恒频-调频蝙蝠下丘神经元的恢复周期决定声脉冲跟随率

为探究恒频-调频蝙蝠下丘神经元恢复周期特点及其对声脉冲跟随率的影响，实验采用模拟的大蹄蝠(Hipposideros armiger)自然状态下的恒频-调频发声信号为声刺激，在5只听力正常的大蹄蝠上记录了下丘神经元的声反应和恢复周期(n = 93)．结果发现，根据神经元恢复率达50%时的双声刺激间隔(inter pulse interval，IPI)，可将其分为长时恢复型(long recovery，LR；47.4%)、中等时间恢复型(moderate recovery，MR；35.1%)和短时恢复型(short recovery，SR；17.5%)．每种类型依据其恢复率随IPI增加而呈现的不同变化又可进一步分为单IPI反应区神经元，多IPI反应区神经元，以及单调IPI反应神经元．LR，MR和SR型神经元恢复率达50%时的平均IPI分别为(64.0 ± 24.8)，(19.6 ± 5.8)和(7.1 ± 2.4) ms (P < 0.001)，相对应的平均理论每秒声脉冲数分别为(18.2 ± 7.0)，(55.4 ± 15.7)和(171.3 ± 102.9) Hz (P < 0.001)．结果提示，单IPI和多IPI反应区神经元具有特殊IPI反应特性，能对蝙蝠捕食和巡航期间所处的时相做出准确判断，而单调IPI反应神经元对IPI变化的敏感性较强，但时相判断性较差．另外LR，MR和SR型神经元恢复周期和理论脉冲跟随率的平均结果均能与这种蝙蝠回声定位期间3个时相的发声行为相匹配，且神经元恢复周期参与决定声脉冲跟随率，满足了蝙蝠巡航、捕食的行为学需要．

Recovery Cycle of Inferior Collicular Neurons Determine Pulse Following Rate in CF-FM Bat

The characteristics of recovery cycles in inferior collicular (IC) neurons of leaf-nosed bat (Hipposideros armiger) and effect of the recovery cycle on the following pulse repetition rate were studied using mimic CF-FM sound stimuli emitted by free flying bat. Recovery cycle of 93 IC neurons were obtained from IC of five bats with normal hearing. These neurons were classified into three types, i.e. long recovery (LR, 47.4%), moderate recovery (MR, 35.1%), and short recovery (SR, 17.5%), according to their inter pulse interval (IPI) (ms) of 50% recovery under two CF-FM sound stimulation condition. Each type of the neurons could also be categorized into different sub-types according to changes induced by IPI increasing such as single-IPI response area neurons, multi-IPI response area neurons, and monotonic-IPI response neurons. Mean IPIs of 50% recovery of LR, MR, and SR neurons were (64.0 ± 24.8), (19.6 ± 5.8), and (7.1 ± 2.4) ms, respectively (P < 0.001). The calculated theoretically following pulse repetition rate (pulse per second, Hz) of LR, MR, and SR neurons by mean IPI of 50% recovery for each type were (18.2 ± 7.0), (55.4 ± 15.7), and (171.3 ± 102.9) Hz, respectively (P < 0.001). These three types of IC neurons were well corresponding to their three hunting phases, search, approach, and catch phases. The sub-types of single-IPI response area neurons and multi-IPI response area neurons had hunting phase selectivity, and sub-type of monotonic-IPI response neurons had well sensitivity to IPI change, but their hunting phase selectivity was of a sort. These results demonstrated that recovery cycle of IC neurons determined the ability to follow pulse repetition rate and matched this bat's echolocation behavior.