Li An-An, Chen Qi-Cai, Wu Fei-Jian
School of Life Sciences, Central China Normal University, Wuhan 430079, China.
Sheng Li Xue Bao. 2006 Apr 25;58(2):141-8.
Although there has been a growing body of literature showing the neural correlation of forward masking caused by a pure tone masker in the auditory neurons, relative few studies have addressed the description of how the forward masking caused by a noise burst, especially a sequence of noise burst, is transformed into neuronal representation in the central auditory system. Using a noise forward masking paradigm under free field stimuli conditions, this in vivo study was devoted to exploring it in the inferior collicular (IC) neurons of the mouse (Mus musculus KM). A total of 96 IC neurons were recorded. Rate-intensity functions (RIFs) with and without the presentation of masker, sustained noise burst (SNB) or segmental noise burst (SGNB), were measured in 51 neurons. We found that the relative masker intensities were distributed over a wide range between 21 dB below the minimum threshold (MT) and 19 dB above the MT of the corresponding probe tone. The masking effect of the SGNB on firing rate in nearly half of neurons (type I, 45.10%) was stronger than that of the SNB (P<0.001), whereas in a smaller fraction of neurons (type III, 17.65%), it was weaker than that of the SNB (P<0.001). There was no significant difference in masking effect between the SNB and SGNB in type II neurons (37.25%, P>0.05). Irrespective of type I or type III neurons, the inhibitory effects of both kinds of maskers were all greater at lower probe intensities but decreased significantly with the increase of probe intensity (P<0.001). Interestingly, as the probe intensity increased, the difference of masking effect between the SNB and SGNB disappeared (P>0.05). In addition, we observed that temporal masking pattern could be transformed when the masker was changed from the SNB to SGNB. The main type of this transformation was from early-inhibition to proportional-inhibition pattern (53.85%, 7/13). Our data provide the evidence that the inhibitory effects of these two maskers have differential weights over time and intensity domains of the IC neurons responding to a pure tone. This suggests that the forward masking of noise is by no means the source of simply suppression in neuronal firing rate. There might be a few of active neural modulating ways in which the coding of temporal acoustical information can be operated.
尽管已有越来越多的文献表明纯音掩蔽器在听觉神经元中引起的前向掩蔽的神经相关性，但相对较少的研究涉及噪声突发，尤其是噪声突发序列所引起的前向掩蔽如何在中枢听觉系统中转化为神经元表征的描述。本体内研究利用自由场刺激条件下的噪声前向掩蔽范式，致力于在小鼠（小家鼠KM）的下丘（IC）神经元中对此进行探索。共记录了96个IC神经元。在51个神经元中测量了有无掩蔽器、持续噪声突发（SNB）或分段噪声突发（SGNB）时的速率-强度函数（RIF）。我们发现相对掩蔽强度分布在对应探测音最小阈值（MT）以下21 dB至MT以上19 dB的较宽范围内。在近一半的神经元（I型，45.10%）中，SGNB对放电率的掩蔽效应强于SNB（P<0.001），而在较小比例的神经元（III型，17.65%）中，其掩蔽效应弱于SNB（P<0.001）。II型神经元（37.25%）中，SNB和SGNB的掩蔽效应无显著差异（P>0.05）。无论I型还是III型神经元，两种掩蔽器的抑制作用在较低探测强度时均更大，但随探测强度增加而显著降低（P<0.001）。有趣的是，随着探测强度增加，SNB和SGNB之间的掩蔽效应差异消失（P>0.05）。此外，我们观察到当掩蔽器从SNB变为SGNB时，时间掩蔽模式可能会发生转变。这种转变的主要类型是从早期抑制到比例抑制模式（53.85%，7/13）。我们的数据提供了证据，表明这两种掩蔽器的抑制作用在响应纯音的IC神经元的时间和强度域上具有不同权重。这表明噪声的前向掩蔽绝不是简单抑制神经元放电率的来源。可能存在一些活跃的神经调节方式，通过这些方式可以对时间声学信息进行编码。
