PROJECT SUMMARY ABSTRACT Dopamine (DA) is an critical modulator of brain activity. Disruption of DA signaling in the prefrontal cortex (PFC) has been proposed to underlie cognitive deficits in major mental disorders including schizophrenia and attention- deficit hyperactivity disorder (ADHD). Working memory (WM) is an important cognitive process for temporarily holding and manipulating goal-directed information, that depends on DA in the PFC. Yet despite decades of investigation, the key circuit mechanisms underlying dopaminergic modulation of PFC cells during WM remain poorly understood. This gap in knowledge has in turn limited our ability to gain better insights into the pathophysiology of such mental disorders. The overall goal of this study is to use multiple complementary state-of-the-art techniques to investigate DA signaling in PFC during a well-established parametric WM task. Technical limitations have hindered our ability to reliably measure rapidly-evolving DA signals in the PFC. This is now changing. I will use retrograde viral infection tools to optogenetically distinguish PFC-projecting from striatal-projecting DA cells in VTA. I will test the hypothesis that PFC-projecting DA cells encode a cue saliency signal, gating information flow to PFC. Using a novel optical DA sensor, I will characterize the DA dynamics in subregions of medial PFC and test the hypothesis that DA transiently increases during the delay-period, and that the magnitude of this increase is linked to WM performance. Finally, using head-mounted microendoscopes I will optogenetically manipulate PFC DA release while simultaneously monitoring distinct subpopulations of PFC neurons. If successful, this project will provide a novel window onto dopaminergic modulation of PFC during cognitive processes. My long-term career goal is to investigate the circuits mechanisms of cognitive control in the brain with a specific interest in how impairment in these circuits contributes to major psychiatric disorders. I have a strong computational and signal processing background. I have received rigorous training in behavioral neuroscience, optogenetics, neurophysiology, and fiber photometry. Yet, I need additional technical and conceptual training critical to my mission. My mentor and co-mentor are ideally situated to provide critical guidance to this project and to my career development. The UCSF environment provides numerous training opportunities with an emphasis on preparing the next generation of leaders in biomedical research. These include speaking opportunities at various internal programs, scientific leadership and management workshops courses, grant writing courses and internal review panels, and mentoring opportunities specific to postdoctoral scholars seeking independence. I plan to take advantage of all the opportunities provided through this mentored career development award to establish myself as a highly effective neuroscientist and independent investigator.