Sadagopan Srivatsun, Wang Xiaoqin
Laboratory of Auditory Neurophysiology, Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Neurosci. 2008 Mar 26;28(13):3415-26. doi: 10.1523/JNEUROSCI.2743-07.2008.
A fundamental feature of auditory perception is the constancy of sound recognition over a large range of intensities. Although this invariance has been described in behavioral studies, the underlying neural mechanism is essentially unknown. Here we show a putative level-invariant representation of sounds by populations of neurons in primary auditory cortex (A1) that may provide a neural basis for the behavioral observations. Previous studies reported that pure-tone frequency tuning of most A1 neurons widens with increasing sound level. In sharp contrast, we found that a large proportion of neurons in A1 of awake marmosets were narrowly and separably tuned to both frequency and sound level. Tuning characteristics and firing rates of the neural population were preserved across all tested sound levels. These response properties lead to a level-invariant representation of sounds over the population of A1 neurons. Such a representation is an important step for robust feature recognition in natural environments.
听觉感知的一个基本特征是在大范围强度内声音识别的恒常性。尽管这种不变性已在行为研究中有所描述，但其潜在的神经机制基本上仍不为人知。在此，我们展示了初级听觉皮层（A1）中神经元群体对声音的一种假定的水平不变表征，这可能为行为观察提供神经基础。先前的研究报道，大多数A1神经元的纯音频率调谐会随着声级增加而变宽。与之形成鲜明对比的是，我们发现清醒狨猴A1中的很大一部分神经元对频率和声级都有狭窄且可分离的调谐。在所有测试声级下，神经群体的调谐特性和放电率都得以保留。这些反应特性导致了A1神经元群体对声音的水平不变表征。这样一种表征是在自然环境中进行稳健特征识别的重要一步。
