The slow movement seen in Parkinson's disease is driven by a warped perception of effort rather than a loss of motivation.
March 31, 2026
Original Paper
Perception of effort but not reward sensitivity is impaired in people with Parkinsons disease
bioRxiv · 10.64898/2026.03.26.714286
The Takeaway
Scientists have long debated if Parkinson's patients move slowly because they lack muscle power or simply don't care about rewards. This study demonstrates that reward sensitivity is actually normal; instead, the brain over-calculates the physical 'cost' of a movement, making every action feel like heavy lifting.
From the abstract
Deciding whether and how to act depends on a trade-off between the effort required to execute a given action and the potential reward for completing it. Impairments in this effort-reward trade-off have been proposed to underlie reduced movement vigor, or bradykinesia, in Parkinsons disease (PD). However, several mechanisms could alter the effort-reward trade-off in PD, each with unique implications for understanding and treating bradykinesia. Therefore, we individually examined whether people wi