Economic choice is specifically disrupted in mental and neurological disorders such as major depression, frontotemporal dementia, and drug addiction. Established literature links this behavior to the orbitofrontal cortex (OFC). In recent years, my lab has examined neuronal activity in the OFC of monkeys and mice choosing between different juice types. Our studies revealed the presence of different cell groups: offer value cells encoding the value of individual offers; choice outcome cells encoding the identity of the chosen offer or the chosen action; and chosen value cells. In a computational sense, these variables capture both the input (offer value) and the output (choice outcome, chosen value) of the choice process, suggesting that the cell groups identified in OFC constitute the building blocks of a decision circuit. Indirect evidence supports this hypothesis. However, the anatomical organization of this circuit and the contributions of different cell groups are not known. Consequently, the decision mechanisms remain poorly understood. To shed light on these fundamental questions, we developed a preparation in which mice perform economic choices while we record from OFC using two-photon (2P) calcium (Ca2+) imaging through a GRIN lens. Longitudinal recordings showed that the encoding of specific decision variables by individual cells is very stable. Moreover, the representation of decision variables differs significantly across cortical layers: input variables populate mostly layers 2/3 (L2/3), while spatial and output variables populate mostly layer 5 (L5). These results support the notion of a stable decision circuit and provide a glimpse of its anatomical organization. However, to truly unravel the decision mechanisms, one needs to have a detailed understanding of how different cell groups connect with each other, how they influence each other’s activity, and how the activity of each cell group affects choices. Here we propose to address these questions using a combination of 2P imaging and single cell optogenetics. In Aim 1, we will assess the effective connectivity between cell groups. Mice will (a) be implanted with a GRIN lens accessing L2/3 and/or L5, (b) express a green Ca2+ indicator and a red shifted channelrhodopsin (ChR), and (c) perform choices under the microscope. In each mouse, we will image ~500 cells. First, we will assess the variable encoded by each cell. In separate sessions, while animals rest, we will holographically stimulate one specific cell group while imaging the entire population. Measuring the activity evoked by the stimulation, we will assess the effective connectivity between different cell groups. In Aim 2, we will use the same preparation, but we will deliver the stimulation while mice perform choices (in half of the trials). We will measure how optical stimulation affects performance, and thus assess the causal links between individual cell groups and choices. Relevance to R21. These experiments are innovat...