Physiological effects of dual target DBS in an individual with Parkinson's disease and a sensing-enabled pulse generator

INTRODUCTION

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or globus pallidus (GP) is an established therapy for Parkinson's disease (PD). Novel DBS devices can record local field potential (LFP) physiomarkers from the STN or GP. While beta (13-30 Hz) and gamma (40-90 Hz) STN and GP LFP oscillations correlate with PD motor severity and with therapeutic effects of treatments, STN-GP interactions in electrophysiology in patients with PD are not well characterized.

METHODS

Simultaneous bilateral STN and GP LFPs were recorded in a patient with PD who received bilateral STN-DBS and GP-DBS. Power spectra in each target and STN-GP coherence were assessed in various ON- and OFF-levodopa and DBS states, both at rest and with voluntary movement.

RESULTS

OFF-levodopa and OFF-DBS, beta peaks were present at bilateral STN and GP, coincident with prominent STN-GP beta coherence. Levodopa and dual-target-DBS (simultaneous STN-DBS and GP-DBS) completely suppressed STN-GP coherence. Finely-tuned gamma (FTG) activity at half the stimulation frequency (62.5 Hz) was seen in the STN during GP-DBS at rest. To assess the effects of movement on FTG activity, we recorded LFPs during instructed movement. We observed FTG activity in bilateral GP and bilateral STN during contralateral body movements while on GP-DBS and ON-levodopa. No FTG was seen with STN-DBS or dual-target-DBS.

CONCLUSION

Dual-target-DBS and levodopa suppressed STN-GP coherence. FTG throughout the basal ganglia was induced by GP-DBS in the presence of levodopa and movement. This bilateral STN-FTG and GP-FTG corresponded with the least severe bradykinesia state, suggesting a pro-kinetic role for FTG.

Motor network gamma oscillations in chronic home recordings predict dyskinesia in Parkinson's disease

In Parkinson's disease, imbalances between "antikinetic" and "prokinetic" patterns of neuronal oscillatory activity are related to motor dysfunction. Invasive brain recordings from the motor network have suggested that medical or surgical therapy can promote a prokinetic state by inducing narrowband gamma rhythms (65-90 Hz). Excessive narrowband gamma in the motor cortex promotes dyskinesia in rodent models, but the relationship between narrowband gamma and dyskinesia in humans has not been well established. To assess this relationship, we used a sensing-enabled deep brain stimulator system, attached to both motor cortex and basal ganglia (subthalamic or pallidal) leads, paired with wearable devices that continuously tracked motor signs in the contralateral upper limbs. We recorded 984 hours of multisite field potentials in 30 hemispheres of 16 subjects with Parkinson's disease (2/16 female, mean age 57 ± 12 years) while at home on usual antiparkinsonian medications. Recordings were done two to four weeks after implantation, prior to starting therapeutic stimulation. Narrowband gamma was detected in the precentral gyrus, subthalamic nucleus, or both structures on at least one side of 92% of subjects with a clinical history of dyskinesia. Narrowband gamma was not detected in the globus pallidus. Narrowband gamma spectral power in both structures co-fluctuated similarly with contralateral wearable dyskinesia scores (mean correlation coefficient of ρ=0.48 with a range of 0.12-0.82 for cortex, ρ=0.53 with a range of 0.5-0.77 for subthalamic nucleus). Stratification analysis showed the correlations were not driven by outlier values, and narrowband gamma could distinguish "on" periods with dyskinesia from "on" periods without dyskinesia. Time lag comparisons confirmed that gamma oscillations herald dyskinesia onset without a time lag in either structure when using 2-minute epochs. A linear model incorporating the three oscillatory bands (beta, theta/alpha, and narrowband gamma) increased the predictive power of dyskinesia for several subject hemispheres. We further identified spectrally distinct oscillations in the low gamma range (40-60 Hz) in three subjects, but the relationship of low gamma oscillations to dyskinesia was variable. Our findings support the hypothesis that excessive oscillatory activity at 65-90 Hz in the motor network tracks with dyskinesia similarly across both structures, without a detectable time lag. This rhythm may serve as a promising control signal for closed-loop deep brain stimulation using either cortical or subthalamic detection.

Advances in Deep Brain Stimulation: From Mechanisms to Applications

Deep brain stimulation (DBS) is an effective therapy for various neurologic and neuropsychiatric disorders, involving chronic implantation of electrodes into target brain regions for electrical stimulation delivery. Despite its safety and efficacy, DBS remains an underutilized therapy. Advances in the field of DBS, including in technology, mechanistic understanding, and applications have the potential to expand access and use of DBS, while also improving clinical outcomes. Developments in DBS technology, such as MRI compatibility and bidirectional DBS systems capable of sensing neural activity while providing therapeutic stimulation, have enabled advances in our understanding of DBS mechanisms and its application. In this review, we summarize recent work exploring DBS modulation of target networks. We also cover current work focusing on improved programming and the development of novel stimulation paradigms that go beyond current standards of DBS, many of which are enabled by sensing-enabled DBS systems and have the potential to expand access to DBS.

Weight and survival after deep brain stimulation for Parkinson's disease

BACKGROUND

Weight loss in Parkinson's disease (PD) is common and associated with increased mortality. The clinical significance of weight changes following deep brain stimulation (DBS) of the subthalamic nucleus (STN) and globus pallidus internus (GPi) is unclear.

OBJECTIVES

To address (1) whether PD patients exhibit progressive weight loss, (2) whether staged DBS surgery is associated with weight changes, and (3) whether survival after DBS correlates with post-DBS weight.

METHODS

This is a single-center, longitudinal, retrospective cohort study of 1625 PD patients. We examined trends in weight over time and the relationship between weight and years survival after DBS using regression and mixed model analyses.

RESULTS

There was a decline in body weight predating motor symptom onset (n = 756, 0.70 ± 0.03% decrease per year, p < 0.001). Weight decline accelerated in the decade preceding death (n = 456, 2.18 ± 0.31% decrease per year, p < 0.001). DBS patients showed a weight increase of 2.0 ± 0.33% at 1 year following the first DBS lead implant (n = 455) and 2.68 ± 1.1% at 3 years if a contralateral DBS lead was placed (n = 249). The bilateral STN DBS group gained the most weight after surgery during 6 years of follow up (vs bilateral GPi, 3.03 ± 0.45% vs 1.89 ± 0.31%, p < 0.01). An analysis of the DBS cohort with date of death available (n = 72) revealed that post-DBS weight (0-12 months after the first or 0-36 months after the second surgery) was positively associated with survival (R2 = 0.14, p < 0.001).

DISCUSSION

Though PD is associated with significant weight loss, DBS patients gained weight following surgery. Higher post-operative weight was associated with increased survival. These results should be replicated in other cohorts.

Sub-harmonic entrainment of cortical gamma oscillations to deep brain stimulation in Parkinson's disease: Model based predictions and validation in three human subjects

OBJECTIVES

The exact mechanisms of deep brain stimulation (DBS) are still an active area of investigation, in spite of its clinical successes. This is due in part to the lack of understanding of the effects of stimulation on neuronal rhythms. Entrainment of brain oscillations has been hypothesised as a potential mechanism of neuromodulation. A better understanding of entrainment might further inform existing methods of continuous DBS, and help refine algorithms for adaptive methods. The purpose of this study is to develop and test a theoretical framework to predict entrainment of cortical rhythms to DBS across a wide range of stimulation parameters.

MATERIALS AND METHODS

We fit a model of interacting neural populations to selected features characterising PD patients' off-stimulation finely-tuned gamma rhythm recorded through electrocorticography. Using the fitted models, we predict basal ganglia DBS parameters that would result in 1:2 entrainment, a special case of sub-harmonic entrainment observed in patients and predicted by theory.

RESULTS

We show that the neural circuit models fitted to patient data exhibit 1:2 entrainment when stimulation is provided across a range of stimulation parameters. Furthermore, we verify key features of the region of 1:2 entrainment in the stimulation frequency/amplitude space with follow-up recordings from the same patients, such as the loss of 1:2 entrainment above certain stimulation amplitudes.

CONCLUSION

Our results reveal that continuous, constant frequency DBS in patients may lead to nonlinear patterns of neuronal entrainment across stimulation parameters, and that these responses can be predicted by modelling. Should entrainment prove to be an important mechanism of therapeutic stimulation, our modelling framework may reduce the parameter space that clinicians must consider when programming devices for optimal benefit.

Personalized chronic adaptive deep brain stimulation outperforms conventional stimulation in Parkinson's disease

Deep brain stimulation is a widely used therapy for Parkinson's disease (PD) but currently lacks dynamic responsiveness to changing clinical and neural states. Feedback control has the potential to improve therapeutic effectiveness, but optimal control strategy and additional benefits of "adaptive" neurostimulation are unclear. We implemented adaptive subthalamic nucleus stimulation, controlled by subthalamic or cortical signals, in three PD patients (five hemispheres) during normal daily life. We identified neurophysiological biomarkers of residual motor fluctuations using data-driven analyses of field potentials over a wide frequency range and varying stimulation amplitudes. Narrowband gamma oscillations (65-70 Hz) at either site emerged as the best control signal for sensing during stimulation. A blinded, randomized trial demonstrated improved motor symptoms and quality of life compared to clinically optimized standard stimulation. Our approach highlights the promise of personalized adaptive neurostimulation based on data-driven selection of control signals and may be applied to other neurological disorders.

Proceedings of the 10th annual deep brain stimulation think tank: Advances in cutting edge technologies, artificial intelligence, neuromodulation, neuroethics, interventional psychiatry, and women in neuromodulation

The deep brain stimulation (DBS) Think Tank X was held on August 17-19, 2022 in Orlando FL. The session organizers and moderators were all women with the theme women in neuromodulation. Dr. Helen Mayberg from Mt. Sinai, NY was the keynote speaker. She discussed milestones and her experiences in developing depression DBS. The DBS Think Tank was founded in 2012 and provides an open platform where clinicians, engineers and researchers (from industry and academia) can freely discuss current and emerging DBS technologies as well as the logistical and ethical issues facing the field. The consensus among the DBS Think Tank X speakers was that DBS has continued to expand in scope however several indications have reached the "trough of disillusionment." DBS for depression was considered as "re-emerging" and approaching a slope of enlightenment. DBS for depression will soon re-enter clinical trials. The group estimated that globally more than 244,000 DBS devices have been implanted for neurological and neuropsychiatric disorders. This year's meeting was focused on advances in the following areas: neuromodulation in Europe, Asia, and Australia; cutting-edge technologies, closed loop DBS, DBS tele-health, neuroethics, lesion therapy, interventional psychiatry, and adaptive DBS.

Embedded Human Closed-Loop Deep Brain Stimulation for Tourette Syndrome: A Nonrandomized Controlled Trial

Importance

Because Tourette syndrome (TS) is a paroxysmal disorder, symptomatic relief in individuals with TS may be possible through the application of stimulation only during the manifestation of human tic neural signatures. This technique could be capable of suppressing both motor and vocal tics and would have similar effectiveness to conventional continuous deep brain stimulation (DBS).

Objective

To evaluate the feasibility, safety, and clinical effectiveness of bilateral centromedian-parafascicular complex thalamic closed-loop DBS as a treatment for medication-refractory TS.

Design, Setting, and Participants

This single-center double-blinded safety and feasibility trial was conducted between February 2014 and June 2020. Six individuals with TS were screened and recruited from the Norman Fixel Institute at the University of Florida. The primary outcome was measured at 6 months, and participants were followed up for the duration of the neurostimulator battery life. Independent ratings that compared closed-loop and conventional DBS were videotaped. The first 2 of 6 individuals with TS were excluded from the study because the technology for embedded closed-loop capability was not yet available. The date of analysis was August 2020.

Interventions

DBS therapy controlled by an embedded closed-loop stimulation system.

Main Outcomes and Measures

The primary clinical outcome measure was a minimum of a 40% reduction in the YGTSS score at 6 months following DBS. There was also a comparison of conventional DBS with closed-loop DBS using the Modified Rush Videotape Rating Scale for Tic.

Results

The mean (SD) age at TS diagnosis for the cohort was 8.5 (2.9), and the mean (SD) disease duration was 23.7 (5.8) years. Four individuals with TS were analyzed (2 male, 2 female; mean [SD] age, 23.7 [5.8] years). The study showed the closed-loop approach was both feasible and safe. One of the novelties of this study was that a patient-specific closed-loop paradigm was created for each participant. The features and stimulation transition speed were customized based on the signal quality and the tolerance to adverse reactions. The mean (SD) therapeutic outcome with conventional DBS was 33.3% (35.7%) improvement on the YGTSS and 52.8% (21.9%) improvement on the Modified Rush Videotape Rating Scale. Two of 4 participants had a primary outcome variable improvement of 40% meeting the primary efficacy target. When comparing closed-loop DBS with conventional DBS using a Wilcoxon sign-rank test, there was no statistical difference between tic severity score and both approaches revealed a lower tic severity score compared with baseline. The study was feasible in all 4 participants, and there were 25 total reported adverse events with 3 study-related events (12%). The most common adverse events were headache and anxiety.

Conclusions and Relevance

Embedded closed-loop deep DBS was feasible, safe, and had a comparable outcome to conventional TS DBS for the treatment of tics.

Trial Registration

ClinicalTrials.gov Identifier: NCT02056873.

Distinct Roles of the Human Subthalamic Nucleus and Dorsal Pallidum in Parkinson's Disease Impulsivity

BACKGROUND

Impulsivity and impulse control disorders are common in Parkinson's disease and lead to increased morbidity and reduced quality of life. Impulsivity is thought to arise from aberrant reward processing and inhibitory control, but it is unclear why deep brain stimulation of either the subthalamic nucleus (STN) or globus pallidus internus (GPi) affects levels of impulsivity. Our aim was to assess the role of the STN and GPi in impulsivity using invasive local field potential (LFP) recordings from deep brain stimulation electrodes.

METHODS

We measured LFPs during a simple rewarding Go/NoGo paradigm in 39 female and male human patients with Parkinson's disease manifesting variable amounts of impulsivity who were undergoing unilateral deep brain stimulation of either the STN (18 nuclei) or GPi (28 nuclei). We identified reward-specific LFP event-related potentials and correlated them to impulsivity severity.

RESULTS

LFPs in both structures modulated during reward-specific Go and NoGo stimulus evaluation, reward feedback, and loss feedback. Motor and limbic functions were anatomically separable in the GPi but not in the STN. Across participants, LFP reward processing responses in the STN and GPi uniquely depended on the severity of impulsivity.

CONCLUSIONS

This study establishes LFP correlates of impulsivity within the STN and GPi regions. We propose a model for basal ganglia reward processing that includes the bottom-up role of the GPi in reward salience and the top-down role of the STN in cognitive control.

The Human Tic Detector: An automatic approach to tic characterization using wearable sensors

OBJECTIVE

Current rating scales for Tourette syndrome (TS) are limited by recollection bias or brief assessment periods. This proof-of-concept study aimed to develop a sensor-based paradigm to detect and classify tics.

METHODS

We recorded both electromyogram and acceleration data from seventeen TS patients, either when voluntarily moving or experiencing tics and during the modified Rush Video Tic Rating Scale (mRVTRS). Spectral properties of voluntary and tic movements from the sensor that captured the dominant tic were calculated and used as features in a support vector machine (SVM) to detect and classify movements retrospectively.

RESULTS

Across patients, the SVM had an accuracy, sensitivity, and specificity of 96.69 ± 4.84%, 98.24 ± 4.79%, and 96.03 ± 6.04%, respectively, when classifying movements in the test dataset. Furthermore, each patient's SVM was validated using data collected during the mRVTRS. Compared to the expert consensus, the tic detection accuracy was 85.63 ± 15.28% during the mRVTRS, while overall movement classification accuracy was 94.23 ± 5.97%.

CONCLUSIONS

These results demonstrate that wearable sensors can capture physiological differences between tic and voluntary movements and are comparable to expert consensus.

SIGNIFICANCE

Ultimately, wearables could individualize and improve care for people with TS, provide a robust and objective measure of tics, and allow data collection in real-world settings.

Chronic embedded cortico-thalamic closed-loop deep brain stimulation for the treatment of essential tremor

Deep brain stimulation (DBS) is an approved therapy for the treatment of medically refractory and severe movement disorders. However, most existing neurostimulators can only apply continuous stimulation [open-loop DBS (OL-DBS)], ignoring patient behavior and environmental factors, which consequently leads to an inefficient therapy, thus limiting the therapeutic window. Here, we established the feasibility of a self-adjusting therapeutic DBS [closed-loop DBS (CL-DBS)], fully embedded in a chronic investigational neurostimulator (Activa PC + S), for three patients affected by essential tremor (ET) enrolled in a longitudinal (6 months) within-subject crossover protocol (DBS OFF, OL-DBS, and CL-DBS). Most patients with ET experience involuntary limb tremor during goal-directed movements, but not during rest. Hence, the proposed CL-DBS paradigm explored the efficacy of modulating the stimulation amplitude based on patient-specific motor behavior, suppressing the pathological tremor on-demand based on a cortical electrode detecting upper limb motor activity. Here, we demonstrated how the proposed stimulation paradigm was able to achieve clinical efficacy and tremor suppression comparable with OL-DBS in a range of movements (cup reaching, proximal and distal posture, water pouring, and writing) while having a consistent reduction in energy delivery. The proposed paradigm is an important step toward a behaviorally modulated fully embedded DBS system, capable of delivering stimulation only when needed, and potentially mitigating pitfalls of OL-DBS, such as DBS-induced side effects and premature device replacement.

Proceedings of the Eighth Annual Deep Brain Stimulation Think Tank: Advances in Optogenetics, Ethical Issues Affecting DBS Research, Neuromodulatory Approaches for Depression, Adaptive Neurostimulation, and Emerging DBS Technologies

We estimate that 208,000 deep brain stimulation (DBS) devices have been implanted to address neurological and neuropsychiatric disorders worldwide. DBS Think Tank presenters pooled data and determined that DBS expanded in its scope and has been applied to multiple brain disorders in an effort to modulate neural circuitry. The DBS Think Tank was founded in 2012 providing a space where clinicians, engineers, researchers from industry and academia discuss current and emerging DBS technologies and logistical and ethical issues facing the field. The emphasis is on cutting edge research and collaboration aimed to advance the DBS field. The Eighth Annual DBS Think Tank was held virtually on September 1 and 2, 2020 (Zoom Video Communications) due to restrictions related to the COVID-19 pandemic. The meeting focused on advances in: (1) optogenetics as a tool for comprehending neurobiology of diseases and on optogenetically-inspired DBS, (2) cutting edge of emerging DBS technologies, (3) ethical issues affecting DBS research and access to care, (4) neuromodulatory approaches for depression, (5) advancing novel hardware, software and imaging methodologies, (6) use of neurophysiological signals in adaptive neurostimulation, and (7) use of more advanced technologies to improve DBS clinical outcomes. There were 178 attendees who participated in a DBS Think Tank survey, which revealed the expansion of DBS into several indications such as obesity, post-traumatic stress disorder, addiction and Alzheimer’s disease. This proceedings summarizes the advances discussed at the Eighth Annual DBS Think Tank.

Closed-Loop Deep Brain Stimulation to Treat Medication-Refractory Freezing of Gait in Parkinson's Disease

Background: Treating medication-refractory freezing of gait (FoG) in Parkinson’s disease (PD) remains challenging despite several trials reporting improvements in motor symptoms using subthalamic nucleus or globus pallidus internus (GPi) deep brain stimulation (DBS). Pedunculopontine nucleus (PPN) region DBS has been used for medication-refractory FoG, with mixed findings. FoG, as a paroxysmal phenomenon, provides an ideal framework for the possibility of closed-loop DBS (CL-DBS).

Methods: In this clinical trial (NCT02318927), five subjects with medication-refractory FoG underwent bilateral GPi DBS implantation to address levodopa-responsive PD symptoms with open-loop stimulation. Additionally, PPN DBS leads were implanted for CL-DBS to treat FoG. The primary outcome of the study was a 40% improvement in medication-refractory FoG in 60% of subjects at 6 months when “on” PPN CL-DBS. Secondary outcomes included device feasibility to gauge the recruitment potential of this four-lead DBS approach for a potentially larger clinical trial. Safety was judged based on adverse events and explantation rate.

Findings: The feasibility of this approach was demonstrated as we recruited five subjects with both “on” and “off” medication freezing. The safety for this population of patients receiving four DBS leads was suboptimal and associated with a high explantation rate of 40%. The primary clinical outcome in three of the five subjects was achieved at 6 months. However, the group analysis of the primary clinical outcome did not reveal any benefit.

Interpretation: This study of a human PPN CL-DBS trial in medication-refractory FoG showed feasibility in recruitment, suboptimal safety, and a heterogeneous clinical effect in FoG outcomes.

Long-term Parkinson's disease quality of life after staged DBS: STN vs GPi and first vs second lead

Deep brain stimulation (DBS) for Parkinson’s disease (PD) improves quality of life (QoL), but longitudinal follow-up data are scarce. We sought to quantify long-term benefits of subthalamic nucleus (STN) vs globus pallidus internus (GPi), and unilateral vs staged bilateral PD-DBS on postoperative QoL. This is a retrospective, longitudinal, non-randomized study using the PD QoL questionnaire (PDQ)-39 in patients with STN- or GPi-DBS, and with unilateral (N = 191) or staged bilateral (an additional contralateral lead implant) surgery (N = 127 and 156 for the first and second lead, respectively). Changes in PDQ-39 summary index (PDQ-39SI) and subscores throughout 60 months of follow-up were used as the primary analysis. We applied mixed models that included levodopa and covariates that differed at baseline across groups. For unilateral implantation, we observed an initial improvement in PDQ-39SI of 15.55 ± 3.29% (µ ± SE) across both brain targets at 4 months postoperatively. Unilateral STN patients demonstrated greater improvement in PDQ-39SI than GPi patients at 4 and 18 months postoperatively. Analysis of patients with staged bilateral leads revealed an initial 25.34 ± 2.74% (µ ± SE) improvement in PDQ-39SI at 4 months after the first lead with further improvement until 18 months, with no difference across targets. Scores did not improve after the second lead with gradual worsening starting at 18 months postoperatively. STN-DBS provided greater short-term QoL improvement than GPi-DBS for unilateral surgery. For staged bilateral DBS, overall QoL improvement was explained primarily by the first lead. Decision-making for patients considering DBS should include a discussion surrounding the potential risks and benefits from a second DBS lead.

Differentiating tic electrophysiology from voluntary movement in the human thalamocortical circuit

OBJECTIVES

Tourette syndrome is a neurodevelopmental disorder commonly associated with involuntary movements, or tics. We currently lack an ideal animal model for Tourette syndrome. In humans, clinical manifestation of tics cannot be captured via functional imaging due to motion artefacts and limited temporal resolution, and electrophysiological studies have been limited to the intraoperative environment. The goal of this study was to identify electrophysiological signals in the centromedian (CM) thalamic nucleus and primary motor (M1) cortex that differentiate tics from voluntary movements.

METHODS

The data were collected as part of a larger National Institutes of Health-sponsored clinical trial. Four participants (two males, two females) underwent monthly clinical visits for collection of physiology for a total of 6 months. Participants were implanted with bilateral CM thalamic macroelectrodes and M1 subdural electrodes that were connected to two neurostimulators, both with sensing capabilities. MRI scans were performed preoperatively and CT scans postoperatively for localisation of electrodes. Electrophysiological recordings were collected at each visit from both the cortical and subcortical implants.

RESULTS

Recordings collected from the CM thalamic nucleus revealed a low-frequency power (3-10 Hz) increase that was time-locked to the onset of involuntary tics but was not present during voluntary movements. Cortical recordings revealed beta power decrease in M1 that was present during tics and voluntary movements.

CONCLUSION

We conclude that a human physiological signal was detected from the CM thalamus that differentiated tic from voluntary movement, and this physiological feature could potentially guide the development of neuromodulation therapies for Tourette syndrome that could use a closed-loop-based approach.

Proceedings of the Seventh Annual Deep Brain Stimulation Think Tank: Advances in Neurophysiology, Adaptive DBS, Virtual Reality, Neuroethics and Technology

The Seventh Annual Deep Brain Stimulation (DBS) Think Tank held on September 8th of 2019 addressed the most current: (1) use and utility of complex neurophysiological signals for development of adaptive neurostimulation to improve clinical outcomes; (2) Advancements in recent neuromodulation techniques to treat neuropsychiatric disorders; (3) New developments in optogenetics and DBS; (4) The use of augmented Virtual reality (VR) and neuromodulation; (5) commercially available technologies; and (6) ethical issues arising in and from research and use of DBS. These advances serve as both "markers of progress" and challenges and opportunities for ongoing address, engagement, and deliberation as we move to improve the functional capabilities and translational value of DBS. It is in this light that these proceedings are presented to inform the field and initiate ongoing discourse. As consistent with the intent, and spirit of this, and prior DBS Think Tanks, the overarching goal is to continue to develop multidisciplinary collaborations to rapidly advance the field and ultimately improve patient outcomes.

A Review of Cognitive Outcomes Across Movement Disorder Patients Undergoing Deep Brain Stimulation

Introduction: Although the benefit in motor symptoms for well-selected patients with deep brain stimulation (DBS) has been established, cognitive declines associated with DBS can produce suboptimal clinical responses. Small decrements in cognition can lead to profound effects on quality of life. The growth of indications, the expansion of surgical targets, the increasing complexity of devices, and recent changes in stimulation paradigms have all collectively drawn attention to the need for re-evaluation of DBS related cognitive outcomes.

Methods: To address the impact of cognitive changes following DBS, we performed a literature review using PubMed. We searched for articles focused on DBS and cognition. We extracted information about the disease, target, number of patients, assessment of time points, cognitive battery, and clinical outcomes. Diseases included were dystonia, Tourette syndrome (TS), essential tremor (ET), and Parkinson's disease (PD).

Results: DBS was associated with mild cognitive issues even when rigorous patient selection was employed. Dystonia studies reported stable or improved cognitive scores, however one study using reliable change indices indicated decrements in sustained attention. Additionally, DBS outcomes were convoluted with changes in medication dose, alleviation of motor symptoms, and learning effects. In the largest, prospective TS study, an improvement in attentional skills was noted, whereas smaller studies reported variable declines across several cognitive domains. Although, most studies reported stable cognitive outcomes. ET studies largely demonstrated deficits in verbal fluency, which had variable responses depending on stimulation setting. Recently, studies have focused beyond the ventral intermediate nucleus, including the post-subthalamic area and zona incerta. For PD, the cognitive results were heterogeneous, although deficits in verbal fluency were consistent and related to the micro-lesion effect.

Conclusion: Post-DBS cognitive issues can impact both motor and quality of life outcomes. The underlying pathophysiology of cognitive changes post-DBS and the identification of pathways underpinning declines will require further investigation. Future studies should employ careful methodological designs. Patient specific analyses will be helpful to differentiate the effects of medications, DBS and the underlying disease state, including disease progression. Disease progression is often an underappreciated factor that is important to post-DBS cognitive issues.

A review of basal ganglia circuits and physiology: Application to deep brain stimulation

INTRODUCTION

Drawing on the seminal work of DeLong, Albin, and Young, we have now entered an era of basal ganglia neuromodulation. Understanding, re-evaluating, and leveraging the lessons learned from neuromodulation will be crucial to facilitate an increased and improved application of neuromodulation in human disease.

METHODS

We will focus on deep brain stimulation (DBS) - the most common form of basal ganglia neuromodulation - however, similar principles can apply to other neuromodulation modalities. We start with a brief review of DBS for Parkinson's disease, essential tremor, dystonia, and Tourette syndrome. We then review hallmark studies on basal ganglia circuits and electrophysiology resulting from decades of experience in neuromodulation. The organization and content of this paper follow Dr. Okun's Lecture from the 2018 Parkinsonism and Related Disorders World Congress.

RESULTS

Information gained from neuromodulation has led to an expansion of the basal ganglia rate model, an enhanced understanding of nuclei dynamics, an emerging focus on pathological oscillations, a revision of the tripartite division of the basal ganglia, and a redirected focus toward individualized symptom-specific stimulation. Though there have been many limitations of the basal ganglia "box model," the construct provided the necessary foundation to advance the field. We now understand that information in the basal ganglia is encoded through complex neural responses that can be reliably measured and used to infer disease states for clinical translation.

CONCLUSIONS

Our deepened understanding of basal ganglia physiology will drive new neuromodulation strategies such as adaptive DBS or cell-specific neuromodulation through the use of optogenetics.

Longitudinal Follow-up of Impedance Drift in Deep Brain Stimulation Cases

Background

Impedance is an integral property of neuromodulation devices that determines the current delivered to brain tissue. Long-term variability in therapeutic impedance following deep brain stimulation (DBS) has not been extensively investigated across different brain targets. The aim was to evaluate DBS impedance drift and variability over an extended postoperative period across common DBS targets.

Methods

Retrospective data from 1,764 electrode leads were included and drawn from 866 DBS patients enrolled in the University of Florida Institutional Review Board-approved INFORM database and analyzed up to 84 months post implantation. An exploratory analysis was conducted to identify trends in impedances using a Mann–Kendall test of trend.

Results

There were 866 patients and 1,764 leads available for analysis. The majority of subjects had Parkinson’s disease (60.7%). The mean age at implantation was 58.7 years old and the mean follow-up time was 36.8 months. There were significant fluctuations in the mean impedance of all electrodes analyzed that largely stabilized by 6 months except for the subthalamic nucleus (STN) target, in which fluctuations persisted throughout the duration of follow-up with a continued downward trend (p < 0.001).

Discussion

The drift in impedance observed primarily within the first 6 months is in keeping with prior studies and is likely due to surgical micro-lesioning effects and brain parenchyma remodeling at the electrode–tissue interface, typically at values approximating 1,000 Ω. The differences in impedance trends over time in the various DBS targets may be due to underlying differences in structure and tissue composition.