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

Abstract

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 sequences. We uncovered that a similar proportion of SNc DANs increased their activity before ipsi- vs. contralateral sequences. However, the magnitude of this activity was higher for contralateral actions, and was related to contralateral but not ipsilateral sequence length. 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, sequence length. These results indicate that movement-initiation DANs encode more than a general motivation signal, and invigorate kinematic aspects of contralateral movements. TeaserTransient activity in substantia nigra compacta dopamine neurons encodes contralateral, but not ipsilateral action vigor.