Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
PLoS One. 2011;6(10):e25895. doi: 10.1371/journal.pone.0025895. Epub 2011 Oct 5.
Repeated acoustic events are ubiquitous temporal features of natural sounds. To reveal the neural representation of the sound repetition rate, a number of electrophysiological studies have been conducted on various mammals and it has been proposed that both the spike-time and firing rate of primary auditory cortex (A1) neurons encode the repetition rate. However, previous studies rarely examined how the experimental animals perceive the difference in the sound repetition rate, and a caveat to these experiments is that they compared physiological data obtained from animals with psychophysical data obtained from humans. In this study, for the first time, we directly investigated acoustic perception and the underlying neural mechanisms in the same experimental animal by examining spike activities in the A1 of free-moving cats while performing a Go/No-go task to discriminate the click-trains at different repetition rates (12.5-200 Hz). As reported by previous studies on passively listening animals, A1 neurons showed both synchronized and non-synchronized responses to the click-trains. We further found that the neural performance estimated from the precise temporal information of synchronized units was good enough to distinguish all 16.7-200 Hz from the 12.5 Hz repetition rate; however, the cats showed declining behavioral performance with the decrease of the target repetition rate, indicating an increase of difficulty in discriminating two slower click-trains. Such behavioral performance was well explained by the firing rate of some synchronized and non-synchronized units. Trial-by-trial analysis indicated that A1 activity was not affected by the cat's judgment of behavioral response. Our results suggest that the main function of A1 is to effectively represent temporal signals using both spike timing and firing rate, while the cats may read out the rate-coding information to perform the task in this experiment.
重复的声学事件是自然声音普遍存在的时间特征。为了揭示声音重复率的神经表示，许多电生理学研究已经在各种哺乳动物中进行，并提出初级听觉皮层 (A1) 神经元的尖峰时间和放电率都编码了重复率。然而，以前的研究很少研究实验动物如何感知声音重复率的差异，这些实验的一个警告是，它们将从动物身上获得的生理数据与从人类身上获得的心理物理数据进行了比较。在这项研究中，我们首次通过在自由移动的猫中检查 A1 的尖峰活动，直接在同一实验动物中研究了声音感知和潜在的神经机制，同时执行 Go/No-go 任务来区分不同重复率 (12.5-200 Hz) 的点击序列。正如以前对被动聆听动物的研究报告的那样，A1 神经元对点击序列表现出同步和非同步的反应。我们进一步发现，从同步单元的精确时间信息估计的神经性能足以区分所有 16.7-200 Hz 与 12.5 Hz 的重复率；然而，随着目标重复率的降低，猫的行为表现下降，表明区分两个较慢的点击序列的难度增加。这种行为表现很好地解释了一些同步和非同步单元的放电率。逐次分析表明，A1 活动不受猫对行为反应判断的影响。我们的结果表明，A1 的主要功能是使用尖峰时间和放电率有效地表示时间信号，而猫可能会读取速率编码信息来执行本实验中的任务。
