Rapid Dopaminergic Signatures in Movement: Reach Vigor Reflects Reward Prediction Error and Learned Expectation

Area of Science:

• Neuroscience
• Motor Control
• Decision Making

Background:

• Movement vigor scales with reward value, suggesting neural circuits representing value influence motor control.
• Dopaminergic neurons (DANs) are hypothesized to mediate the link between value representation and movement vigor.
• DAN activity is modulated by learning signals, including reward expectation and reward prediction error.

Purpose of the Study:

• To investigate if movement vigor in reaching tasks exhibits a time-locked response to reward expectation and reward prediction error.
• To explore the relationship between dopaminergic learning signals and the modulation of movement vigor.

Main Methods:

• A probabilistic reaching task was designed with varying reward probabilities (0%, 33%, 66%, 100%).
• Two experiments were conducted: one with explicit reward probabilities and another where participants learned probabilities.
• Reaching kinematics, including peak velocity, were analyzed to assess movement vigor.

Main Results:

• Peak movement velocity increased with higher reward expectation.
• A short-latency response in movement vigor was observed, tracking reward prediction error (invigorating or enervating velocity).
• Trial-to-trial kinematic changes reflected value updates, similar to dopamine-mediated striatal activity; reach vigor also increased with reward history.

Conclusions:

• Movement vigor is directly influenced by reward expectation and reward prediction error signals.
• Dopaminergic learning signals play a crucial role in modulating movement vigor, both at initiation and during ongoing movements.
• This study provides evidence for the integration of value-based learning signals into motor control during reaching tasks.