| Echolocation bats can judge their surroundings by analyzing the echoes.Among them,constant frequency-frequency modulation(CF-FM)bats use Doppler-shift compensation(DSC)behavior to ensure accuracy of echo frequency analysis during flight.Constant frequency component of echo frequency is very important for bats to better process frequency information,but few people pay attention to the effect of frequency compensation on the analysis of echo frequency in the central auditory.Its physiological mechanism is not clear.Therefore,we take CF-FM bat(Hipposidero spratti)as the research object,we simulate the pulse-echo effect of DSC in bats and use extracellular recording technology,and explore the effect of frequency compensation on inferior colliculus(IC)neurons processing echo frequency information.The main results are as follows:(1)149 IC acoustically sensitive neurons were recorded in the experiment.It was found that BW10%(6.5±6.3 VS 8.7±6.7 kHz,P<0.001)and BW50%(3.9±4.5 VS 5.3±4.9 kHz,p<0.001)of the frequency spike curve of IC neurons after DSC were significantly increased,and the corresponding frequency points(BF)of the maximum spike of most 149 IC neurons(79.2%,118/149)were broadened to one frequency band.The results showed that DSC broadened the FSC of IC neurons.(2)After DSC,the frequency of the maximum spike of neurons was almost unchanged(40.2± 12.2 VS 40.3± 12.2,p>0.05),but the maximum spike of neurons increased significantly(21.3± 12.3 VS 31.9±16.5,p<0.001),suggesting that neurons can obtain more accurate target and environmental information by increasing the number of neurons after DSC.(3)There was no significant difference between the Upper-slope and Lower-slope of IC neurons(10.8± 11.1VS 11.4± 11.2 kHz-1,p>0.05,no compensation)under any two-tone stimulation(11.1±11.6 VS 13.2±11.9 kHz-1,p>0.05,the best compensation).However,compared with no compensation condition,Lower-slope of neuronal FSC increased significantly after DSC(11.4±11.2 VS 13.2±11.9 kHz-1p<0.05),while Upper-slope did not change significantly(10.8±11.1 VS 11.1±11.6 kHz-1,p>0.05).The results show that the effect of DSC on the frequency analysis of neurons mainly occurs at the low-frequency band,and the sensitivity to the frequency analysis of echoes can be enchanced by increasing Lower-slope.(4)For PCA-neuron and NCA-neuron,it was found that although BW10%and BW50%of PCA-neuron and NCA-neuron increased after DSC,the effects of DSC on Upper-slope and Lower-slope of these two types of neurons were different.PCA-neuron's Lower-slope increased significantly(11.4±11.7 VS 14.0±11.5 kHz-1,p<0.05),Upper-slope did not change(10.6±11.4 VS 11.2±11.7 kHz-1,p>0.05),while NCA-neuron's Lower-slope(11.4± 10.6 VS 12.1 ± 12.4 kHz-1,P>0.05)and Upper-slope(12.8±17.4 VS 11.0±11.5 kHz-1,p>0.05)did no change.Combining with the results of behavioral studies,it is inferred that positive DSC often occurs in the critical period when bats approach and catch prey,so bats need to take advantage of the increased slope of PCA-neuron to enhance their frequency sensitivity in order to accurately perceive the target information.In conclusion,bat DSC behavior can obtain more target and environmental information by increasing the spike of IC neurons and broadening the frequency response field of neurons.It can also improve the sensitivity of echo frequency analysis by increasing the Lower-slope of the frequency spike curve.In addition,PCA-neuron may play a more important role in IC than NCA-neuron in analyzing echolocation signals after DSC. |
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