# Dopamine neuron activity encodes the length of upcoming contralateral movement sequences

## TL;DR

Dopamine neurons in mice signal the length of upcoming movements on the opposite side of the body, linking their activity to movement vigor.

## Contribution

The study reveals that dopamine neuron activity specifically encodes contralateral movement sequence length, beyond general motivation.

## Key findings

- Dopamine neuron activity before movement is higher for contralateral actions and correlates with sequence length.
- Reward-modulated dopamine neurons show no lateralization in activity.
- Unilateral dopamine depletion impairs contralateral movement sequence length but not ipsilateral.

## Abstract

Dopaminergic neurons (DANs) in the substantia nigra pars compacta (SNc) have been related to movement speed, and loss of these neurons leads to bradykinesia in Parkinson’s disease (PD). However, other aspects of movement vigor are also affected in PD; for example, movement sequences are typically shorter. However, the relationship between the activity of DANs and the length of movement sequences is unknown. We imaged activity of SNc DANs in mice trained in a freely moving operant task, which relies on individual forelimb sequences. We uncovered a similar proportion of SNc DANs increasing their activity before either ipsilateral or 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-modulated 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 aspects of contralateral movements.

•Developed a freely moving task where mice learn individual forelimb sequences•Movement-modulated DANs encode the length of contralateral movement sequences•The activity of reward-modulated DANs is not lateralized•Dopamine depletion impaired contralateral, but not ipsilateral, sequence length

Developed a freely moving task where mice learn individual forelimb sequences

Movement-modulated DANs encode the length of contralateral movement sequences

The activity of reward-modulated DANs is not lateralized

Dopamine depletion impaired contralateral, but not ipsilateral, sequence length

Mendonça et al. show that dopamine neuron activity preceding movement in the substantia nigra pars compacta encodes the length of contralateral, but not ipsilateral, movement sequences. Consistently, unilateral dopamine depletion impairs the length of contralateral, but not ipsilateral, sequences.