For decades, neuroscientists assumed dopamine worked like a throttle. Quick bursts of the chemical were supposed to set how fast and forcefully we move, rising and falling with each action. A new study says that picture is probably wrong.
Researchers at McGill University found that changing dopamine levels during an ongoing movement made no difference to how mice performed. What mattered was the baseline level already sitting in the brain. The finding, published in Nature Neuroscience, reframes dopamine as a permissive signal rather than an active controller, a shift that could change how Parkinson’s disease is treated.
The team used light-based sensors to watch dopamine in real time as mice pressed a weighted lever for water rewards. They expected spikes right before forceful presses. Instead, dopamine often dipped slightly at movement onset. When they used optogenetics to artificially trigger or silence dopamine neurons mid-action, the animals kept pressing with the same speed and strength.
The bursts weren’t doing anything.
Engine Oil, Not a Gas Pedal
Parkinson’s disease kills dopamine-producing neurons in the midbrain, leading to slowed movement, tremors, and balance problems. The standard treatment, levodopa, has worked for decades, but researchers have struggled to explain exactly why. If dopamine bursts control movement vigor, why does a drug that raises overall dopamine levels help so much?
The McGill study offers an answer. When researchers broadly depleted dopamine on one side of the brain, mice struggled to produce strong movements with the opposite forelimb. Levodopa restored those movements even though the fast fluctuations never came back. The drug worked by raising baseline tone, not by recreating moment-to-moment signals.
“Dopamine appears to function more like engine oil. It’s essential for the system to run, but not the signal that determines how fast each action is executed,” explains Nicolas Tritsch, Assistant Professor of Psychiatry at McGill University.
This also helps explain why some newer therapies aimed at mimicking rapid dopamine signaling have delivered mixed results. They may have been chasing the wrong target.
What This Means for Treatment
More than 110,000 Canadians live with Parkinson’s, and that number is expected to double by 2050. The findings suggest future therapies might focus on maintaining steady dopamine levels rather than trying to recreate complex, fleeting bursts. Simpler targets could mean fewer side effects.
Older drugs called dopamine receptor agonists already improve movement but often cause problems because they activate receptors too broadly. Understanding that baseline matters most could guide more precise versions that support motor function without overstimulating other brain systems.
The study was conducted in mice, but it addresses a core assumption that has shaped Parkinson’s research for years. Other brain regions likely handle the fine-tuned adjustments to speed and force. Dopamine just keeps the whole system ready to respond.
Nature Neuroscience: 10.1038/s41593-025-02102-1
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