The superior paraolivary nucleus shapes temporal response properties of neurons in the inferior colliculus
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The mammalian superior paraolivary nucleus (SPON) is a major source of GABAergic inhibition to neurons in the inferior colliculus (IC), a well-studied midbrain nucleus that is the site of convergence and integration for the majority ascending auditory pathways en route to the cortex. Neurons in the SPON and IC exhibit highly precise responses to temporal sound features, which are important perceptual cues for naturally occurring sounds. To determine how inhibitory input from the SPON contributes to the encoding of temporal information in the IC, a reversible inactivation procedure was conducted to silence SPON neurons, while recording responses to amplitude-modulated tones and silent gaps between tones in the IC. The results show that SPON-derived inhibition shapes responses of onset and sustained units in the IC via different mechanisms. Onset neurons appear to be driven primarily by excitatory inputs and their responses are shaped indirectly by SPON-derived inhibition, whereas sustained neurons are heavily influenced directly by transient offset inhibition from the SPON. The findings also demonstrate that a more complete dissection of temporal processing pathways is critical for understanding how biologically important sounds are encoded by the brain.
KeywordsAmplitude modulation Gap detection Superior olive Sound envelopes Temporal processing
This work was supported by NIH/National Institute on Deafness and Other Communication Disorders Grant RO1 DC-002266 to A.S.B. R.A.F. II was supported, in part, by training grant T32 GM081741 from the NIH/National Institute of General Medical Sciences to West Virginia University. A.K.M. was supported by the Swedish Research Council grants 80326601 and K2014-63X-22536-01-3.
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