| When constant frequency-frequency modulation(CF-FM)bats capture prey or avoid barrier,their echolocation signals change regularly.As the decrease of distance between bat and target,bats short the pulse duration and decrease the amplitude of call.Meanwhile,the echo delay short.Adjusting the frequency is more careful than other parameters of CFFM bats,even they evolved the Doppler-shift compensation(DSC)behavior.In other words,to overcome the Doppler-shift caused during the process of predation,bats will constantly adjust the frequency of pulse to ensure the echo frequency consistently maintain at the range of dominant frequency.Some behavioral studies show that the pulse-echo overlapping caused by shorting of pulse-echo delay is the stone of DSC behavior.But other studies do not support this view.Thus,the relationship between DSC and pulse-echo overlapping is still unclear.Therefore,this study uses extracellular recording method.Simulating the pulse and echo of CF-FM bats in natural,it is aimed to study the characteristics and physiological mechanism of IC neurons about how it is dealing with the echo which is overlapped by pulse under different DSC.A total of 21 1 IC neurons were obtained in this experiment.The depth,best frequency(BF),minimum threshold(MT),response latency(RL)and response duration(RD)are 118-4062(1835±750)μm,9.4-63.0(44.7± 12.5)kHz,0-100(54±27)dB SPL,6.5-33(14.7±4.8)ms and 0.5-23(5.9±3.8)ms,respectively.1.Analyzing the basic parameters of 211 IC neurons,we found that there are linear relations of IC neurons among BF,depth and MT,that is to say,with the increase of depth,BF increases gradually(p<0.001),and there is also a positive correlation between MT and BF(p<0.001).2.When analyzing the relationship among DSC,pulse-echo delay,and the recovery rate of IC neurons,it found,whatever pulse-echo delay,that the recovery rate of IC neurons under different DCS is significantly different(p<0.001).Specially,under every echo delay,the recovery rate of IC neuron for positive compensated 4kHz is higher than other frequency compensated condition.In addition,with the increase of compensation value of frequency,IC neurons can recover to same level with shorter echo delay.The when 3D reconstruct the echo response of these 107 neurons under different stimuli,it was found that there is an obvious peak for recovery when the positive compensate 4kHz and the delay is small(1ms～2ms).3.As the increase of DSC degree,the recovery rate of neurons increased even when the pulse and echo overlapped.Meanwhile,the bigger of the compensation degree is given,the smaller of the echo delay is required by the neuron to recover to the same level(20%).That is to say,IC neurons can better tolerate the overlapping and overcome the complexity of overlapping components of sound.4.107 IC neurons were divided into two groups by their BF inside or outside the second harmonic.Then we compared their recovery rate under different stimuli.The result showed that while the variation law of two groups are same,with the increased value of DSC and the reduced degree of overlapping the recovery rate increased gradually,the neurons whose BF inside 2nd harmonic can endure bigger overlapping degree of pulse and echo.Even when the value of compensation is relatively small(-2,+2 kHz),the endurance of the neurons in 2nd harmonic for overlapping degree can be as high as 91.7%,at which time CF and FM components of echo overlapped with the pulse.However,when the frequency compensation value increases to-4 or+4 kHz,neurons whose BF without 2nd harmonic can tolerate the overlapping of multiple sound components.To sum up,in order to overcome the negative effect of the overlap of pulse and echo,CF-FM bats can ensure the accurate extraction and efficient analysis of echo information by improving the DSC behavior.During this process,IC neurons which inside 2nd harmonic play a very important role in processing the covariant relationship between DSC and pulse-echo overlapping. |
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