Transient dopamine neuron activity precedes and encodes the vigor of contralateral movements

Dopamine neurons (DANs) in the substantia nigra pars compacta (SNc) have been related to movement vigor, and loss of these neurons leads to bradykinesia in Parkinsons disease. However, it remains unclear whether DANs encode a general motivation signal or modulate movement kinematics. We imaged activity of SNc DANs in mice trained in a novel operant task which relies on individual forelimb movement sequences. We uncovered that a similar proportion of SNc DANs increased their activity before ipsi- vs. contralateral forelimb movements. However, the magnitude of this activity was higher for contralateral actions, and was related to contralateral but not ipsilateral action vigor. In contrast, the activity of reward-related DANs, largely distinct from those modulated by movement, was not lateralized. Finally, unilateral dopamine depletion impaired contralateral, but not ipsilateral, movement vigor. These results indicate that movement-initiation DANs encode more than a general motivation signal, and invigorate kinematic aspects of contralateral movements. HighlightsO_LIDeveloped a freely-moving task where mice learn rapid individual forelimb sequences. C_LIO_LIMovement-related DANs encode contralateral but not ipsilateral action vigor. C_LIO_LIThe activity of reward-related DANs is not lateralized. C_LIO_LIUnilateral dopamine depletion impaired contralateral, but not ipsilateral, movement vigor. C_LIO_LIeTOC summary: Mendonca et al. show that transient activity in movement-related dopamine neurons in substantia nigra pars compacta encodes contralateral, but not ipsilateral action vigor. Consistently, unilateral dopamine depletion impaired contralateral, but not ipsilateral, movement vigor. C_LI