Spectral Contrast and Context Preference in the Auditory Cortex Is Shaped by Specific Inhibitory Neuron-Based...

The neurons in the primary auditory cortex show sensitivity to rare sound objects that are of behavioral significance. Mechanistic models based on synaptic depression can explain some aspects of this phenomenon, along with predictive processing mechanisms. Synaptic depression can only explain selectivity toward pure frequency tones, based on the tonotopic hierarchical arrangement found across the auditory pathway. In the present study, we have used an oddball presentation of stimuli with different spectral contents to study the selectivity toward specific spectral shapes of auditory stimuli. We used the metric of auditory contrast as a measure of heterogeneity in the spectral shape. We performed in vivo electrophysiology in the primary auditory cortex of adult mice and found selectivity shown by the neurons toward specific spectral shapes of relatively high- or low-contrast values. This selectivity was further dependent on the context of the stimulus presentation. Estimation of functional connectivity using pairwise noise correlation revealed the differential connectivity within the local circuitry shown by neurons preferring spectral shapes of different contrast values in different contexts. Furthermore, we also studied the heterogeneity across the population data using the Jaccard index and found a higher degree of heterogeneity among populations that prefer spectral shapes with low-contrast values. Using 2-photon Ca²⁺ imaging, we investigated the role of two inhibitory interneuron types, namely, the parvalbumin-expressing (PV) and somatostatin-expressing (SOM) interneurons, in modulating the selectivity for spectral shapes. We found that selective inhibitory neurons form selective subnetworks with specific excitatory neurons, and their coordinated activity plays an important role in encoding for the spectral shape and context information in the auditory stimuli.