# Circuit Mechanisms for Auditory Processing in the Inferior Colliculus

> **NIH NIH R01** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2021 · $434,652

## Abstract

Abstract
The inferior colliculus (IC) is the midbrain hub of the central auditory system. Although the IC is a critical
processing center for speech, vocalizations, and other complex sounds, the neuronal mechanisms underlying
computations in the IC remain largely unknown. This gap in knowledge persists because it has proven difficult
to reliably identify specific classes of IC neurons. By combining molecular markers with anatomical and
physiological measures, we recently overcame this obstacle and have identified two novel classes of IC
principal neurons: vasoactive intestinal peptide (VIP) neurons and neuropeptide Y (NPY) neurons. VIP neurons
are excitatory, glutamatergic neurons, while NPY neurons are inhibitory, GABAergic neurons. Both VIP and
NPY neurons are stellate neurons with dendritic arbors that spread across the tonotopic axis of the central
nucleus of the IC (ICc), and both project to multiple brain regions, including the auditory thalamus. Because
they can sample input from a range of sound frequencies, it has long been hypothesized that ICc stellate
neurons play important roles in sound processing, but the functional roles of stellate neurons have previously
been inaccessible. By identifying VIP and NPY neurons, we possess the tools for the first time to selectively
target and manipulate an excitatory and an inhibitory class of ICc stellate neurons. The overall objective of this
proposal is to establish a functional wiring diagram for the inputs and outputs of VIP and NPY neurons and to
determine the differences in how VIP and NPY neurons respond to sounds. To pursue this objective, we will
use viral tract tracing, optogenetic circuit mapping, brain slice electrophysiology, and optogenetically-targeted
in vivo recordings. In Aim 1, we will identify the ascending sources of auditory input to VIP and NPY neurons
and determine how these inputs vary their synaptic strength during trains of activity. In Aim 2, we will identify
the long-range targets and terminal arborization patterns of VIP and NPY neurons and determine how synaptic
transmission from VIP and NPY neurons influences neurons in the auditory thalamus. In Aim 3, we will test the
hypothesis that excitatory VIP neurons and inhibitory NPY neurons differ in their responses to tones and noise
and to amplitude- and frequency-modulated sounds, stimuli that represent important features of speech and
other vocalizations. The expected outcome of this research is that we will determine for the first time how two
classes of ICc stellate neurons, one excitatory and one inhibitory, integrate ascending and descending auditory
input, influence long-range postsynaptic targets, and respond to simple and complex sounds. These results will
generate evidence-based hypotheses about how ICc stellate neurons contribute to sound processing and will
provide a launching point for investigations into the circuit computations that underlie speech and vocalization
coding in the midbrain.

## Key facts

- **NIH application ID:** 10188494
- **Project number:** 5R01DC018284-02
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Michael Thomas Roberts
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $434,652
- **Award type:** 5
- **Project period:** 2020-06-10 → 2025-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10188494

## Citation

> US National Institutes of Health, RePORTER application 10188494, Circuit Mechanisms for Auditory Processing in the Inferior Colliculus (5R01DC018284-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10188494. Licensed CC0.

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