NEURONAL CIRCUITS SUPPORTING LEARNING-DRIVEN CHANGES IN AUDITORY PERCEPTION. Learning to discriminate sounds in noise is fundamental to auditory processing and is critically important for everyday communication and navigation. Both the auditory thalamus and the auditory cortex have been shown as involved in detection of sounds in noise, yet how the microcircuits within intra-cortical, cortico-thalamic and intra- thalamic interactions facilitate detection of signal in noise remains unknown. Our goal is to close this gap in knowledge and determine whether and how multiple microcircuits within the cortico-thalamic loop, including excitatory-inhibitory circuits within the primary auditory cortex; feedback loop between the auditory cortex and the lemniscal and non- lemniscal auditory thalamus; and the cortical feedback via the inhibitory thalamic reticular, contribute to the learning- driven improvement in auditory perception in noise. We will train mice to detect or discriminate between auditory targets in noise using operant conditioning. Detecting and discriminating sounds in noise activates multiple processes, including selective adaptation to background noise and learned amplification of the target representation. We will change noise contrast prior to target presentation to test how contrast adaptation interacts with target detection. We will record the neuronal responses in the cortical and sub-cortical regions during behavior, and use temporally precise, cell specific manipulations to establish the circuit that allows the mouse to learn and carry out this complex task. We will implement a novel generalized linear-non-linear model to continuously estimate gain adaptation in neuronal responses to test whether and how the distinct microcircuits adapt to contrast, detect the target and control neuronal gain. Combined, our results will reveal novel circuit-level mechanisms for hearing in noise across micro-circuits within the cortico-thalamic loop.