In addition to its well-known contributions to motor control and motor learning, the cerebellum is involved in language, emotional regulation, anxiety, and affect 1-4 . We found that suppressing the firing of cerebellar Purkinje cells (PCs) rapidly excites forebrain areas that could contribute to such functions, including the amygdala, basal forebrain, and septum, but that the classic cerebellar outputs, the deep cerebellar nuclei (DCN), do not project to these regions. Here we show that parabrachial nuclei (PBN) neurons that receive direct PC input, project to and influence all of these forebrain regions and many others. Furthermore, the function of this pathway is distinct from the canonical pathway: suppressing PC to PBN activity is aversive, whereas suppressing the PC to DCN pathway is rewarding. Therefore, the PBN pathway allows the cerebellum to influence the entire spectrum of valence, modulate the activity of forebrain regions known to regulate diverse nonmotor behaviors, and may be the substrate for many nonmotor disorders related to cerebellar dysfunction.The posterior vermis of the cerebellar cortex has been implicated in many nonmotor behaviors. In animal models, disruption or stimulation of different regions of the vermis modulates aggression 5 , motor planning 6,7 , spatial memory 8-10 , aspects of fear [11][12][13] , and hippocampal epilepsy 14,15 . In humans, damage to the vermis is associated with deficits in emotional control, language, memory, and executive function 3,4 . Cerebellar damage can also result in emotional disturbances consistent with limbic system dysfunction 1,2 .It is not known how the posterior vermis influences these behaviors, but it seems likely that it somehow influences regions associated with them. Electrical stimulation of the cerebellum rapidly increases activity in the hypothalamus 16,17 , the amygdala [17][18][19] , basal forebrain 17 , septum 17,19 , hippocampus [17][18][19][20] , and specific regions of the cortex [16][17][18] . The interpretation of these results is complicated, because electrical stimulation can antidromically activate mossy fibers and other modulatory fibers.To assess the influence of the posterior vermis of the cerebellum on other brain regions, we used optogenetics to selectively suppress spontaneous PC firing. This disinhibits PC targets, and is more selective than electrical stimulation. We briefly (20 ms) illuminated the posterior vermis through a .