Abstract
The inferior colliculus (IC) is known as a neuronal structure involved in the integration of acoustic information in the ascending auditory pathway. However, the processing of paired acoustic stimuli containing different sound types, especially when they are applied closely, in the IC remains poorly studied. We here firstly investigated the IC neuronal response to the paired stimuli comprising click and pure tone with different inter-stimulus (click-tone) intervals using in vivo loose-patch recordings in anesthetized BALB/c mice. It was found that the total acoustic evoked spike counts decreased under certain click-tone interval conditions on some neurons with or without click-induced supra-threshold responses. Application of click could enhance the minimum threshold of the neurons responding to the tone in a pair without changing other characteristics of the neuronal tone receptive fields. We further studied the paired acoustic stimuli evoked excitatory/inhibitory inputs, IC neurons received, by holding the membrane potential at -70/0 mV using in vivo whole-cell voltage-clamp techniques. The curvature and peak amplitude of the excitatory/inhibitory post-synaptic current (EPSC/IPSC) could be almost unchanged under different inter-stimulus interval conditions. Instead of showing the summation of synaptic inputs, most recorded neurons only had the EPSC/IPSC with the amplitude similar as the bigger one evoked by click or tone in a pair when the inter-stimulus interval was small. We speculated that the IC could inherit the paired click-tone information which had been integrated before reaching it.
Highlights
In the natural environments, acoustic stimuli are always performed in a temporal complicated context which is affecting their perception and processing in the brain
Tonotopic organization and sharp frequency tuning in the inferior colliculus (IC) have been widely studied in the cat (Aitkin et al, 1975; Semple and Aitkin, 1979; Serviere and Webster, 1981; Brown et al, 1997; Schreiner and Langner, 1997), gerbil (Ryan et al, 1982; Grana et al, 2017), monkey (FitzPatrick, 1975), bat (Zook et al, 1985; Poon et al, 1990), rat (Clopton and Winfield, 1973; Huang and Fex, 1986; Malmierca et al, 2008), mouse (Stiebler and Ehret, 1985), and human (De Martino et al, 2013; Ress and Chandrasekaran, 2013)
We found in this study that even on those IC neurons only having the supra-threshold responses to tones (i.e., “click −” neurons), the application of click could depress their tone responses (Figures 2C,D,F,F’)
Summary
Acoustic stimuli are always performed in a temporal complicated context which is affecting their perception and processing in the brain. Paired sounds are commonly adopted to investigate the effect of temporal context on the neuronal responses. Temporal separation of two sounds in a pair could affect the perceptual grouping causing the auditory stream segregation (Bregman, 1990) as well as determine the response to the second sound, i.e., forward masking/suppression (Calford and Semple, 1995; Moore, 1995; Brosch and Schreiner, 1997; Wehr and Zador, 2005). The neuronal processing and integration of paired acoustic information with different interstimulus intervals, especially being given nearly at the same time, are still unclear
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