Parvalbumin neurons, temporal coding, and cortical noise in complex scene analysis

Cortical representations underlying many cognitive abilities emerge from underlying circuits with several different cell types. However, cell type-specific contributions to rate and timing-based 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 which are highly dynamic in time and compete with stimuli at other spatial locations. PV neurons play a fundamental role in balancing excitation and inhibition in cortex and sculpting cortical temporal dynamics; yet their specific role in encoding complex scenes via timing-based codes, and the robustness of temporal representations to spatial competition, has 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 spike-distance metrics, to dissect PV neurons’ contributions 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, over a wide range of time-scales. Our findings suggest that PV neurons play a critical role in enhancing cortical temporal coding and reducing cortical noise, thereby improving cortical representations of dynamic stimuli in complex scenes. Significance Statement One impressive example 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 a variety of impairments, e.g., hearing impairments, ADHD, and autism. The brain mechanisms underlying complex scene analysis remain poorly understood. Here, we recorded neural activity in auditory cortex in a complex auditory scene. When we suppressed PV neuron activity in auditory cortex, cortical performance decreased, and the timing of cortical responses was degraded. Our findings suggest that PV neurons improve the brain’s ability to analyze complex scenes by enhancing the timing of cortical responses while reducing cortical noise.