Project 2: The Neural Basis of Motor Pattern Loops Abstract The goal of Project 2 is to understand how motor pattern loops link high-level behavioral goals with low-level control of muscles. In the fly, such motor pattern loops are comprised of populations of descending neurons (DNs), which integrate dendritic signals in the central brain and project their axons to the ventral nerve cord (VNC). We will take advantage of cell-type specific Split-Gal4 lines to record and manipulate activity in DNs that target VNC circuits that control the fly legs and wings. We will combine optogenetic manipulation of DNs with fine-scale analysis of walking and flight behavior, and measure intracellular DN signals in behaving animals with whole whole-cell electrophysiology recordings. These efforts are divided into the following Specific Aims: Specific Aim 1: Determine how wing muscle action groups are recruited into functional actions by descending control. Specific Aim 2: Determine how leg muscle action groups are recruited into functional actions by descending control. Specific Aim 3: Characterize the activity patterns of identified descending neurons in behaving flies using in vivo whole-cell recordings.