Eggermont J J
Department of Physiology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
J Neurophysiol. 1998 Oct;80(4):2151-61. doi: 10.1152/jn.1998.80.4.2151.
This study was designed to explore a potential representation of sound azimuth in the primary auditory cortex (AI) of the cat by the relative latencies of a population of neurons. An analysis of interspike intervals (ISI) was done to asses azimuth information in the firings of the neurons after the first spike. Thus latencies of simultaneously recorded single-unit (SU) spikes and local field potentials (LFP) in AI of cats were evaluated for sound presented from nine speakers arranged horizontally in the frontal half field in a semicircular array with a radius of 55 cm and the cat's head in the center. SU poststimulus time histograms (PSTH) were made for each speaker location for a 100-ms window after noise-burst onset using 1-ms bins. PSTH peak response latencies for SUs and LFPs decreased monotonically with intensity, and most of the change occurred within 15 dB of the threshold at that particular azimuth. After correction for threshold differences, all latency-intensity functions had roughly the same shape, independent of sound azimuth. Differences with the minimum spike latency observed in an animal at each intensity were calculated for all azimuth-intensity combinations. This relative latency showed a weakly sigmoidal dependence on azimuth that was independent of intensity level >40 dB SPL. SU latency differences also were measured with respect to the latencies of the LFP triggers, simultaneously recorded on the same electrode. This difference was independent of stimulus intensity and showed a nearly linear dependence on sound azimuth. The mean differences across animals for both measures, however, were only significant between contralateral azimuths on one hand and frontal and ipsilateral azimuths on the other hand. Mean unit-LFP latency differences showed a monotonic dependence on azimuth with nearly constant variance and may provide the potential for an unbiased conversion of azimuth into neural firing times. The general trend for the modal ISI was the same as for relative spike latency: the shortest ISIs were found for contralateral azimuths (ISI usually 3 ms) and the longer ones for ipsilateral azimuths (the most frequent ISI was 4 ms, occasionally 5 ms was found). This trend was also independent of intensity level. This suggests that there is little extra information in the timing of extra spikes in addition to that found in the peak PSTH latency.
本研究旨在通过一群神经元的相对潜伏期来探索猫初级听觉皮层（AI）中声音方位的潜在表征。对峰间间隔（ISI）进行分析，以评估神经元首次放电后放电中的方位信息。因此，针对从九个扬声器水平排列于前半场、半径为55厘米的半圆形阵列中且猫的头部位于中心位置发出的声音，评估了猫AI中同时记录的单单元（SU）尖峰和局部场电位（LFP）的潜伏期。使用1毫秒的时间间隔，针对每个扬声器位置在噪声爆发开始后的100毫秒窗口内制作了SU刺激后时间直方图（PSTH）。SU和LFP的PSTH峰值响应潜伏期随强度单调下降，且大部分变化发生在该特定方位阈值的15分贝范围内。在对阈值差异进行校正后，所有潜伏期 - 强度函数大致具有相同的形状，与声音方位无关。针对所有方位 - 强度组合，计算了在每个强度下动物中观察到的最小尖峰潜伏期的差异。这种相对潜伏期显示出对方位的弱S形依赖性，且与强度水平>40分贝声压级无关。还相对于在同一电极上同时记录的LFP触发的潜伏期测量了SU潜伏期差异。这种差异与刺激强度无关，并且显示出对声音方位的近似线性依赖性。然而，两种测量方法在不同动物之间的平均差异仅在对侧方位与前侧和同侧方位之间具有显著性。平均单元 - LFP潜伏期差异显示出对方位的单调依赖性，且方差几乎恒定，这可能为将方位无偏转换为神经放电时间提供了潜力。模态ISI的总体趋势与相对尖峰潜伏期相同：对侧方位的ISI最短（通常为3毫秒），同侧方位的ISI较长（最常见的ISI为4毫秒，偶尔发现为5毫秒）。这种趋势也与强度水平无关。这表明除了在PSTH峰值潜伏期发现的信息外，额外尖峰的时间中几乎没有额外信息。
