Objective: This study aims to define a method to synchronize inertial signals recorded using wearable sensors and local field potentials recorded by the neurostimulator implanted in people with Parkinson’s disease.
Background: The subthalamic nucleus deep brain stimulation (STN-DBS) is an effective long-term treatment in Parkinson’s disease (PD), which improves symptoms such as tremor, rigidity, and bradykinesia . Wearable sensors can provide objective and quantitative measures of motor impairment [2,3]. To the best of our knowledge, in literature, there is no validated method to synchronize inertial sensors and neurostimulators without an additional instrument. This study aims to define a method to synchronize movement signals collected by an Inertial Measurement Unit (IMU) and local field potentials (LFPs) to allow a correlation analysis between brain signals and motor performance.
Method: PD patients treated with STN-DBS were recruited to perform a motor protocol in four different conditions of medication and stimulation: med off-stim on, med off-stim off, med on-stim off, med on-stim on. LFPs were recorded by the implanted DBS neurostimulator. Video recordings were made using a mobile phone. At the beginning of each condition, an IMU was placed on the chest near the implanted neurostimulator, and four taps were performed with a forefinger on the neurostimulator with a progressive time interval of one second between each tap. The detection of at least two taps was required to correctly synchronize the two different devices. If no taps were detected on the signals, synchronization was performed by video analysis.
Results: Each tap produces a mechanical artifact that can be detected by post-processing signal analysis. The inertial sensor always detected the taps performed, whereas the taps were not always visible from LFPs signals. In 58% of the patients, artifacts were detected on LFPs in at least one condition, and among them, 75% of the protocols were correctly synchronized by analyzing LFPs and IMU signals. Synchronization based on video analysis was characterized by an error of 116±70 ms in the med off-stim off condition.
Conclusion: The present work defines a new method to synchronize inertial signals and LFPs to allow further analysis on how LFPs are affected by stimulation, medication, and different motor tasks. The proposed method does not require an external system and it can be easily integrated in clinical practice.
References:  Dayal, Limousin and Foltynie, “Subthalamic nucleus deep brain stimulation in Parkinson’s disease: the effect of varying stimulation parameters,” 2017.
 Picardi M, Redaelli V, Antoniotti P, et al. Turning and sit-to-walk measures from the instrumented Timed Up and Go test return valid and responsive measures of dynamic balance in Parkinson’s disease. Clin Biomech (Bristol, Avon). 2020;80:105177. doi:10.1016/j.clinbiomech.2020.105177
 Schlachetzki JCM, Barth J, Marxreiter F, et al. Wearable sensors objectively measure gait parameters in Parkinson’s disease. PLoS One. 2017;12(10):e0183989. Published 2017 Oct 11. doi:10.1371/journal.pone.0183989
To cite this abstract in AMA style:I. D'Ascanio, G. Giannini, L. Baldelli, I. Cani, A. Giannoni, G. Leogrande, G. Lopane, G. Calandra-Buonaura, P. Cortelli, L. Chiari, L. Palmerini. A new synchronization method between inertial signals and local field potentials [abstract]. Mov Disord. 2023; 38 (suppl 1). https://www.mdsabstracts.org/abstract/a-new-synchronization-method-between-inertial-signals-and-local-field-potentials/. Accessed September 21, 2023.
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