Goldberg R L, Henson O W
Department of Cell Biology and Anatomy, Chapel Hill, NC 27599, USA.
Hear Res. 1998 Aug;122(1-2):71-81. doi: 10.1016/s0378-5955(98)00078-1.
The mustached bat, Pteronotus p. parnellii, has a finely tuned cochlea that rings at its resonant frequency in response to an acoustic tone pip. The decay time (DT) and frequency of these damped oscillations can be measured from the cochlear microphonic potential (CM) to study changes in cochlear mechanics. In this report, we describe phasic changes that occur in synchrony with communication sound vocalizations of the bat. Three animals with chronically implanted electrodes were studied. During the experiments, 1-2 ms tone pips were emitted from a speaker every 200 ms. This triggered a computer analysis of the resulting CM to determine the DT and cochlear resonance frequency (CRF) of the ringing. The time relative to vocalizations was determined by monitoring the output of a microphone placed near a bat's mouth. Similar results were obtained from all three bats tested. In a representative case, the average DT was 2.33 +/- 0.25 ms while the bat was quiet, but it decreased by 46% to 1.26 +/- 0.75 during vocalizations, which indicates a greater damping of the cochlear partition. Sometimes, DT started decreasing immediately before the bat vocalized. After the end of a vocalization, the return to baseline values varied from rapid (milliseconds) to gradual (1-2 seconds). The CRF also changed from baseline values during vocalization, although the amount and direction of change were not predictable. When gentamicin was administered to block the action of medial olivocochlear (MOC) efferents, DT reduction was still evident during vocalization but less pronounced. We conclude that phasic changes in damping occur in synchrony with vocalization, and that the MOC system plays a role in causing suppression. Since suppression can begin prior to vocalization, this may be a synkinetic effect, mediated by neural outflow to the ear in synchrony with neural outflow to the middle ear muscles and the muscles used for vocalization.
髭蝠（Pteronotus p. parnellii）拥有经过精细调节的耳蜗，其会在受到音调短声刺激时以共振频率发出响声。这些阻尼振荡的衰减时间（DT）和频率可通过耳蜗微音器电位（CM）进行测量，以研究耳蜗力学的变化。在本报告中，我们描述了与蝙蝠交流声音发声同步发生的相位变化。对三只长期植入电极的动物进行了研究。实验期间，每隔200毫秒从扬声器发出1 - 2毫秒的音调短声。这触发了对由此产生的CM进行计算机分析，以确定响声的DT和耳蜗共振频率（CRF）。通过监测放置在蝙蝠嘴附近的麦克风的输出来确定相对于发声的时间。对所有三只测试蝙蝠都获得了类似的结果。在一个典型案例中，蝙蝠安静时的平均DT为2.33±0.25毫秒，但在发声时下降了46%，降至1.26±0.75毫秒，这表明耳蜗隔的阻尼更大。有时，DT在蝙蝠发声前就立即开始下降。发声结束后，恢复到基线值的速度从快速（几毫秒）到逐渐（1 - 2秒）不等。CRF在发声期间也偏离了基线值，尽管变化的幅度和方向无法预测。当给予庆大霉素以阻断内侧橄榄耳蜗（MOC）传出神经的作用时，发声期间DT的降低仍然明显，但不太显著。我们得出结论，阻尼的相位变化与发声同步发生，并且MOC系统在引起抑制方面发挥作用。由于抑制可能在发声之前就开始，这可能是一种联带运动效应，由与流向中耳肌肉和用于发声的肌肉的神经流出同步的流向耳朵的神经流出介导。
