Long-Duration Sound-Induced Facilitation Changes Population Activity in the Inferior Colliculus

Abstract

The inferior colliculus (IC) is at the midpoint of the auditory system and integrates virtually all information ascending from the auditory brainstem, organizes it, and transmits the results to the auditory forebrain. Its abundant, excitatory local connections are crucial for this task. This study describes a long duration sound (LDS)-induced potentiation in the IC that changes both subsequent tone-evoked responses and spontaneous activity. Afterdischarges, changes of spontaneous spiking following an LDS, were seen previously in single neurons. Here, we used multi-channel probes to record activity before and after a single, tetanic sound and describe the changes in a population of IC neurons. Following a 60 s narrowband-noise stimulation, a subset of recording channels (∼16%) showed afterdischarges. A facilitated response spike rate to tone pips following an LDS was also observed in ∼16% of channels. Both channels with an afterdischarge and channels with facilitated tone responses had higher firing rates in response to LDS, and the magnitude of the afterdischarges increased with increased responses to the LDS. This is the first study examining the effect of LDS stimulation on tone-evoked responses. This observed facilitation in vivo has similarities to post-tetanic potentiation in vitro as both manner of induction (strong stimulation for several seconds) as well as time-course of the facilitation (second to minute range) are comparable. Channels with and without facilitation appear to be intermixed and distributed widely in the central nucleus of IC, and this suggests a heretofore unknown property of some IC neurons or their circuits. Consequently, this sound-evoked facilitation may enhance the sound-evoked output of these neurons, while, simultaneously, most other IC neurons have reduced or unchanged output in response to the same stimulus.

Mice prone to tinnitus after acoustic trauma show increased pre-exposure sensitivity to background noise

“…The increased slope of growth functions for ABR amplitudes that we observed in +T mice would be consistent with this assumption (Koebis et al, 2019;but see Tziridis et al, 2015 for differences). Thus, intrinsic variability in the strength of GABAergic inhibition in the auditory pathway of mice could underlie the differential ability of their auditory circuits to adapt to prolonged background noise, and hence altered sensorimotor gating in +T mice (Ison and Silverstein, 1978;Swerdlow et al, 2000;Resnik and Polley, 2021;Burghard et al, 2022).…”