Bradykinesia and Its Progression Are Related to Interhemispheric Beta Coherence

Area of Science:

• Neuroscience
• Neurology
• Biomedical Engineering

Background:

• Bradykinesia is a primary motor symptom of Parkinson disease (PD).
• The precise neural mechanisms underlying bradykinesia, especially in relation to subthalamic nucleus (STN) deep brain stimulation (DBS), remain incompletely understood.
• Long-term STN-DBS effects on bradykinesia require further investigation into local and network-level brain dynamics.

Purpose of the Study:

• To investigate the neural correlates of bradykinesia changes after long-term STN-DBS.
• To determine if local STN beta-band (13-30 Hz) activity or broader bilateral network dysfunction is associated with bradykinesia progression.
• To explore the relationship between STN beta-band dynamics and bradykinesia in PD patients over time.

Main Methods:

• A longitudinal study involving 21 PD patients with implanted STN sensing neurostimulators.
• Participants underwent periodic medication withdrawal and DBS 'off' periods over an average of 3 years.
• Bradykinesia was assessed quantitatively using a wrist-flexion extension task, with simultaneous local field potential recordings from the STN to analyze beta power, burst duration, and interhemispheric coherence.

Main Results:

• Higher interhemispheric STN beta coherence, not local beta power or burst duration, was significantly linked to more severe bradykinesia.
• Over time, bradykinesia worsened, and interhemispheric STN-STN beta coherence increased, while local beta power and burst duration remained stable.
• The progression of bradykinesia correlated with increased interhemispheric beta synchrony.

Conclusions:

• Interhemispheric STN beta synchrony serves as a neural marker for the progression of bradykinesia in PD patients receiving chronic STN-DBS.
• These findings suggest that pathological bilateral network dysfunction, characterized by increased interhemispheric synchrony, may contribute to bradykinesia in Parkinson disease.
• Targeting bilateral network dynamics could offer new therapeutic strategies for managing bradykinesia in PD.