Benefits of subthalamic nucleus deep brain stimulation on visually-guided saccades depend on stimulation side and classic paradigm in Parkinson's disease.

OBJECTIVE: We aimed to gain further insight into previously reported beneficial effects of subthalamic nucleus deep brain stimulation (STN-DBS) on visually-guided saccades by examining the effects of unilateral compared to bilateral stimulation, paradigm, and target eccentricity on saccades in individuals with Parkinson's disease (PD). METHODS: Eleven participants with PD and STN-DBS completed the visually-guided saccade paradigms with OFF, RIGHT, LEFT, and BOTH stimulation. Rightward saccade performance was evaluated for three paradigms and two target eccentricities. RESULTS: First, we found that BOTH and LEFT increased gain, peak velocity, and duration compared to OFF stimulation. Second, we found that BOTH and LEFT stimulation decreased latency during the gap and step paradigms but had no effect on latency during the overlap paradigm. Third, we found that RIGHT was not different compared to OFF at benefiting rightward saccade performance. CONCLUSIONS: Left unilateral and bilateral stimulation both improve the motor outcomes of rightward visually-guided saccades. Additionally, both improve latency, a cognitive-motor outcome, but only in paradigms when attention does not require disengagement from a present stimulus. SIGNIFICANCE: STN-DBS primarily benefits motor and cognitive-motor aspects of visually-guided saccades related to reflexive attentional shifting, with the latter only evident when the fixation-related attentional system is not engaged.

Medication only improves limb movements while deep brain stimulation improves eye and limb movements during visually-guided reaching in Parkinson's disease.

Background: Antiparkinson medication and subthalamic nucleus deep brain stimulation (STN-DBS), two common treatments of Parkinson's disease (PD), effectively improve skeletomotor movements. However, evidence suggests that these treatments may have differential effects on eye and limb movements, although both movement types are controlled through the parallel basal ganglia loops. Objective: Using a task that requires both eye and upper limb movements, we aimed to determine the effects of medication and STN-DBS on eye and upper limb movement performance. Methods: Participants performed a visually-guided reaching task. We collected eye and upper limb movement data from participants with PD who were tested both OFF and ON medication (n = 34) or both OFF and ON bilateral STN-DBS while OFF medication (n = 11). We also collected data from older adult healthy controls (n = 14). Results: We found that medication increased saccade latency, while having no effect on reach reaction time (RT). Medication significantly decreased saccade peak velocity, while increasing reach peak velocity. We also found that bilateral STN-DBS significantly decreased saccade latency while having no effect on reach RT, and increased saccade and reach peak velocity. Finally, we found that there was a positive relationship between saccade latency and reach RT, which was unaffected by either treatment. Conclusion: These findings show that medication worsens saccade performance and benefits reaching performance, while STN-DBS benefits both saccade and reaching performance. We explore what the differential beneficial and detrimental effects on eye and limb movements suggest about the potential physiological changes occurring due to treatment.

The Effects of Subthalamic Nucleus Deep Brain Stimulation and Retention Delay on Memory-Guided Reaching Performance in People with Parkinson's Disease.

BACKGROUND: Subthalamic nucleus deep brain stimulation (STN-DBS) improves intensive aspects of movement (velocity) in people with Parkinson's disease (PD) but impairs the more cognitively demanding coordinative aspects of movement (error). We extended these findings by evaluating STN-DBS induced changes in intensive and coordinative aspects of movement during a memory-guided reaching task with varying retention delays. OBJECTIVE: We evaluated the effect of STN-DBS on motor control during a memory-guided reaching task with short and long retention delays in participants with PD and compared performance to healthy controls (HC). METHODS: Eleven participants with PD completed the motor section of the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS III) and performed a memory-guided reaching task under four different STN-DBS conditions (DBS-OFF, DBS-RIGHT, DBS-LEFT, and DBS-BOTH) and two retention delays (0.5 s and 5 s). An additional 13 HC completed the memory-guided reaching task. RESULTS: Unilateral and bilateral STN-DBS improved the MDS-UPDRS III scores. In the memory-guided reaching task, both unilateral and bilateral STN-DBS increased the intensive aspects of movement (amplitude and velocity) in the direction toward HC but impaired coordinative aspects of movement (error) away from the HC. Furthermore, movement time was decreased but reaction time was unaffected by STN-DBS. Shorter retention delays increased amplitude and velocity, decreased movement times, and decreased error, but increased reaction times in the participants with PD. There were no interactions between STN-DBS condition and retention delay. CONCLUSION: STN-DBS may affect cognitive-motor functioning by altering activity throughout cortico-basal ganglia networks and the oscillatory activity subserving them.

Encoding type, medication, and deep brain stimulation differentially affect memory-guided sequential reaching movements in Parkinson's disease.

Memory-guided movements, vital to daily activities, are especially impaired in Parkinson's disease (PD). However, studies examining the effects of how information is encoded in memory and the effects of common treatments of PD, such as medication and subthalamic nucleus deep brain stimulation (STN-DBS), on memory-guided movements are uncommon and their findings are equivocal. We designed two memory-guided sequential reaching tasks, peripheral-vision or proprioception encoded, to investigate the effects of encoding type (peripheral-vision vs. proprioception), medication (on- vs. off-), STN-DBS (on- vs. off-, while off-medication), and compared STN-DBS vs. medication on reaching amplitude, error, and velocity. We collected data from 16 (analyzed n = 7) participants with PD, pre- and post-STN-DBS surgery, and 17 (analyzed n = 14) healthy controls. We had four important findings. First, encoding type differentially affected reaching performance: peripheral-vision reaches were faster and more accurate. Also, encoding type differentially affected reaching deficits in PD compared to healthy controls: peripheral-vision reaches manifested larger deficits in amplitude. Second, the effect of medication depended on encoding type: medication had no effect on amplitude, but reduced error for both encoding types, and increased velocity only during peripheral-vision encoding. Third, the effect of STN-DBS depended on encoding type: STN-DBS increased amplitude for both encoding types, increased error during proprioception encoding, and increased velocity for both encoding types. Fourth, STN-DBS was superior to medication with respect to increasing amplitude and velocity, whereas medication was superior to STN-DBS with respect to reducing error. We discuss our findings in the context of the previous literature and consider mechanisms for the differential effects of medication and STN-DBS.

Intraoperative Neuromonitoring.

Intraoperative neuromonitoring encompasses a variety of different modalities in which different neuropathways are monitored either continuously or at defined time points throughout a neurosurgical procedure. Surgical morbidity can be mitigated with careful patient selection and thoughtful implementation of the appropriate neuromonitoring modalities through the identification of eloquent areas or early detection of iatrogenic pathway disruption. Modalities covered in this article include somatosensory and motor evoked potentials, electromyography, electroencephalography, brainstem auditory evoked responses, and direct cortical stimulation.

Factors involved in long-term efficacy of deep brain stimulation of the thalamus for essential tremor.

OBJECT: Although nucleus ventralis intermedius stimulation has been shown to be safe and efficacious in the treatment of essential tremor, there is a subset of patients who eventually lose benefit from their stimulation. Proposed causes for this phenomenon include tolerance, disease progression, and suboptimal location. The goal of this study was to assess the factors that may lead to both stimulation failure, defined as loss of meaningful tremor relief, and less satisfactory outcomes, defined as leads requiring voltages>3.6 V for effective tremor control. METHODS: The authors present their clinical outcomes from 31 leads in 27 patients who had effective tremor control for >1 year following nucleus ventralis intermedius stimulation. All patients postoperatively had a mean decrease in both the writing and drawing subscales of the Fahn-Tolosa-Marin Tremor Rating Scale (p<0.001). RESULTS: After a mean follow-up of 40 months, 22 patients continued to have tremor control with stimulation. Four patients eventually lost efficacy of their stimulation at a mean of 39 months. There was no difference in age, duration of disease, or disease severity between the groups. Examination of perioperative factors revealed that suboptimal anteroposterior positioning as evidenced on intraoperative fluoroscopy occurred significantly more frequently in patients with stimulation failure (p=0.018). In patients with less satisfactory outcomes, no difference was seen between group demographics. Fluoroscopy again revealed suboptimal positioning more frequently in these patients (p=0.005). CONCLUSIONS: This study provides further evidence that suboptimal lead position in combination with disease progression or tolerance may result in less satisfactory long-term outcomes.