COMBINATION-SENSITIVE NEURONS IN THE MEDIAL GENICULATE-BODY OF THE MOUSTACHED BAT - ENCODING OF TARGET RANGE INFORMATION
COMBINATION-SENSITIVE NEURONS IN THE MEDIAL GENICULATE-BODY OF THE MOUSTACHED BAT - ENCODING OF TARGET RANGE INFORMATION
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DOI：
10.1152/jn.1991.65.6.1275
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发表时间：
1991-06-01
影响因子：
2.5
通讯作者：
SUGA, N
中科院分区：
文献类型：
--
作者：
OLSEN, JF;SUGA, N
1. 延迟调谐组合敏感神经元（FM-FM神经元）存在于髭须蝠（Pteronotus parnellii）内侧曲状体（MGB）的背侧和内侧分裂中。在这篇论文中，我们提出了FM-FM神经元的丘脑起源的证据。我们对FM-FM神经元响应特性的研究表明，延迟调谐的神经机制依赖于重合检测，并且涉及神经抑制和神经兴奋之间的相互作用。髭须蝠产生和听到的生物声纳脉冲(P)及其回声(E)由四个谐波组成；每个谐波包含一个恒频（CF）分量和一个调频（FM）分量。因此脉冲回波对包含8个CF分量（PCF1-4, ECF1-4）和8个FM分量（PFM1-4, EFM1-4）。本研究使用的刺激包括CF、FM和CF-FM声音；配对的CF-FM声音用来模拟脉冲回波对的任意两个谐波。在细胞外记录MGB中FM-FM神经元的反应。我们发现FM-FM神经元对单个声音的反应很差或根本没有反应，对成对的声音反应强烈，并且对成对的每个声音的频率和幅度以及将它们分开的时间间隔（模拟回声延迟）进行调整。所有FM-FM神经元都受到成对FM声音的促进，而大多数神经元受到成对CF声音的促进。配对的CF声音测量的最佳促进频率落在生物声纳信号的CF分量的频率范围之外，而配对的FM声音测量的最佳促进频率落在生物声纳信号的FM分量的频率范围内。因此，FM-FM神经元有望选择性地对生物声纳信号中FM成分的组合做出反应。对促进FM-FM神经元至关重要的脉冲回波对的FM分量是脉冲基频（PFM1）的FM分量与回波的第二、三、四次谐波（EFM2、EFM3、EFM4；统称为EFM(n)）的FM分量。FM-FM神经元调谐到的频率组合反映了谐波关系的微小偏差，例如脉冲和多普勒移回波的FM分量组合。然而，与CF/CF神经元相比，FM-FM神经元对刺激频率具有广泛的调谐。因此FM-FM神经元具有多普勒频移容错性，并且相对而言不专门用于处理频域中的速度信息。在回声定位中，回波延迟是目标距离的主要线索。FM-FM神经元的最佳延迟范围为0 ~ 23ms，对应的目标距离为0 ~ 3.9 m，这是回声定位中生物学上重要的目标距离范围。MGB是听觉上行通路中含有FM-FM神经元的最低核；FM-FM神经元曾在下丘中寻找，但尚未发现。丘脑FM-FM神经元的反应潜伏期平均比皮质神经元的反应潜伏期短2.6毫秒。这些数据有力地表明MGB是FM-FM神经元最初产生的地方。先前的研究表明，FM1是空气中生物声纳信号中最弱的成分，但它存在于耳蜗对蝙蝠自身脉冲的超阈值反应中。这里提供的数据表明，蝙蝠的听觉系统利用FM1的选择性衰减来区分蝙蝠自己的脉冲和回声。FM-FM神经元的易化阈值，FM1比FM平均高17 dB (n)。这些FM1促进阈值的升高是在MGB内或之前的中央听觉系统中产生的。原则上，提高FM1的促进阈值可以抑制回波的FM1分量，同时通过脉冲的更强的FM1分量。因此，脉冲和回声的不同通道可以在一个tonotopically有组织的系统中创建，这样脉冲由调谐到基本谐波的听觉通路表示，而回声由调谐到第二、第三和第四谐波的听觉通路表示。调频-调频神经元的延迟调谐依赖于一致性检测。分别对FM1和FM(n)作出反应的FM-FM神经元的最佳延迟，与FM1和FM(n)引起的兴奋之间的延迟差异密切匹配。最佳延迟与fm1诱发的兴奋潜伏期呈正相关，但与FM(n)诱发的兴奋潜伏期不相关。因此，蝙蝠的听觉系统通过延迟表示脉冲基本信号的通路中的兴奋来产生一系列延迟调谐的神经元。丘脑FM-FM神经元的FM1兴奋性潜伏期范围大于丘脑传入事件的范围，这表明额外的FM1传递延迟在mmb中产生。对于具有大于或等于4 ms的最佳延迟的FM-FM神经元，FM1的刺激会产生一段抑制期，该抑制期在FM1引起的兴奋发生之前开始和结束。这种抑制期的持续时间与FM-FM神经元的最佳延迟呈正相关，表明这种抑制是fm1诱发的兴奋延迟的内在机制。这些结果与FM1诱发的兴奋在MGB中延迟的过程是一致的，在FM1和FM(n)通道的收敛处。
1. Delay-tuned combination-sensitive neurons (FM-FM neurons) have been discovered in the dorsal and medial divisions of the medial geniculate body (MGB) of the mustached bat (Pteronotus parnellii). In this paper we present evidence for a thalamic origin for FM-FM neurons. Our examination of the response properties of FM-FM neurons indicates that the neural mechanism of delay-tuning depends on coincidence detection and involves an interaction between neural inhibition and excitation.2. The biosonar pulse (P) and its echo (E) produced and heard by the mustached bat consist of four harmonics; each harmonic contains a constant frequency (CF) component and a frequency modulated (FM) component. Thus the pulse-echo pair contains eight CF components (PCF1-4, ECF1-4) and eight FM components (PFM1-4, EFM1-4). The stimuli used in this study consisted of CF, FM, and CF-FM sounds; paired CF-FM sounds were used to simulate any two harmonics of pulse-echo pairs. The responses of FM-FM neurons in the MGB were recorded extracellularly. We found that FM-FM neurons respond poorly or not at all to single sounds, respond strongly to paired sounds, and are tuned to the frequency and amplitude of each sound of the pair and to the time interval separating them (simulated echo delay).3. All FM-FM neurons are facilitated by paired FM sounds and most are facilitated by paired CF sounds. Best facilitative frequencies measured with paired CF sounds fall outside the frequency ranges of the CF components of biosonar signals, whereas best facilitative frequencies measured with paired FM sounds fall within the frequency ranges of the FM components of biosonar signals. Thus FM-FM neurons are expected to respond selectively to combinations of FM components in biosonar signals. The FM components of pulse-echo pairs essential to facilitate FM-FM neurons are the FM component of the fundamental of the pulse (PFM1) in combination with the FM component of the second, third, or fourth harmonic of an echo (EFM2, EFM3, EFM4; collectively, EFM(n)).4. The frequency combinations to which FM-FM neurons are tuned reflect small deviations from the harmonic relationship such as occurs in combinations of FM components from pulses and Doppler-shifted echoes. Compared with CF/CF neurons, however, FM-FM neurons are broadly tuned to stimulus frequency. Thus FM-FM neurons are Doppler-shift tolerant and relatively unspecialized for processing velocity information in the frequency domain.5. In echolocation, echo delay is the primary cue for target distance. Best delays of FM-FM neurons range from 0 to 23 ms, corresponding to target distances from 0 to 3.9 m, which is the biologically important range of target distances in echolocation.6. The MGB is the lowest nucleus in the ascending auditory pathway that contains FM-FM neurons; FM-FM neurons have been sought in the inferior colliculus, but none has been found. Response latencies of thalamic FM-FM neurons are 2.6 ms shorter, on the average, than those of their counterparts in the cortex. These data strongly suggest that the MGB is where FM-FM neurons are first created.7. Previous studies have shown that FM1 is the weakest component in airborne biosonar signals but is present in the cochlear microphonic response to the bat's own pulse at suprathreshold levels for FM-FM neurons. The data presented here suggest that the bat's auditory system exploits the selective attenuation of FM1 to differentiate the bat's own pulse from echoes. Thresholds for facilitation of FM-FM neurons are, on the average, 17 dB higher for FM1 than for FM(n). These elevated thresholds for facilitation by FM1 are created within the central auditory system within or before the MGB. In principle, the elevated facilitative thresholds for FM1 can reject the FM1 component of echoes while passing the stronger FM1 component of pulses. As a consequence, different channels for pulses and echoes may be created within a tonotopically organized system such that pulses are represented by auditory pathways tuned to the fundamental, whereas echoes are represented by auditory pathways tuned to the second, third, and fourth harmonics.8. Delay tuning in FM-FM neurons depends on coincidence detection. Best delays of FM-FM neurons that respond to FM1 and to FM(n), presented individually, closely match the difference in latency between FM1- and FM(n)-evoked excitation. Best delays correlate strongly and positively with latencies of FM1-evoked excitation, but do not correlate with latencies of FM(n)-evoked excitation. Thus the auditory system of the bat creates a range of delay-tuned neurons by delaying excitation in the pathway in which the fundamental of the pulse is represented. The range of FM1 excitatory latencies of thalamic FM-FM neurons is greater than the range reported for tectothalamic afferents, suggesting that additional FM1 transmission delays are created in the MGB.9. For FM-FM neurons that have best delays of greater-than-or-equal-to 4 ms, stimulation by FM1 produces a period of inhibition that begins and ends before FM1-evoked excitation occurs. The duration of this inhibitory period is positively correlated with best delays of FM-FM neurons, suggesting that this inhibition is intrinsic to the mechanism by which FM1-evoked excitation is delayed. These results are consistent with a process in which FM1-evoked excitation is delayed in the MGB, at the site of convergence of the FM1 and FM(n) channels.