Cortical synthesis of azimuth-sensitive single-unit responses with nonmonotonic level tuning: A thalamocortical comparison in the cat
Cortical synthesis of azimuth-sensitive single-unit responses with nonmonotonic level tuning: A thalamocortical comparison in the cat
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DOI：
10.1152/jn.1996.75.3.1206
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发表时间：
1996-03-01
影响因子：
2.5
通讯作者：
Imig, TJ
中科院分区：
文献类型：
--
作者：
Barone, P;Clarey, JC;Imig, TJ
1.从初级听觉皮质(AI)和投射到AI的内侧膝状体(MGB)获得的单个单位样本的方位和声压级(SPL)被表征。这项研究的主要目的是验证这样的假设，即Al是合成单个单位反应的重要场所，这些反应既表现出方位敏感性(倾向于方向受限的反应)，也表现出非单调(NM)水平调节(随着SPL的增加，反应性降低的趋势)。这是通过比较人工智能和MGB中此类反应的比例来实现的。巴比妥钠麻醉猫MGB区(n=217)和AI区(n=216)的高频(BF)单单位。MGB标本主要来源于投射到Ai的两个核团的记录部位，即腹侧核(VN，n=118)和丘脑后核群外侧核(Po，n=84)。此外，少数MGB单位来自内侧部(n=8)或不确定的位置(n=7)。每个单元的反应是使用从方位声方向呈现的噪声爆发来研究的，这些噪声脉冲分布在0度仰角的额半场的180度处。SPL在80-分贝范围内以每个位置小于或等于20分贝的步长变化。通过将AT样品与整个MGB样品进行比较，统计地评估了方位和水平调谐方面的异同。如果发现它们不同，则比较AI、VN和Po样本。方位函数调制被用来衡量方位敏感度，其平均值在人工智能中大于在MGB中。NM强度定义为75dBSPL时水平函数值下降的百分比，其平均值在AI组大于MGB组(表现出更大的反应性降低趋势)。通过根据方位敏感度(敏感和不敏感类别)和近距强度(近距和单调类别)对每个样本进行联合分类来识别方位敏感(AS)近距单位。因为NM单位在人工智能样本中比在任何MGB样本中都要常见得多，这表明一些这样的反应是在AI.4中合成的。据报道，绝大多数人工智能NM单位都是AS，显示出这两种反应特性之间的优先关联(联系)。这一发现在人工智能中得到了证实，但在MGB中没有发现这种情况。这表明这些反应特性之间的联系在大脑皮层中出现，可能是由于NM作为反应合成的结果。虽然这种联系的功能意义尚不清楚，但NM反应可能反映了兴奋/抑制拮抗，这为AS AI神经元提供了对MGB.5以外的刺激特征的敏感性。AS细胞的方位调谐宽度被测量为方位函数值为最大值(优选方位范围，PAR)的75%的额半视野部分。PAR广泛分布于各结构，AI较MGB平均PAR更窄。NM水平函数的首选水平范围(PLR)被定义为其值为最大值的75%的范围，并且每个样本的平均PLR相似。在人工智能中，PARS和PLR之间存在微弱但显著的正相关，而在MGB中则不是。这进一步表明，在人工智能中，方位角和水平调谐之间存在着MGB中不存在的联系。最佳方位角(PAR的中点)用于将细胞分为对侧偏爱、同侧偏爱、中线偏爱或多峰。AI和MGB的样本显示出这些类别的相似分布。对侧偏爱细胞代表每个样本的大多数，而中线偏爱、同侧偏爱和多峰细胞各自代表较小的比例。这表明人工智能的方位偏好分布在很大程度上反映了MGB.7的方位偏好分布。最佳SPL定义为PLR的中点。这在MGB和AI中都广泛地分布在最佳方位角和BF上。不同结构的平均最佳SPL相似。在AI和MGB中，最佳SPL与PLR大小均呈正相关，表明最佳SPL的变化至少部分地反映了水平调谐广度的变化。
1. Azimuth and sound pressure level (SPL) tuning to noise stimulation was characterized in single-unit samples obtained from primary auditory cortex (AI) and in areas of the medial geniculate body (MGB) that project to AI. The primary aim of the study was to test the hypothesis that Al is an important site of synthesis of single-unit responses that exhibit both azimuth sensitivity (tendency for directionally restricted responsiveness) and nonmonotonic (NM) level tuning (tendency for decreased responsiveness with increasing SPL). This was accomplished by comparing the proportions of such responses in AI and MGB.2. Samples consisted of high-best-frequency (BF) single units located in MGB (n = 217) and AI (n = 216) of barbiturate-anesthetized cats. The MGB sample was obtained mainly from recording sites located in two nuclei that project to AI, the ventral nucleus (VN, n = 118) and the lateral part of the posterior group of thalamic nuclei (Po, n = 84). In addition, a few MGB units were obtained from the medial division (n = 8) or uncertain locations (n = 7). Each unit's responses were studied using noise bursts presented from azimuthal sound directions distributed throughout 180 degrees of the frontal hemifield at 0 degrees elevation. SPL was varied over an 80-dB range in steps of less than or equal to 20 dB at each location. Similarities and differences in azimuth and level tuning were evaluated statistically by comparing the AT sample with the entire MGB sample. If they were found to differ, the AI, VN, and Po samples were compared.3. Azimuth function modulation was used as a measure of azimuth sensitivity, and its mean was greater in AI than in MGB. NM strength was defined as the percentage reduction in level function value at 75 dB SPL and its mean was greater in AI (showing a greater tendency for decreased responsiveness) than in MGB. Azimuth-sensitive (AS) NM units were identified by jointly categorizing each sample according to both azimuth sensitivity (sensitive and insensitive categories) and NM strength (NM and monotonic categories). AS NM units were much more common in the AI sample than in any of the MGB samples, suggesting that some such responses are synthesized in AI.4. A vast majority of AI NM units have been reported to be AS, showing a preferential association (linkage) between these two response properties. This finding was confirmed in AI, but was not found to be the case in MGB. This suggests that a linkage between these response properties emerges in the cortex, presumably as a result of synthesis of NM AS responses. Although the functional significance of the linkage is unknown, NM responses may reflect excitatory/inhibitory antagonism that provides AS AI neurons with sensitivity to stimulus features beyond that which is present in MGB.5. Breadth of azimuth tuning of AS cells was measured as the portion of the frontal hemifield over which azimuth function values were >75% of maximum (preferred azimuth range, PAR). PARs were broadly distributed in each structure, and mean PAR was narrower in AI than in MGB. A preferred level range (PLR) was defined for NM level functions as the range over which values were >75% of maximum, and mean PLRs were similar in each sample. There was a weak, but significant, positive correlation between PARs and PLRs in AI but not in MGB. This further suggests a linkage between azimuth and level tuning in AI that does not exist in MGB.6. Best azimuth (midpoint of the PAR) was used to classify cells as contralateral preferring, ipsilateral preferring, midline preferring, or multipeaked. Samples from AI and MGB exhibited similar distributions of these categories. Contralateral-preferring cells represented a majority of each sample, whereass midline-preferring, ipsilateral-preferring, and multipeaked cells each represented smaller proportions. This suggests that the azimuth preference distribution in AI largely reflects that in MGB.7. A best SPL was defined as the midpoint of the PLR. This was broadly distributed with respect to best azimuths and BFs in both MGB and AI. Mean best SPLs in different structures were similar. Best SPL was positively correlated with PLR size in both AI and MGB, showing that variation in best SPL reflected, at least in part, variation in breadth of level tuning.