Variations Of Masking And Recovery Cycle Induced By Different Sound Stimulus Patterns In Inferior Collicular Neurons

Using the excellular recording method under free field stimulation condition,we studied the response property of 289 inferior colliculus neurons of mouse(Mus musculus Km),and bats(Pipistrellus abramus) to different sound stimulus pattern.We measured the forward masking,recovery cycle,frequency tuning of IC neurons.The obtained results are summarized as following:1.The forward masking induced by weak noise(masker) could sharpen frequency tuning curves(FTC) of most IC neurons(P<0.01,n=25) in mouse and this effect increased with masker duration increasing(P<0.05).By calculating the inverse-slope(IS) of both limbs on FTC,we found the inhibitory rate caused by forward masking to high limb of FTC was notably higher than low limb of FTC.Most IShigh of FTC was decreased with masker duration increasing(P<0.01),however,there was no a regular change in IS_low of FTC.The masker could also increase the minimum threshold(MT) of response to probe sound in IC neurons(P<0.001,n=31) and this threshold up-shift was elevated with masker duration increasing.2.After BIC application to 33 IC neurons by ionophoresis,the neural inhibition induced by 40-ms masker(weak noise) was decreased or compltely cancelled and the percent change of Q₁₀ and Q₃₀ of FTCs decreased from 26.15±18.52%to 13.21±8.85% and 39.85±24.27%to 17.89±13.78%,respectively.Under the 80-ms masker stimulation condition,BIC application caused the percent change of Q₁₀ and Q₃₀ decreasing from 33.57±16.24%to 15.62±7.51%and 52.64±23.61%to 26.98±12.77%,respectively.These results showed that GABAergic disinhibition by BIC application could partly or compeletly remove the masking caused by masker(weak noise).3.During hunting,the insectivorous bats can analyze echo of their emitted sound signal and extrac information from echo,which is used to guide their prey.Therefore,the neurons in brain of bats must have an ability to generate the response to the pulse-echo (P-E) pairs.By delivering P-E pairs at three amplitude differences and three durations, we examined the recovery cycle of bat's IC neurons under each amplitude difference and three duration conditions.Nine recovery cycles were plotted for each neuron.The recovery cycle of these IC neurons prolonged with the duration increasing at the amplitude difference of 0 dB(one-way ANOVA,p<0.05) and 10 dB(one-way ANOVA,p<0.01),but this phenomenon was not observed at the amplitude difference of 20 dB(one-way ANOVA,p>0.05).These results demonstrated that the duration of P-E pairs and amplitude difference between P-E pairs could affect the recovery cycle of IC neurons and there was a correlation between the duration and amplitude difference.4.The sound duration was both a basic sound parameter and one kind of the sound information to be extracted by central auditory neurons.In order to further analyze effect of sound duration and amplitude of P-E pairs on the recovery cycle of IC neurons,we examined that IC neurons having the best duration of 1-2 ms had the shortest recovery cycle at amplitude difference of 10 dB under P-E pair stimulation condition with 1.5-ms duration.The IC neurons having the best duration of 4-6 ms had the shortest recovery cycle at the amplitude differences of 10 and 20 dB under P-E pair stimulation condition with 4-ms duration.The IC neurons having the best duration of 8-20 ms had the shortest recovery cycle at the amplitude differences of 20 dB under P-E pair stimulation condition with 10-ms duration.These results suggested that the different IC neurons had the different best duration and the duration selectivity of IC neurons could modulate their recovery cycles,which fitted to accept the echo of different repetition rate and duration and process echo information through temporal integration and neural modulation.