursts were evoked by an earlier phase of the stimulus than was the tonic response component. We thus conclude that the temporal difference between the LT burst and tonic response components was due primarily to phase and not to latency.10. We conclude that LT spikes contribute to the transfer of visual signals through the lateral geniculate nucleus to visual cortex. They do not represent an obligatory disconnection of thalamic relay cells from their sensory inputs. Instead, they can provide a nonlinear amplification that permits hyperpolarized relay cells to signal cortex about the presence of a salient stimulus.