Deep-brain stimulation for Parkinson's disease

Dual-Site Transcranial Magnetic Stimulation for the Treatment of Parkinson's Disease

Abnormal oscillatory activity in the subthalamic nucleus (STN) may be relevant for motor symptoms in Parkinson's disease (PD). Apart from deep brain stimulation, transcranial magnetic stimulation (TMS) may be suitable for altering these oscillations. We speculated that TMS to different cortical areas (primary motor cortex, M1, and dorsal premotor cortex, PMd) may activate neuronal subpopulations within the STN via corticofugal neurons projecting directly to the nucleus. We hypothesized that PD symptoms can be ameliorated by a lasting decoupling of STN neurons by associative dual-site repetitive TMS (rTMS). Associative dual-site rTMS (1 Hz) directed to PMd and M1 ("ADS-rTMS") was employed in 20 PD patients treated in a blinded, placebo-controlled cross-over design. Results: No adverse events were noted. We found no significant improvement in clinical outcome parameters (videography of MDS-UPDRS-III, finger tapping, spectral tremor power). Variation of the premotor stimulation site did not induce beneficial effects either. A single session of ADS-rTMS was tolerated well, but did not produce a clinically meaningful benefit on Parkinsonian motor symptoms. Successful treatment using TMS targeting subcortical nuclei may require an intervention over several days or more detailed physiological information about the individual brain state and stimulation-induced subcortical effects.

Progress in Dopaminergic Cell Replacement and Regenerative Strategies for Parkinson's Disease

Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder symptomatically characterized by resting tremor, rigidity, bradykinesia, and gait impairment. These motor deficits suffered by PD patients primarily result from selective dysfunction or loss of dopaminergic neurons of the substantia nigra pars compacta (SNpc). Most of the existing therapies for PD are based on the replacement of dopamine, which is symptomatically effective in the early stage but becomes increasingly less effective and is accompanied by serious side effects in the advanced stages of the disease. Currently, there are no strategies to slow neuronal degeneration or prevent the progression of PD. Thus, the prospect of regenerating functional dopaminergic neurons is very attractive. Over the last few decades, significant progress has been made in the development of dopaminergic regenerative strategies for curing PD. The most promising approach seems to be cell-replacement therapy (CRT) using human embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs), which are unlimitedly available and have gained much success in preclinical trials. Despite the challenges, stem cell-based CRT will make significant steps toward the clinic in the coming decade. Alternatively, direct lineage reprogramming, especially in situ direct conversion of glia cells to induced neurons, which exhibits some advantages including no ethical concerns, no risk of tumor formation, and even no need for transplantation, has gained much attention recently. Evoking the endogenous regeneration ability of neural stem cells (NSCs) is an idyllic method of dopaminergic neuroregeneration which remains highly controversial. Here, we review many of these advances, highlighting areas and strategies that might be particularly suited to the development of regenerative approaches that restore dopaminergic function in PD.

Adjunctive Therapies in Parkinson's Disease: How to Choose the Best Treatment Strategy Approach

End-of-dose motor fluctuations are regarded as one of the core troublesome symptoms by patients with Parkinson's disease (PD). Treatment of levodopa (L-dopa)-induced motor fluctuations is still an unmet medical need. L-dopa is the gold standard in the treatment of motor PD symptoms; notwithstanding, a wide range of adjunct therapies are currently available for the treatment of end-of-dose motor fluctuations. Additionally, device-aided therapies, such as deep brain stimulation, L-dopa-carbidopa intestinal gel infusion, and on-demand injection or continuous apomorphine infusion, may be considered when oral treatments are not sufficient to control motor fluctuations. In spite of the several evidence-based reviews and guidelines available, there is no agreement on which add-on therapy should be started first or its optimal timing. Equally challenging is the choice and timing between device-aided therapies. Herein, we propose a general overview of oral and device-aided treatments for PD patients with end-of-dose motor fluctuations, offering two possible algorithms that can guide clinicians during the therapeutic decision process.

Novel Targets for Parkinson's Disease: Addressing Different Therapeutic Paradigms and Conundrums

Parkinson's disease (PD) is a neurodegenerative disease that is pathologically characterized by degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc). PD leads to clinical motor features that include rigidity, tremor, and bradykinesia. Despite multiple available therapies for PD, the clinical features continue to progress, and patients suffer progressive disability. Many advances have been made in PD therapy which directly target the cause of the disease rather than providing symptomatic relief. A neuroprotective or disease modifying strategy that can slow or cease clinical progression and worsening disability remains as a major unmet medical need for PD management. The present review discusses potential novel therapies for PD that include recent interventions in the form of immunomodulatory techniques and stem cell therapy. Further, an introspective approach to identify numerous other novel targets that can alleviate PD pathogenesis and enable physicians to practice multitargeted therapy and that may provide a ray of hope to PD patients in the future are discussed.

The neural response to deep brain stimulation of the anterior nucleus of the thalamus: A MEMRI and c-Fos study

BACKGROUND

Deep brain stimulation (DBS) refers to the delivery of electric current to specific deep brain structures through implanted electrodes. Recently approved for use in United States, DBS to the anterior nucleus of thalamus (ANT) is a safe and effective alternative treatment for medically refractory seizures. Despite the anti-seizure effects of ANT DBS, preclinical and clinical studies have failed to demonstrate it actions at a whole brain level.

OBJECTIVE

Here, we used a magnetic resonance imaging (MRI)-based approach in healthy adult rats to investigate the effects of ANT DBS through the circuit of Papez, which has central role in the generation and propagation of limbic seizures, in temporal lobe epilepsy (TLE).

METHODS

After ANT electrode implantation and recovery, ANT DBS and SHAM (sham animals had electrodes implanted but were not stimulated) rats received one single injection of the contrast enhancer, manganese chloride (60 mg/kg, ip). Twelve hours after, rats underwent the baseline scan using the MEMRI (Manganese-Enhanced Magnetic Resonance Imaging) technique. We used the same MEMRI and parvalbumin sequence to follow the DBS delivered during 1 h (130 Hz and 200 μA). Perfusion was followed by subsequent c-Fos and parvalbumin immunostaining of brain sections.

RESULTS

Acute unilateral ANT DBS significantly reduced the overall manganese uptake and consequently, the MEMRI contrast in the circuit of Papez. Additionally, c-Fos expression was bilaterally increased in the cingulate cortex and posterior hypothalamus, areas directly connected to ANT, as well as in amygdala and subiculum, within the limbic circuitry.

CONCLUSION

Our data indicate that MEMRI can be used to detect whole-brain responses to DBS, as the high frequency stimulation parameters used here caused a significant reduction of cell activity in the circuit of Papez that might help to explain the antiepileptic effects of ANT DBS.

Why would Parkinson's disease lead to sudden changes in creativity, motivation, or style with visual art?: A review of case evidence and new neurobiological, contextual, and genetic hypotheses

Parkinson's disease (PD) is a devastating diagnosis with, however, potential for an extremely intriguing aesthetic component. Despite motor and cognitive deficits, an emerging collection of studies report a burst of visual artistic output and alterations in produced art in a subgroup of patients. This provides a unique window into the neurophysiological bases for why and how we might create and enjoy visual art, as well as into general brain function and the nature of PD or other neurodegenerative diseases. However, there has not been a comprehensive organization of literature on this topic. Nor has there been an attempt to connect case evidence and knowledge on PD with present understanding of visual art making in psychology and neuroaesthetics in order to propose hypotheses for documented artistic changes. Here, we collect the current research on this topic, tie this to PD symptoms and neurobiology, and provide new theories focusing on dopaminergic neuron damage, over-stimulation from dopamine agonist therapy, and context or genetic factors revealing the neurobiological basis of the visual artistic brain.

Hydrogel bioelectronics

Hydrogels have emerged as a promising bioelectronic interfacing material. This review discusses the fundamentals and recent advances in hydrogel bioelectronics.

Indirect Targeting of Subthalamic Deep Brain Stimulation Guided by Stereotactic Computed Tomography and Microelectrode Recordings in Patients With Parkinson's Disease

Objective: Magnetic resonance imaging fusion techniques guided by frame-based stereotactic computed tomography and microelectrode recordings are widely used to target the subthalamic nucleus. However, MRI is not always available. The aim of this study was to determine whether the indirect targeting of the subthalamic nucleus for deep brain stimulation using frame-based stereotactic computed tomography and microelectrode recording guidance in patients with advanced idiopathic Parkinson’s disease was an effective and safe treatment and to determine the factors that contributed to outcome.

Methods: Thirty-four consecutive patients with Parkinson’s disease who were treated from 2010 to 2012 were enrolled in this retrospective cohort study. The patients were assessed with the Unified Parkinson’s Disease Rating Scale-part III (UPDRS-III) and other clinical profiles peri- and post-operatively. The horizontal and vertical distances between the midpoint of the head frame and the brain midline at the septum pellucidum level and the upper edge of the bilateral lens, respectively, on a thin-section brain computed tomography scan were defined as the horizontal and vertical deviations, respectively.

Results: After the deep brain stimulation surgery, the patients’ UPDRS-III scores improved 48 ± 2.8% (range, 20–81%) compared to the patients’ baseline off-levodopa scores. No surgery-associated complications were found. The mean recorded length difference of the subthalamic nucleus between the initial and final single microelectrode recording trajectories was 5.37 ± 0.16 mm (range, 3.99–7.50). Multiple linear regression analyses revealed that the increased lengths of the vertical (regression coefficient [B]: -0.0626; 95% confidence interval [CI]: -0.113 to -0.013) and horizontal deviations (B: -0.0497; 95% CI: -0.083 to -0.017) were associated with less improvement in the patients’ UPDRS scores.

Conclusion: These results showed that the indirect targeting of the subthalamic nucleus for deep brain stimulation using frame-based stereotactic computed tomography and microelectrode recording guidance in patients with advanced idiopathic Parkinson’s disease was effective and safe. Greater symmetry of the head frame fixation resulted in better outcomes of the deep brain stimulation of the subthalamic nucleus in patients with Parkinson’s disease, especially when the horizontal deviation was 2 mm or less and the vertical deviation was 1 mm or less.

Urinary symptoms are correlated with quality of life after deep brain stimulation in Parkinson's disease

AIMS

Deep brain stimulation (DBS) is known to dramatically improve motor complications in patients with Parkinson's disease (PD), but its effect on urinary symptoms and health-related quality of life (HRQOL) remains unknown. We aimed to examine the relationship between urinary symptoms and HRQOL in patients with PD who underwent DBS.

METHODS

The International Prostate Symptom Score (IPSS) and overactive bladder symptom score (OABSS) were determined to evaluate urinary symptoms in patients with PD who underwent DBS. Postoperative evaluations were performed at 3 months, 1 year, and 3 years postoperatively. We also performed a urodynamic study (UDS) in 13 patients with PD preoperatively and postoperatively. A follow-up UDS was performed 2.0 ± 0.5 years postoperatively.

RESULTS

The preoperative urinary symptoms questionnaire was completed by 28 patients, of whom 14 completed the postoperative urinary symptoms questionnaire after 3 months, 18 after 1 year, and 10 after 3 years. The mean OABSS and IPSS did not change significantly at any follow-up periods postoperatively. When assessing the relationship between urinary symptoms and HRQOL and motor functions, the OABSS and IPSS showed significant positive correlations with HRQOL at 3 months postoperatively. The OABSS and IPSS showed significant positive correlations with activities of daily living (ADL) during the off-phase at 3 years postoperatively. All urodynamic parameters remained unchanged postoperatively.

CONCLUSIONS

Deep brain stimulation did not significantly affect urinary dysfunctions in patients with PD. Urinary symptoms might partially contribute to HRQOL at 3 months postoperatively and ADL during the off-phase at 3 years postoperatively.

BDNF provides many routes toward STN DBS-mediated disease modification

The concept that subthalamic nucleus deep brain stimulation (STN DBS) may be disease modifying in Parkinson's disease (PD) is controversial. Several clinical trials that enrolled subjects with late‐stage PD have come to disparate conclusions on this matter. In contrast, some clinical studies in early‐ to midstage subjects have suggested a disease‐modifying effect. Dopaminergic innervation of the putamen is essentially absent in PD subjects within 4 years after diagnosis, indicating that any neuroprotective therapy, including STN DBS, will require intervention within the immediate postdiagnosis interval. Preclinical prevention and early intervention paradigms support a neuroprotective effect of STN DBS on the nigrostriatal system via increased brain‐derived neurotrophic factor (BDNF). STN DBS‐induced increases in BDNF provide a multitude of mechanisms capable of ameliorating dysfunction and degeneration in the parkinsonian brain. A biomarker for measuring brain‐derived neurotrophic factor‐trkB signaling, though, is not available for clinical research. If a prospective clinical trial were to examine whether STN DBS is disease modifying, we contend the strongest rationale is not dependent on a preclinical neuroprotective effect per se, but on the myriad potential mechanisms whereby STN DBS‐elicited brain‐derived neurotrophic factor‐trkB signaling could provide disease modification. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Efficacy and Safety of Deep Brain Stimulation in the Treatment of Parkinson's Disease: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Deep brain stimulation (DBS) is a neurosurgical procedure indicated for patients with advanced Parkinson's disease (PD). Whether similar benefits may be realized by patients with early PD, however, is currently unclear, especially given the potential risks of the procedure. This systematic review and meta-analysis aimed to investigate the relative efficacy and safety of DBS in comparison to best medical therapy (BMT) in the treatment of PD. It also aimed to compare the efficacy of DBS between patients with early and advanced PD. A systematic search was performed in Medline, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL). Randomized controlled trials (RCTs) comparing DBS to BMT in PD patients were included. Outcome measures were impairment/disability using the Unified Parkinson's Disease Rating Scale (UPDRS), quality of life (QoL) using the Parkinson's Disease Questionnaire (PDQ-39), levodopa equivalent dose (LED) reduction, and rates of serious adverse events (SAE). Eight eligible RCTs (n = 1,189) were included in the meta-analysis, two of which recruited early PD patients. Regarding efficacy outcomes, there were significant improvements in UPDRS, PDQ-39, and LED scores in favour of DBS (P < 0.00001). There was a significantly greater reduction of LED in patients with early PD (P < 0.00001), but no other differences between early and advanced PD patients were found. The risk of a patient experiencing an SAE was significantly higher in the DBS group (P = 0.005), as was the total number of SAEs (P < 0.00188). Overall, DBS was superior to BMT at improving impairment/disability, QoL, and reducing medication doses, but these benefits need to be weighed against the higher risk of SAEs. There was insufficient evidence to determine the impact of the PD stage on the efficacy of DBS.

Top Ten Tips Palliative Care Clinicians Should Know About Parkinson's Disease and Related Disorders

Parkinson's disease (PD) affects 1%-2% of individuals older than 60 years and is the 14th leading cause of death in the United States. People with PD, across all stages of the disease, suffer from a significant symptom burden that includes many nonmotor symptoms (such as depression, fatigue, pain, and dementia), and most will ultimately die from complications of this degenerative and incurable illness. Even at diagnosis, a palliative care (PC) approach can help the patient adjust to his or her diagnosis and maintain an optimal quality of life. We brought together a team of PD and PC experts to assemble practical tips for the care of people with PD. The "Top 10" format emphasizes the most relevant issues to enable PC clinicians to provide optimal care for those suffering with this complex neurodegenerative disease.

Parkinson Disease

Parkinson disease is a common neurodegenerative disorder that causes progressive motor and nonmotor disability. It is diagnosed clinically and requires a detailed history and neurologic examination to exclude alternative diagnoses. Although disease-modifying therapies do not exist for Parkinson disease, effective symptomatic therapies, including dopaminergic medications and surgery, allow patients to maintain good quality of life for many years. Nonmotor symptoms, including mood, cognitive, sleep, autonomic, and gastrointestinal symptoms, should be managed by a multidisciplinary team of clinicians. Recent advances include new diagnostic criteria from the Movement Disorder Society and the addition of new symptomatic therapies for treating motor complications and nonmotor symptoms in advanced disease.

Pluripotent stem cell-based therapy for Parkinson's disease: Current status and future prospects

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, which affects about 0.3% of the general population. As the population in the developed world ages, this creates an escalating burden on society both in economic terms and in quality of life for these patients and for the families that support them. Although currently available pharmacological or surgical treatments may significantly improve the quality of life of many patients with PD, these are symptomatic treatments that do not slow or stop the progressive course of the disease. Because motor impairments in PD largely result from loss of midbrain dopamine neurons in the substantia nigra pars compacta, PD has long been considered to be one of the most promising target diseases for cell-based therapy. Indeed, numerous clinical and preclinical studies using fetal cell transplantation have provided proof of concept that cell replacement therapy may be a viable therapeutic approach for PD. However, the use of human fetal cells as a standardized therapeutic regimen has been fraught with fundamental ethical, practical, and clinical issues, prompting scientists to explore alternative cell sources. Based on groundbreaking establishments of human embryonic stem cells and induced pluripotent stem cells, these human pluripotent stem cells have been the subject of extensive research, leading to tremendous advancement in our understanding of these novel classes of stem cells and promising great potential for regenerative medicine. In this review, we discuss the prospects and challenges of human pluripotent stem cell-based cell therapy for PD.

Functional Connectivity-Based Modelling Simulates Subject-Specific Network Spreading Effects of Focal Brain Stimulation

Neurostimulation remarkably alleviates the symptoms in a variety of brain disorders by modulating the brain-wide network. However, how brain-wide effects on the direct and indirect pathways evoked by focal neurostimulation elicit therapeutic effects in an individual patient is unknown. Understanding this remains crucial for advancing neural circuit-based guidance to optimize candidate patient screening, pre-surgical target selection, and post-surgical parameter tuning. To address this issue, we propose a functional brain connectome-based modeling approach that simulates the spreading effects of stimulating different brain regions and quantifies the rectification of abnormal network topology in silico. We validated these analyses by pinpointing nuclei in the basal ganglia circuits as top-ranked targets for 43 local patients with Parkinson’s disease and 90 patients from a public database. Individual connectome-based analysis demonstrated that the globus pallidus was the best choice for 21.1% and the subthalamic nucleus for 19.5% of patients. Down-regulation of functional connectivity (up to 12%) at these prioritized targets optimally maximized the therapeutic effects. Notably, the priority rank of the subthalamic nucleus significantly correlated with motor symptom severity (Unified Parkinson’s Disease Rating Scale III) in the local cohort. These findings underscore the potential of neural network modeling for advancing personalized brain stimulation therapy, and warrant future experimental investigation to validate its clinical utility.

Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue

Conductive and stretchable materials that match the elastic moduli of biological tissue (0.5–500 kPa) are desired for enhanced interfacial and mechanical stability. Compared with inorganic and dry polymeric conductors, hydrogels made with conducting polymers are promising soft electrode materials due to their high water content. Nevertheless, most conducting polymer-based hydrogels sacrifice electronic performance to obtain useful mechanical properties. Here we report a method that overcomes this limitation using two interpenetrating hydrogel networks, one of which is formed by the gelation of the conducting polymer PEDOT:PSS. Due to the connectivity of the PEDOT:PSS network, conductivities up to 23 S m⁻¹ are achieved, a record for stretchable PEDOT:PSS-based hydrogels. Meanwhile, the low concentration of PEDOT:PSS enables orthogonal control over the composite mechanical properties using a secondary polymer network. We demonstrate tunability of the elastic modulus over three biologically relevant orders of magnitude without compromising stretchability ( > 100%) or conductivity ( > 10 S m⁻¹).

Conductive and stretchable materials that match the elastic moduli of biological tissue are desired for enhanced interfacial and mechanical stability. Here the authors show a method for fabricating highly conductive hydrogels comprising two interpenetrating networks.

Non-motor Characterization of the Basal Ganglia: Evidence From Human and Non-human Primate Electrophysiology

Although the basal ganglia have been implicated in a growing list of human behaviors, they include some of the least understood nuclei in the brain. For several decades studies have employed numerous methodologies to uncover evidence pointing to the basal ganglia as a hub of both motor and non-motor function. Recently, new electrophysiological characterization of the basal ganglia in humans has become possible through direct access to these deep structures as part of routine neurosurgery. Electrophysiological approaches for identifying non-motor function have the potential to unlock a deeper understanding of pathways that may inform clinical interventions and particularly neuromodulation. Various electrophysiological modalities can also be combined to reveal functional connections between the basal ganglia and traditional structures throughout the neocortex that have been linked to non-motor behavior. Several reviews have previously summarized evidence for non-motor function in the basal ganglia stemming from behavioral, clinical, computational, imaging, and non-primate animal studies; in this review, instead we turn to electrophysiological studies of non-human primates and humans. We begin by introducing common electrophysiological methodologies for basal ganglia investigation, and then we discuss studies across numerous non-motor domains–emotion, response inhibition, conflict, decision-making, error-detection and surprise, reward processing, language, and time processing. We discuss the limitations of current approaches and highlight the current state of the information.

Parkinson's disease and the risk of osteoporotic vertebral compression fracture: a nationwide population-based study

Patients with Parkinson's disease (PD) were at higher risk of osteoporotic vertebral compression fractures (OVCF) compared to controls and had elevated mortality rates. Compared to conservative treatment, surgical treatment for OVCF in PD patients seemed to be associated with better outcomes.

INTRODUCTION

The purpose of this study was to evaluate the risk of OVCF in patients with PD.

METHODS

Data from patients over the age of 60 years who were diagnosed with PD were collected between 2004 and 2013 from the Korean National Health Insurance Database (n = 3370). The comparison group (non-PD) consisted of randomly selected patients (five per patient with PD; n = 16,850) matched to the PD group, who were newly diagnosed annually according to age and sex. Cox proportional hazard regressions were used to examine the relationships between osteoporosis, OVCF, surgery for OVCF, and PD. Household income and residential area of patients were also assessed. Overall survival rates were calculated after adjusting for confounding factors, such as hypertension, diabetes mellitus, and chronic kidney disease.

RESULTS

OVCF was developed in 12.5% of patients in the PD group and in 7.4% of patients in the control group. PD was associated with increased risk of osteoporosis (hazard ratio [HR], 1.32; 95% confidence interval [CI], 1.21-1.43; p < 0.001), OVCF (HR 1.66; 95% CI, 1.47-1.87; p < 0.001), and surgery for OVCF (HR 2.69; 95% CI, 1.78-4.08; p < 0.001). Household income was not significantly related with development of osteoporosis, incidence of OVCF, or surgery for OVCF. Residential area was statistically associated with osteoporosis, OVCF, and surgery for OVCF. The mortality rate of the PD group was about 1.7 times higher than that of the non-PD group after adjusting for potential confounders, and the mortality rate of the PD with OVCF group was higher than that of the non-PD group, but not significantly (p = 0.09). The survival rate of the PD group with surgery for OVCF showed a trend toward a more positive prognosis compared with that of the PD group with conservative treatment.

CONCLUSIONS

Patients with PD had significantly increased risk of osteoporosis and OVCF. Surgical treatment for OVCF in PD patients was associated with a better prognosis than conservative treatment.

Deep Brain Stimulation of the Subthalamic Nucleus Parameter Optimization for Vowel Acoustics and Speech Intelligibility in Parkinson's Disease

PURPOSE

The settings of 3 electrical stimulation parameters were adjusted in 12 speakers with Parkinson's disease (PD) with deep brain stimulation of the subthalamic nucleus (STN-DBS) to examine their effects on vowel acoustics and speech intelligibility.

METHOD

Participants were tested under permutations of low, mid, and high STN-DBS frequency, voltage, and pulse width settings. At each session, participants recited a sentence. Acoustic characteristics of vowel production were extracted, and naive listeners provided estimates of speech intelligibility.

RESULTS

Overall, lower-frequency STN-DBS stimulation (60 Hz) was found to lead to improvements in intelligibility and acoustic vowel expansion. An interaction between speaker sex and STN-DBS stimulation was found for vowel measures. The combination of low frequency, mid to high voltage, and low to mid pulse width led to optimal speech outcomes; however, these settings did not demonstrate significant speech outcome differences compared with the standard clinical STN-DBS settings, likely due to substantial individual variability.

CONCLUSIONS

Although lower-frequency STN-DBS stimulation was found to yield consistent improvements in speech outcomes, it was not found to necessarily lead to the best speech outcomes for all participants. Nevertheless, frequency may serve as a starting point to explore settings that will optimize an individual's speech outcomes following STN-DBS surgery.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.5899228.

An investigation into closed-loop treatment of neurological disorders based on sensing mitochondrial dysfunction

Dynamic feedback based closed-loop medical devices offer a number of advantages for treatment of heterogeneous neurological conditions. Closed-loop devices integrate a level of neurobiological feedback, which allows for real-time adjustments to be made with the overarching aim of improving treatment efficacy and minimizing risks for adverse events. One target which has not been extensively explored as a potential feedback component in closed-loop therapies is mitochondrial function. Several neurodegenerative and psychiatric disorders including Parkinson's disease, Major Depressive disorder and Bipolar disorder have been linked to perturbations in the mitochondrial respiratory chain. This paper investigates the potential to monitor this mitochondrial function as a method of feedback for closed-loop neuromodulation treatments. A generic model of the closed-loop treatment is developed to describe the high-level functions of any system designed to control neural function based on mitochondrial response to stimulation, simplifying comparison and future meta-analysis. This model has four key functional components including: a sensor, signal manipulator, controller and effector. Each of these components are described and several potential technologies for each are investigated. While some of these candidate technologies are quite mature, there are still technological gaps remaining. The field of closed-loop medical devices is rapidly evolving, and whilst there is a lot of interest in this area, widespread adoption has not yet been achieved due to several remaining technological hurdles. However, the significant therapeutic benefits offered by this technology mean that this will be an active area for research for years to come.

Indications and prospects of neural transplantation for chronic neurological diseases

PURPOSE OF REVIEW

The replacement of damaged cells in the central nervous system (CNS) affected by degenerative disorders represents an attractive therapeutic strategy. The advent of stem cell technology may offer the possibility of generating a large number of renewable, specifically differentiated cells to potentially cure large cohorts of patients. In this review, we discuss current knowledge and issues involved in neural cell transplantation. The most important preclinical and clinical results of cellular transplantation applied to Parkinson's, Huntington's disease and amyotrophic lateral sclerosis will be summarized.

RECENT FINDINGS

Cellular transplantation is emerging as a possible therapy for a variety of incurable neurological disorders. The disorders that will primarily take advantage from neural stem cell grafting are those involving a well defined cell population in a restricted area of the CNS. Several clinical trials have been initiated to assess safety and efficacy of different stem cell-derived products, and promising results have been obtained for disorders such as Parkinson's disease. However, several scientific questions remain unanswered. Among these, the impact of the immunological interaction between host and graft in the particular environment of the CNS still requires additional investigations.

SUMMARY

Several chronic neurological disorders appear to be amenable to cell regenerative therapies. However, safety, efficacy and immunological issues will need to be carefully evaluated beforehand.

Infection related to deep brain stimulation in patients with Parkinson disease: Clinical characteristics and risk factors

OBJECTIVE

Risk factors of infection after deep brain stimulation (DBS) surgery in patients with Parkinson disease (PD) have been controversial. We aimed to investigate the clinical characteristics and risk factors of infection after DBS surgery in PD patients.

METHODS

We retrospectively investigated 246 consecutive DBS surgeries in 169 advanced PD patients. Clinical data were collected and analyzed to clarify the clinical characteristics associated with infection after DBS surgery. Multivariate logistic regression analysis was used to assess risk factors for infection after DBS surgery.

RESULTS

Infection occurred in 5% of all DBS surgeries and in 7% of all PD patients who received DBS surgery. Most infections (75%) occurred within 3months after DBS surgery but it also occurred 21months after DBS surgery. Gram-positive bacteria were the most common pathogens (75%). Infection after DBS surgery was associated with short period of prophylactic antibiotic therapy (OR=0.62, 95% CI=0.45-0.85, P=0.002) and intensive care unit (ICU) management immediate after DBS surgery (OR=5.43, 95% CI=1.12-26.45, P=0.036).

CONCLUSION

Our study suggests that short period of prophylactic antibiotic therapy and ICU management after surgery may increase the risk of infection in PD patients who received DBS surgery.

Nanotechnology for Neuroscience: Promising Approaches for Diagnostics, Therapeutics and Brain Activity Mapping

Unlocking the secrets of the brain is a task fraught with complexity and challenge - not least due to the intricacy of the circuits involved. With advancements in the scale and precision of scientific technologies, we are increasingly equipped to explore how these components interact to produce a vast range of outputs that constitute function and disease. Here, an insight is offered into key areas in which the marriage of neuroscience and nanotechnology has revolutionized the industry. The evolution of ever more sophisticated nanomaterials culminates in network-operant functionalized agents. In turn, these materials contribute to novel diagnostic and therapeutic strategies, including drug delivery, neuroprotection, neural regeneration, neuroimaging and neurosurgery. Further, the entrance of nanotechnology into future research arenas including optogenetics, molecular/ion sensing and monitoring, and piezoelectric effects is discussed. Finally, considerations in nanoneurotoxicity, the main barrier to clinical translation, are reviewed, and direction for future perspectives is provided.

Theta-phase closed-loop stimulation induces motor paradoxical responses in the rat model of Parkinson disease

BACKGROUND

High-frequency deep brain stimulation (DBS) has become a widespread therapy used in the treatment of Parkinson's Disease (PD) and other diseases. Although it has proved beneficial, much recent attention has been centered around the potential of new closed-loop DBS implementations.

OBJECTIVE

Here we present a new closed-loop DBS scheme based on the phase of the theta activity recorded from the motor cortex. By testing the implementation on freely moving 6-OHDA lesioned and control rats, we assessed the behavioral and neurophysiologic effects of this implementation and compared it against the classical high-frequency DBS.

RESULTS

Results show that both stimulation modalities produce significant and opposite changes on the movement and neurophysiological activity. Close-loop stimulation, far from improving the animals' behavior, exert contrary effects to those of high-frequency DBS which reverts the parkinsonian symptoms. Motor improvement during open-loop, high-frequency DBS was accompanied by a reduction in the amount of cortical beta oscillations while akinetic and disturbed behavior during close-loop stimulation coincided with an increase in the amplitude of beta activity.

CONCLUSION

Cortical-phase-dependent close-loop stimulation of the STN exerts significant behavioral and oscillatory changes in the rat model of PD. Open-loop and close-loop stimulation outcomes differed dramatically, thus suggesting that the scheme of stimulation determines the output of the modulation even if the target structure is maintained. The current framework could be extended in future studies to identify the correct parameters that would provide a suitable control signal to the system. It may well be that with other stimulation parameters, this sort of DBS could be beneficial.

Clinical quantitative susceptibility mapping (QSM): Biometal imaging and its emerging roles in patient care

Quantitative susceptibility mapping (QSM) has enabled magnetic resonance imaging (MRI) of tissue magnetic susceptibility to advance from simple qualitative detection of hypointense blooming artifacts to precise quantitative measurement of spatial biodistributions. QSM technology may be regarded to be sufficiently developed and validated to warrant wide dissemination for clinical applications of imaging isotropic susceptibility, which is dominated by metals in tissue, including iron and calcium. These biometals are highly regulated as vital participants in normal cellular biochemistry, and their dysregulations are manifested in a variety of pathologic processes. Therefore, QSM can be used to assess important tissue functions and disease. To facilitate QSM clinical translation, this review aims to organize pertinent information for implementing a robust automated QSM technique in routine MRI practice and to summarize available knowledge on diseases for which QSM can be used to improve patient care. In brief, QSM can be generated with postprocessing whenever gradient echo MRI is performed. QSM can be useful for diseases that involve neurodegeneration, inflammation, hemorrhage, abnormal oxygen consumption, substantial alterations in highly paramagnetic cellular iron, bone mineralization, or pathologic calcification; and for all disorders in which MRI diagnosis or surveillance requires contrast agent injection. Clinicians may consider integrating QSM into their routine imaging practices by including gradient echo sequences in all relevant MRI protocols.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:951-971.

Optogenetics and its application in neural degeneration and regeneration

Neural degeneration and regeneration are important topics in neurological diseases. There are limited options for therapeutic interventions in neurological diseases that provide simultaneous spatial and temporal control of neurons. This drawback increases side effects due to non-specific targeting. Optogenetics is a technology that allows precise spatial and temporal control of cells. Therefore, this technique has high potential as a therapeutic strategy for neurological diseases. Even though the application of optogenetics in understanding brain functional organization and complex behaviour states have been elaborated, reviews of its therapeutic potential especially in neurodegeneration and regeneration are still limited. This short review presents representative work in optogenetics in disease models such as spinal cord injury, multiple sclerosis, epilepsy, Alzheimer's disease and Parkinson's disease. It is aimed to provide a broader perspective on optogenetic therapeutic potential in neurodegeneration and neural regeneration.

Impact of Sjogren's syndrome on Parkinson's disease: A nationwide case-control study

Objective

To investigate whether Sjogren’s syndrome would have an influence on the development of Parkinson’s disease.

Methods

A population-based case-control study was conducted. Participants consisted of 7716 subjects with newly diagnosed Parkinson’s disease and a population of 75129 matched control subjects between 2000 and 2010. We measured the risk of Parkinson’s disease in association with Sjogren’s syndrome by using adjusted odds ratios.

Results

A total of 143 Parkinson’s disease subjects (1.9%) and 893 control subjects (1.2%) suffered from Sjogren’s syndrome (p < 0.001). The crude odds ratio for Parkinson’s disease among subjects with Sjogren’s syndrome was 1.56 (95% CI 1.30–1.86; p < 0.01). After adjustment for potential confounders which have been proposed that would increase the risk of development of Parkinson’s disease, Sjogren’s syndrome was found to be significantly associated with the risk of Parkinson’s disease with an odds ratio of 1.37 (95% CI 1.15–1.65; p < 0.01).

Conclusion

This study preliminarily proposed that Sjogren’s syndrome was significant associated with an increased risk of Parkinson’s disease.

Inhibiting subthalamic nucleus decreases cocaine demand and relapse: therapeutic potential

Preclinical evidence indicates that inactivation of subthalamic nucleus (STN) may be effective for treating cocaine addiction, and therapies that target STN, e.g. deep brain stimulation, are available indicating that this may have clinical promise. Here, we assessed the therapeutic potential of STN inactivation using a translationally relevant economic approach that quantitatively describes drug-taking behavior, and tested these results with drug-seeking tasks. Economic demand for cocaine was assessed in rats (n = 11) using a within-session threshold procedure in which cocaine price (responses/mg cocaine) was sequentially increased throughout the session. Cocaine demand was assessed in this manner immediately after bilateral microinfusions into STN of either vehicle (artificial cerebrospinal fluid) or the GABAA receptor agonist muscimol. A separate group of animals (n = 8) was tested for changes in cocaine seeking either during extinction or in response to cocaine-associated cues. Muscimol-induced inhibition of STN significantly attenuated cocaine consumption at high prices, drug seeking during extinction and cued reinstatement of cocaine seeking. In contrast, STN inhibition did not reduce cocaine consumption at low prices or locomotor activity. Thus, STN inactivation reduced economic demand for cocaine and multiple measures of drug seeking during extinction. In view of the association between economic demand and addiction severity in both rat and human, these results indicate that STN inactivation has substantial clinical potential for treatment of cocaine addiction.

Oscillatory Activities in Neurological Disorders of Elderly: Biomarkers to Target for Neuromodulation

Non-invasive brain stimulation (NIBS) has been under investigation as adjunct treatment of various neurological disorders with variable success. One challenge is the limited knowledge on what would be effective neuronal targets for an intervention, combined with limited knowledge on the neuronal mechanisms of NIBS. Motivated on the one hand by recent evidence that oscillatory activities in neural systems play a role in orchestrating brain functions and dysfunctions, in particular those of neurological disorders specific of elderly patients, and on the other hand that NIBS techniques may be used to interact with these brain oscillations in a controlled way, we here explore the potential of modulating brain oscillations as an effective strategy for clinical NIBS interventions. We first review the evidence for abnormal oscillatory profiles to be associated with a range of neurological disorders of elderly (e.g., Parkinson's disease (PD), Alzheimer's disease (AD), stroke, epilepsy), and for these signals of abnormal network activity to normalize with treatment, and/or to be predictive of disease progression or recovery. We then ask the question to what extent existing NIBS protocols have been tailored to interact with these oscillations and possibly associated dysfunctions. Our review shows that, despite evidence for both reliable neurophysiological markers of specific oscillatory dis-functionalities in neurological disorders and NIBS protocols potentially able to interact with them, there are few applications of NIBS aiming to explore clinical outcomes of this interaction. Our review article aims to point out oscillatory markers of neurological, which are also suitable targets for modification by NIBS, in order to facilitate in future studies the matching of technical application to clinical targets.

Next-generation probes, particles, and proteins for neural interfacing

Bidirectional interfacing with the nervous system enables neuroscience research, diagnosis, and therapy. This two-way communication allows us to monitor the state of the brain and its composite networks and cells as well as to influence them to treat disease or repair/restore sensory or motor function. To provide the most stable and effective interface, the tools of the trade must bridge the soft, ion-rich, and evolving nature of neural tissue with the largely rigid, static realm of microelectronics and medical instruments that allow for readout, analysis, and/or control. In this Review, we describe how the understanding of neural signaling and material-tissue interactions has fueled the expansion of the available tool set. New probe architectures and materials, nanoparticles, dyes, and designer genetically encoded proteins push the limits of recording and stimulation lifetime, localization, and specificity, blurring the boundary between living tissue and engineered tools. Understanding these approaches, their modality, and the role of cross-disciplinary development will support new neurotherapies and prostheses and provide neuroscientists and neurologists with unprecedented access to the brain.

La Enfermedad de Parkinson: Etiología, Tratamientos y Factores Preventivos

La enfermedad de Parkinson (EP) es la patología neurodegenerativa motora con mayor incidencia a nivel mundial. Esta afecta a aproximadamente 2-3% de la población mayor a 60 años de edad y sus causas aún no han sido bien determinadas. Actualmente no existe cura para esta patología; sin embargo, es posible contar con diferentes tratamientos que permiten aliviar algunos de sus síntomas y enlentecer su curso. Estos tratamientos tienen como premisa contrarrestar los efectos ocasionados por la pérdida de la función dopaminérgica de la sustancia nigra (SN) sobre estructuras como el núcleo subtálamico (NST) o globo pálido interno (GPi) ya sea por medio de tratamientos farmacológicos, estimulación cerebral profunda (ECP) o con el implante celular. Existen también investigaciones que están dirigiendo su interés al desarrollo de fármacos con potencial terapéutico, que presenten alta especificidad a receptores colinérgicos de nicotina (nAChRs) y antagonistas de receptores de adenosina, específicamente del subtipo A2A. Estos últimos, juegan un papel importante en el control de liberación dopaminérgica y en los procesos de neuroprotección. En esta revisión se pretende ofrecer una panorámica actual sobre algunos de los factores de riesgo asociados a EP, algunos de los tratamientos actuales más utilizados y acerca del rol de sustancias potencialmente útiles en la prevención de esta enfermedad.

Electrical stimulation of the dorsal columns of the spinal cord for Parkinson's disease

Spinal cord stimulation has been used for the treatment of chronic pain for decades. In 2009, our laboratory proposed, based on studies in rodents, that electrical stimulation of the dorsal columns of the spinal cord could become an effective treatment for motor symptoms associated with Parkinson's disease (PD). Since our initial report in rodents and a more recent study in primates, several clinical studies have now described beneficial effects of dorsal column stimulation in parkinsonian patients. In primates, we have shown that dorsal column stimulation activates multiple structures along the somatosensory pathway and desynchronizes the pathological cortico-striatal oscillations responsible for the manifestation of PD symptoms. Based on recent evidence, we argue that neurological disorders such as PD can be broadly classified as diseases emerging from abnormal neuronal timing, leading to pathological brain states, and that the spinal cord could be used as a "channel" to transmit therapeutic electrical signals to disrupt these abnormalities. © 2017 International Parkinson and Movement Disorder Society.

Comparison of Pallidal and Subthalamic Deep Brain Stimulation in Parkinson's Disease: Therapeutic and Adverse Effects

OBJECTIVE

To compare the therapeutic and adverse effects of globus pallidus interna (GPi) and subthalamic nucleus (STN) deep brain stimulation (DBS) for the treatment of advanced Parkinson's disease (PD).

METHODS

We retrospectively analyzed the clinical data of patients with PD who underwent GPi (n = 14) or STN (n = 28) DBS surgery between April 2002 and May 2014. The subjects were matched for age at surgery and disease duration. The Unified Parkinson's Disease Rating Scale (UPDRS) scores and levodopa equivalent dose (LED) at baseline and 12 months after surgery were used to assess the therapeutic effects of DBS. Adverse effects were also compared between the two groups.

RESULTS

At 12 months, the mean changes in the UPDRS total and part I-IV scores did not differ significantly between the two groups. However, the subscores for gait disturbance/postural instability and dyskinesia were significantly more improved after GPi DBS than those after STN DBS (p = 0.024 and 0.016, respectively). The LED was significantly more reduced in patients after STN DBS than that after GPi DBS (p = 0.004). Serious adverse effects did not differ between the two groups (p = 0.697).

CONCLUSION

The patients with PD showed greater improvement in gait disturbance/postural instability and dyskinesia after GPi DBS compared with those after STN DBS, although the patients had a greater reduction in LED after STN DBS. These results may provide useful information for optimal target selection for DBS in PD.

Differentiated effects of deep brain stimulation and medication on somatosensory processing in Parkinson's disease

OBJECTIVES

Deep brain stimulation (DBS) and dopaminergic medication effectively alleviate the motor symptoms in Parkinson's disease (PD) patients, but their effects on the sensory symptoms of PD are still not well understood. To explore early somatosensory processing in PD, we recorded magnetoencephalography (MEG) from thirteen DBS-treated PD patients and ten healthy controls during median nerve stimulation.

METHODS

PD patients were measured during DBS-treated, untreated and dopaminergic-medicated states. We focused on early cortical somatosensory processing as indexed by N20m, induced gamma augmentation (31-45Hz and 55-100Hz) and induced beta suppression (13-30Hz). PD patients' motor symptoms were assessed by UPDRS-III.

RESULTS

Using Bayesian statistics, we found positive evidence for differentiated effects of treatments on the induced gamma augmentation (31-45Hz) with highest gamma in the dopaminergic-medicated state and lowest in the DBS-treated and untreated states. In contrast, UPDRS-III scores showed beneficial effects of both DBS and dopaminergic medication on the patients' motor symptoms. Furthermore, treatments did not affect the amplitude of N20m.

CONCLUSIONS

Our results suggest differentiated effects of DBS and dopaminergic medication on cortical somatosensory processing in PD patients despite consistent ameliorating effects of both treatments on PD motor symptoms.

SIGNIFICANCE

The differentiated effect suggests differences in the effect mechanisms of the two treatments.

Acute symptomatic peri-lead edema 33 hours after deep brain stimulation surgery: a case report

Background

Symptomatic peri-lead edema is a rare complication of deep brain stimulation that has been reported to develop 4 to 120 days postoperatively.

Case presentation

Here we report the case of a 63-year-old Hispanic man with an 8-year history of Parkinson’s disease who underwent bilateral placement of subthalamic nucleus deep brain stimulation leads and presented with acute, symptomatic, unilateral, peri-lead edema just 33 hours after surgery.

Conclusions

We document a thorough radiographic time course showing the evolution of these peri-lead changes and their regression with steroid therapy, and discuss the therapeutic implications of these findings. We propose that the unilateral peri-lead edema after bilateral deep brain stimulation is the result of severe microtrauma with blood–brain barrier disruption. Knowledge of such early manifestation of peri-lead edema after deep brain stimulation is critical for ruling out stroke and infection and preventing unnecessary diagnostic testing or hardware removal in this rare patient population.

Long-Term Efficacy of Constant Current Deep Brain Stimulation in Essential Tremor

OBJECTIVES

Ventralis intermedius deep brain stimulation is an established intervention for medication-refractory essential tremor. Newer constant current stimulation technology offers theoretical advantage over the traditional constant voltage systems in terms of delivering a more biologically stable therapy. There are no previous reports on the outcomes of constant current deep brain stimulation in the treatment of essential tremor. This study aimed to evaluate the long-term efficacy of ventralis intermedius constant current deep brain stimulation in patients diagnosed with essential tremor.

MATERIALS AND METHODS

Essential tremor patients implanted with constant current deep brain stimulation for a minimum of three years were evaluated. Clinical outcomes were assessed using the Fahn-Tolosa-Marin tremor rating scale at baseline and postoperatively at the time of evaluation. The quality of life in the patients was assessed using the Quality of Life in Essential Tremor questionnaire.

RESULTS

Ten patients were evaluated with a median age at evaluation of 74 years (range 66-79) and a mean follow up time of 49.7 (range 36-78) months since starting stimulation. Constant current ventralis intermedius deep brain stimulation was well tolerated and effective in all patients with a mean score improvement from 50.7 ± 5.9 to 17.4 ± 5.7 (p = 0.0020) in the total Fahn-Tolosa-Marin rating scale score (65.6%). Furthermore, the total combined mean Quality of Life in Essential Tremor score was improved from 56.2 ± 4.9 to 16.8 ± 3.5 (p value = 0.0059) (70.1%).

CONCLUSION

This report shows that long-term constant current ventralis intermedius deep brain stimulation is a safe and effective intervention for essential tremor patients.

Currents of memory: recent progress, translational challenges, and ethical considerations in fornix deep brain stimulation trials for Alzheimer's disease

The serendipitous discovery of triggered autobiographical memories and eventual memory improvement in an obese patient who received fornix deep brain stimulation in 2008 paved the way for several phase I and phase II clinical trials focused on the safety and efficacy of this potential intervention for people with Alzheimer's disease. In this article, we summarize clinical trials and case reports on fornix deep brain stimulation for Alzheimer's disease and review experiments on animal models evaluating the physiological or behavioral effects of this intervention. Based on information from these reports and studies, we identify potential translational challenges of this approach and determine practical and ethical considerations for clinical trials, focusing on issues regarding selection criteria, trial design, and outcome evaluation. Based on initial results suggesting greater benefit for those with milder disease stage, we find it essential that participant expectations are carefully managed to avoid treatment disenchantment and/or frustration from participants and caregivers. Finally, we urge for collaboration between centers to establish proper clinical standards and to promote better trial results comparison.

Functional circuit mapping of striatal output nuclei using simultaneous deep brain stimulation and fMRI

The substantia nigra pars reticulata (SNr) and external globus pallidus (GPe) constitute the two major output targets of the rodent striatum. Both the SNr and GPe converge upon thalamic relay nuclei (directly or indirectly, respectively), and are traditionally modeled as functionally antagonistic relay inputs. However, recent anatomical and functional studies have identified unanticipated circuit connectivity in both the SNr and GPe, demonstrating their potential as far more than relay nuclei. In the present study, we employed simultaneous deep brain stimulation and functional magnetic resonance imaging (DBS-fMRI) with cerebral blood volume (CBV) measurements to functionally and unbiasedly map the circuit- and network level connectivity of the SNr and GPe. Sprague-Dawley rats were implanted with a custom-made MR-compatible stimulating electrode in the right SNr (n=6) or GPe (n=7). SNr- and GPe-DBS, conducted across a wide range of stimulation frequencies, revealed a number of surprising evoked responses, including unexpected CBV decreases within the striatum during DBS at either target, as well as GPe-DBS-evoked positive modulation of frontal cortex. Functional connectivity MRI revealed global modulation of neural networks during DBS at either target, sensitive to stimulation frequency and readily reversed following cessation of stimulation. This work thus contributes to a growing literature demonstrating extensive and unanticipated functional connectivity among basal ganglia nuclei.

Neuroversion: using electroconvulsive therapy as a bridge to deep brain stimulation implantation

Parkinson's disease (PD) is a movement disorder with significant neuropsychiatric comorbidities. Electroconvulsive therapy (ECT) is effective in treating these neuropsychiatric symptoms; however, clinicians are reluctant to use ECT in patients with deep brain stimulation (DBS) implantations for fear of damaging the device, as well as potential cognitive side effects. Right unilateral ultra-brief pulse (RUL UBP) ECT has a more favorable cognitive side-effect profile yet has never been reported in PD patients with DBS implants. We present a case series of three patients with a history of PD that all presented with psychiatric decompensation immediately prior to planned DBS surgery. All three patients had DBS electrode(s) in place at the time and an acute course of ECT was utilized in a novel method to "bridge" these individuals to neurosurgery. The patients all experienced symptom resolution (psychosis and/or depression and/or anxiety) without apparent cognitive side effects. This case series not only illustrates that right unilateral ultra-brief pulse can be utilized in patients with DBS electrodes but also illustrates that this intervention can be utilized as a neuromodulatory "bridge", where nonoperative surgical candidates with unstable psychiatric symptoms can be converted to operative candidates in a manner similar to electrical cardioversion.