Objective: Here, we test the hypothesis that beta bursts not only involve dynamically elevated local synchronisation but also distributed coupling across circuit nodes, further restricting information coding capacity in patients with Parkinson’s disease (PD).

Background: Exaggerated activity in the beta band (13-35Hz) is a hallmark of basal ganglia signals in patients with Parkinson’s disease (PD). Beta activity however is not constantly elevated, but comes in bursts. In previous work we showed that the longer beta bursts are maintained, the more the local oscillatory synchronisation within the subthalamic nucleus increases, which is believed to limit the information coding capacity of the circuits. And indeed, a higher incidence of longer bursts is positively related with clinical impairment, while the opposite is true for short, probably more physiological bursts.

Methods: Local field potentials from the subthalamic nucleus and EEG from the motor cortex area were recorded in eight PD patients during temporary lead externalization during surgery for deep brain stimulation and overnight withdrawal of levodopa. Beta bursts were defined as periods exceeding the 75th percentile of signal amplitude and the coupling between bursts was considered on two temporal scales: % overlapping (OVL) of beta bursts over the order of hundreds of milliseconds and the synchronisation of successive beta cycles over shorter time periods, termed phase synchrony index (PSI).

Results: %OVL between STN and cortex and between the two STN was strikingly higher than expected by chance. Similarly, PSI was higher during bursts as opposed to non-bursts periods. In addition, %OVL was greater for long compared to short bursts. The increase in PSI during long compared to short burst was more subtle, although synchronisation on this time scale was clearly more sustained during long duration bursts.

Conclusions: Our results support the hypothesis of long range coupling of beta bursts between nodes in the basal ganglia-cortical network, which is greater during long as opposed to short duration beta bursts. Accordingly, we posit that episodes of simultaneously elevated coupling at multiple nodes in the basal ganglia-cortical circuit further limit information coding capacity and have a key impact upon motor function.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/beta-burst-coupling-across-the-motor-circuit-in-patients-with-parkinsons-disease/