A cholinergic medial septum input to medial habenula mediates generalization formation and extinction of visual aversion

Generalization formation and extinction of visual aversion are critical functions of the brain that support survival and emotional well-being, but the neurobiological mechanisms are still unclear. Here, we established a rapid generalization procedure for induction of visual aversion by a dynamic stripe image on digital screens in mice. Using fiber photometry, apoptosis, chemogenetic and optogenetic, pharmacological, in vitro electrophysiological recording techniques and behavioral tests, we found that decreased activity of cholinergic neurons in the medial septum (MS), an important part of basal forebrain cholinergic system, led to generalization loss of visual aversion. Strikingly, we identified a new projection from MS cholinergic neurons to medial habenula (MHb), and first found that inhibition of the MS→MHb cholinergic circuit disrupted aversion generalization formation, while continuous activation of this circuit disrupted subsequent extinction. The further studies showed that blockade of M1 mAChRs rather than α4β2 and α7 nAChRs on downstream neurons co-releasing glutamate and acetylcholine blunted aversion generalization enhancement and extinction deficit caused by activation of MS→MHb cholinergic circuits. These findings reveal that MS→MHb cholinergic circuit is a new and critical node in aversion generalization formation and extinction and potentially provide insight into the pathogenesis of neuropsychiatric diseases, such as anxiety disorders and post-traumatic stress disorder.