Summary: Unexpected rewards can make people move faster in a fraction of a second, highlighting how closely motivation and movement are tied in the brain. In a joystick-based reaching task, participants reached faster toward targets with higher reward probability, and their movements received a brief burst of extra speed when a low-probability reward appeared unexpectedly.
The timing of this change matched classic dopamine reward-prediction signals, indicating that movement vigor reflects the brain’s internal value computations. Over longer stretches, sequences of positive or negative outcomes shifted overall movement speed, showing that recent experience continuously recalibrates how energetically we act. These results suggest that movement could serve as a simple, noninvasive marker for tracking dopamine-related function in conditions such as Parkinson’s disease and depression.
Key Facts
- Surprise Speeds Movement: Unexpected rewards increased movement vigor within roughly 220 milliseconds.
- Reward Probability Matters: Participants reached more rapidly toward targets that were more likely to deliver a reward.
- Second Dopamine Signal: The extra speed appeared only when outcomes were uncertain and the result was better than expected.
- Experience Shapes Energy: Repeated successes raised overall movement speed, while repeated failures slowed it.
- Clinical Potential: Small changes in motion could help monitor dopamine-related disorders over time.
Source: University of Colorado
New research by engineers at the University of Colorado Boulder explores why people often report a “skip in their step” when they’re happy.
The study emphasizes the central role of dopamine—a brain chemical closely tied to reward—in increasing how quickly people move when motivated. The findings may eventually help researchers better understand and even monitor conditions that affect motivation and movement, including Parkinson’s disease and depression.
“Anecdotally, we know this feeling,” said senior author Alaa Ahmed, professor in the Paul M. Rady Department of Mechanical Engineering at CU Boulder. “If you’re meeting family at the airport you might run, while meeting a coworker you’re likely to walk.”
Ahmed and Colin Korbisch, a former graduate student at CU Boulder, designed an experiment to investigate how value signals in the brain influence motor behavior.
Participants used a joystick-like device to reach toward targets on a screen. Each target offered a probabilistic reward: a brief flash of light and a beep. One target delivered a reward every time, another never did, and two were intermediate. The researchers measured how quickly and energetically participants moved toward those targets.
As expected, people reached faster toward targets with higher reward probability. But the team also observed a striking short-lived effect: when a participant reached for a low-probability target and unexpectedly received a reward, their ongoing movement became noticeably faster even after receiving the feedback.
That transient increase in vigor appeared about 220 milliseconds after the auditory feedback. It was subtle and not visible without precise measurement, yet consistent across trials—suggesting a rapid motivational signal triggered by pleasantly surprising outcomes.
The authors cannot directly measure dopamine levels in human subjects, but the timing and pattern of these speed changes align with known dopaminergic reward-prediction error signals observed in animal studies. When an outcome is already certain, the team found no additional boost in vigor following feedback, consistent with the idea that a second, phasic dopamine signal accompanies unexpectedly positive outcomes.
Experience also shaped behavior across trials: strings of successful rewards led participants to move faster overall, while repeated non-rewards produced a gradual reduction in vigor. These trial-by-trial adjustments mirror value-updating processes attributed to dopaminergic learning mechanisms.
Ahmed noted the clinical implications: many neurological and psychiatric conditions alter both dopamine signaling and movement. Tracking subtle changes in movement vigor over days, months, or years could provide a noninvasive behavioral readout to complement clinical assessment of disorders such as Parkinson’s disease and depression.
“If you’ve had a good run of outcomes, you tend to move with more energy. After a streak of setbacks, you slow down,” she said. “That skip in your step is a behavioral reflection of internal value computations.”
Juice time
Decades of research link dopamine to learning and motivation. Classic studies in the 1990s showed that dopaminergic neurons in primates signal both reward expectation and reward prediction errors: dopamine spikes when a predictive cue appears, and it dips if an anticipated reward fails to materialize. These error signals teach the brain which choices are worth pursuing.
Ahmed and Korbisch tested whether similar signals influence movement vigor in humans, and their results support the idea that motor vigor reflects rapid, value-based neural computations.
Reach for it
To probe the link between dopamine and motor control, subjects performed repeated reaches to targets with different reward probabilities (0%, 33%, 66%, and 100%). Peak reach velocity scaled with expected value: higher-probability targets elicited faster reaches. Crucially, feedback produced immediate changes in speed—positive prediction errors transiently invigorated ongoing motion, while negative errors transiently reduced it.
These trial-by-trial kinematic changes tracked the sign and magnitude of reward prediction error, consistent with the temporal profile of dopaminergic phasic activity recorded in animal studies. The authors suggest that movement vigor provides a real-time behavioral readout of the brain’s motivational computations.
Key Questions Answered:
A: When an outcome was better than expected, participants’ movements became faster within about 220 milliseconds, reflecting internal reward prediction signals linked to dopamine that increase movement vigor.
A: The extra burst of speed appeared only for uncertain outcomes that were pleasantly surprising, indicating an additional motivational signal when results exceed expectations.
A: Because dopamine-related disorders often alter movement, measuring subtle shifts in movement speed over time could offer a noninvasive way to monitor conditions such as Parkinson’s disease and depression.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was provided by staff.
About this neuroscience research news
Author: Daniel Strain
Source: University of Colorado
Contact: Daniel Strain – University of Colorado
Image: The image is credited to Neuroscience News
Original Research: Open access. “Rapid Dopaminergic Signatures in Movement: Reach Vigor Reflects Reward Prediction Error and Learned Expectation” by Colin C. Korbisch and Alaa A. Ahmed. Science Advances
DOI: 10.1126/sciadv.adz9361
Abstract
Rapid Dopaminergic Signatures in Movement: Reach Vigor Reflects Reward Prediction Error and Learned Expectation
Movements grow more vigorous when rewards are anticipated, implying that motivational signals modulate motor control. Dopaminergic neurons encode reward expectation and prediction error, making them prime candidates to connect value and vigor.
This study demonstrates that human reach vigor dynamically tracks canonical dopaminergic learning signals not only at movement onset but also during ongoing motion. Using a reaching task with probabilistic rewards (0%, 33%, 66%, and 100%), researchers found that peak velocity scaled with expected value.
Importantly, after feedback, reach velocity was transiently invigorated or subdued in proportion to the sign and magnitude of the reward prediction error. Trial-by-trial kinematic changes reflected value updating, consistent with phasic dopaminergic learning signals.
These results show that movement vigor is modulated by reward-learning signals on rapid timescales, offering a real-time behavioral measure of motivational computation in the brain.