Mendelson J R, Grasse K L
Division of Life Sciences, University of Toronto, Scarborough, Ontario, Canada.
Exp Brain Res. 1992;91(3):435-54. doi: 10.1007/BF00227840.
Monaural and binaural single unit responses to frequency-modulated (FM) sweeps were compared in cat primary auditory cortex (AI). Both upward-directed (changing from low to high frequency) and downward-directed (changing from high to low frequency) FM sweeps were presented monaurally and binaurally at five rates of frequency modulation (referred to here as the speed of FM sweep). Two types of binaural FM sweep conditions were presented: (1) like-directed FM sweeps, in which identical FM sweeps were presented to both ears, and (2) opposite-directed FM sweeps, in which one ear was presented with one direction of FM sweep while the other ear was simultaneously presented with the opposite direction of FM sweep. In a sample of 78 cells, 33 cells were classified as EE (binaural facilitatory) and 45 were classified as EI (binaural inhibitory). Ninety-four percent of all units were sensitive to the direction and/or speed of FM sweeps. In general, under binaural stimulus conditions, EE cells responded optimally to like-directed FM sweeps, while EI cells preferred opposite-directed FM sweeps. When tested monaurally, 59% of all cells (both EE and EI) were direction selective, with the majority (76%) preferring downward-directed FM sweeps. When tested binaurally, most direction selective EE cells (60%) preferred upward-directed FM sweeps, while the majority of direction selective EI cells (71%) preferred downward-directed FM sweeps. Our analysis also allowed us to classify inhibitory responses of EI cells as either direction selective (37%) or non-direction selective (63%). For FM speed selectivity under monaural conditions, most EE cells preferred fast FM sweep rates (0.4-0.8 kHz/ms), while approximately equal numbers of EI cells preferred either slow (i.e., 0.05-0.1 kHz/ms) or fast (i.e., 0.4-0.8 kHz/ms) speeds. Under binaural conditions, the majority of EE and EI cells responded best to high speeds when tested with like-directed FM sweeps, while the preferred speed with opposite-directed FM sweeps was more broadly tuned. The results suggest the presence of binaural neural mechanisms underlying cortical FM sweep direction and speed selectivity.
在猫的初级听觉皮层（AI）中，比较了单耳和双耳对调频（FM）扫描的单个单元反应。向上定向（从低频变为高频）和向下定向（从高频变为低频）的FM扫描以五种调频速率（在此称为FM扫描速度）进行单耳和双耳呈现。呈现了两种类型的双耳FM扫描条件：（1）同向FM扫描，即向双耳呈现相同的FM扫描；（2）反向FM扫描，即一只耳朵呈现一个方向的FM扫描，而另一只耳朵同时呈现相反方向的FM扫描。在78个细胞样本中，33个细胞被分类为EE（双耳促进），45个被分类为EI（双耳抑制）。所有单元中有94%对FM扫描的方向和/或速度敏感。一般来说，在双耳刺激条件下，EE细胞对同向FM扫描反应最佳，而EI细胞更喜欢反向FM扫描。单耳测试时，所有细胞（EE和EI）中有59%具有方向选择性，大多数（76%）更喜欢向下定向的FM扫描。双耳测试时，大多数具有方向选择性的EE细胞（60%）更喜欢向上定向的FM扫描，而大多数具有方向选择性的EI细胞（71%）更喜欢向下定向的FM扫描。我们的分析还使我们能够将EI细胞的抑制反应分类为方向选择性（37%）或非方向选择性（63%）。对于单耳条件下的FM速度选择性，大多数EE细胞更喜欢快速FM扫描速率（0.4 - 0.8 kHz/ms），而大约相同数量的EI细胞更喜欢慢速（即0.05 - 0.1 kHz/ms）或快速（即0.4 - 0.8 kHz/ms）速度。在双耳条件下，当用同向FM扫描测试时，大多数EE和EI细胞对高速反应最佳，而反向FM扫描的首选速度调谐更宽。结果表明存在皮层FM扫描方向和速度选择性的双耳神经机制。
