Cortical mechanisms for contrast gain control in auditory perception in noise.

PROJECT SUMMARY Cortical mechanisms for contrast gain control in auditory perception in noise. Everyday natural auditory environments are variable, ranging from quiet beaches to raging waterfalls. In order to identify and robustly encode important sounds like speech from the background noise, the auditory system

needs to flexibly adapt to the current environment. One way the auditory system does this is by modifying neuron response properties according to the statistics of the auditory environment. Neurons in the primary auditory cortex (A1) adapt response function slope (gain) to account for changes in auditory variability (contrast). This

gain adaptation process is associated with corresponding changes in perceptual sensitivity. The mechanisms driving this process are still unknown. The goal of this proposal is to identify the circuit mechanisms responsible for contrast-dependent perceptual changes and neuronal gain adaptation in A1. In addition

to excitatory neurons, A1 comprises many types of inhibitory interneurons. Two subtypes, parvalbumin-positive (PV) and somatostatin-positive (SST) interneurons, are capable of shaping the gain of their surrounding excitatory neurons. We hypothesize that PV and SST neurons work together to differentially adapt neuron gain

to auditory contrast. We will first test this hypothesis by establishing whether PV and SST neurons are sensitive to the environment’s contrast. Using electrophysiological recordings with optotagging, we will record PV and SST neuron activity in mouse A1. Next, we will test whether SST and PV activity drives the perceptual sensitivity

changes associated with gain adaptation. By optogenetically perturbing PV and SST activity in A1 of mice performing target-in-noise detection tasks with variable stimulus contrasts, we will quantify the relative contributions of PV and SST neurons to perceptual sensitivity changes. Together, these results will characterize

the roles of inhibitory cortical circuits in adaptation to the current auditory environment, deepening our understanding of effective auditory processing in noisy environments.