At Carnegie Mellon University in Pittsburgh, neuroscientist Aryn Gittis has made a discovery that could reshape how doctors treat Parkinson's disease: tremor and slowed movement, the disorder's two most visible symptoms, spring from entirely different broken circuits in the brain.
For more than 1.1 million people living with Parkinson's in the United States, this distinction matters profoundly. The disease has long been treated as a single condition, but Gittis and her colleagues have found that a one-size-fits-all approach may be why current medications fail so many patients. Their work, published in The Journal of Neuroscience, centers on the motor thalamus—a crucial relay station in the brain that serves as a communication hub for movement, linking the basal ganglia (long implicated in Parkinson's) with the cerebellum, which fine-tunes our motions.
The research team used two different mouse models to trace these divergent pathways. One model, standard in Parkinson's research, mimics the dopamine loss that causes bradykinesia—that characteristic slowing of movement. The other, newly developed by Gittis's team, produces tremor, something most animal models have never achieved. This innovation proved crucial. When the researchers recorded neural activity in the thalamus, the patterns told a striking story.
In mice with slowed movement, abnormal activity spread widely across the thalamus, reflecting broad disruption in motor circuits. But in mice with tremor, the dysfunction was more localized, concentrated in regions connected to the cerebellum. "You can tell from the neural signals whether an animal has tremor or slow movement," Gittis explained. The cerebellum, which receives sensory information, acts as a predictor for real-time motor control. When it malfunctions, it can create a feedback loop of endless overcorrection—the brain constantly trying to fix a movement it perceives as wrong, getting stuck in that back-and-forth rhythm that produces tremor.
This insight cracks open a clinical puzzle that has baffled doctors for decades: why dopamine-targeting medications work brilliantly for bradykinesia but often fail for tremor. "Dopamine therapies work really well for slow movement, but they're hit or miss for tremor," Gittis said. "That suggests they're not affecting the right circuit for that symptom." Because these medications influence the basal ganglia, not the cerebellum, they address one broken circuit while leaving another untouched.
Shruti Nanivadekar, a recent Ph.D. graduate from the University of Pittsburgh's Neuroscience Institute and the paper's first author, sees profound implications: "This study shows that different Parkinson's symptoms may emerge from different brain circuits. That's important because it suggests treatments may need to target those circuits differently."
The research unlocks a new laboratory tool as well. For years, tremor has been difficult to study in animal models because so few could produce it. Now researchers finally have a way to examine the neural circuits underlying tremor directly—work that was simply not possible before.
That capability could eventually lead to personalized treatments tailored to whether a patient's Parkinson's manifests primarily as tremor or slowed movement. For patients living with this disease, the possibility of therapies matched precisely to their symptoms represents genuine hope.