普氏蹄蝠下丘单反应和双反应神经元加工多普勒频移补偿信号的特点及生理机制

The Response Properties and Physiological Mechanism of Processing Doppler-shift Compensation Signal of The Single-on and Double-on Neurons in The Inferior Colliculus of Hipposideros pratti

恒频-调频(constant frequency-frequency modulation,CF-FM)蝙蝠独特的多普勒频移补偿(Doppler-shift compensation,DSC)行为可保证其对回声信息的精确提取.那么听中枢加工DSC信号的适应性机制是什么?本实验模拟CF-FM蝙蝠DSC后的回声定位信号,研究下丘(inferior colliculus,IC)神经元加工DSC信号的特点及生理机制.实验共获得117个IC神经元,在CF-FM声刺激下,神经元表现为single-on(SO,n=83)和double-on(DO,n=34)两种反应模式.无论是在蝙蝠的正向还是负向补偿过程中,SO和DO神经元对回声反应恢复到50%时的双声刺激间隔(inter-pulse interval,IPI)值,均会随补偿条件的改变而发生变化.当双声刺激由无补偿转变为最佳补偿条件时,两类神经元的50%IPI显著缩短(P<0.001),但SO神经元50%IPI缩短率超过70%的神经元数目较DO神经元多,且偏好正向补偿的IC神经元中,SO神经元的平均DSC范围也要显著宽于DO神经元(P<0.05).该研究结果提示,IC中SO神经元可能较DO神经元更能充分利用蝙蝠DSC行为,来提高对回声反应的恢复能力,以最大程度地获取猎物信息并准确判断与猎物的相对速度.

The special Doppler-shift compensation（DSC） behavior of the constant frequency-frequency modulation（CF-FM） bats ensures accurate extraction information of echo. Then how the auditory center of bats to process the echo after DSC behavior, and what is the adaptive physiological mechanism？ In this study, we simulated the echolocation signal of the CF-FM bat in the DSC behavior, and studied the response properties and physiological mechanism of the inferior collicular（IC） neurons in processing the DSC information. A total of 117 IC neurons were recorded, and under the CF-FM sound stimulation, these neurons showed two response patterns of single-on（SO, n = 83） and double-on（DO, n = 34）, the former type only discharged impulses to the onset of CF-FM sounds, and the latter type discharged impulses to the onset of both CF and FM components of CF-FM sound. The results also showed that whatever the bat processed the positive DSC signal or negative DSC signal, the50% inter-pulse intervals（50% IPIs, i.e. 50% recovery time of response to echo）of SO and DO neurons were significantly shortened（P 〈 0.001） and concentrated in the short recovery region when the paired sounds were changed from the uncompensated condition to the best compensated condition. Moreover, the number of SO neurons whose rate of shortening of 50% IPI exceeded 70% was larger than that of DO neurons, and among those IC neurons which preferred positive DSC, the mean DSC selective range of SO neurons was also significantly wider than that of DO neurons. The above results suggested that SO neurons among IC neurons might make better use of bat’s DSC behavior than DO neurons do to improve the response to echo so as to obtain the information of prey to the maximum and determine its relative velocity with the prey.