Tonotopy is not preserved in a descending stage of auditory cortex
Previous studies based on layer specificity suggest that ascending signals from the thalamus to sensory neocortex preserve spatially organized information, but it remains unknown whether sensory information descending from sensory neocortex to thalamus also maintains such spatial organization pattern. By focusing on projection specificity, we mapped tone response properties of two groups of cortical neurons in the primary auditory cortex (A1), based on the relationship between their specific connections to other regions and their function in ascending (thalamocortical recipient, TR neurons) or descending (corticothalamic, CT neurons) auditory information. A clear tonotopic gradient was observed among TR, but not CT neurons. Additionally, CT neurons exhibited markedly higher heterogeneity in their frequency tuning and had broader bandwidth than TR neurons. These results reveal that the information flow descending from A1 to thalamus via CT neurons does not arrange tonotopically, suggesting that the descending information flow possibly contributes to higher-order feedback processing of diverse auditory inputs.