4Signaling of expected outcomes in the orbitofrontal cortex (OFC) is critical for 5 outcome-guided and learning behavior. The OFC projects to primary visual 6 cortex (V1), yet the function of this top-down projection is unclear. We found 7 that optogenetic activation of OFC projection to V1 reduced the amplitude of V1 8 visual responses via the recruitment of local somatostatin-expressing (SST) 9interneurons. Using mice performing a Go/No-Go visual task, we showed that 10 the OFC projection to V1 mediated the suppression of V1 responses to the 11 reward-irrelevant No-Go stimulus. Furthermore, the responses of V1-projecting 12 OFC neurons to No-Go stimulus were reduced when the mice's expectation was 13 incorrect. In addition, optogenetic inactivation of OFC projection to V1 14 impaired, whereas activation of SST interneurons in V1 improved the learning of 15 Go/No-Go visual task. Thus, OFC top-down projection to V1 is crucial to drive 16 visual associative learning by reducing the response gain of V1 neurons to non-17 relevant stimulus. 18
19The OFC is a critical brain region for using the information about expected 20 outcomes to guide learning and behavior 1-3 . Studies in rodents and monkeys have 21 demonstrated that the identity and expected values of specific outcomes are 22 represented by activities in the OFC 4-14 . Lesions or inactivation of the OFC impair 23 behavior guided by outcome expectancy and learning driven by the discrepancy 24 48 V1 visual response by recruiting SST interneurons. We thus hypothesized that OFC 49 projection to V1 may filter out non-relevant visual information, and tested this 50 hypothesis in mice performing a Go/No-Go visual task. We found that the OFC 51 projection to V1 contributed to the suppression of V1 responses to the No-Go 52 stimulus, which was not associated with reward. Optogenetic tagging of V1-53 projecting OFC neurons revealed that their responses to the No-Go stimulus were 54 reduced in wrong trials but not in correct trials. We further showed that optogenetic 55 inactivation of OFC projection to V1 slowed the learning of Go/No-Go visual 56 behavior. Thus, the OFC projection to V1 plays a key role in filtering out non-relevant 57 visual information to facilitate associative learning. 58
59Results 60
OFC top-down projection controls V1 response amplitude by activation of local 61SST interneurons. We injected Cholera toxin subunit B (CTB) in V1 and found that 62 the retrograde labeled neurons were in the ventrolateral OFC (vlOFC) (Fig. 1a), 63 consistent with the finding in a previous study 38 . By injecting rAAV2-retro-hSyn-Cre 64 in V1 and AAV-DIO-EYFP in the OFC, we found that the axons of OFC neurons 65 terminated in both superficial and deep layers of V1 (Fig. 1b). To examine how the 66 5 OFC top-down projection influences V1 neuronal responses, we expressed excitatory 67 opsin Channelrhodopsin-2 (ChR2) or ChrimsonR in the OFC, and measured V1 68 responses with and without laser stimulation of OFC axons in mice passively viewing 69 drifting gratings (Fig. 1c)....