PV neurons and cortical temporal coding in complex scene analysis

Cortical representations underlying a wide range of cognitive abilities, which employ both rate and spike timing-based coding, emerge from underlying cortical circuits with a tremendous diversity of cell types. However, cell-type specific contributions to cortical coding are not well-understood. Here, we investigate the role of parvalbumin (PV) neurons in cortical complex scene analysis. Many complex scenes contain sensory stimuli, e.g., natural sounds, images, odors, or vibrations, which are highly dynamic in time and compete with stimuli at other locations in space. PV neurons are thought to play a fundamental role in sculpting cortical temporal dynamics; yet their specific role in encoding complex scenes via timing-based codes, and the robustness of such temporal representations to spatial competition, have not been investigated. Here, we address these questions in auditory cortex using a cocktail party-like paradigm; integrating electrophysiology, optogenetic manipulations, and a family of novel spike-distance metrics, to dissect the contributions of PV neurons towards rate and timing-based coding. We find that suppressing PV neurons degrades cortical discrimination of dynamic sounds in a cocktail party-like setting via changes in rapid temporal modulations in rate and spike timing. These findings suggest a critical role of PV neurons in cortical temporal coding underlying complex scene analysis. Significance Statement One of the most impressive examples of sensory perception by the brain is its ability to analyze complex scenes, e.g., following what a friend is saying at a party amongst other speakers. Although some humans can solve this problem with relative ease, it remains very difficult for humans with hearing impairments, ADHD, and autism; and assistive devices, e.g., hearing aids. The brain mechanisms underlying complex scene analysis remain poorly understood. We investigated this by recording neural activity in auditory cortex in a complex auditory scene. When we suppressed the activity of PV neurons, cortical performance decreased via changes in response timing. Our findings suggest that PV neurons improve the brain’s ability to analyze complex scenes by enhancing cortical response timing.