Top-down mechanisms underlying contextual and adaptive processing in the auditory system - PROJECT SUMMARY Sensory environments are cluttered and dynamic, with salient features 1) often masked or degraded by other stimuli and 2) capable of holding multiple meanings depending on the surrounding context. To account for this variability, sensory systems must process information in an adaptive manner by using contextual cues and prior information to bias incoming sensory information. Though this flexibility is critical for accurate sensory processing, the mechanisms underlying adaptive processing remain poorly understood. Descending projections from hierarchically higher brain regions to lower regions are a hypothesized anatomical substrate for top-down modulation of incoming sensory information. In the central auditory system, descending connections from the auditory cortex target numerous subcortical structures and these cortico-fugal pathways have been implicated in top-down processes such as predictive coding and attentional modulation of speech in noise. Specifically, projections from the auditory cortex have been found to carry contextual information about sound statistics to the auditory midbrain, or inferior colliculus, and to enhance responses to degraded sounds in the auditory thalamus, or medial geniculate body. Though these cortico-fugal pathways have been implicated in contextual processing and perceptual adaptation to degraded sounds, the broader circuit and physiological mechanisms underlying these phenomena remain unknown. Therefore, the goal of this proposal is to 1) determine the mechanisms by which cortico-fugal neurons enable contextual processing, with the hypothesis that they induce receptive field plasticity in IC neurons, 2) determine if top-down inputs alter context-dependent network reorganization, and 3) test how top-down circuits mediate adaptation to challenging listening conditions at the physiological and network level. This proposal uses a combination of behavior, large-scale electrophysiology, two-photon calcium imaging, optogenetics, and network analysis methods to address these aims. The results of these studies will reveal the circuit and physiological mechanisms underlying auditory contextual processing and perceptual adaptation. The impact of these experiments extends beyond the auditory system, as it may reveal generalizable principles about adaptive processing and behavior.
