Dichotomy of functional organization in the mouse auditory cortex

The sensory areas of the cerebral cortex possess multiple topographic representations of sensory dimensions. Gradient of frequency selectivity (tonotopy) is the dominant organizational feature in the primary auditory cortex, while other feature-based organizations are less well established. We probed the topographic organization of the mouse auditory cortex at the single cell level using in vivo two-photon Ca(2+) imaging. Tonotopy was present on a large scale but was fractured on a fine scale. Intensity tuning, important in level-invariant representation, was observed in individual cells but was not topographically organized. The presence or near-absence of putative sub-threshold responses revealed a dichotomy in topographic organization. Inclusion of sub-threshold responses revealed a topographic clustering of neurons with similar response properties, while such clustering was absent in supra-threshold responses. This dichotomy indicates that groups of nearby neurons with locally shared inputs can perform independent parallel computations in ACX.