Orthogonal spectral and temporal envelope representation in auditory cortex

Speech perception relies on two fundamental acoustic components: spectral and temporal. While spectral information is known to be represented in the auditory cortex through tonotopy, how temporal features are organized has remained unclear. Here, by varying rise-ramp steepness and frequencies, we reveal that the steepness of the temporal envelope—a critical cue for phonemes discrimination and sound source perception—is systematically mapped in the mouse auditory cortex. Using widefield calcium imaging, we discovered that the envelope steepness is represented orthogonally to the tonotopic axis, forming a two-dimensional cortical map that mirrors the dual structure of sounds. This organization was observed in primary-like auditory regions but not in higher-order-like areas, indicating distinct auditory processing streams. These findings uncover a principle of cortical organization, suggesting that the auditory cortex encodes sound along two independent axes and thereby provides a neural basis for parallel processing for complex sounds such as speech and natural acoustic environments.