BMI Progress Reports 2020 // Prof. Ramdya's Lab: Chin-Lin Chen - Uncovering behavioral information sent to the brain by ascending neurons

To achieve coordinated movements there must be a dynamic loop sending information between the descending command and ascending reporting systems. The command system – the brain –, has received the  most attention. However, little is known about higher-order ascending neurons (ANs) that integrate information from motor circuits. This is because the tissues in which motor circuits are located were inaccessible for recording in intact and behaving animals. We recently developed an approach permitting 2-photon functional imaging of the ventral nerve cord (VNC) of behaving adult Drosophila melanogaster. We are thus now able to focus on the kinds of behavioral information sent to the brain. We recorded activity from 75 driver lines labelling approximately 250 ANs to understand the correlation between behavior and AN activity by relating the calcium signal to limb motion class. Our preliminary results reveal that two thirds of ANs are activated during different behavioral states – walking, grooming, and standing. One third of the ANs did not show any activity. Among responsive ANs, about 50% encode walking. Similarly, ANs encode specific types of foreleg grooming movements. Moreover, we also find ANs that are activated during proboscis-extension during standing only, indicating an intersection of two behavioral states. In conclusion, these findings suggest that ANs do not only relay raw sensory signals but also send information about behavioral state to the brain.