Low-frequency Versus High-frequency Subthalamic Nucleus Deep Brain Stimulation on Postural Control and Gait in Parkinson's Disease: A Quantitative Study

Low-Frequency Dual Target Deep Brain Stimulation May Relieve Parkinsonian Symptoms

Background

Deep brain stimulation (DBS) reduces the motor symptoms of Parkinson's disease. The two most common targets are the subthalamic nucleus and the globus pallidus. Dual target deep brain stimulation may better reduce symptoms and minimize side effects, but the optimal parameters of dual target deep brain stimulation and their potential interactions are unknown.

Objective

Our purpose was to quantify the frequency response of dual target DBS on bradykinesia and beta oscillations in participants with Parkinson's disease, and to explore intrahemispheric pulse delays as a means to reduce total energy delivered.

Methods

We applied dual target DBS using the Summit RC+S in six participants, varying deep brain stimulation frequency.

Results

Dual target DBS at 50 Hz was effective at reducing bradykinesia, whereas increasing deep brain stimulation frequency up to 125 Hz also significantly reduced beta power. This frequency effect on beta power was replicated in a biophysical model. The model suggested that 22 Hz dual target deep brain stimulation, with an intrahemispheric delay of 40 ms, can reduce beta power by 87%.

Conclusion

We conclude that dual target DBS at 125 Hz best reduced bradykinesia. However, low frequency DBS with an appropriate intrahemispheric delay could improve symptom relief.

Pointing in the right direction: Greater motor improvements with directional versus circular subthalamic nucleus deep brain stimulation for Parkinson's disease

BackgroundDirectional deep brain stimulation (DBS) provides more precise control of current spread than conventional ring-shaped electrodes. Whether this enhanced flexibility improves motor function is unclear.ObjectiveHere we examine whether directional and circular stimulation differentially impact motor performance in patients with Parkinson's disease.MethodsMotor behaviors were assessed in 31 patients who underwent unilateral subthalamic nucleus brain stimulation surgery (SUNDIAL, NCT03353688). Eight configurations, including 6 directional contacts and their corresponding rings), were evaluated during device activation. Objective measures of motor performance related to limb dexterity, gait, and overall mobility were evaluated in a double-blind fashion in the "off" medication state versus preoperative baseline, with stimulus amplitude at the center of the therapeutic window.ResultsSignificant changes in performance were observed across each of five motor tasks between the best and worst directional contacts on a given DBS row (p < 0.001 each task). Certain stimulation directions led to functional declines versus baseline, whereas the best direction yields greater improvement than ring stimulation (p = 0.005, p = 0.001, p = 0.007, p < 0.001, respectively, across tasks). Directional DBS improves therapeutic window and side effect thresholds versus ring stimulation (0.40 ± 0.94 and 0.35 ± 0.51 mA, p < 0.001, respectively), but these variables correlated only modestly with motor performance at a given stimulation site.ConclusionsOptimized directional subthalamic nucleus DBS yields better group-level motor performance than ring stimulation, in addition to its known advantages related to tolerability. Prospective studies should evaluate whether these improvements persist over longer time intervals.

Modeling and Optimizing Deep Brain Stimulation to Enhance Gait in Parkinson's Disease: Personalized Treatment with Neurophysiological Insights

Although high-frequency deep brain stimulation (DBS) is effective at relieving many motor symptoms of Parkinson's disease (PD), its effects on gait can be variable and unpredictable. This is due to 1) a lack of standardized and robust metrics for gait assessment in PD patients, 2) the challenges of performing a thorough evaluation of all the stimulation parameters space that can alter gait, and 3) a lack of understanding for impacts of stimulation on the neurophysiological signatures of walking. In this study, our goal was to develop a data-driven approach to identify optimal, personalized DBS stimulation parameters to improve gait in PD patients and identify the neurophysiological signature of improved gait. Local field potentials from the globus pallidus and electrocorticography from the motor cortex of three PD patients were recorded using an implanted bidirectional neural stimulator during overground walking. A walking performance index (WPI) was developed to assess gait metrics with high reliability. DBS frequency, amplitude, and pulse width on the "clinically-optimized" stimulation contact were then systemically changed to study their impacts on gait metrics and underlying neural dynamics. We developed a Gaussian Process Regressor (GPR) model to map the relationship between DBS settings and the WPI. Using this model, we identified and validated personalized DBS settings that significantly improved gait metrics. Linear mixed models were employed to identify neural spectral features associated with enhanced walking performance. We demonstrated that improved walking performance was linked to the modulation of neural activity in specific frequency bands, with reduced beta band power in the pallidum and increased alpha band pallidal-motor cortex coherence synchronization during key moments of the gait cycle. Integrating WPI and GPR to optimize DBS parameters underscores the importance of developing and understanding personalized, data-driven interventions for gait improvement in PD.

Evaluating the Effects of Frequency of Subthalamic Nucleus Deep Brain Stimulation on Postural Control in Parkinson's Disease: A Case-Series Study

Background/Objectives: Subthalamic nucleus deep brain stimulation (STN-DBS) is a standard treatment for motor complications in Parkinson's disease (PD). Its impact on axial symptoms is still not fully understood. This study aimed to quantitatively evaluate the effect of frequency changes within the therapeutic window on postural control performances of individuals with PD who underwent bilateral STN-DBS. Methods: Postural control was assessed using Computerized Dynamic Posturography with randomized DBS frequency parameters, low (60 Hz), high (130 Hz), and very high (180 Hz), across six sensory organization test (SOT) conditions. Results: Twenty PD participants with a mean age of 61.2 ± 10.1 years were included. There were no differences in equilibrium scores of SOT conditions between 60, 130, and 180 Hz frequencies (p > 0.05), except the SOT6 score (p = 0.003), where 60 Hz showed better equilibrium performance in SOT6, indicating an advantage in postural control when visual cues are disturbed. Discussion: Low-frequency settings (60 Hz) in STN-DBS may benefit those who rely heavily on visual cues while ineffectively using somatosensory and vestibular inputs. Conclusions: A tailored approach to the DBS frequency setting could optimize postural stability and reduce fall risk in these patients. Future research is needed to explore these mechanisms to enhance therapeutic strategies.

Efficacy of subthalamic deep brain stimulation programming strategies for gait disorders in Parkinson's disease: a systematic review and meta-analysis

Patients with advanced Parkinson's disease often suffer from severe gait and balance problems, impacting quality of live and persisting despite optimization of standard therapies. The aim of this review was to systematically review the efficacy of STN-DBS programming techniques in alleviating gait disturbances in patients with advanced PD. Searches were conducted in PubMed, Embase, and Lilacs databases, covering studies published until May 2024. The review identified 36 articles that explored five distinct STN-DBS techniques aimed at addressing gait and postural instability in Parkinson's patients: low-frequency stimulation, ventral STN stimulation for simultaneous substantia nigra activation, interleaving, asymmetric stimulation and a short pulse width study. Among these, 21 articles were included in the meta-analysis, which revealed significant heterogeneity among studies. Notably, low-frequency STN-DBS demonstrated positive outcomes in total UPDRS-III score and FOG-Q, especially when combined with dopaminergic therapy. The most favorable results were found for low-frequency STN stimulation. The descriptive analysis suggests that unconventional stimulation approaches may be viable for gait problems in patients who do not respond to standard therapies.

Effectiveness of Deep Brain Stimulation in Improving Balance in Parkinson's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Balance dysfunction is a debilitating feature of advanced Parkinson's disease (PD), potentially improved by deep brain stimulation (DBS). This systematic review and meta-analysis pooled evidence from randomized controlled trials (RCTs) on DBS effectiveness in improving balance in PD.

METHODS

A systematic search was conducted to identify eligible RCTs investigating the effectiveness of DBS on improving balance in people with PD. Meta-analysis was performed using random effects models and reported as mean difference and 95% confidence intervals. Risk of bias was assessed using Cochrane's ROB-2 tool.

RESULTS

Seventeen RCTs were eligible (n = 333), utilizing a range of stimulation sites, parameters, reporting tools for balance outcomes, and control/comparator groups, making the identification of clear trends and recommendations difficult. Eleven studies were deemed as having some risk of bias, 4 having low risk of bias and 2 having high risk of bias. One small meta-analysis was conducted and found no significant difference in balance outcomes. Most studies reported no significant improvement in Timed Up-and-Go scores, Berg Balance Scale scores, frequency of falls, and balance-related items of the Movement Disorder Society's Unified Parkinson's Disease Rating Scales. Some studies reported improvements in the Tinetti balance test, posturography readings, and reduction in falls though these were not supported by other studies due to a lack of reporting on these items or conflicting findings.

CONCLUSIONS

Current research suggests that DBS results in no significant improvement in balance dysfunction for people with PD, though such assertions require larger RCTs with clear reporting methods using validated reporting tools.

Effects of subthalamic nucleus deep brain stimulation using different frequency programming paradigms on axial symptoms in advanced Parkinson's disease

BACKGROUND

In advanced Parkinson's disease (PD), axial symptoms are common and can be debilitating. Although deep brain stimulation (DBS) significantly improves motor symptoms, conventional high-frequency stimulation (HFS) has limited effectiveness in improving axial symptoms. In this study, we investigated the effects on multiple axial symptoms after DBS surgery with three different frequency programming paradigms comprising HFS, low-frequency stimulation (LFS), and variable-frequency stimulation (VFS).

METHODS

This study involved PD patients who had significant preoperative axial symptoms and underwent bilateral subthalamic nucleus (STN) DBS. Axial symptoms, motor symptoms, medications, and quality of life were evaluated preoperatively (baseline). One month after surgery, HFS was applied. At 6 months post-surgery, HFS assessments were performed, and HFS was switched to LFS. A further month later, we conducted LFS assessments and switched LFS to VFS. At 8 months after surgery, VFS assessments were performed.

RESULTS

Of the 21 PD patients initially enrolled, 16 patients were ultimately included in this study. Regarding HFS, all axial symptoms except for the Berg Balance Scale (p < 0.0001) did not improve compared with the baseline (all p > 0.05). As for LFS and VFS, all axial symptoms improved significantly compared with both the baseline and HFS (all p < 0.05). Moreover, motor symptoms and medications were significantly better than the baseline (all p < 0.05) after using LFS and VFS. Additionally, the quality of life of the PD patients after receiving LFS and VFS was significantly better than at the baseline and with HFS (all p < 0.0001).

CONCLUSION

Our findings indicate that HFS is ineffective at improving the majority of axial symptoms in advanced PD. However, both the LFS and VFS programming paradigms exhibit significant improvements in various axial symptoms.

Does Impaired Plantar Cutaneous Vibration Perception Contribute to Axial Motor Symptoms in Parkinson's Disease? Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation

OBJECTIVE

To investigate whether impaired plantar cutaneous vibration perception contributes to axial motor symptoms in Parkinson's disease (PD) and whether anti-parkinsonian medication and subthalamic nucleus deep brain stimulation (STN-DBS) show different effects.

METHODS

Three groups were evaluated: PD patients in the medication "on" state (PD-MED), PD patients in the medication "on" state and additionally "on" STN-DBS (PD-MED-DBS), as well as healthy subjects (HS) as reference. Motor performance was analyzed using a pressure distribution platform. Plantar cutaneous vibration perception thresholds (VPT) were investigated using a customized vibration exciter at 30 Hz.

RESULTS

Motor performance of PD-MED and PD-MED-DBS was characterized by greater postural sway, smaller limits of stability ranges, and slower gait due to shorter strides, fewer steps per minute, and broader stride widths compared to HS. Comparing patient groups, PD-MED-DBS showed better overall motor performance than PD-MED, particularly for the functional limits of stability and gait. VPTs were significantly higher for PD-MED compared to those of HS, which suggests impaired plantar cutaneous vibration perception in PD. However, PD-MED-DBS showed less impaired cutaneous vibration perception than PD-MED.

CONCLUSIONS

PD patients suffer from poor motor performance compared to healthy subjects. Anti-parkinsonian medication in tandem with STN-DBS seems to be superior for normalizing axial motor symptoms compared to medication alone. Plantar cutaneous vibration perception is impaired in PD patients, whereas anti-parkinsonian medication together with STN-DBS is superior for normalizing tactile cutaneous perception compared to medication alone. Consequently, based on our results and the findings of the literature, impaired plantar cutaneous vibration perception might contribute to axial motor symptoms in PD.

Frequency settings of subthalamic nucleus DBS for Parkinson's disease: A systematic review and network meta-analysis

INTRODUCTION

Deep Brain Stimulation (DBS) is an effective treatment for the motor symptoms of Parkinson's Disease. The targeted physiological structure for lead location is commonly the subthalamic nucleus (STN). The efficacy of DBS for improving motor symptoms is assessed via the Unified Parkinson's Disease Rating III Scale (UPDRS-III). In this study, we sought to compare the efficacy of frequency settings utilized for STN-DBS.

METHODS

Following PRISMA Guidelines, a search on PUBMED and MEDLINE was performed to include full-length randomized controlled trials evaluating STN-DBS. The frequency stimulation parameters and Unified Parkinson's Disease Rating Scale (UPDRS-III) outcomes were extracted in the search. High-frequency stimulation (HFS) was defined as ≥100 Hz and low-frequency stimulation (LFS) was defined as <100 Hz. A frequentist network meta-analysis was performed with odds ratios (OR) and pooling performed using the Mantel-Haenszel method. Statistics are presented as OR [95% CI].

RESULTS

15 studies consisting of 298 patients were included for analysis. Bilateral HFS -0.68 [-0.89; -0.46] was associated with better UPDRS-III scores compared to bilateral LFS. On the other hand, bilateral LFS with medications (MEDS) was favored over HFS with MEDS (-0.28 [-0.63; 0.07]). Bilateral LFS and MEDS, HFS and MEDS, stimulation (STIM) OFF MEDS ON, HFS, LFS, STIM OFF MEDS OFF UPDRS outcomes were ranked from best to worst outcomes.

DISCUSSION

The outcomes of this study suggest that bilateral HFS has better utility for those with no response to medication, while LFS has additive benefits to medication by improving unique symptoms via different neurophysiological mechanisms.

Long-term effects of bilateral subthalamic nucleus deep brain stimulation on gait disorders in Parkinson's disease: a clinical-instrumental study

OBJECTIVE

To assess the long-term effects of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) on gait in a cohort of advanced Parkinson's Disease (PD) patients.

METHODS

This observational study included consecutive PD patients treated with bilateral STN-DBS. Different stimulation and drug treatment conditions were assessed: on-stimulation/off-medication, off-stimulation/off-medication, and on-stimulation/on-medication. Each patient performed the instrumented Timed Up and Go test (iTUG). The instrumental evaluation of walking ability was carried out with a wearable inertial sensor containing a three-dimensional (3D) accelerometer, gyroscope, and magnetometer. This device could provide 3D linear acceleration, angular velocity, and magnetic field vector. Disease motor severity was evaluated with the total score and subscores of the Unified Parkinson Disease Rating Scale part III.

RESULTS

Twenty-five PD patients with a 5-years median follow-up after surgery (range 3-7) were included (18 men; mean disease duration at surgery 10.44 ± 4.62 years; mean age at surgery 58.40 ± 5.73 years). Both stimulation and medication reduced the total duration of the iTUG and most of its different phases, suggesting a long-term beneficial effect on gait after surgery. However, comparing the two treatments, dopaminergic therapy had a more marked effect in all test phases. STN-DBS alone reduced total iTUG duration, sit-to-stand, and second turn phases duration, while it had a lower effect on stand-to-sit, first turn, forward walking, and walking backward phases duration.

CONCLUSIONS

This study highlighted that in the long-term after surgery, STN-DBS may contribute to gait and postural control improvement when used together with dopamine replacement therapy, which still shows a substantial beneficial effect.

Alternative patterns of deep brain stimulation in neurologic and neuropsychiatric disorders

Deep brain stimulation (DBS) is a widely used clinical therapy that modulates neuronal firing in subcortical structures, eliciting downstream network effects. Its effectiveness is determined by electrode geometry and location as well as adjustable stimulation parameters including pulse width, interstimulus interval, frequency, and amplitude. These parameters are often determined empirically during clinical or intraoperative programming and can be altered to an almost unlimited number of combinations. Conventional high-frequency stimulation uses a continuous high-frequency square-wave pulse (typically 130-160 Hz), but other stimulation patterns may prove efficacious, such as continuous or bursting theta-frequencies, variable frequencies, and coordinated reset stimulation. Here we summarize the current landscape and potential clinical applications for novel stimulation patterns.

WITHDRAWN: Laterality and frequency settings of subthalamic nucleus DBS for Parkinson's disease: A systematic review and network meta-analysis

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Anticipatory Postural Adjustments and Compensatory Postural Responses to Multidirectional Perturbations-Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease

BACKGROUND

Postural instability is one of the most restricting motor symptoms for patients with Parkinson's disease (PD). While medication therapy only shows minor effects, it is still unclear whether medication in conjunction with deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves postural stability. Hence, the aim of this study was to investigate whether PD patients treated with medication in conjunction with STN-DBS have superior postural control compared to patients treated with medication alone.

METHODS

Three study groups were tested: PD patients on medication (PD-MED), PD patients on medication and on STN-DBS (PD-MED-DBS), and healthy elderly subjects (HS) as a reference. Postural performance, including anticipatory postural adjustments (APA) prior to perturbation onset and compensatory postural responses (CPR) following multidirectional horizontal perturbations, was analyzed using force plate and electromyography data.

RESULTS

Regardless of the treatment condition, both patient groups showed inadequate APA and CPR with early and pronounced antagonistic muscle co-contractions compared to healthy elderly subjects. Comparing the treatment conditions, study group PD-MED-DBS only showed minor advantages over group PD-MED. In particular, group PD-MED-DBS showed faster postural reflexes and tended to have more physiological co-contraction ratios.

CONCLUSION

medication in conjunction with STN-DBS may have positive effects on the timing and amplitude of postural control.

Does subthalamic nucleus deep brain stimulation affect the static balance at different frequencies?

PURPOSE

To investigate the effects of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) with different stimulation frequencies on static balance.

MATERIALS AND METHODS

Twenty patients (15 males and 5 females), aged between 43 and 81 (mean: 60.05±7.4) years, who had been diagnosed with idiopathic Parkinson's disease (PD) and undergone STN-DBS surgery were included in the study. Static balance was assessed with TecnoBody Rehabilitation System at four different frequencies: 230, 130, 90 and 60Hz and off-stimulation. Static balance tests were 'stabilometric test, stabilometric compared bipedal closed/opened eye, stabilometric compared mono pedal (right/left foot)'. These tests reported the centre of pressure data 'ellipse area, perimeter, front/back and mediolateral standard deviations'.

RESULTS

There were no statically differences between the static balance test results at any frequency (p>0.05), but results were found better at 90Hz. Stabilometric compared bipedal opened eye forward-backward standard deviation result was significant between off-stimulation and 130Hz (p=0.04). Different frequency stimulation affected the static balance categories percentage with no statistical significance between off-stimulation and others (all p>0.05).

CONCLUSION

This study showed that STN-DBS did not affect the static balance negatively. Low-frequency (LF) stimulation improved the static equilibrium. Posturography systems will give more precise and quantitative results in similar studies with wide frequency ranges.

Clinical parameters predict the effect of bilateral subthalamic stimulation on dynamic balance parameters during gait in Parkinson's disease

We investigated the effect of deep brain stimulation on dynamic balance during gait in Parkinson's disease with motion sensor measurements and predicted their values from disease-related factors. We recruited twenty patients with Parkinson's disease treated with bilateral subthalamic stimulation for at least 12 months and 24 healthy controls. Six monitors with three-dimensional gyroscopes and accelerometers were placed on the chest, the lumbar region, the two wrists, and the shins. Patients performed the instrumented Timed Up and Go test in stimulation OFF, stimulation ON, and right- and left-sided stimulation ON conditions. Gait parameters and dynamic balance parameters such as double support, peak turn velocity, and the trunk's range of motion and velocity in three dimensions were analyzed. Age, disease duration, the time elapsed after implantation, the Hoehn-Yahr stage before and after the operation, the levodopa, and stimulation responsiveness were reported. We individually calculated the distance values of stimulation locations from the subthalamic motor center in three dimensions. Sway values of static balance were collected. We compared the gait parameters in the OFF and stimulation ON states and controls. With cluster analysis and a machine-learning-based multiple regression method, we explored the predictive clinical factors for each dynamic balance parameter (with age as a confounder). The arm movements improved the most among gait parameters due to stimulation and the horizontal and sagittal trunk movements. Double support did not change after switching on the stimulation on the group level and did not differ from control values. Individual changes in double support and horizontal range of trunk motion due to stimulation could be predicted from the most disease-related factors and the severity of the disease; the latter also from the stimulation-related changes in the static balance parameters. Physiotherapy should focus on double support and horizontal trunk movements when treating patients with subthalamic deep brain stimulation.

Effects of deep brain stimulation on the kinematics of gait and balance in patients with idiopathic Parkinson's disease

BACKGROUND

Advanced stages of idiopathic Parkinson's disease are often characterised by gait alterations and postural instability. Despite improvements in patients' motor symptoms after deep brain stimulation of the subthalamic nucleus, its effects on gait and balance remain a matter of debate. This study investigated the effects of deep brain stimulation on balance and kinematic parameters of gait.

METHODS

The gait of 26 patients with advanced idiopathic Parkinson's disease was analysed before and after (between 3 and 6 months) after bilateral deep brain stimulation of the subthalamic nucleus. Computerised analysis was used to study cadence, number of cycles with the correct support sequence, number of cycles, duration of the cycle stages, and knee and ankle goniometry. Balance, postural instability, and mobility were assessed using the Tinetti and Timed Up and Go test.

FINDINGS

After stimulation, the following changes were significant (p < 0.01): number of cycles with the correct support sequence, number of total cycles, and foot contact. Patients improved significantly (p < 0.01) in the Tinetti and Timed Up and Go tests, the risk factors for falls changed from high (median 17) to low (median 25), and they improved from minor dependence (statistical median 14) to normality (statistical median 8.70).

INTERPRETATION

Deep brain stimulation to inhibit hyperactivity of the subthalamic nucleus was associated with an improvement in the space-time variables of gait and balance in patients with Parkinson's disease for up to 3-6 months. These results highlight the major role of the subthalamic nucleus in motor control mechanisms during locomotion and balance.

Deep brain stimulation for Parkinson’s Disease: A Review and Future Outlook

Parkinson's Disease (PD) is a neurodegenerative disorder that manifests as an impairment of motor and non-motor abilities due to a loss of dopamine input to deep brain structures. While there is presently no cure for PD, a variety of pharmacological and surgical therapeutic interventions have been developed to manage PD symptoms. This review explores the past, present and future outlooks of PD treatment, with particular attention paid to deep brain stimulation (DBS), the surgical procedure to deliver DBS, and its limitations. Finally, our group's efforts with respect to brain mapping for DBS targeting will be discussed.

Combined Stimulation of the Substantia Nigra and the Subthalamic Nucleus for the Treatment of Refractory Gait Disturbances in Parkinson's Disease: A Preliminary Study

Deep brain stimulation of the subthalamic nucleus is efficient for the treatment of motor symptoms (i.e., tremors) in patients with Parkinson's disease. Gait disorders usually appear during advanced stages of idiopathic Parkinson's disease in up to 80% of patients and have an important impact on their quality of life. The effects of deep brain stimulation of the subthalamic nucleus on gait and balance are still controversial. For this reason, alternative targets have been considered, such as stimulation of the pedunculopontine nucleus and the pars reticulata of substantia nigra, involved in the integration of the functional connections for gait. Due to the proximity of the subthalamic nucleus to the substantia nigra, their combined stimulation is feasible and may lead to better outcomes, improving axial symptoms. Our objective was to prospectively compare simultaneous stimulation of both structures versus conventional subthalamic stimulation in improving gait disorders. In ten patients with advanced Parkinson's disease, deep brain stimulation leads (eight linear contacts) were implanted, and gait analysis was performed 6 months after surgery in off-stimulation and after 4 weeks of dual or single subthalamic stimulation. An improvement in gait parameters was confirmed with both stimulation conditions, with better results with combined substantia nigra and subthalamic stimulation compared with conventional subthalamic stimulation. Further studies are needed to determine if this effect remains after long-term dual-target stimulation.

Past, Present, and Future of Deep Brain Stimulation: Hardware, Software, Imaging, Physiology and Novel Approaches

Deep brain stimulation (DBS) has advanced treatment options for a variety of neurologic and neuropsychiatric conditions. As the technology for DBS continues to progress, treatment efficacy will continue to improve and disease indications will expand. Hardware advances such as longer-lasting batteries will reduce the frequency of battery replacement and segmented leads will facilitate improvements in the effectiveness of stimulation and have the potential to minimize stimulation side effects. Targeting advances such as specialized imaging sequences and "connectomics" will facilitate improved accuracy for lead positioning and trajectory planning. Software advances such as closed-loop stimulation and remote programming will enable DBS to be a more personalized and accessible technology. The future of DBS continues to be promising and holds the potential to further improve quality of life. In this review we will address the past, present and future of DBS.

Comparison of the Efficacy of Deep Brain Stimulation in Different Targets in Improving Gait in Parkinson's Disease: A Systematic Review and Bayesian Network Meta-Analysis

Background: Although a variety of targets for deep brain stimulation (DBS) have been found to be effective in Parkinson's disease (PD), it remains unclear which target for DBS leads to the best improvement in gait disorders in patients with PD. The purpose of this network meta-analysis (NMA) is to compare the efficacy of subthalamic nucleus (STN)-DBS, internal globus pallidus (GPi)-DBS, and pedunculopontine nucleus (PPN)-DBS, in improving gait disorders in patients with PD.

Methods: We searched the PubMed database for articles published from January 1990 to December 2020. We used various languages to search for relevant documents to reduce language bias. A Bayesian NMA and systematic review of randomized and non-randomized controlled trials were conducted to explore the effects of different targets for DBS on gait damage.

Result: In the 34 included studies, 538 patients with PD met the inclusion criteria. The NMA results of the effect of the DBS “on and off” on the mean change of the gait of the patients in medication-off show that GPi-DBS, STN-DBS, and PPN-DBS are significantly better than the baseline [GPi-DBS: –0.79(–1.2, –0.41), STN-DBS: –0.97(–1.1, –0.81), and PPN-DBS: –0.56(–1.1, –0.021)]. According to the surface under the cumulative ranking (SUCRA) score, the STN-DBS (SUCRA = 74.15%) ranked first, followed by the GPi-DBS (SUCRA = 48.30%), and the PPN-DBS (SUCRA = 27.20%) ranked last. The NMA results of the effect of the DBS “on and off” on the mean change of the gait of the patients in medication-on show that, compared with baseline, GPi-DBS and STN-DBS proved to be significantly effective [GPi-DBS: –0.53 (–1.0, –0.088) and STN-DBS: –0.47(–0.66, –0.29)]. The GPi-DBS ranked first (SUCRA = 59.00%), followed by STN-DBS(SUCRA = 51.70%), and PPN-DBS(SUCRA = 35.93%) ranked last.

Conclusion: The meta-analysis results show that both the STN-DBS and GPi-DBS can affect certain aspects of PD gait disorder.

Deep brain stimulation programming strategies: segmented leads, independent current sources, and future technology

Introduction: Advances in neuromodulation and deep brain stimulation (DBS) technologies have facilitated opportunities for improved clinical benefit and side effect management. However, new technologies have added complexity to clinic-based DBS programming.Areas covered: In this article, we review basic basal ganglia physiology, proposed mechanisms of action and technical aspects of DBS. We discuss novel DBS technologies for movement disorders including the role of advanced imaging software, lead design, IPG design, novel programming techniques including directional stimulation and coordinated reset neuromodulation. Additional topics include the use of potential biomarkers, such as local field potentials, electrocorticography, and adaptive stimulation. We will also discuss future directions including optogenetically inspired DBS.Expert opinion: The introduction of DBS for the management of movement disorders has expanded treatment options. In parallel with our improved understanding of brain physiology and neuroanatomy, new technologies have emerged to address challenges associated with neuromodulation, including variable effectiveness, side-effects, and programming complexity. Advanced functional neuroanatomy, improved imaging, real-time neurophysiology, improved electrode designs, and novel programming techniques have collectively been driving improvements in DBS outcomes.

Low-frequency STN-DBS provides acute gait improvements in Parkinson's disease: a double-blinded randomised cross-over feasibility trial

Background

Some people with Parkinson’s disease (PD) report poorer dynamic postural stability following high-frequency deep brain stimulation of the subthalamic nucleus (STN-DBS), which may contribute to an increased falls risk. However, some studies have shown low-frequency (60 Hz) STN-DBS improves clinical measures of postural stability, potentially providing support for this treatment. This double-blind randomised crossover study aimed to investigate the effects of low-frequency STN-DBS compared to high-frequency stimulation on objective measures of gait rhythmicity in people with PD.

Methods

During high- and low-frequency STN-DBS and while off-medication, participants completed assessments of symptom severity and walking (e.g., Timed Up-and-Go). During comfortable walking, the harmonic ratio, an objective measures of gait rhythmicity, was derived from head- and trunk-mounted accelerometers to provide insight in dynamic postural stability. Lower harmonic ratios represent less rhythmic walking and have discriminated people with PD who experience falls. Linear mixed model analyses were performed on fourteen participants.

Results

Low-frequency STN-DBS significantly improved medial–lateral and vertical trunk rhythmicity compared to high-frequency. Improvements were independent of electrode location and total electrical energy delivered. No differences were noted between stimulation conditions for temporal gait measures, clinical mobility measures, motor symptom severity or the presence of gait retropulsion.

Conclusions

This study provides evidence for the acute benefits of low-frequency stimulation for gait outcomes in STN-DBS PD patients, independent of electrode location. However, the perceived benefits of this therapy may be diminished for people who experienced significant tremor pre-operatively, as lower frequencies may cause these symptoms to re-emerge.

Trial registration: This study was prospectively registered with the Australian and New Zealand Clinical Trials Registry on 5 June 2018 (ACTRN12618000944235).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-021-00921-4.

Low-frequency electrical stimulation reduces cortical excitability in the human brain

Effective seizure control remains challenging for about 30% of epilepsy patients who are resistant to present-day pharmacotherapy. Novel approaches that not only reduce the severity and frequency of seizures, but also have limited side effects are therefore desirable. Accordingly, various neuromodulation approaches such as cortical electrical stimulation have been implemented to reduce seizure burden; however, the underlying mechanisms are not completely understood. Given that the initiation and spread of epileptic seizures critically depend on cortical excitability, understanding the neuromodulatory effects of cortical electrical stimulation on cortical excitability levels is paramount. Based on observations that synchronization in the electrocorticogram closely tracks brain excitability level, the effects of low-frequency (1 Hz) intracranial brain stimulation on the levels of cortical phase synchronization before, during, and after 1 Hz electrical stimulation were assessed in twelve patients. Analysis of phase synchronization levels across three broad frequency bands (1-45 Hz, 55-95 Hz, and 105-195 Hz) revealed that in patients with stimulation sites in the neocortex, phase synchronization levels were significantly reduced within the 55-95 Hz and 105-195 Hz bands during post-stimulation intervals compared to baseline; this effect persisted for at least 30 min post-stimulation. Similar effects were observed when phase synchronization levels were examined in the classic frequency bands, whereby a significant reduction was found during the post-stimulation intervals in the alpha, beta, and gamma bands. The anatomical extent of these effects was then assessed. Analysis of the results from six patients with intracranial electrodes in both hemispheres indicated that reductions in phase synchronization in the 1-45 Hz and 55-95 Hz frequency ranges were more prominent in the stimulated hemisphere. Overall, these findings demonstrate that low-frequency electrical stimulation reduces phase synchronization and hence cortical excitability in the human brain. Low-frequency stimulation of the epileptic focus may therefore contribute to the prevention of impending epileptic seizures.

Long-term success of low-frequency subthalamic nucleus stimulation for Parkinson's disease depends on tremor severity and symptom duration

Patients with Parkinson’s disease can develop axial symptoms, including speech, gait and balance difficulties. Chronic high-frequency (>100 Hz) deep brain stimulation can contribute to these impairments while low-frequency stimulation (<100 Hz) may improve symptoms but only in some individuals. Factors predicting which patients benefit from low-frequency stimulation in the long term remain unclear. This study aims to confirm that low-frequency stimulation improves axial symptoms, and to go further to also explore which factors predict the durability of its effects. We recruited patients who developed axial motor symptoms while using high-frequency stimulation and objectively assessed the short-term impact of low-frequency stimulation on axial symptoms, other aspects of motor function and quality of life. A retrospective chart review was then conducted on a larger cohort to identify which patient characteristics were associated with not only the need to trial low-frequency stimulation, but also those which predicted its sustained use. Among 20 prospective patients, low-frequency stimulation objectively improved mean motor and axial symptom severity and quality of life in the short term. Among a retrospective cohort of 168 patients, those with less severe tremor and those in whom axial symptoms had emerged sooner after subthalamic nucleus deep brain stimulation were more likely to be switched to and remain on long-term low-frequency stimulation. These data suggest that low-frequency stimulation results in objective mean improvements in overall motor function and axial symptoms among a group of patients, while individual patient characteristics can predict sustained long-term benefits. Longer follow-up in the context of a larger, controlled, double-blinded study would be required to provide definitive evidence of the role of low-frequency deep brain stimulation.

Gait and Balance Changes with Investigational Peripheral Nerve Cell Therapy during Deep Brain Stimulation in People with Parkinson's Disease

Background: The efficacy of deep brain stimulation (DBS) and dopaminergic therapy is known to decrease over time. Hence, a new investigational approach combines implanting autologous injury-activated peripheral nerve grafts (APNG) at the time of bilateral DBS surgery to the globus pallidus interna. Objectives: In a study where APNG was unilaterally implanted into the substantia nigra, we explored the effects on clinical gait and balance assessments over two years in 14 individuals with Parkinson’s disease. Methods: Computerized gait and balance evaluations were performed without medication, and stimulation was in the off state for at least 12 h to best assess the role of APNG implantation alone. We hypothesized that APNG might improve gait and balance deficits associated with PD. Results: While people with a degenerative movement disorder typically worsen with time, none of the gait parameters significantly changed across visits in this 24 month study. The postural stability item in the UPDRS did not worsen from baseline to the 24-month follow-up. However, we measured gait and balance improvements in the two most affected individuals, who had moderate PD. In these two individuals, we observed an increase in gait velocity and step length that persisted over 6 and 24 months. Conclusions: Participants did not show worsening of gait and balance performance in the off therapy state two years after surgery, while the two most severely affected participants showed improved performance. Further studies may better address the long-term maintanenace of these results.

Use of Functional MRI to Assess Effects of Deep Brain Stimulation Frequency Changes on Brain Activation in Parkinson Disease

BACKGROUND

Models have been developed for predicting ideal contact and amplitude for subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson disease (PD). Pulse-width is generally varied to modulate the size of the energy field produced. Effects of varying frequency in humans have not been systematically evaluated.

OBJECTIVE

To examine how altered frequencies affect blood oxygen level-dependent activation in PD.

METHODS

PD subjects with optimized DBS programming underwent functional magnetic resonance imaging (fMRI). Frequency was altered and fMRI scans/Unified Parkinson Disease Rating Scale motor subunit (UPDRS-III) scores were obtained. Analysis using DBS-OFF data was used to determine which regions were activated during DBS-ON. Peak activity utilizing T-values was obtained and compared.

RESULTS

At clinically optimized settings (n = 14 subjects), thalamic, globus pallidum externa (GPe), and posterior cerebellum activation were present. Activation levels significantly decreased in the thalamus, anterior cerebellum, and the GPe when frequency was decreased (P < .001). Primary somatosensory cortex activation levels significantly decreased when frequency was increased by 30 Hz, but not 60 Hz. Sex, age, disease/DBS duration, and bilaterality did not significantly affect the data. Retrospective analysis of fMRI activation patterns predicted optimal frequency in 11/14 subjects.

CONCLUSION

We show the first data with fMRI of STN DBS-ON while synchronizing cycling with magnetic resonance scanning. At clinically optimized settings, an fMRI signature of thalamic, GPe, and posterior cerebellum activation was seen. Reducing frequency significantly decreased thalamic, GPe, and anterior cerebellum activation. Current standard-of-care programming can take up to 6 mo using UPDRS-III testing alone. We provide preliminary evidence that using fMRI signature of frequency may have clinical utility and feasibility.

Clinical outcome prediction from analysis of microelectrode recordings using deep learning in subthalamic deep brain stimulation for Parkinson`s disease

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for improving the motor symptoms of advanced Parkinson's disease (PD). Accurate positioning of the stimulation electrodes is necessary for better clinical outcomes.

OBJECTIVE

We applied deep learning techniques to microelectrode recording (MER) signals to better predict motor function improvement, represented by the UPDRS part III scores, after bilateral STN DBS in patients with advanced PD. If we find the optimal stimulation point with MER by deep learning, we can improve the clinical outcome of STN DBS even under restrictions such as general anesthesia or non-cooperation of the patients.

METHODS

In total, 696 4-second left-side MER segments from 34 patients with advanced PD who underwent bilateral STN DBS surgery under general anesthesia were included. We transformed the original signal into three wavelets of 1-50 Hz, 50-500 Hz, and 500-5,000 Hz. The wavelet-transformed MER was used for input data of the deep learning. The patients were divided into two groups, good response and moderate response groups, according to DBS on to off ratio of UPDRS part III score for the off-medication state, 6 months postoperatively. The ratio were used for output data in deep learning. The Visual Geometry Group (VGG)-16 model with a multitask learning algorithm was used to estimate the bilateral effect of DBS. Different ratios of the loss function in the task-specific layer were applied considering that DBS affects both sides differently.

RESULTS

When we divided the MER signals according to the frequency, the maximal accuracy was higher in the 50-500 Hz group than in the 1-50 Hz and 500-5,000 Hz groups. In addition, when the multitask learning method was applied, the stability of the model was improved in comparison with single task learning. The maximal accuracy (80.21%) occurred when the right-to-left loss ratio was 5:1 or 6:1. The area under the curve (AUC) was 0.88 in the receiver operating characteristic (ROC) curve.

CONCLUSION

Clinical improvements in PD patients who underwent bilateral STN DBS could be predicted based on a multitask deep learning-based MER analysis.

Systematic Evaluation of DBS Parameters in the Hemi-Parkinsonian Rat Model

Electrical stimulation of the subthalamic nucleus (STN) is clinically employed to ameliorate several symptoms of manifest Parkinson’s Disease (PD). Stimulation parameters utilized by chronically implanted pulse generators comprise biphasic rectangular short (60–100 μs) pulses with a repetition frequency between 130 and 180 Hz. A better insight into the effect of electrical stimulation parameters could potentially reveal new possibilities for the improvement of deep brain stimulation (DBS) as a treatment. To this end, we employed single-sided 6-hydroxidopamine (6-OHDA) lesioning of the medial forebrain bundle (MFB) in rats to systematically investigate alternative stimulation parameters. These hemi-parkinsonian (hemi-PD) rats underwent individualized, ipsilateral electrical stimulation to the STN of the lesioned hemisphere, while the transiently induced contralateral rotational behavior was quantified to assess the effect of DBS parameter variations. The number of induced rotations during 30 s of stimulation was strongly correlated with the amplitude of the stimulation pulses. Despite a general linear relation between DBS frequency and rotational characteristics, a plateau effect was observed in the rotation count throughout the clinically used frequency range. Alternative waveforms to the conventional biphasic rectangular (Rect) pulse shapes [Triangular (Tri), Sinusoidal (Sine), and Sawtooth (Lin.Dec.)] required higher charges per phase to display similar behavior in rats as compared to the conventional pulse shape. The Euclidean Distance (ED) was used to quantify similarities between different angular trajectories. Overall, our study confirmed that the effect of different amplitude and frequency parameters of STN-DBS in the hemi-PD rat model was similar to those in human PD patients. This shows that induced contralateral rotation is a valuable readout in testing stimulation parameters. Our study supports the call for more pre-clinical studies using this measurement to assess the effect of other DBS parameters such as pulse-width and interphase intervals.

Deep Brain Stimulation Effects on Gait Pattern in Advanced Parkinson's Disease Patients

Background

Gait disturbance accompanies many neurodegenerative diseases; it is characteristic for Parkinson’s disease (PD). Treatment of advanced PD often includes deep brain stimulation (DBS) of the subthalamic nucleus. Regarding gait, previous studies have reported non-significant or conflicting results, possibly related to methodological limitations.

Objective

The objective of this prospective study was to assess the effects of DBS on biomechanical parameters of gait in patients with PD.

Methods

Twenty-one patients with advanced PD participated in this prospective study. Gait was examined in all patients using the Zebris FDM-T pressure-sensitive treadmill (Isny, Germany) before DBS implantation and after surgery immediately, further immediately after the start of neurostimulation, and 3 months after neurostimulator activation. We assessed spontaneous gait on a moving treadmill at different speeds. Step length, stance phase of both lower limbs, double-stance phase, and cadence were evaluated.

Results

In this study, step length increased, allowing the cadence to decrease. Double-stance phase duration, that is, the most sensitive parameter of gait quality and unsteadiness, was reduced, in gait at a speed of 4.5 km/h and in the narrow-based gaits at 1 km/h (tandem gait), which demonstrates improvement.

Conclusion

This study suggests positive effects of DBS treatment on gait in PD patients. Improvement was observed in several biomechanical parameters of gait.

The effect of STN DBS on modulating brain oscillations: consequences for motor and cognitive behavior

In this review, we highlight Professor John Rothwell's contribution towards understanding basal ganglia function and dysfunction, as well as the effects of subthalamic nucleus deep brain stimulation (STN DBS). The first section summarizes the rate and oscillatory models of basal ganglia dysfunction with a focus on the oscillation model. The second section summarizes the motor, gait, and cognitive mechanisms of action of STN DBS. In the final section, we summarize the effects of STN DBS on motor and cognitive tasks. The studies reviewed in this section support the conclusion that high-frequency STN DBS improves the motor symptoms of Parkinson's disease. With respect to cognition, STN DBS can be detrimental to performance especially when the task is cognitively demanding. Consolidating findings from many studies, we find that while motor network oscillatory activity is primarily correlated to the beta-band, cognitive network oscillatory activity is not confined to one band but is subserved by activity in multiple frequency bands. Because of these findings, we propose a modified motor and associative/cognitive oscillatory model that can explain the consistent positive motor benefits and the negative and null cognitive effects of STN DBS. This is clinically relevant because STN DBS should enhance oscillatory activity that is related to both motor and cognitive networks to improve both motor and cognitive performance.

The turning and barrier course reveals gait parameters for detecting freezing of gait and measuring the efficacy of deep brain stimulation

Freezing of gait (FOG) is a devastating motor symptom of Parkinson’s disease that leads to falls, reduced mobility, and decreased quality of life. Reliably eliciting FOG has been difficult in the clinical setting, which has limited discovery of pathophysiology and/or documentation of the efficacy of treatments, such as different frequencies of subthalamic deep brain stimulation (STN DBS). In this study we validated an instrumented gait task, the turning and barrier course (TBC), with the international standard FOG questionnaire question 3 (FOG-Q3, r = 0.74, p < 0.001). The TBC is easily assembled and mimics real-life environments that elicit FOG. People with Parkinson’s disease who experience FOG (freezers) spent more time freezing during the TBC compared to during forward walking (p = 0.007). Freezers also exhibited greater arrhythmicity during non-freezing gait when performing the TBC compared to forward walking (p = 0.006); this difference in gait arrhythmicity between tasks was not detected in non-freezers or controls. Freezers’ non-freezing gait was more arrhythmic than that of non-freezers or controls during all walking tasks (p < 0.05). A logistic regression model determined that a combination of gait arrhythmicity, stride time, shank angular range, and asymmetry had the greatest probability of classifying a step as FOG (area under receiver operating characteristic curve = 0.754). Freezers’ percent time freezing and non-freezing gait arrhythmicity decreased, and their shank angular velocity increased in the TBC during both 60 Hz and 140 Hz STN DBS (p < 0.05) to non-freezer values. The TBC is a standardized tool for eliciting FOG and demonstrating the efficacy of 60 Hz and 140 Hz STN DBS for gait impairment and FOG. The TBC revealed gait parameters that differentiated freezers from non-freezers and best predicted FOG; these may serve as relevant control variables for closed loop neurostimulation for FOG in Parkinson’s disease.

A Novel DBS Paradigm for Axial Features in Parkinson's Disease: A Randomized Crossover Study

BACKGROUND

High-frequency (130-185 Hz) deep brain stimulation (DBS) of the subthalamic nucleus is more effective for appendicular than axial symptoms in Parkinson's disease (PD). Low-frequency (60-80 Hz) stimulation (LFS) may reduce gait/balance impairment but typically results in worsening appendicular symptoms. We created a "dual-frequency" programming paradigm (interleave-interlink, IL-IL) to address both axial and appendicular symptoms. In IL-IL, 2 overlapping LFS programs are applied to the DBS lead, with the overlapping area focused on the optimal cathode. The nonoverlapping area (LFS) is thought to reduce gait/balance impairment, whereas the overlapping area (high-frequency stimulation, HFS) aims to control appendicular symptoms.

METHODS

We performed a randomized, double-blind crossover trial comparing patients' previously optimized IL-IL and conventional HFS paradigms. Each arm was 2 weeks in duration. The primary outcome measure was the patient/caregiver Modified Clinical Global Impression Severity (CGI-S). Secondary outcome measures included blinded motor evaluations, timed tests, patient/caregiver questionnaires, and Personal KinetiGraphs (PKG).

RESULTS

Twenty-five patients were enrolled, and 20 completed. The patient/caregiver CGI-S for gait/balance (P = 0.01) and appendicular symptom control (P = 0.001), and the blinded rater MDS-UPDRS-III (-5.22, P = 0.02), CGI-S gait/balance (P = 0.01), and CGI-S speech (P = 0.02) were better while on IL-IL. Scores on Parkinson's Disease Quality of Life (P = 0.002) and Freezing-of-Gait Questionnaires (P = 0.04) were better on IL-IL. The Timed-Up-and-Go was 9.8% faster (P = 0.01), with 11.8% reduction in steps (P = 0.001) on IL-IL. There was no difference in PKG bradykinesia (P = 0.18) or tremor (P = 0.23) between paradigms.

CONCLUSIONS

Our results prompt consideration of this novel programming paradigm (IL-IL) for PD patients with axial symptom impairment as a new treatment option for both axial and appendicular symptoms. © 2020 International Parkinson and Movement Disorder Society.

Speech Intelligibility During Clinical and Low Frequency

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an effective and widely used tool in the treatment of Parkinson’s disease (PD). STN-DBS has varied effects on speech. Clinical speech ratings suggest worsening following STN-DBS, but quantitative intelligibility, perceptual, and acoustic studies have produced mixed and inconsistent results. Improvements in phonation and declines in articulation have frequently been reported during different speech tasks under different stimulation conditions. Questions remain about preferred STN-DBS stimulation settings. Seven right-handed, native speakers of English with PD treated with bilateral STN-DBS were studied off medication at three stimulation conditions: stimulators off, 60 Hz (low frequency stimulation—LFS), and the typical clinical setting of 185 Hz (High frequency—HFS). Spontaneous speech was recorded in each condition and excerpts were prepared for transcription (intelligibility) and difficulty judgements. Separate excerpts were prepared for listeners to rate abnormalities in voice, articulation, fluency, and rate. Intelligibility for spontaneous speech was reduced at both HFS and LFS when compared to STN-DBS off. On the average, speech produced at HFS was more intelligible than that produced at LFS, but HFS made the intelligibility task (transcription) subjectively more difficult. Both voice quality and articulation were judged to be more abnormal with DBS on. STN-DBS reduced the intelligibility of spontaneous speech at both LFS and HFS but lowering the frequency did not improve intelligibility. Voice quality ratings with STN-DBS were correlated with the ratings made without stimulation. This was not true for articulation ratings. STN-DBS exacerbated existing voice problems and may have introduced new articulatory abnormalities. The results from individual DBS subjects showed both improved and reduced intelligibility varied as a function of DBS, with perceived changes in voice appearing to be more reflective of intelligibility than perceived changes in articulation.

Correlation between programmed stimulation parameters and their efficacy after deep brain electrode implantation for Parkinson’s disease

Purpose:

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an indispensable and effective surgery for patients with primary Parkinson’s disease (PD). Nonetheless, its postoperative effects can be decided by many factors including the optimal programmed stimulation parameters. In this study, we analyzed the correlation between different postoperative programmed stimulation parameters and their efficacy after STN–DBS electrode implantation in patients with PD.

Methods:

A total of 87 patients underwent electrode implantation and completed at least one year follow-up. Then, various combinations of stimulation parameters, including stimulus intensity, frequency, and pulse width, were examined for their effects on the clinical improvement of the patients. Improvements in motor and nonmotor symptoms were analyzed using Mini-Mental State Examination, Parkinson’s Disease Quality of Life Questionnaire-39, and Unified Parkinson’s Disease Rating Scale (UPDRS) scores before and after surgery.

Results:

We found significantly improved UPDRS scores, quality of life, and neuropsychiatric symptoms postoperatively considering the findings of the aforementioned stimulation parameters compared with those observed preoperatively.

Conclusion:

This study provides a better understanding on how programmed stimulation parameters help relieve PD symptoms and improve quality of life in patients with PD undergoing STN–DBS.

Variable- versus constant-frequency deep-brain stimulation in patients with advanced Parkinson's disease: study protocol for a randomized controlled trial

BACKGROUND

Deep-brain stimulation targeting the subthalamic nucleus (STN) can be used to treat motor symptoms and dyskinesia in the advanced stages of Parkinson's disease (PD). High-frequency stimulation (HFS) of the STN can lead to consistent, long-term improvement of PD symptoms. However, the effects of HFS on the axial symptoms of PD, specifically freezing of gait, can be limited or cause further impairment. While this can be alleviated via relatively low-frequency stimulation (LFS) in selected patients, LFS does not control all motor symptoms of PD. Recently, the National Engineering Laboratory for Neuromodulation reported preliminary findings regarding an efficient way to combine the advantages of HFS and LFS to form variable-frequency stimulation (VFS). However, this novel therapeutic strategy has not been formally tested in a randomized trial.

METHODS/DESIGN

We propose a multicenter, double-blind clinical trial involving 11 study hospitals and an established deep-brain stimulation team. The participants will be divided into a VFS and a constant-frequency stimulation group. The primary outcome will be changes in stand-walk-sit task scores after 3 months of treatment in the "medication off" condition. Secondary outcome measures include specific item scores on the Freezing of Gait Questionnaire and quality of life. The aim of this trial is to investigate the efficacy and safety of VFS compared with constant-frequency stimulation.

DISCUSSION

This is the first randomized controlled trial to comprehensively evaluate the effectiveness and safety of VFS of the STN in patients with advanced PD. VFS may represent a new option for clinical treatment of PD in the future.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03053726. Registered on February 15, 2017.

A Novel Dual-Frequency Deep Brain Stimulation Paradigm for Parkinson's Disease

INTRODUCTION

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) using high-frequency (130-185 Hz) stimulation (HFS) is more effective for appendicular than for axial symptoms. Low-frequency stimulation (LFS) of the STN may reduce gait/balance and speech impairment but can result in worsened appendicular symptoms, limiting its clinical usefulness. A novel dual-frequency paradigm (interleave-interlink, IL-IL) was created in order to reduce gait/balance and speech impairment while maintaining appendicular symptom control in Parkinson's disease (PD) patients chronically stimulated with DBS.

METHODS

Two overlapping LFS programs are applied to each DBS lead, with the overlapping area focused around the optimal electrode contact. As a result, this area receives HFS, controlling appendicular symptoms. The non-overlapping area receives LFS, potentially reducing gait/balance and speech impairment. Patients were separated into three categories based on their chief complaint(s): gait/balance impairment, speech impairment, and/or incomplete PD symptom control. The Clinical- Global Impression of Change scale (CGI-C) was completed retrospectively based on patient/caregiver feedback in patients who remained on IL-IL (at 3 months and at the last follow-up).

RESULTS

Seventy-six patients were switched from optimized HFS to IL-IL. Fifty-five (72%) patients remained on IL-IL after 22 ± 8.7 months. The median (range) CGI-C for gait was 2 (1-5) at 3 months and 3 (1-4) at last follow-up, for dysarthria it was 4 (1-4) at 3 months and 4 (1-5) at last follow-up, and for PD motor it was 2 (1-3) at 3 months and 2 (1-3) at last follow-up.

CONCLUSION

A substantial number of patients remained on IL-IL because of subjective improvements in gait/balance, speech, or PD symptoms. A prospective, double-blind, crossover study with objective/quantitative outcome measures is underway.

Treatment options for postural instability and gait difficulties in Parkinson's disease

Introduction: Gait and balance disorders in Parkinson's disease (PD) represent a major therapeutic challenge as frequent falls and freezing of gait impair quality of life and predict mortality. Limited dopaminergic therapy responses implicate non-dopaminergic mechanisms calling for alternative therapies.Areas covered: The authors provide a review that encompasses pathophysiological changes involved in axial motor impairments in PD, pharmacological approaches, exercise, and physical therapy, improving physical activity levels, invasive and non-invasive neurostimulation, cueing interventions and wearable technology, and cognitive interventions.Expert opinion: There are many promising therapies available that, to a variable degree, affect gait and balance disorders in PD. However, not one therapy is the 'silver bullet' that provides full relief and ultimately meaningfully improves the patient's quality of life. Sedentariness, apathy, and emergence of frailty in advancing PD, especially in the setting of medical comorbidities, are perhaps the biggest threats to experience sustained benefits with any of the available therapeutic options and therefore need to be aggressively treated as early as possible. Multimodal or combination therapies may provide complementary benefits to manage axial motor features in PD, but selection of treatment modalities should be tailored to the individual patient's needs.

Deep Brain Stimulation Programming for Movement Disorders: Current Concepts and Evidence-Based Strategies

Deep brain stimulation (DBS) has become the treatment of choice for advanced stages of Parkinson's disease, medically intractable essential tremor, and complicated segmental and generalized dystonia. In addition to accurate electrode placement in the target area, effective programming of DBS devices is considered the most important factor for the individual outcome after DBS. Programming of the implanted pulse generator (IPG) is the only modifiable factor once DBS leads have been implanted and it becomes even more relevant in cases in which the electrodes are located at the border of the intended target structure and when side effects become challenging. At present, adjusting stimulation parameters depends to a large extent on personal experience. Based on a comprehensive literature search, we here summarize previous studies that examined the significance of distinct stimulation strategies for ameliorating disease signs and symptoms. We assess the effect of adjusting the stimulus amplitude (A), frequency (f), and pulse width (pw) on clinical symptoms and examine more recent techniques for modulating neuronal elements by electrical stimulation, such as interleaving (Medtronic®) or directional current steering (Boston Scientific®, Abbott®). We thus provide an evidence-based strategy for achieving the best clinical effect with different disorders and avoiding adverse effects in DBS of the subthalamic nucleus (STN), the ventro-intermedius nucleus (VIM), and the globus pallidus internus (GPi).

Electric stimulation of the medial forebrain bundle influences sensorimotor gaiting in humans

Background

Prepulse inhibition (PPI) of the acoustic startle response, a measurement of sensorimotor gaiting, is modulated by monoaminergic, presumably dopaminergic neurotransmission. Disturbances of the dopaminergic system can cause deficient PPI as found in neuropsychiatric diseases. A target specific influence of deep brain stimulation (DBS) on PPI has been shown in animal models of neuropsychiatric disorders. In the present study, three patients with early dementia of Alzheimer type underwent DBS of the median forebrain bundle (MFB) in a compassionate use program to maintain cognitive abilities. This provided us the unique possibility to investigate the effects of different stimulation conditions of DBS of the MFB on PPI in humans.

Results

Separate analysis of each patient consistently showed a frequency dependent pattern with a DBS-induced increase of PPI at 60 Hz and unchanged PPI at 20 or 130 Hz, as compared to sham stimulation.

Conclusions

Our data demonstrate that electrical stimulation of the MFB modulates PPI in a frequency-dependent manner. PPI measurement could serve as a potential marker for optimization of DBS settings independent of the patient or the examiner.

An update on best practice of deep brain stimulation in Parkinson's disease

During the last 30 years, deep brain stimulation (DBS) has evolved into the clinical standard of care as a highly effective treatment for advanced Parkinson’s disease. Careful patient selection, an individualized anatomical target localization and meticulous evaluation of stimulation parameters for chronic DBS are crucial requirements to achieve optimal results. Current hardware-related advances allow for a more focused, individualized stimulation and hence may help to achieve optimal clinical results. However, current advances also increase the degrees of freedom for DBS programming and therefore challenge the skills of healthcare providers. This review gives an overview of the clinical effects of DBS, the criteria for patient, target, and device selection, and finally, offers strategies for a structured programming approach.

Chronic Subthalamic Nucleus Stimulation in Parkinson's Disease: Optimal Frequency for Gait Depends on Stimulation Site and Axial Symptoms

Axial symptoms emerge in a significant proportion of patients with Parkinson's disease (PD) within 5 years of deep brain stimulation (STN-DBS). Lowering the stimulation frequency may reduce these symptoms. The objectives of the current study were to establish the relationship between gait performance and STN-DBS frequency in chronically stimulated patients with PD, and to identify factors underlying variability in this relationship. Twenty-four patients treated chronically with STN-DBS (>4 years) were studied off-medication. The effect of stimulation frequency (40–140 Hz, 20 Hz-steps, constant energy) on gait was assessed in 6 sessions spread over 1 day. Half of the trials/session involved walking through a narrow doorway. The influence of stimulation voltage was investigated separately in 10 patients. Gait was measured using 3D motion capture and axial symptoms severity was assessed clinically. A novel statistical method established the optimal frequency(ies) for each patient by operating on frequency-tuning curves for multiple gait parameters. Narrowly-tuned optimal frequencies (20 Hz bandwidth) were found in 79% of patients. Frequency change produced a larger effect on gait performance than voltage change. Optimal frequency varied between patients (between 60 and 140 Hz). Contact site in the right STN and severity of axial symptoms were independent predictors of optimal frequency (P = 0.009), with lower frequencies associated with more dorsal contacts and worse axial symptoms. We conclude that gait performance is sensitive to small changes in STN-DBS frequency. The optimal frequency varies considerably between patients and is associated with electrode contact site and severity of axial symptoms. Between-subject variability of optimal frequency may stem from variable pathology outside the basal ganglia.

Alternate Subthalamic Nucleus Deep Brain Stimulation Parameters to Manage Motor Symptoms of Parkinson's Disease: Systematic Review and Meta-analysis

Background

The use of alternate frequencies, amplitudes, and pulse widths to manage motor symptoms in Parkinson's disease (PD) patients with subthalamic nucleus deep brain stimulation (STN-DBS) is of clinical interest, but currently lacks systematic evidence.

Objective/Hypothesis

Systematically review whether alternate STN-DBS settings influence the therapy's efficacy for managing PD motor symptoms.

Methods

Systematic searches identified studies that; involved bilateral STN-DBS PD patients; manipulated ≥ 1 STN-DBS parameter (e.g., amplitude); assessed ≥ 1 motor symptom (e.g., tremor); and contrasted the experimental and chronic stimulation settings. A Mantel-Haenszel random-effects meta-analysis compared the UPDRS-III sub-scores at low (60-Hz) and high frequencies ( ≥ 130 Hz). Inter-study heterogeneity was assessed with the Cohen's χ² and I² index, while the standard GRADE evidence assessment examined strength of evidence.

Results

Of the 21 included studies, 17 investigated the effect of alternate stimulation frequencies, five examined alternate stimulation amplitudes, and two studied changes in pulse width. Given the available data, meta-analyses were only possible for alternate stimulation frequencies. Analysis of the heterogeneity amongst the included studies indicated significant variability between studies and, on the basis of the GRADE framework, the pooled evidence from the meta-analysis studies was of very low quality due to the significant risks of bias.

Conclusions

The meta-analysis reported a very low quality of evidence for the efficacy of low-frequency STN-DBS for managing PD motor symptoms. Furthermore, it highlighted that lower amplitudes lead to the re-emergence of motor symptoms and further research is needed to understand the potential benefits of alternate STN-DBS parameters for PD patients.

The Neuromodulatory Impact of Subthalamic Nucleus Deep Brain Stimulation on Gait and Postural Instability in Parkinson's Disease Patients: A Prospective Case Controlled Study

Background: Subthalamic nucleus deep brain stimulation (STN-DBS) has been an established method in improvement of motor disabilities in Parkinson's disease (PD) patients. It has been also claimed to have an impact on balance and gait disorders in PD patients, but the previous results are conflicting. Objective: The aim of this prospective controlled study was to evaluate the impact of STN-DBS on balance disorders in PD patients in comparison with Best-Medical-Therapy (BMT) and Long-term-Post-Operative (POP) group. Methods: DBS-group consisted of 20 PD patients (8F, 12M) who underwent bilateral STN DBS. POP-group consisted of 14 post-DBS patients (6F, 8M) in median 30 months-time after surgery. Control group (BMT-group) consisted of 20 patients (11F, 9M) who did not undergo surgical intervention. UPDRS III scale and balance tests (Up And Go Test, Dual Task- Timed Up And Go Test, Tandem Walk Test) and posturography parameters were measured during 3 visits in 9 ± 2months periods (V1, V2, V3) 4 phases of treatment (BMT-ON/OFF, DBS-ON/OFF). Results: We have observed the slowdown of gait and postural instability progression in first 9 post-operative months followed by co-existent enhancement of balance disorders in next 9-months evaluation (p < 0.05) in balance tests (Up and Go, TWT) and in posturography examination parameters (p < 0.05). The effect was not observed neither in BMT-group nor POP-group (p > 0.05): these groups revealed constant progression of static and dynamic instability (p > 0.05). Conclusions: STN-DBS can have modulatory effect on static and dynamic instability in PD patients: it can temporarily improve balance disorders. mainly during first 9 post-operative months, but with possible following deterioration of the symptoms in next post-operative months.

Frequency-dependent effects of subthalamic deep brain stimulation on motor symptoms in Parkinson's disease: a meta-analysis of controlled trials

This study aims to investigate how the frequency settings of deep brain stimulation (DBS) targeting the subthalamic nucleus (STN) influence the motor symptoms of Parkinson's disease (PD). Stimulation with frequencies less than 100 Hz (mostly 60 or 80 Hz) is considered low-frequency stimulation (LFS) and with frequencies greater than 100 Hz (mostly 130 or 150 Hz) is considered high-frequency stimulation (HFS). We conducted a comprehensive literature review and meta-analysis with a random-effect model. Ten studies with 132 patients were included in our analysis. The pooled results showed no significant difference in the total Unified Parkinson Disease Rating Scale part III (UPDRS-III) scores (mean effect, -1.50; p = 0.19) or the rigidity subscore between HFS and LFS. Compared to LFS, HFS induced greater reduction in the tremor subscore within the medication-off condition (mean effect, 1.01; p = 0.002), while no significance was shown within the medication-on condition (mean effect, 0.01; p = 0.92). LFS induced greater reduction in akinesia subscore (mean effect, -1.68, p = 0.003), the time to complete the stand-walk-sit (SWS) test (mean effect, -4.84; p < 0.00001), and the number of freezing of gait (FOG) (mean effect, -1.71; p = 0.03). These results suggest that two types of frequency settings may have different effects, that is, HFS induces better responses for tremor and LFS induces greater response for akinesia, gait, and FOG, respectively, which are worthwhile to be confirmed in future study, and will ultimately inform the clinical practice in the management of PD using STN-DBS.

Neuromodulation targets pathological not physiological beta bursts during gait in Parkinson's disease

Freezing of gait (FOG) is a devastating axial motor symptom in Parkinson's disease (PD) leading to falls, institutionalization, and even death. The response of FOG to dopaminergic medication and deep brain stimulation (DBS) is complex, variable, and yet to be optimized. Fundamental gaps in the knowledge of the underlying neurobiomechanical mechanisms of FOG render this symptom one of the unsolved challenges in the treatment of PD. Subcortical neural mechanisms of gait impairment and FOG in PD are largely unknown due to the challenge of accessing deep brain circuitry and measuring neural signals in real time in freely-moving subjects. Additionally, there is a lack of gait tasks that reliably elicit FOG. Since FOG is episodic, we hypothesized that dynamic features of subthalamic (STN) beta oscillations, or beta bursts, may contribute to the Freezer phenotype in PD during gait tasks that elicit FOG. We also investigated whether STN DBS at 60 Hz or 140 Hz affected beta burst dynamics and gait impairment differently in Freezers and Non-Freezers. Synchronized STN local field potentials, from an implanted, sensing neurostimulator (Activa® PC + S, Medtronic, Inc.), and gait kinematics were recorded in 12 PD subjects, off-medication during forward walking and stepping-in-place tasks under the following randomly presented conditions: NO, 60 Hz, and 140 Hz DBS. Prolonged movement band beta burst durations differentiated Freezers from Non-Freezers, were a pathological neural feature of FOG and were shortened during DBS which improved gait. Normal gait parameters, accompanied by shorter bursts in Non-Freezers, were unchanged during DBS. The difference between the mean burst duration between hemispheres (STNs) of all individuals strongly correlated with the difference in stride time between their legs but there was no correlation between mean burst duration of each STN and stride time of the contralateral leg, suggesting an interaction between hemispheres influences gait. These results suggest that prolonged STN beta burst durations measured during gait is an important biomarker for FOG and that STN DBS modulated long not short burst durations, thereby acting to restore physiological sensorimotor information processing, while improving gait.

Long-term effect of low frequency stimulation of STN on dysphagia, freezing of gait and other motor symptoms in PD

OBJECTIVE

To evaluate the long-term effect of 60 Hz stimulation of the subthalamic nucleus (STN) on dysphagia, freezing of gait (FOG) and other motor symptoms in patients with Parkinson's disease (PD) who have FOG at the usual 130 Hz stimulation.

METHODS

This is a prospective, sequence randomised, crossover, double-blind study. PD patients with medication refractory FOG at 130 Hz stimulation of the STN were randomised to the sequences of 130 Hz, 60 Hz or deep brain stimulation off to assess swallowing function (videofluoroscopic evaluation and swallowing questionnaire), FOG severity (stand-walk-sit test and FOG questionnaire) and motor function (Unified PD Rating Scale, Part III motor examination (UPDRS-III)) at initial visit (V1) and follow-up visit (V2, after being on 60 Hz stimulation for an average of 14.5 months), in their usual medications on state. The frequency of aspiration events, perceived swallowing difficulty and FOG severity at 60 Hz compared with 130 Hz stimulation at V2, and their corresponding changes at V2 compared with V1 at 60 Hz were set as primary outcomes, with similar comparisons in UPDRS-III and its subscores as secondary outcomes.

RESULTS

All 11 enrolled participants completed V1 and 10 completed V2. We found the benefits of 60 Hz stimulation compared with 130 Hz in reducing aspiration frequency, perceived swallowing difficulty, FOG severity, bradykinesia and overall axial and motor symptoms at V1 and persistent benefits on all of them except dysphagia at V2, with overall decreasing efficacy when comparing V2 to V1.

CONCLUSIONS

The 60 Hz stimulation, when compared with 130 Hz, has long-term benefits on reducing FOG, bradykinesia and overall axial and motor symptoms except dysphagia, although the overall benefits decrease with long-term use.

CLINICAL TRIAL REGISTRATION

NCT02549859; Pre-results.