Department of Zoology and Physiology, University of Wyoming Laramie, WY, USA.
Front Neural Circuits. 2012 Aug 17;6:54. doi: 10.3389/fncir.2012.00054. eCollection 2012.
Auditory neurons in the inferior colliculus (IC) of the pallid bat have highly rate selective responses to downward frequency modulated (FM) sweeps attributable to the spectrotemporal pattern of their echolocation call (a brief FM pulse). Several mechanisms are known to shape FM rate selectivity within the pallid bat IC. Here we explore how two mechanisms, stimulus duration and high-frequency inhibition (HFI), can interact to shape FM rate selectivity within the same neuron. Results from extracellular recordings indicated that a derived duration-rate function (based on tonal response) was highly predictive of the shape of the FM rate response. Longpass duration selectivity for tones was predictive of slowpass rate selectivity for FM sweeps, both of which required long stimulus durations and remained intact following iontophoretic blockade of inhibitory input. Bandpass duration selectivity for tones, sensitive to only a narrow range of tone durations, was predictive of bandpass rate selectivity for FM sweeps. Conversion of the tone duration response from bandpass to longpass after blocking inhibition was coincident with a change in FM rate selectivity from bandpass to slowpass indicating an active inhibitory component to the formation of bandpass selectivity. Independent of the effect of duration tuning on FM rate selectivity, the presence of HFI acted as a fastpass FM rate filter by suppressing slow FM sweep rates. In cases where both mechanisms were present, both had to be eliminated, by removing inhibition, before bandpass FM rate selectivity was affected. It is unknown why the auditory system utilizes multiple mechanisms capable of shaping identical forms of FM rate selectivity though it may represent distinct but convergent modes of neural signaling directed at shaping response selectivity for important biologically relevant sounds.
下丘中的听觉神经元对向下调频 (FM) 扫频具有高度的率选择性反应，这归因于它们回声定位叫声的频谱时间模式（一个短暂的 FM 脉冲）。有几种机制已知可以在苍白蝙蝠的 IC 内塑造 FM 率选择性。在这里，我们探讨了两种机制，刺激持续时间和高频抑制 (HFI)，如何在同一神经元内相互作用以塑造 FM 率选择性。细胞外记录的结果表明，衍生的持续时间 - 率函数（基于音调反应）高度预测了 FM 率响应的形状。音调的长通持续时间选择性可预测 FM 扫频的慢通率选择性，这两者都需要长的刺激持续时间，并且在抑制性输入的离子电渗阻断后仍然保持完整。音调的带通持续时间选择性对仅窄范围的音调持续时间敏感，可预测 FM 扫频的带通率选择性。在抑制性输入阻断后，音调持续时间响应从带通转换为长通，与 FM 率选择性从带通转换为慢通一致，表明带通选择性的形成存在主动抑制成分。独立于持续时间调谐对 FM 率选择性的影响，HFI 的存在通过抑制慢 FM 扫频速率充当快速 FM 率滤波器。在存在这两种机制的情况下，只有通过消除抑制作用，才能在不影响带通 FM 率选择性的情况下消除它们。目前尚不清楚为什么听觉系统利用多种能够塑造相同形式的 FM 率选择性的机制，尽管它可能代表针对生物相关声音的响应选择性进行塑造的不同但趋同的神经信号模式。
