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.

Public Health Relevance

Acceptable social behavior including speech communication and production relies on proper interhemispheric communication. This proposed research aims to increase the understanding of the circuits and patterns of neuronal activity, giving rise to mental experience and behavior by dissecting auditory cortex (AC) circuits associated with interhemispheric communication. Particularly, this research will reveal fundamental mechanisms of interhemispheric communication in AC that are relevant for understanding pathology of AC circuitry that contributes to abnormal social behavior observed in autism spectrum disorders, schizophrenia, and other neuropathology affecting central auditory processing disorder.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Enhancement Award (SC1)
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Special Emphasis Panel (ZGM1)
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Krasnova, Irina N
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University of Texas Health Science Center San Antonio
Schools of Arts and Sciences
San Antonio
United States
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Zurita, Hector; Feyen, Paul L C; Apicella, Alfonso Junior (2018) Layer 5 Callosal Parvalbumin-Expressing Neurons: A Distinct Functional Group of GABAergic Neurons. Front Cell Neurosci 12:53
Zurita, Hector; Rock, Crystal; Perkins, Jessica et al. (2018) A Layer-specific Corticofugal Input to the Mouse Superior Colliculus. Cereb Cortex 28:2817-2833