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Introduction: For deep brain stimulation (DBS) surgery of the subthalamic nucleus (STN) in Parkinson’s disease (PD), many centers employ visualization of the nucleus on magnetic resonance imaging (MRI), intraoperative microelectrode recordings (MER), and test stimulation in awake patients. The value of these steps is a subject for ongoing debate. In the current study, we determined the relative contribution of MRI targeting, multitrack MER, and awake test stimulation in final lead placement during STN DBS surgery for PD. Methods: Data on PD patients undergoing MRI-targeted STN DBS surgery with three-channel MER and awake test stimulation between February 2010 and January 2014 were analyzed to determine in which MER trajectory final leads were implanted and why this tract was chosen. Results: Seventy-six patients underwent implantation of 146 DBS leads. In 92% of the STN, the final leads were implanted in one of the three planned channels. In 6%, additional channels were needed. In 2%, surgery was aborted before final lead implantation due to anxiety or fatigue. The final leads were implanted in the channels with the longest STN MER signal trajectory in 60% of the STN (38% of the bilaterally implanted patients). This was the central channel containing the MRI target in 39% of the STN (18% bilaterally). The most frequently noted reasons why another channel than the central channel was chosen for final lead placement were (1) a lower threshold for side effects (54%) and (2) no or a too short trajectory of the STN MER signal (40%) in the central channel. The latter reason correlated with larger 2D (x and y) errors in our stereotactic method. Conclusions: STN DBS leads were often not implanted in the MRI-planned trajectory or in the trajectory with the longest STN MER signal. Thresholds for side effects during awake test stimulation were decisive for final target selection in the majority of patients.

Background Multi-directional electrodes in STN-DBS give the possibility to steer the high frequency current into the direction for clinical improvement and moreover recording of multi-array local field potential recordings (LFPs) give the possibility to determine the spatiotemporal distribution of oscillatory power across the STN that is related to the symptomatology in PD patients. Ultimately this information can be used as a feedback to optimize the stimulation parameters. Methods Eight PD patients were included in the study. After micro-electrode recording (MER), to determine the boundaries of the STN, temporarily a prototype of a new 32-contact DBS lead was inserted during the DBS procedure. Different modes of current steering were employed to improve motor symptoms and patients were scored on beneficial and adverse effects. Prior to and immediately after stimulation the distribution of spectral power was recorded by LFPs and spatiotemporal changes were evaluated with Fourier analysis. Results Thresholds of the effects of spherical stimulation were comparable to thresholds of stimulation through the conventional electrode at the same location in 89% of the cases. In eight of fourteen side effects, steering stimulation current increased the threshold for side effects by ⩾ 1 mA compared to spherical stimulation. The size of the therapeutic window could be widened in patient 6, 7 and 8 by steering stimulation in the posterior, posterior and anterior direction, respectively. LFP recordings prior to stimulation yielded the boundaries of the STN by showing increased spectral power particularly in the 13–40 Hz range. Recordings across all directions showed distinct spatiotemporal patterns of neuronal activity, which were related to the pattern of stimulation and the PD symptoms of the patient. Conclusions With a new DBS lead it is possible to steer stimulation current in STN-DBS such that it leads to a larger therapeutic window than with conventional spherical stimulation. Simultaneous LFP recordings across the entire STN provide spatial information about the location of the STN and its disease-related electrical activity. This may potentially be of benefit in predicting how to steer the current towards the sensorimotor part, while avoiding adverse effects.

Computer simulation with a model of the saccadic burst generator, proposed by C. A. Scudder (1988), demonstrated that metrics of saccades as well as their velocity characteristics can be altered without changing the characteristics of the burst generator itself. The model could be used to explain impairment of saccadic eye movements in, for instance, Parkinson's disease (PD), since in this disorder at brainstem level pontine structures, where the burst generator is located, are unaffected. Comparison of saccades in PD patients with computer simulations showed that the model provided reasonable explanation for the observed reduction in maximum saccade velocity, but is not appropriate to explain hypometria of saccades.