Deep brain stimulation (DBS) has transformed the lives of many people with Parkinson's disease, easing tremors and stiffness with tiny electrical pulses delivered deep inside the brain. But doctors have never fully understood why it works — or why it works brilliantly in some patients and barely at all in others.

A new study published in Brain may hold the answer. Scientists at University Hospitals of Cologne and Düsseldorf, Harvard Medical School and Charité Berlin have identified a specific brain network — and the electrical rhythm it uses to communicate — that appears to drive the benefits of DBS. The network, which connects the subthalamic nucleus with frontal brain regions, operates within a relatively fast "high beta" band of 20 to 35 hertz.

"For the first time, we were able to characterize the DBS response network in Parkinson's disease in terms of space and time, simultaneously," said Professor Andreas Horn of the University of Cologne, who led the study. Previous research had studied either brain imaging or electrophysiology separately; this study brings both together for the first time.

The team studied 50 patients and 100 brain hemispheres, recording brain activity simultaneously through implanted DBS electrodes and with magnetoencephalography (MEG). The strength of the network's connection correlated with how much individual patients' motor symptoms improved after electrode implantation.

First author Dr. Bahne Bahners of Düsseldorf University Hospital said the rhythm appears to act as a communication channel between the subthalamic nucleus and the cerebral cortex, potentially mediating DBS's therapeutic effects. "By stimulating regions that are connected to the identified network, we will probably be able to adjust DBS settings more precisely in the future — especially in patients who have not yet benefited optimally from deep brain stimulation," she said.

The findings could provide a foundation for making deep brain stimulation more precisely tailored to an individual patient's brain network, particularly when existing settings do not provide the desired level of symptom relief. The researchers now plan to investigate more directly how DBS causes changes within brain networks; studies examining these causal effects are already underway. The study was largely funded by the Professor Klaus Thiemann Foundation.

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