Objective: We compare information transfer between forearm muscles and two subthalamic regions, namely the subthalamic nucleus (STN) and the zona incerta (ZI), during an isometric hold condition in Parkinson’s patients.

Background: For Parkinson’s patients, more causalities have been found for connections from electromyographic activity (EMG) of forearm muscles to STN local field potentials (LFP) than in the opposite direction (Florin et al., 2010). However, since a linear technique derived from Granger causality was used, we speculate that nonlinear techniques might capture a slightly different picture of information transfer between the subthalamic area (SA) and forearm muscles. It has been shown that the posterior SA, including the ZI might be a better target for deep brain stimulation (DBS) than the STN (Plaha et al., 2006). Therefore, we hypothesize that information transfer between ZI and forearm muscles might be more pronounced and modulated to a stronger degree by voluntary movement than between STN and forearm muscles.

Methods: Transfer entropy was used to capture information transfer and quantify information transmission delays between three different contralateral forearm muscles and either STN or ZI. TE is a nonlinear, model-free implementation of Wiener-Granger causality. We included 19 akinetic-rigid Parkinson patients in this study. At two recording heights, namely 5-6 mm dorsal of the STN and within the STN, at least 20 sec of LFP and EMG activity, during a tonic hold condition of the contralateral forearm, followed by at least 30 sec of a rest condition were measured. Data was preprocessed offline using a low-pass filter at 320 Hz and a high-pass filter at 2 Hz.

Results: For LFP recorded in the ZI, we found a bidirectional significant increase of causalities from the rest to the hold condition. During rest and independent of the direction, more causalities were found between STN and muscles than between ZI and muscles. Only at rest, interaction delays from muscles to LFP were significantly shorter than in the opposite direction.

Conclusions: Using nonlinear techniques, our results indicate a more distinct role of the ZI in voluntary movement modulation than of STN, which might explain better therapy effects observed when stimulating this area. Interaction delays for afferent connections to the SA indicate direct proprioceptive feedback, which is in line with previous findings.

References: Florin, E., Gross, J., Reck, C., Maarouf, M., Schnitzler, A., Sturm, V., Fink, G.R., Timmermann, L., 2010. Causality between local field potentials of the subthalamic nucleus and electromyograms of forearm muscles in Parkinson’s disease. Eur. J. Neurosci. 31, 491–498. doi:10.1111/j.1460-9568.2010.07083.x

Plaha, P., Ben-Shlomo, Y., Patel, N.K., Gill, S.S., 2006. Stimulation of the caudal zona incerta is superior to stimulation of the subthalamic nucleus in improving contralateral parkinsonism. Brain 129, 1732–1747. doi:10.1093/brain/awl127

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MDS Abstracts - https://www.mdsabstracts.org/abstract/information-transfer-between-subthalamic-area-and-forearm-muscles-during-tonic-muscle-activity-in-parkinsons-patients/