Objective: To investigate the dependency of antisaccade (AS) amplitude improvement by the subthalamic nucleus (STN) deep brain stimulation (DBS) on the target eccentricity in Parkinson’s disease (PD) patients. We hypothesize that the improvement of AS amplitude increases with increasing target eccentricity.

Background: Although PD patients have impairments not only in limb movements but also in eye movements, they rarely notice the latter or its improvements by the STN DBS. We reported the impaired saccade latencies and amplitudes were improved by the STN DBS in PD patients (Yugeta, et al. 2010). We reported that in both visually guided saccades (VGS) and memory guided saccades (MGS), the saccade amplitude improvement by the STN DBS increased in parallel with target eccentricity increment. In this study, we planned to study the dependency of saccade amplitude improvement on the target eccentricity in AS.

Methods: We recorded DC electro-oculography in 32 PD patients both with and without bilateral STN stimulation during horizontal AS task using target eccentricities of 5, 10, 20, and 30 degrees. We analyzed effects of DBS and target eccentricity on the first saccade amplitude by two-way analysis of variant (ANOVA). We also analyzed effects of target eccentricity on the improvement ratio, which was a ratio of saccade amplitude with the STN stimulation to that without stimulation, by one-way ANOVA.

Results: Saccade amplitudes were improved by the STN DBS (p<0.01), and they increased in parallel with the target eccentricity increment (p<0.01). No interaction was observed between DBS and target eccentricity (p>0.05). Improvement ratio of AS amplitudes did not differ among the target eccentricity (p>0.05), that is inconsistent with those of VGS (p<0.01) and MGS (p<0.01).

Conclusions: The difference in target eccentricity dependence of the amplitude ratio response to STN DBS indicates that the STN DBS modulates differently the neural circuits for automatic saccades generating VGS, working memory controlling MGS, and AS generation circuits for estimation of target position and inhibition of unwanted saccades.

References: Yugeta et al. (2010) Neurology;74:743-748. Terao et al. (2013) Clin Neurophysiol;124:1491-1506.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/improvement-of-antisaccade-amplitude-by-the-stn-dbs-and-target-eccentricity/