ENCODING OF AMPLITUDE-MODULATION IN THE COCHLEAR NUCLEUS OF THE CAT
ENCODING OF AMPLITUDE-MODULATION IN THE COCHLEAR NUCLEUS OF THE CAT
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DOI：
10.1152/jn.1994.71.5.1797
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发表时间：
1994-05-01
影响因子：
2.5
通讯作者：
GREENBERG, S
中科院分区：
文献类型：
--
作者：
RHODE, WS;GREENBERG, S
1.幅度调制(AM)是水声通信系统的普遍特性。在本研究中，我们研究了戊巴比妥钠麻醉猫的听神经和耳蜗核中与100%AM音神经编码相关的神经时间机制，包括在安静和存在宽带、准平谱噪声的情况下。AM载波频率设置为神经元的特征频率(CF)，声刺激的声压级(SPL)在较大的动态强度范围内变化(小于或等于40分贝)。通过计算神经元对信号调制和载波频率响应的同步系数(SC)来衡量听神经元的时间AM编码能力。然后通过测量神经元对变量f(Mod)(50-2550 Hz)信号的响应的SC来计算神经元的时间调制传递函数(TMTF)。平均而言，耳蜗核中的神经元与调制频率的同步性比听神经中具有可比的Cf、阈值和自发频率的纤维更高。在高SPL和低信噪比时，性能差异最大。然而，耳蜗核和听神经中的神经元在AM编码能力上存在着显著的差异。在听神经纤维(ANF)中，中低自发频率(SR)单位(SR1 KHz)。因此，锁相性能是基于两个参数来测量的，最大同步与激励频率无关，以及显著锁相的频率上限。根据最大同步能力的不同，可将耳蜗核神经元分为三个不同的组。第1组为前腹区初级类(PL)单位，其锁相能力与高SR ANF相当。第二组包括斩波型(C)、起始型L(O-L)和暂停型(P/B)单元，在响应低频音调和AM信号时表现出优于PL单元的锁相能力，与低SR ANF大致相当。第三组由起始斩波器(O-c)和初级类带陷波(PL(N))单元组成，对AM信号表现出比第1组和2.5组显著增强的锁相能力。稳健锁相调幅编码的频率上限由TMTF的拐角频率和截止频率描述。这些上限与CFS为2 kHz的ANF的特征频率(对于PL和O-L单位的程度较小)高度相关。在高CF单元中，ANF表现出对f(Mod)>；1.5 khz最精确的锁相。这些单元的平均TMTF转角频率为744赫兹。O-C、PL和O-L单元也能够稳健地锁相到f(Mod)>；1 khz。另一方面，C和P/B单元很少能在f(Mod)>；600赫兹范围内很好地锁相。锁相能力对高f(Mod)的排序为：ANF>；PL(N)>；(O-L=PL=O-C)>；C>；P/B。
1. Amplitude modulation (AM) is a pervasive property of acoustic communication systems. In the present study we investigate neural temporal mechanisms in the auditory nerve and cochlear nuclei of the pentobarbital sodium-anesthesized cat associated with the neural coding of 100% AM tones, both in quiet and in the presence of wideband, quasi-flat-spectrum noise. The AM carrier frequency was set to the neuron's characteristic frequency (CF) and the sound pressure level (SPL) of acoustic stimuli was varied over a wide dynamic range of intensities (less than or equal to 40 dB). The temporal AM-encoding capability of auditory neurons was measured by computing the synchronization coefficient (SC) of the neural response to the signal's modulation and carrier frequency. The temporal modulation transfer function (tMTF) of a neuron was then computed by measuring the SC of the response to signals of variable f(mod) (50-2550 Hz).2. Neurons in the cochlear nuclei synchronize on average more highly to the modulation frequency than fibers of comparable CF, threshold, and spontaneous rate in the auditory nerve. The disparity in performance is greatest at high SPLs and low signal-to-noise ratios. However, there is a significant degree of diversity in AM-encoding capability among neurons in both the cochlear nuclei and auditory nerve. Among auditory nerve fibers (ANFs), low-and medium-spontaneous-rate (SR) units (SR 1 kHz. As a result, phase-locking performance is measured on the basis of two parameters, maximum synchronization, irrespective of stimulus frequency, and the upper frequency limit for significant phase-locking.4. Cochlear nucleus neurons may be divided into three distinct groups on the basis of maximum synchronization capability. In group 1 are the primary-like (PL) units of the anteroventral division, whose phase-locking capabilities are comparable with those of high-SR ANFs. A second group, comprising the chopper (C), onset-L (O-L) and pauser-buildup (P/B) unit types, exhibits phase-locking capability superior to that of PL units in response to low-frequency tones and AM signals and roughly equal to that of low-SR ANFs. A third group, consisting of the onset-chopper (O-c) and primary-like-with-notch (PL(N)) units, exhibits phase-locking capability to AM signals that is considerably enhanced relative to that of groups 1 and 2.5. The upper frequency limit of robust phase-locked AM encoding is described by the corner and cutoff frequencies of the tMTF. These upper limits are highly correlated with characteristic frequency for ANFs (and to a lesser extent, for PL and O-L units) with CFs 2 kHz. Among high-CF units ANFs exhibit the most precise phase-locking to f(mod) >1.5 kHz. The average tMTF corner frequency for these units is 744 Hz. O-C, PL, and O-L units are also capable of robustly phase-locking to f(mod) >1 kHz. On the other hand, C and P/B units rarely phase-lock well to f(mod) >600 Hz. The rank order for phase-locking capability to high f(mod) is: ANF > PL(N) > (O-L = PL = O-C) > C > P/B.