New Electrical Signature Of Parkinson's Disease

So‑called "noise" represents a previously overlooked signature that reflects Parkinson's disease symptoms.

To the point

• New Discovery: Researchers found that previously ignored brain signals, called noise, reflect symptoms of Parkinson's disease.
• Rhythmic vs. Nonrhythmic Activity: The researchers distinguished between rhythmic and nonrhythmic brain activity, finding that this separation offers better insights into movement symptoms.
• Adaptive Stimulation: The newly identified electrical signature may enable more precise deep brain stimulation by adjusting impulses based on real-time brain activity.

What happens in the brain when a person experiences the characteristic movement symptoms of Parkinson's disease? Researchers around the world are seeking answers through various approaches. One of these builds on a treatment already established in clinical care: deep brain stimulation. In this therapy, stimulating electrodes are implanted in patients' brains to alleviate symptoms using electrical impulses. The same electrodes also enable unique electrical measurements from areas otherwise inaccessible in humans. These data can help uncover the neural mechanisms of Parkinson's disease and inspire new therapeutic strategies.

In close collaboration with leading European deep brain stimulation centers-including Charité Berlin, Heinrich-Heine University Düsseldorf, University College London, and the University of Oxford-the Max Planck team has now taken an important step forward. For their study, the researchers focused on so-called "beta waves," which oscillate ca. 20 times per second and whose strength is thought to correlate with the severity of movement symptoms. However, when reviewing the literature, the team encountered considerable heterogeneity in the results. "We wondered why earlier studies from different centers had produced such mixed results," says Vadim Nikulin of the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig. "Did the patient groups differ, the recording equipment, or the analysis methods?"

Larger data set

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To find out, the team initiated a close collaboration with leading European university hospitals - a previously unprecedented collaboration in the field of deep brain stimulation, funded by the German Research Foundation through the collaborative research center 'Retune'. Together, they aggregated several independent data sets, for which they developed a uniform analysis procedure, and arrived at a clear answer: differences in equipment or analysis were minor-sample size was the key factor. The link between beta waves and symptom severity was present, but weaker than expected. Detecting it reliably required data from over 100 patients, while most earlier studies had examined far fewer.

Furthermore, a systematic comparison of previous analysis strategies revealed that many studies did not distinguish between rhythmic and non-rhythmic brain activity - even though both reflect distinct neuronal processes. "You can imagine the brain as a concert hall full of musicians before a rehearsal," explains Moritz Gerster, who led the study. "Some groups play together, creating a distinct rhythm. Others practice on their own, merging into a non-rhythmic 'noise'. If you only measure the overall volume, you miss this distinction."

Using new analysis methods, the researchers separated rhythmic activity from the non‑rhythmic 'noise of neurons'-and found that this separation provided a far better explanation for patients' movement symptoms. Moreover, the anatomical origin of the rhythmic beta waves corresponded more precisely to the most therapeutically effective electrode contact - a potential step toward automated electrode selection, which currently relies on manual expertise.

Diversity of patients

Another challenge was the clinical diversity of the patients: age, disease duration, and symptom combinations varied widely, and no healthy control group could be included, as deep brain stimulation is used only in severely affected patients. To address this challenge, the researchers leveraged a key feature of the disease: its asymmetry. Parkinson's symptoms often affect one side of the body more strongly than the other. "That gave us the idea to compare the more‑affected hemisphere with the less‑affected one," says Moritz Gerster. "This way, each patient could practically serve as their own control."

The analysis revealed that in the more-affected hemisphere, non-rhythmic, noise-like activity was significantly elevated. "That suggests an increased firing rate of neurons - a finding that has already been described in animal models of Parkinson's disease," explains Gerster. This newly identified electrical signature could help to control deep brain stimulation more precisely: instead of continuously sending impulses, stimulation could be tailored to ongoing brain activity - applied only when it's actually needed. First 'adaptive' stimulators capable of such real‑time adjustments are already available. To what extent the new signature withstands everyday conditions can now be explored in follow‑up studies using these modern devices.