PROJECT SUMMARY/ ABSTRACT Although smoothly linking individual actions into sequences is critical for execution of complex behaviors, we still have a limited understanding of how behavioral sequences are encoded in the brain. Accumulating evidence suggests that striatal activity patterns are linked to performance of sequenced behaviors, but the role of cortical inputs in their initiation and control is less clear. We therefore used the SAPAP3-knockout (KO) mouse experimental system, which displays repetitive grooming behavior associated with central striatal (CS) hyperactivity, to investigate how cortical and striatal regions interact to generate both normal and perseverative action patterns. In our recent work, we demonstrated that SAPAP3-KOs do not have abnormalities in striatal intrinsic properties using ex vivo electrophysiology. However, we observed large (~6 fold) increases in extrinsic drive to CS from the major cortical input to this region: anterolateral motor area (ALM- also known as M2). (Corbit et al, 2019). These results suggested that repeated selection of motor programs could be caused by excessive drive from ALM, an area whose human homologues (SMA/pre- SMA) have been linked to Tourette Syndrome (TS) and OCD. Our preliminary optogenetics and photometry data support this theory by identifying ALM activity that ramps up during grooming, and terminates at grooming bout cessation. Together, these results indicate that ALM may be a key under- recognized hub for the regulation of innate sequenced behaviors. However, 1) this idea has not yet been rigorously tested, and 2) it is unclear if the same principles apply to learned sequenced behaviors. Here we will use state-dependent optogenetics, ex vivo electrophysiology, and longitudinal in vivo Ca+2 imaging to determine the role of ALM in the generation of normal and abnormal innate and learned sequenced behaviors. In Aim 1, we will Identify the ALM ensemble responsible for grooming-associated ramping activit