12 Activation of the subthalamic nucleus (STN) is associated with the stopping of ongoing 13 behavior via the basal ganglia. However, we recently observed that optogenetic STN 14 excitation induced a strong jumping/escaping behavior. We hypothesized that STN activation 15 is aversive. To test this, place preference was assessed. Optogenetic excitation of the STN 16 caused potent place aversion. Causality between STN activation and aversion has not been 17 demonstrated previously. The lateral habenula (LHb) is a critical hub for aversion. 18 Optogenetic stimulation of the STN indeed caused firing of LHb neurons, but with delay, 19 suggesting the involvement of a polysynaptic circuit. To unravel a putative pathway, the 20 ventral pallidum (VP) was investigated. VP receives projections from the STN and in turn 21 projects to the LHb. Optogenetic excitation of STN-VP terminals caused firing of VP neurons 22 and induced aversive behavior. This study identifies the STN as critical hub for aversion, 23 potentially mediated via an STN-VP-LHb pathway. 24 25 Total word count 4994. 26 27 Introduction 28