Researchers from the University of Turku and Turku University Hospital, Finland, have identified new insights into the biological mechanisms underlying Parkinson’s disease symptoms. By analysing clinical data and dopamine transporter (DAT) imaging data from 414 Finnish patients, the team uncovered evidence suggesting that rest tremor may arise from a different neurobiological mechanism than other motor symptoms.
The researchers examined patients who were evaluated in routine clinical practice for uncertain parkinsonism or tremor, making the findings highly representative of real-world clinical settings. The study results were published on 19 March 2026 in Neurology®, the official medical journal of the American Academy of Neurology.
Understanding the Core Motor Symptoms of Parkinson’s Disease
Parkinson’s disease typically presents with three cardinal motor symptoms: bradykinesia (slowness of movement), rigidity (muscle stiffness), and rest tremor. Scientists already understand that bradykinesia and rigidity largely result from the degeneration of dopamine-producing neurons in the brain.
Because most neural pathways cross between brain hemispheres and body sides, these symptoms generally correspond to dopamine deficits in the striatum on the opposite side of the body where symptoms appear. However, the biological basis of rest tremor has remained unclear for decades.
Key Finding: Tremor Linked to Dopamine Activity on the Same Side
As per the press release, the study identified a clear and consistent pattern. Researchers found that rest tremor correlated with higher dopamine transporter binding in the striatum on the same side as the tremor. In contrast, the other major motor symptoms followed the expected pattern, showing an association with dopamine deficits in the opposite hemisphere.
This observation suggests that tremor may involve distinct neural processes that differ from those responsible for movement slowing and stiffness.
Expert Insight from the Research Team
Lead author Dr Kalle Niemi, MD, PhD, neurologist, explained the implications of the findings:
“More severe rest tremor does not simply indicate more advanced damage to the dopamine system. Instead, tremor appears to involve a partly distinct neurobiological mechanism.”
Validation Through Independent Patient Cohorts
Importantly, these findings also confirm earlier observations made by the same research group using data from the international Parkinson’s Progression Markers Initiative (PPMI) cohort. In that earlier work, the researchers applied a novel imaging analysis technique developed by their team.
By replicating the results in an independent and clinically representative patient group, the researchers strengthened the reliability and scientific validity of the phenomenon.
Different Symptoms May Involve Different Brain Networks
According to Dr Niemi, the findings support an evolving view of Parkinson’s disease.
“Our results suggest that different symptoms of Parkinson’s disease may arise from partly distinct neural networks and neurotransmitter systems. This may explain why tremor behaves differently from symptoms such as bradykinesia.”
Thus, Parkinson’s symptoms may not originate from a single uniform disease mechanism, but rather from multiple interacting brain pathways.
Insights Into Non-Motor Symptoms
Using the same analytical approach, the research team also examined non-motor symptoms of Parkinson’s disease. These symptoms often include depression, anxiety, and REM sleep behaviour disorder, which significantly affect patients’ quality of life.
Interestingly, the study found that these symptoms are primarily linked to monoaminergic systems other than dopamine, indicating the involvement of additional neurotransmitters within complex brain networks.
Toward More Personalised Parkinson’s Treatments
Taken together, the findings reinforce the understanding of Parkinson’s disease as a complex neurological disorder involving multiple neural circuits and neurotransmitter systems rather than a single dopamine-related pathway.
Consequently, a deeper understanding of the biological differences between individual symptoms may eventually help researchers and clinicians develop more targeted and personalised treatment strategies. Such approaches could improve symptom control and enhance long-term outcomes for patients living with Parkinson’s disease.