Forward Masking Effects Of Static And Dynamic Frequency Maskers On The Response Of Inferior Collicular Neurons In Mouse

In this study, two-tone stimulus paradigm with inter-pulse interval of 50 ms was used and two kinds of maskers, static frequency masker (tone burst) and dynamic frequency masker (up-sweep frequency modulation sound) , were delivered to the animal before the probe under free field stimulation conditions. The probe was tone burst(TB) and its frequency was the same as neuronal characteristic frequency (CF) . The effects of different maskers on the minimum threshold (MT), response latency, dynamic range ( DR ) and firing rate of the mouse inferior colliculus (IC ) neurons were observed in the experiment.20 healthy adult mice (20-25 g. b.wt.) with normal hearing were used in this study without consideration of sex. A total of 133 inferior colliculus neurons were recorded before and during the application of the masker, 113 of them had complete data. The results showed that: (1) The characteristic frequency of IC neurons of house mouse was increased with increasing recording depth, and the masker intensity used was positive relevant to the IC neurons' minimum threshold. When the minimum threshold was high, the masker intensity needed was loud, vice versa. (2) According to the masking rate at MT+10dB of IC neurons to frequency modulation and tone burst, the IC neurons were classified as three types: type I neurons ( 72/113, 63.7% ) , in which the masking effect of TB was better than frequency modulation (FM) ;type II neurons (32/113, 28.3%) , in which the masking effects of the two maskers were same; type III neurons( 9/113, 8.0% ) , in which the masking effect of FM was better than TB. (3) Type I neurons, the minimum threshold of which was low, but the Q₁₀ and DR values of which were large; in type III neurons, the minimum threshold was high, the Q₁₀ and DR values were narrow; in type III neurons, the MT Q₁₀ and DR values were in between. (4) Both FM and TB could make the MT of type I neurons shift upward distinctively, but the effect of TB was more significant than FM. (5) The Q₁₀ values of type I neurons became narrower under the influence of TB, were unaffected under the influence of FM. There was evident difference between TB and FM. (6) Both FM and TB could cause significant reduction of DR values on the neurons of type I, but the effect of TB was more evident. (7) Both FM and TB could lengthen the response latencies of type I neurons, and TB's effect was more significant. (8) Increasing the probe's...