| Presentation rate of sound stimulations (PR) is the parameter representing the energy and information received by animals in limited time. In our experiment, to study the effect of PR on the sound response properties of mouse inferior collicular (IC) neurons and the relationship between the neurons' ability to follow sound presentations and the duration as well as intensity of the sounds, the tones with different durations (10, 40 and 100 ms), intensities(5, 15, 25, 35, and 45 dB SPL above minimal threshold) at characteristic frequency(CF) of recorded neurons were presented to pentobarbital anesthetized mice (Mus musculus, Km) at different PR (0.5,1, 2, 3.3, 5, 7,10, and 20 Hz) under free field stimulation conditions.11 healthy adult mice (male or female) with natural hearing were used for this study and a total of 176 IC neurons were recorded. The PR at which the response changed to 50% in PR- normalized response function was defined as critical presentation rate(CPR), and the PR at which the neurons stopped firing was defined as maximal presentation rate(MPR). The results were as follows: 1) When the intensity of the stimulations was 5 dB SPL above MT and the duration was 40 ms, with the PR increasing, the sound response properties of most recorded neurons were dramatically influenced by changing the PR even within low PR range (< 3.3 Hz). The firing rate of the majority of neurons (87.3%, 103/118) monotonically decreased with the PR increasing, whereas in a smaller fraction of neurons (12.7%, 15/118)it non-monotonically varied. There was significant correlation between the firing rate and the PR (P < 0.01). 2) The discharge patterns in part of neurons (17.8%, 21/118) were transformed with the PR alteration. Many tonic responder (T) and phasic-burst responder (PB) were changed into the phasic responder (P). 3) The total number of neurons with CPR and MPR lower than 3.3 Hz were more than 70% (75.4%, 89/118) and 40% (44.9%, 53/118), respectively. 4) With the duration prolonging, the firing rates of the neurons changed in different patterns(increasing, decreasing, and non-monotonic). The proportion of neurons with low CPR and MPR (ranged from 0.5 to 3.3 Hz) increased, and the proportion of neurons with high CPR and MPR (higher than 6.7 Hz) decreased. 5) With the stimulus intensity increasing, thefiring rate of the majority of the neurons increased. 6) With the stimulus intensity increasing, the proportion of neurons with low CPR and low MPR decreased, while the proportion of neurons with high CPR and high MPR increased. The neurons with low CPR took a important part (38.5 %~ 90%) at these intensity.The results suggests that the sound response properties of IC neurons are closely correlated to the PR of sound stimulation even in relatively low PR range. The effect of the PR on sound response properties of auditory neurons could not be overlooked in hearing studies. Increasing intensity of sound stimulations could enhance the ability to follow the sound presentations of the most IC neurons. The effect of sound duration on the ability was various. Shortening the duration usually could enhance the ability. Properly shortening the duration and increasing the intensity of the sound generally favored the IC neurons to pool more information for neural processing and to represent sound information. The PR's effect on response of the IC neurons may be mainly ascribed to the neurons' excitability and the relationship between inhibitory input and excitatory input onto the IC neurons. The difference of the effect of PR on different neurons maybe reflected the neurons' diverse coding mechanisms and function. How PR, intensity, and duration of sound stimulations jointly affect the response of auditory neurons should be further studied.
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