Abstract
Intensity and frequency are the two main properties of sound. The non-monotonic neurons in the auditory system are thought to represent sound intensity. The central nucleus of the inferior colliculus (ICC), as an important information integration nucleus of the auditory system, is also involved in the processing of intensity encoding. Although previous researchers have hinted at the importance of inhibitory effects on the formation of non-monotonic neurons, the specific underlying synaptic mechanisms in the ICC are still unclear. Therefore, we applied the in vivo whole-cell voltage-clamp technique to record the excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) in the ICC neurons, and compared the effects of excitation and inhibition on the membrane potential outputs. We found that non-monotonic neuron responses could not only be inherited from the lower nucleus but also be created in the ICC. By integrating with a relatively weak IPSC, approximately 35% of the monotonic excitatory inputs remained in the ICC. In the remaining cases, monotonic excitatory inputs were reshaped into non-monotonic outputs by the dominating inhibition at high intensity, which also enhanced the non-monotonic nature of the non-monotonic excitatory inputs.
Highlights
Intensity and frequency are two fundamental characteristics of an acoustic stimulus
When an inferior colliculus (ICC) neuron was loose patched by the pipette, we attempted to obtain the characteristic frequency (CF) of the cell by examining its spike TFR with a tone burst F-A scan
By obtaining the synaptic inputs using our voltage-clamp whole-cell recordings in ICC non-monotonic neurons, we found differences in the intensity-tuning properties of excitatory and inhibitory inputs; 41% of neurons received non-monotonic excitation, whereas their inhibitory inputs were monotonic
Summary
Intensity and frequency are two fundamental characteristics of an acoustic stimulus. The auditory system coding of sound intensity in people is not as well understood as its coding of frequency (Dean et al, 2005; Uppenkamp and Röhl, 2014). Neurons in the auditory system that differ from other sensory systems exhibit a monotonic change in stimulus intensity (the discharge rate of neurons increases with an increase in stimulus intensity) and a non-monotonic change. Because the intensity of a sound is often an important guide for behavior (Chen et al, 2012; Takeshima and Gyoba, 2013; Clemens et al, 2018) and non-monotonic neurons are rare in other sensory systems (Chapman et al, 2002; Peng and Van Essen, 2005; Peirce, 2007; Sofroniew et al, 2015), the underlying mechanisms of non-monotonic neurons in the auditory system have generated widespread interest
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