Visual-cortex-projecting neurons in mouse auditory cortex show distinct audiovisual responses independent of motor-related activity

Cells in mouse primary visual cortex (V1) not only respond to visual stimulation, but also to sound. Part of this auditory modulation likely originates from auditory cortex (AC). Yet, the circuit-level functionality of the AC-to-V1 projection remains poorly understood. Here we performed acute in vivo high-density recordings in mouse AC during auditory, visual, and audiovisual stimulation, identifying AC-to-V1 projecting neurons by optogenetic tagging. Compared to non-tagged neurons, AC-to-V1 neurons more often responded to auditory, visual, or audiovisual stimuli. Furthermore, most AC-to-V1 neurons responded to specific sound frequencies; a modest but significant fraction was selective for visual orientations. These results could not be explained by motor responses or single-neuron variations in firing rate, cortical recording depth, or waveform type. These findings show that AC-to-V1 neurons carry sensory-specific signals, as opposed to nonspecific modulations, and exhibit distinctive response profiles compared to non-tagged AC neurons.