Department of Psychology, Neuroscience & Behaviour, McMaster University , Hamilton, Ontario , Canada.
J Neurophysiol. 2018 Sep 1;120(3):985-997. doi: 10.1152/jn.00065.2018. Epub 2018 May 23.
Responses of auditory duration-tuned neurons (DTNs) are selective for stimulus duration. We used single-unit extracellular recording to investigate how the inferior colliculus (IC) encodes frequency-modulated (FM) sweeps in the big brown bat. It was unclear whether the responses of so-called "FM DTNs" encode signal duration, like classic pure-tone DTNs, or the FM sweep rate. Most FM cells had spiking responses selective for downward FM sweeps. We presented cells with linear FM sweeps whose center frequency (CEF) was set to the best excitatory frequency and whose bandwidth (BW) maximized the spike count. With these baseline parameters, we stimulated cells with linear FM sweeps randomly varied in duration to measure the range of excitatory FM durations and/or sweep rates. To separate FM rate and FM duration tuning, we doubled (and halved) the BW of the baseline FM stimulus while keeping the CEF constant and then recollected each cell's FM duration tuning curve. If the cell was tuned to FM duration, then the best duration (or range of excitatory durations) should remain constant despite changes in signal BW; however, if the cell was tuned to the FM rate, then the best duration should covary with the same FM rate at each BW. A Bayesian model comparison revealed that the majority of neurons were tuned to the FM sweep rate, although a few cells showed tuning for FM duration. We conclude that the dominant parameter for temporal tuning of FM neurons in the IC is FM sweep rate and not FM duration. NEW & NOTEWORTHY Reports of inferior colliculus neurons with response selectivity to the duration of frequency-modulated (FM) stimuli exist, yet it remains unclear whether such cells are tuned to the FM duration or the FM sweep rate. To disambiguate these hypotheses, we presented neurons with variable-duration FM signals that were systematically manipulated in bandwidth. A Bayesian model comparison revealed that most temporally selective midbrain cells were tuned to the FM sweep rate and not the FM duration.
听觉时长调谐神经元 (DTN) 的反应对刺激时长具有选择性。我们使用单细胞胞外记录技术研究了下丘脑中(IC)如何对调频(FM)扫频进行编码。尚不清楚所谓的“FM DTN”的反应是像经典纯音 DTN 一样编码信号时长,还是编码 FM 扫频速率。大多数 FM 细胞具有对向下 FM 扫频具有选择性的爆发反应。我们向细胞呈现中心频率(CEF)设置为最佳兴奋频率且带宽(BW)最大化尖峰计数的线性 FM 扫频。使用这些基线参数,我们通过随机改变时长来刺激细胞,以测量兴奋 FM 时长和/或扫频速率的范围。为了分离 FM 速率和 FM 时长调谐,我们将基线 FM 刺激的 BW 加倍(和减半),同时保持 CEF 不变,然后重新收集每个细胞的 FM 时长调谐曲线。如果细胞调谐到 FM 时长,则最佳时长(或兴奋时长范围)应保持不变,尽管信号 BW 发生变化;然而,如果细胞调谐到 FM 速率,则最佳时长应与每个 BW 的相同 FM 速率相关。贝叶斯模型比较表明,大多数神经元调谐到 FM 扫频速率,尽管少数细胞显示出对 FM 时长的调谐。我们得出的结论是,IC 中 FM 神经元的时间调谐的主要参数是 FM 扫频速率,而不是 FM 时长。新的和值得注意的是,存在对调频(FM)刺激时长具有反应选择性的下丘脑中(IC)神经元的报告,但仍不清楚这些细胞是调谐到 FM 时长还是 FM 扫频速率。为了消除这些假设,我们向神经元呈现了具有系统带宽变化的可变时长 FM 信号。贝叶斯模型比较表明,大多数时间选择性中脑细胞调谐到 FM 扫频速率,而不是 FM 时长。