Objective: To investigate whether or not the improvement of saccade amplitude by the subthalamic nucleus (STN) deep brain stimulation (DBS) is the same for to visual targets of small and large eccentricities in Parkinson’s disease (PD) patients. We hypothesized that the improvement to target amplitude ratio is equal among the eccentricity conditions.

Background: We reported the impaired saccade latency and amplitude were improved by the STN DBS in PD patients (Yugeta, et al. 2010). PD patients rarely noticed their impairment clinically, and no subjects noticed improvement by the STN DBS. It is unknown whether the saccade amplitude improves equally both saccade towards visual targets of small and large eccentricities. In other words, whether is improvement of saccade amplitude by the STN DBS due to release of saccade angle limitation or due to facilitation of saccade command. What mechanism explains the amplitude improvement? Facilitation of saccade command or the limitation of absolute saccade amplitude or others? To tackle this issue, we planned the present study.

Methods: We recorded DC electro-oculography in 31 PD patients with and without the STN stimulation during horizontal prosaccade task using presented at target eccentricities of 5, 10, 20, and 30 degree. We analyzed the first saccade amplitude using paired t-test (DBS on and off), as well as the deviation angle and ratio of saccade amplitude from the target in each target eccentricity using one-factor (target eccentricity) analysis of variance.

Results: Saccade amplitude was improved by the STN DBS (p<0.01) in any target eccentricity. The deviation angle was increased with target eccentricity (p<0.01), however, the deviation ratio was not (p=0.09). That is to say, improvement of deviation ratio is same for visual targets of small and large eccentricities.

Conclusions: Improvements of the deviation ratio of saccade amplitude to target was not significantly different by target eccentricities. It is to say that the improvements of the deviation ratio did not depend on the target eccentricities. It may indicate that improvement of saccade amplitude by the STN DBS is due to constant facilitation of saccade command regardless of target eccentricities rather than release of (constant) saccade angle limitation.

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