Department of Neurobiology, Chongqing Key Laboratory of Neurobiology, Third Military Medical University, 30 Gaotanyan St., Chongqing, 400038, China.
Sci Rep. 2017 Mar 14;7:44493. doi: 10.1038/srep44493.
Frequency and intensity are two independent attributes of sound stimuli. Psychoacoustic studies have found that the sound intensity can affect the perception of frequency; however, the underlying neuronal mechanism remains largely unknown. To investigate if and how the sound level affects the frequency coding for auditory cortical neurons, we recorded the activities of neuronal ensembles and single neurons, as well as the synaptic input evoked by pure tones of different frequency and intensity combinations, in layer 4 of the rat primary auditory cortex. We found that the best frequency (BF) shifted bidirectionally with the increases in intensity. Specifically, the BF of neurons with a low characteristic frequency (CF) shifted lower, whereas the BF of neurons with a higher CF shifted higher. Meanwhile, we found that these shifts in the BF can lead to the expansion of high- and low-frequency areas in the tonotopic map, increasing the evenness of the BF distribution at high intensities. Our results revealed that the frequency tuning can bidirectionally shift with an increase in the sound intensity at both the cellular and population level. This finding is consistent with the perceptual illusions observed in humans and could provide a potential mechanism for this psychoacoustic effect.
频率和强度是声音刺激的两个独立属性。心理声学研究发现，声音强度会影响对频率的感知；然而，其潜在的神经机制在很大程度上仍是未知的。为了研究声音水平是否以及如何影响听觉皮层神经元的频率编码，我们记录了大鼠初级听觉皮层第 4 层中由不同频率和强度组合的纯音诱发的神经元集合和单个神经元的活动以及突触输入。我们发现，最佳频率（BF）随强度的增加而双向移动。具体来说，具有低特征频率（CF）的神经元的 BF 向下移动，而具有较高 CF 的神经元的 BF 向上移动。同时，我们发现这些 BF 的变化会导致在声图中高频和低频区域的扩展，从而在高强度下增加 BF 分布的均匀性。我们的结果表明，在细胞和群体水平上，随着声音强度的增加，频率调谐可以双向移动。这一发现与在人类中观察到的感知错觉一致，并且可能为这种心理声学效应提供了一种潜在的机制。
