# Cortical Circuits of Interhemispheric Communication

> **NIH NIH SC1** · UNIVERSITY OF TEXAS SAN ANTONIO · 2020 · $294,000

## Abstract

PROJECT SUMMARY/ABSTRACT
Auditory interhemispheric communication remains a neurobiological mystery. Processing of auditory signals at
cortical level requires coordination of sensory input between the two hemispheres. Abnormal circuitry
underlying interhemispheric communication may explain deficits in communication and social behavior
observed in autism spectrum disorders (ASD) and auditory verbal hallucinations (AVH), one of the most
prominent symptoms in schizophrenia, affecting approximately 70% of patients. However, the organization and
functionality of these circuits remain unclear. The inferior colliculus (IC) is a major processing center in the
auditory pathways. Particularly, IC is a major center for processing of information used in localizing sound
sources in space. Importantly, a subset of neurons, in the layer 5 of the auditory cortex (AC), project to the IC
(CCol neurons) and to the contralateral AC (CCort neurons). Callosal projections to layer 5 cells originate in
layer 2/3 and layer 5 of AC. Determining the functional effects and connectivity of layer 2/3 and layer 5
callosal projections onto these neurons is critical for understanding auditory processing at both
cortical and subcortical levels.
The objective of this proposal is to dissect if both layers have a similar effect on the contralateral cortex. In
particular, both layers could excite CCol and inhibit CCort neurons. Alternatively, layer-specific stimulation
could have differing effects on layer 5 neurons, and a different balance of input to CCol and CCort neurons
contributing to different responses of these neurons. Our findings will establish a new framework for
understanding the roles of layer 2/3 and layer 5 callosal projections in the modulation of cortical and subcortical
auditory processing required for the continuity of sensory input between the two hemispheres.
The aims of this proposal are (1) Determine the synaptic organization of layer 2/3 and layer 5 callosal
projections onto CCort and CCol neurons in AC. (2) Establish the synaptic mechanism of callosal disynaptic
inhibition onto CCort and CCol neurons in AC. (3) Determine tone-evoked responses in AC during optogenetic
stimulation of layer 2/3 and layer 5 callosal projections. The approach for addressing these aims will use the
mouse as the experimental model, retrograde and optogenetic labeling, specific opto-physiological recordings
of synaptic connectivity in defined pathways, and in vivo electrophysiology to quantify the excitatory and
inhibitory component of the interlaminar, intralaminar, and the subclass projection specificity of the neurons
recruited during photoactivation of the callosal projections. Discoveries from this work will be significant
because they will provide foundational knowledge regarding circuit and functional aspects of AC neurons
contributing to interhemispheric communication which is clinically relevant to cortical neuropathologies.

## Key facts

- **NIH application ID:** 9888369
- **Project number:** 5SC1GM122645-04
- **Recipient organization:** UNIVERSITY OF TEXAS SAN ANTONIO
- **Principal Investigator:** Alfonso J Apicella
- **Activity code:** SC1 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $294,000
- **Award type:** 5
- **Project period:** 2017-04-10 → 2022-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9888369

## Citation

> US National Institutes of Health, RePORTER application 9888369, Cortical Circuits of Interhemispheric Communication (5SC1GM122645-04). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/9888369. Licensed CC0.

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