Objective: To test whether subthalamic beta bursts in Parkinson’s disease reflect the continuous stochastic fluctuations of an oscillatory random process.

Background: Subthalamic beta oscillations in Parkinson’s disease display irregular intermittent dynamics that can be quantified as beta bursts.^1,2 Beta bursts have expanded the pathophysiology of beta oscillations from the unitary view of beta power in the frequency domain to a dualistic view of burst amplitude and duration in the time domain. However, whether beta bursts truly represent transient isolated events rather than the stochastic fluctuations of ongoing beta oscillations remains unclear.

Method: We recorded subthalamic local field potentials in 21 parkinsonian patients at rest OFF and ON medication, and we modeled beta oscillations as continuous linear random processes, constructed from the same information that was captured by the power spectrum of the recorded signals and driven by random noise. Our null hypothesis was that the dynamics of beta bursts – i.e. their average amplitude and duration – would not differ between recorded and simulated beta oscillations. To quantitatively assess the evidence in favor or against the null hypothesis, we used Bayesian statistics.³

Results: We obtained moderate evidence of absence of difference and extreme evidence of correlation in the dynamics of beta bursts between recorded and simulated beta oscillations. Furthermore, the dualism of beta burst amplitude and duration in the time domain displayed a direct correspondence in the frequency domain: burst amplitude correlated with the power whereas burst duration correlated with the sharpness of the beta peak in the power spectrum. All measures decreased with levodopa, but spectral sharpness and burst duration were more robust than beta power and burst amplitude in differentiating the more affected from the less affected side.

Conclusion: At a mechanistic level, beta bursts are consistent with continuous stochastic fluctuations of ongoing beta oscillations. At a practical level, spectral sharpness is the equivalent in the frequency domain of burst duration, offering an appealing simple measure for adaptive deep brain stimulation applications.

References: 1. Tinkhauser G, Pogosyan A, Tan H, Herz DM, Kühn AA, Brown P. Beta burst dynamics in Parkinson’s disease OFF and ON dopaminergic medication. Brain 2017; 140(11): 2968–2981.
2. Deffains M, Iskhakova L, Katabi S, Israel Z, Bergman H. Longer β oscillatory episodes reliably identify pathological subthalamic activity in Parkinsonism. Mov Disord 2018; 33(10): 1609–1618.
3. Keysers C, Gazzola V, Wagenmakers EJ. Using Bayes factor hypothesis testing in neuroscience to establish evidence of absence. Nat Neurosci 2020; 23(7): 788–799.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/subthalamic-beta-bursts-reflect-the-continuous-stochastic-fluctuations-of-ongoing-oscillations-in-parkinsons-disease/