Effect Of Inhibitory Input Activated By Non-best Frequency Sound On Impulse And Latency Codings Of Sound Amplitude In Inferior Collicular Neurons

Sound amplitude, the same as frequency and duration, is an important sound information carrier. The interaction between excitation and inhibition is the basis of neural coding, representation, modulation and integration in mammal central auditory system. The sound evoked response and information processing could be modulated by excitatory and/or inhibitory inputs induced by synchronized non-best frequency tone stimulation condition. Using extracellular recording, the present study examined the response of inferior collicular (IC) neurons to different sound amplitude before and during giving synchronized non-best frequency tone stimulation condition in mouse (Mus musculus, KM). We also investigated the difference of amplitude cording by firing rate and response latency and the influence of synchronized non-best frequency tone stimulation condition on these two coding modes.Under free field stimulation condition, the rate-amplitude function and latency-amplitude function were recorded before and during synchronized non-best frequency tone stimulation condition. The results show:(1) The RAFs and LAFs of IC neurons could be classified into 3 types, i.e. monotonic, saturated and nonmonotonic; (2) During synchronized non-best frequency tone stimulation condition, the RAF curves were changed in 54.5% of the recorded IC neurons, inducing lower proportion of monotonic (38.6% Vs 13.6%) and saturated types (28.4% Vs 22.7%), and a higher proportion of non-monotonic (33.0% Vs 63.6%). However, the LAF curves in 69.3% of the recorded IC neuron type kept no change; (3)During synchronized non-best frequency tone stimulation condition, best amplitude (BAR), dynamic range (DRR) and slope (slopeR) for impulses firing rate code were significantly changed (P<0.01); but the BA (BAL), DR (DRL) and slope (slopeL) for latency code were not significantly changed (P>0.05); (4) Before and during synchronized non-best frequency tone stimulation condition, BAR and DRR were significantly higher than BAL and DRL (P<0.05), and slopeR was significantly lower than slopeL (P<0.05);(5) With the increasing of sound amplitude, the influence rate on firing rate (IRR) decreased monotonously (one-way ANOVA, P>0.05) in certain amplitude range (MT-MT+40 dB) induced by non-best frequency tone stimulation condition, but the IRR did not show any regularity at higher sound amplitude. While the influence rate on response latency (IRL) did not showed any regularity at all given amplitude(one-way ANOVA, P>0.05).In summary, the inhibitory inputs evoked by synchronized non-best frequency tone stimulation condition can improve the amplitude sensitivity of firing rate coding of IC neurons, and amplitude sensitivity coded by response latency is higher than firing rates before and during non-best frequency tone stimulation condition.