Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, US.
Adv Exp Med Biol. 2013;787:353-61. doi: 10.1007/978-1-4614-1590-9_39.
Both the performance of cochlear implant (CI) listeners and the responses of auditory neurons show limits in temporal processing at high frequencies. However, the upper limit of temporal coding of pulse-train stimuli in the inferior colliculus (IC) of anesthetized animals appears to be lower than that observed in corresponding perceptual tasks. We hypothesize that the neural rate limits have been underestimated due to the effect of anesthesia. To test this hypothesis, we developed a chronic, awake rabbit preparation for recording responses of single IC neurons to CI stimulation without the confound of anesthesia and compared these data with earlier recordings from the IC of anesthetized cats. Stimuli were periodic trains of biphasic pulses with rates varying from 20 to 1,280 pulses per second (pps). We found that the maximum pulse rates that elicited sustained firing and phase-locked responses were 2-3 times higher in the IC of awake rabbits than in anesthetized cats. Moreover, about 25 % of IC neurons in awake rabbit showed sustained responses to periodic pulse trains at much higher pulse rates (>1,000 pps) than observed in anesthetized animals. Similar differences were observed in single units whose responses to pulse trains were monitored while the animal was given an injection of an ultrashort-acting anesthetic. In general, the physiological rate limits of IC neurons in awake rabbit are more consistent with the psychophysical limits in human CI subjects compared to the data from anesthetized animals.
在高频时，人工耳蜗（CI）使用者的表现和听觉神经元的反应都显示出在时间处理方面存在限制。然而，麻醉动物下丘脑中（IC）脉冲串刺激的时间编码上限似乎低于在相应的感知任务中观察到的上限。我们假设，由于麻醉的影响，神经率限制被低估了。为了验证这一假设，我们开发了一种慢性、清醒的兔子准备，用于记录单个 IC 神经元对 CI 刺激的反应，而不受麻醉的干扰，并将这些数据与之前从麻醉猫的 IC 中记录的数据进行了比较。刺激是具有从 20 到 1280 脉冲/秒（pps）变化的双相脉冲周期性串。我们发现，在清醒的兔子中，引起持续放电和锁相反应的最大脉冲率比麻醉猫中的高 2-3 倍。此外，大约 25%的清醒兔子的 IC 神经元在比麻醉动物中观察到的更高的脉冲率（>1000pps）下对周期性脉冲串表现出持续反应。在监测动物接受超短效麻醉剂注射时，对脉冲串的反应的单个单元中也观察到了类似的差异。一般来说，与来自麻醉动物的数据相比，清醒兔子的 IC 神经元的生理率限制更符合人类 CI 受试者的心理物理限制。
