Deep brain stimulation for movement disorders: 2015 and beyond

Real-time field-programmable gate array-based closed-loop deep brain stimulation platform targeting cerebellar circuitry rescues motor deficits in a mouse model of cerebellar ataxia

AIMS

The open-loop nature of conventional deep brain stimulation (DBS) produces continuous and excessive stimulation to patients which contributes largely to increased prevalence of adverse side effects. Cerebellar ataxia is characterized by abnormal Purkinje cells (PCs) dendritic arborization, loss of PCs and motor coordination, and muscle weakness with no effective treatment. We aim to develop a real-time field-programmable gate array (FPGA) prototype targeting the deep cerebellar nuclei (DCN) to close the loop for ataxia using conditional double knockout mice with deletion of PC-specific LIM homeobox (Lhx)1 and Lhx5, resulting in abnormal dendritic arborization and motor deficits.

METHODS

We implanted multielectrode array in the DCN and muscles of ataxia mice. The beneficial effect of open-loop DCN-DBS or closed-loop DCN-DBS was compared by motor behavioral assessments, electromyography (EMG), and neural activities (neurospike and electroencephalogram) in freely moving mice. FPGA board, which performed complex real-time computation, was used for closed-loop DCN-DBS system.

RESULTS

Closed-loop DCN-DBS was triggered only when symptomatic muscle EMG was detected in a real-time manner, which restored motor activities, electroencephalogram activities and neurospike properties completely in ataxia mice. Closed-loop DCN-DBS was more effective than an open-loop paradigm as it reduced the frequency of DBS.

CONCLUSION

Our real-time FPGA-based DCN-DBS system could be a potential clinical strategy for alleviating cerebellar ataxia and other movement disorders.

The altered spontaneous neural activity in patients with Parkinson's disease and its predictive value for the motor improvement of deep brain stimulation

BACKGROUND

This study aims to investigate the altered spontaneous neural activity in patients with Parkinson's disease (PD) revealed by amplitudes of low-frequency fluctuations (ALFF) of resting-state fMRI, and the feasibility of using ALFF as neuroimaging predictors for motor improvement after bilateral subthalamic nucleus (STN) deep brain stimulation (DBS).

METHODS

Fourty-four patients and 44 healthy controls were included in this study. First, the ALFF of patients with PD was compared with that of controls; then significant clusters were correlated with motor improvement after DBS (unified Parkinson's disease rating scale (UPDRS-III)) and other clinical variables. Second, regression and classification of the machine learning models were conducted to predict motor improvement after DBS. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of the classification model.

RESULTS

Compared with healthy controls, patients with PD showed increased ALFF in the bilateral motor area and decreased ALFF in the bilateral temporal cortex and cerebellum. The Hoehn-Yahr stages correlated with ALFF within the bilateral cerebellum (p = 0.021), and UPDRS-III improvement correlated with ALFF in the left (p < 0.001) and right (p = 0.005) motor areas. The regression model showed a significant correlation between the predicted and observed UPDRS-III changes (R = 0.65, p < 0.001). The ROC analysis revealed an area under the curve (AUC) of 0.94 which differentiated moderate and superior DBS responders.

CONCLUSION

The results revealed altered ALFF patterns in patients with PD and their correlations with clinical variables. Both binary and continuous ALFF can potentially serve as predictive biomarkers for DBS response.

Deep brain stimulation - New programming algorithms and teleprogramming

INTRODUCTION

Thanks to a variety of factors, the field of neuromodulation has evolved significantly over the past decade. Developments include new indications and innovations of hardware, software, and stimulation techniques leading to an expansion in scope and role of these techniques as powerful therapies. They also imply the realization that practical application involves new nuances that make patient selection, surgical technique and the programming process even more complex, requiring continuous education and an organized structured approach.

AREAS COVERED

In this review, the authors explore the developments in deep brain stimulation technology, including electrodes, implantable pulse generators, contact configurations (i.e, directional leads and independent current control), remote programming and sensing using local field potentials.

EXPERT OPINION

The innovations in the field of deep brain stimulation discussed in this review potentially provide increased effectiveness and flexibility not only to improve therapeutic response but also to address troubleshooting challenges seen in clinical practice. Directional leads and shorter pulse widths may broaden the therapeutic window of stimulation, avoiding current spread to structures that might trigger stimulation-related side effects. Similarly, independent control of current to individual contacts allows for the shaping of the electric field. Finally, sensing and remote programming represent important developments for more effective and individualized patient care.

Totally Organic Hydrogel-Based Self-Closing Cuff Electrode for Vagus Nerve Stimulation

An intrinsically soft organic electrode consisting of poly(3,4-ethylenedioxythiophene)-modified polyurethane (PEDOT-PU) is embedded into a bilayer film of polyvinyl alcohol (PVA) hydrogels for developing a self-closing cuff electrode for neuromodulation. The curled form of the PVA hydrogel is prepared by releasing internal stress in the bilayer structure. The inner diameter of the cuff electrode is set to less than 2 mm for immobilization to the vagus nerve (VN) of humans and pigs. The stability of the immobilization is examined, while the pressure applied to a nerve bundle is at a harmless level (≈200 Pa). Since the electrode is totally organic, MRI measurements can be conducted without image artifacts. The large electric capacitance of the PEDOT-PU (≈27 mF cm^-2 ) ensures a safe stimulation of living tissues without Faradaic reactions. The practical performance of the cuff electrode for VN stimulation is demonstrated by observation of bradycardia induction in a pig.

Clinical neurophysiology of Parkinson's disease and parkinsonism

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This review is part of the series on the clinical neurophysiology of movement disorders and focuses on Parkinson’s disease and parkinsonism.

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The pathophysiology of cardinal parkinsonian motor symptoms and myoclonus are reviewed.

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The recordings from microelectrode and deep brain stimulation electrodes are reported in detail.

This review is part of the series on the clinical neurophysiology of movement disorders. It focuses on Parkinson’s disease and parkinsonism. The topics covered include the pathophysiology of tremor, rigidity and bradykinesia, balance and gait disturbance and myoclonus in Parkinson’s disease. The use of electroencephalography, electromyography, long latency reflexes, cutaneous silent period, studies of cortical excitability with single and paired transcranial magnetic stimulation, studies of plasticity, intraoperative microelectrode recordings and recording of local field potentials from deep brain stimulation, and electrocorticography are also reviewed. In addition to advancing knowledge of pathophysiology, neurophysiological studies can be useful in refining the diagnosis, localization of surgical targets, and help to develop novel therapies for Parkinson’s disease.

Deep Brain Stimulation of the Interposed Nucleus Reverses Motor Deficits and Stimulates Production of Anti-inflammatory Cytokines in Ataxia Mice

Cerebellum is one of the major targets of autoimmunity and cerebellar damage that leads to ataxia characterized by the loss of fine motor coordination and balance, with no treatment available. Deep brain stimulation (DBS) could be a promising treatment for ataxia but has not been extensively investigated. Here, our study aims to investigate the use of interposed nucleus of deep cerebellar nuclei (IN-DCN) for ataxia. We first characterized ataxia-related motor symptom of a Purkinje cell (PC)-specific LIM homeobox (Lhx)1 and Lhx5 conditional double knockout mice by motor coordination tests, and spontaneous electromyogram (EMG) recording. To validate IN-DCN as a target for DBS, in vivo local field potential (LFP) multielectrode array recording of IN-DCN revealed abnormal LFP amplitude surges in PCs. By synchronizing the EMG and IN-DCN recordings (neurospike and LFP) with high-speed video recordings, ataxia mice showed poorly coordinated movements associated with low EMG amplitude and aberrant IN-DCN neural firing. To optimize IN-DCN-DBS for ataxia, we tested DBS parameters from low (30 Hz) to high stimulation frequency (130 or 150 Hz), and systematically varied pulse width values (60 or 80 µs) to maximize motor symptom control in ataxia mice. The optimal IN-DCN-DBS parameter reversed motor deficits in ataxia mice as detected by animal behavioral tests and EMG recording. Mechanistically, cytokine array analysis revealed that anti-inflammatory cytokines such as interleukin (IL)-13 and IL-4 were upregulated after IN-DCN-DBS, which play key roles in neural excitability. As such, we show that IN-DCN-DBS is a promising treatment for ataxia and possibly other movement disorders alike.

Somatotopic Organization of Hyperdirect Pathway Projections From the Primary Motor Cortex in the Human Brain

Background

The subthalamic nucleus (STN) is an effective neurosurgical target to improve motor symptoms in Parkinson's Disease (PD) patients. MR-guided Focused Ultrasound (MRgFUS) subthalamotomy is being explored as a therapeutic alternative to Deep Brain Stimulation (DBS) of the STN. The hyperdirect pathway provides a direct connection between the cortex and the STN and is likely to play a key role in the therapeutic effects of MRgFUS intervention in PD patients.

Objective

This study aims to investigate the topography and somatotopy of hyperdirect pathway projections from the primary motor cortex (M1).

Methods

We used advanced multi-fiber tractography and high-resolution diffusion MRI data acquired on five subjects of the Human Connectome Project (HCP) to reconstruct hyperdirect pathway projections from M1. Two neuroanatomy experts reviewed the anatomical accuracy of the tracts. We extracted the fascicles arising from the trunk, arm, hand, face and tongue area from the reconstructed pathways. We assessed the variability among subjects based on the fractional anisotropy (FA) and mean diffusivity (MD) of the fibers. We evaluated the spatial arrangement of the different fascicles using the Dice Similarity Coefficient (DSC) of spatial overlap and the centroids of the bundles.

Results

We successfully reconstructed hyperdirect pathway projections from M1 in all five subjects. The tracts were in agreement with the expected anatomy. We identified hyperdirect pathway fascicles projecting from the trunk, arm, hand, face and tongue area in all subjects. Tract-derived measurements showed low variability among subjects, and similar distributions of FA and MD values among the fascicles projecting from different M1 areas. We found an anterolateral somatotopic arrangement of the fascicles in the corona radiata, and an average overlap of 0.63 in the internal capsule and 0.65 in the zona incerta.

Conclusion

Multi-fiber tractography combined with high-resolution diffusion MRI data enables the identification of the somatotopic organization of the hyperdirect pathway. Our preliminary results suggest that the subdivisions of the hyperdirect pathway projecting from the trunk, arm, hand, face, and tongue motor area are intermixed at the level of the zona incerta and posterior limb of the internal capsule, with a predominantly overlapping topographical organization in both regions. Subject-specific knowledge of the hyperdirect pathway somatotopy could help optimize target definition in MRgFUS intervention.

Charting human subcortical maturation across the adult lifespan with in vivo 7 T MRI

The human subcortex comprises hundreds of unique structures. Subcortical functioning is crucial for behavior, and disrupted function is observed in common neurodegenerative diseases. Despite their importance, human subcortical structures continue to be difficult to study in vivo. Here we provide a detailed account of 17 prominent subcortical structures and ventricles, describing their approximate iron and myelin contents, morphometry, and their age-related changes across the normal adult lifespan. The results provide compelling insights into the heterogeneity and intricate age-related alterations of these structures. They also show that the locations of many structures shift across the lifespan, which is of direct relevance for the use of standard magnetic resonance imaging atlases. The results further our understanding of subcortical morphometry and neuroimaging properties, and of normal aging processes which ultimately can improve our understanding of neurodegeneration.

Frameless x-ray-based lead re-implantation after partial hardware removal of deep brain stimulation system with preservation of intracerebral trajectories

Background

Deep brain stimulation (DBS) is an established treatment for patients with medical refractory movement disorders with continuously increasing use also in other neurological and psychiatric diseases. Early and late complications can lead to revision surgeries with partial or complete DBS-system removal. In this study, we aimed to report on our experience with a frameless x-ray-based lead re-implantation technique after partial hardware removal or dysfunction of DBS-system, allowing the preservation of intracerebral trajectories.

Methods

We describe a surgical procedure with complete implant removal due to infection except for the intracranial part of the electrode and with non-stereotactic electrode re-implantation. A retrospective analysis of a patient series treated using this technique was performed and the surgical outcome was evaluated including radiological and clinical parameters.

Results

A total of 8 DBS-patients with lead re-implantation using the frameless x-ray-based method were enrolled in the study. A revision of 14 leads was performed, whereof a successful lead re-implantation could be achieved without any problems in 10 leads (71%). In two patients (one patient with dystonia and one patient with tremor), the procedure was not successful, so we placed both leads frame-based stereotactically.

Conclusions

The described x-ray-based technique allows a reliable frameless electrode re-implantation after infection and electrode dysfunction and might represent an efficient alternative to frame-based procedures for lead revision making the preservation of intracerebral trajectories possible.

On the Right Track to Treat Movement Disorders: Promising Therapeutic Approaches for Parkinson's and Huntington's Disease

Movement disorders are neurological conditions in which patients manifest a diverse range of movement impairments. Distinct structures within the basal ganglia of the brain, an area involved in movement regulation, are differentially affected for every disease. Among the most studied movement disorder conditions are Parkinson’s (PD) and Huntington’s disease (HD), in which the deregulation of the movement circuitry due to the loss of specific neuronal populations in basal ganglia is the underlying cause of motor symptoms. These symptoms are due to the loss principally of dopaminergic neurons of the substantia nigra (SN) par compacta and the GABAergic neurons of the striatum in PD and HD, respectively. Although these diseases were described in the 19th century, no effective treatment can slow down, reverse, or stop disease progression. Available pharmacological therapies have been focused on preventing or alleviating motor symptoms to improve the quality of life of patients, but these drugs are not able to mitigate the progressive neurodegeneration. Currently, considerable therapeutic advances have been achieved seeking a more efficacious and durable therapeutic effect. Here, we will focus on the new advances of several therapeutic approaches for PD and HD, starting with the available pharmacological treatments to alleviate the motor symptoms in both diseases. Then, we describe therapeutic strategies that aim to restore specific neuronal populations or their activity. Among the discussed strategies, the use of Neurotrophic factors (NTFs) and genetic approaches to prevent the neuronal loss in these diseases will be described. We will highlight strategies that have been evaluated in both Parkinson’s and Huntington’s patients, and also the ones with strong preclinical evidence. These current therapeutic techniques represent the most promising tools for the safe treatment of both diseases, specifically those aimed to avoid neuronal loss during disease progression.

Neural oscillations and brain stimulation in Alzheimer's disease

Aging is associated with alterations in cognitive processing and brain neurophysiology. Whereas the primary symptom of amnestic mild cognitive impairment (aMCI) is memory problems greater than normal for age and education, patients with Alzheimer's disease (AD) show impairments in other cognitive domains in addition to memory dysfunction. Resting-state electroencephalography (rsEEG) studies in physiological aging indicate a global increase in low-frequency oscillations' power and the reduction and slowing of alpha activity. The enhancement of slow and the reduction of fast oscillations, and the disruption of brain functional connectivity, however, are characterized as major rsEEG changes in AD. Recent rodent studies also support human evidence of age- and AD-related changes in resting-state brain oscillations, and the neuroprotective effect of brain stimulation techniques through gamma-band stimulations. Cumulatively, current evidence moves toward optimizing rsEEG features as reliable predictors of people with aMCI at risk for conversion to AD and mapping neural alterations subsequent to brain stimulation therapies. The present paper reviews the latest evidence of changes in rsEEG oscillations in physiological aging, aMCI, and AD, as well as findings of various brain stimulation therapies from both human and non-human studies.

Management of Advanced Therapies in Parkinson's Disease Patients in Times of Humanitarian Crisis: The COVID-19 Experience

Background

Although the COVID-19 pandemic is affecting a relatively small proportion of the global population, its effects have already reached everyone. The pandemic has the potential to differentially disadvantage chronically ill patients, including those with Parkinson's disease (PD). The first health care reaction has been to limit access to clinics and neurology wards to preserve fragile patients with PD from being infected. In some regions, the shortage of medical staff has also forced movement disorders neurologists to provide care for patients with COVID-19.

Objective

To share the experience of various movement disorder neurologists operating in different world regions and provide a common approach to patients with PD, with a focus on those already on advanced therapies, which may serve as guidance in the current pandemic and for emergency situations that we may face in the future.

Conclusion

Most of us were unprepared to deal with this condition given that in many health care systems, telemedicine has been only marginally available or only limited to email or telephone contacts. In addition, to ensure sufficient access to intensive care unit beds, most elective procedures (including deep brain stimulation or the initiation of infusion therapies) have been postponed. We all hope there will soon be a time when we will return to more regular hospital schedules. However, we should consider this crisis as an opportunity to change our approach and encourage our hospitals and health care systems to facilitate the remote management of chronic neurological patients, including those with advanced PD.

The Effects of Deep Brain Stimulation on Speech Intelligibility in Persons With Essential Tremor

Purpose The aim of this study was to investigate how deep brain stimulation (DBS) of the caudal zona incerta (cZi) affects speech intelligibility in persons with essential tremor. Method Thirty-five participants were evaluated: off stimulation, on chronic stimulation optimized to alleviate tremor, and during unilateral stimulation at increasing amplitude levels. At each stimulation condition, the participants read 10 unique nonsense sentences from the Swedish Test of Intelligibility. Two listeners, blinded to stimulation condition, transcribed all recorded sentences orthographically in a randomized procedure. A mean speech intelligibility score for each patient and stimulation condition was computed, and comparisons were made between scores off and on stimulation. Results Chronic cZi-DBS had no significant effect on speech intelligibility, and there was no difference in outcome between bilateral and unilateral treatments. During unilateral stimulation at increasing amplitudes, nine participants demonstrated deteriorating speech intelligibility. These nine participants were on average older and had more superior contacts activated during the evaluation compared with the participants without deterioration. Conclusions Chronic cZi-DBS, optimized for tremor suppression, does not generally affect speech intelligibility in persons with essential tremor. Furthermore, speech intelligibility may be preserved in many individuals, even when stimulated at high amplitudes. Adverse effects of high-amplitude unilateral stimulation observed in this study were associated with stimulation originating from a more superior location, as well as with the participants' age. These results, highlighting age and stimulation location as contributing to speech intelligibility outcomes, were, however, based on a limited number of individuals experiencing adverse effects with high-amplitude stimulation and should, therefore, be interpreted with caution.

Metal Artifact Reduction in Head CT Performed for Patients with Deep Brain Stimulation Devices: Effectiveness of a Single-Energy Metal Artifact Reduction Algorithm

BACKGROUND AND PURPOSE

Deep brain stimulation electrodes induce massive artifacts on CT images, deteriorating the diagnostic value of examinations. We aimed to investigate the usefulness and potential limitations of a single-energy metal artifact reduction algorithm in head CT performed in patients with implanted deep brain stimulation devices.

MATERIALS AND METHODS

Thirty-four patients with deep brain stimulation (bilateral, n = 28) who underwent head CT on a 320-detector row scanner and whose images were reconstructed with and without single-energy metal artifact reduction at the examinations were retrospectively included. The severity of artifacts around electrodes was assessed objectively using SDs and an artifact index. Two radiologists subjectively evaluated the severity of artifacts from electrodes, the visibility of electrode localization and surrounding structures, and overall diagnostic confidence on 4-point scales. Background image quality (GM-WM contrast and image noise) was subjectively and objectively assessed. The presence and location of artifacts newly produced by single-energy metal artifact reduction were analyzed.

RESULTS

Single-energy metal artifact reduction provided lower objective and subjective metal artifacts and improved visualization of electrode localization and surrounding structures and diagnostic confidence compared with non-single-energy metal artifact reduction images, with statistical significance (all, P < .01). No significant differences were observed in GM-WM contrast and image noise (all, P ≥ .11). The new artifacts from single-energy metal artifact reduction were prominently observed in patients with bilateral deep brain stimulation at high convexity, possibly induced by deep brain stimulation leads placed under the parietal scalp.

CONCLUSIONS

Single-energy metal artifact reduction substantially reduces the metal artifacts from deep brain stimulation electrodes and improves the visibility of intracranial structures without affecting background image quality. However, non-single-energy metal artifact reduction images should be simultaneously reviewed to accurately assess the entire intracranial area, particularly in patients with bilateral deep brain stimulation.

Biplanar X-Ray Methods for Stereotactic Intraoperative Localization in Deep Brain Stimulation Surgery

BACKGROUND

Efficacy in deep brain stimulation (DBS) is dependent on precise positioning of electrodes within the brain. Intraoperative fluoroscopy, computed tomography (CT), or magnetic resonance imaging are used for stereotactic intraoperative localization (StIL), but the utility of biplanar X-ray has not been evaluated in detail.

OBJECTIVE

To determine if analysis of orthogonal biplanar X-rays using graphical analysis (GA), ray tracing (RT), and/or perspective projection (PP) can be utilized for StIL.

METHODS

A review of electrode tip positions comparing postoperative CT to X-ray methods was performed for DBS operations containing orthogonal biplanar X-ray with referential spheres and pins.

RESULTS

Euclidean (Re) errors for final DBS electrode position on intraoperative X-rays vs postoperative CT using GA, RT, and PP methods averaged 1.58 mm (±0.75), 0.74 mm (±0.45), and 1.07 mm (±0.64), respectively (n = 56). GA was more accurate with a ventriculogram. RT and PP predicted positions that correlated with third ventricular structures on ventriculogram cases. RT was the most stable but required knowledge of the geometric setup. PP was more flexible than RT but required well-distributed reference points. A single case using the O-arm demonstrated Re errors of 0.43 mm and 0.28 mm for RT and PP, respectively. In addition, these techniques could also be used to calculate directional electrode rotation.

CONCLUSION

GA, RT, and PP can be employed for precise StIL during DBS using orthogonal biplanar X-ray. These methods may be generalized to other stereotactic procedures or instances of biplanar imaging such as angiograms, radiosurgery, or injection therapeutics.

Pallidal Deep Brain Stimulation in DYT6 Dystonia: Clinical Outcome and Predictive Factors for Motor Improvement

Pallidal deep brain stimulation is an established treatment in dystonia. Available data on the effect in DYT-THAP1 dystonia (also known as DYT6 dystonia) are scarce and long-term follow-up studies are lacking. In this retrospective, multicenter follow-up case series of medical records of such patients, the clinical outcome of pallidal deep brain stimulation in DYT-THAP1 dystonia, was evaluated. The Burke Fahn Marsden Dystonia Rating Scale served as an outcome measure. Nine females and 5 males were enrolled, with a median follow-up of 4 years and 10 months after implant. All benefited from surgery: dystonia severity was reduced by a median of 58% (IQR 31-62, p = 0.001) at last follow-up, as assessed by the Burke Fahn Marsden movement subscale. In the majority of individuals, there was no improvement of speech or swallowing, and overall, the effect was greater in the trunk and limbs as compared to the cranio-cervical and orolaryngeal regions. No correlation was found between disease duration before surgery, age at surgery, or preoperative disease burden and the outcome of deep brain stimulation. Device- and therapy-related side-effects were few. Accordingly, pallidal deep brain stimulation should be considered in clinically impairing and pharmaco-resistant DYT-THAP1 dystonia. The method is safe and effective, both short- and long-term.

Neurological Worsening After Implantable Pulse Generator Replacement

BACKGROUND

Most of the implantable pulse generators (IPGs) in deep brain stimulation (DBS) used to date are non-rechargeable requiring regular replacements. IPG replacement is a minor surgical procedure, but adverse events including neurological worsening have been reported. In this study, we determine the possibility of neurological worsening after IPG replacement in Parkinson's disease (PD) cases on chronic DBS therapy (CDT) and its electrophysiological basis along with the therapeutic interventions used to alleviate them.

METHODS

This study is a retrospective chart review of PD cases on CDT followed at London Movement Disorders Centre from January 2010 to December 2016. Included cases were those who underwent one or more IPG replacement.

RESULTS

A total of 45 PD cases on CDT underwent 62 IPG replacements involving 121 channels. Neurological worsening was observed in 16 (35.5%) cases following 17 (27.4%) IPG replacements, all following dual-channel IPG replacements. Tremor (41.2%), speech (35.3%), and gait (23.5%) worsened most commonly. Deviation from the pre-replacement parameters including voltage and impedance resulting in change in total electrical energy delivered (TEED) was the most common electrophysiological correlate, observed in 82.4% (14/17) IPGs having neurological worsening. This included switched laterality in a dual-channel IPG. Neurological worsening in the remaining 17.6% cases was hardware-related.

CONCLUSION

Neurological worsening followed 27.4% of IPG replacements in PD cases on CDT with approximately 82.4% of these being avoidable by carefully monitoring stimulation parameters to match pre-replacement TEED values.

Deep Brain Stimulation for Parkinson Disease

Parkinson disease (PD) is the second most common neurodegenerative disorder and affects more than 1 million individuals in the United States. Deep brain stimulation (DBS) is one form of treatment of PD. DBS treatment is still evolving due to technological innovations that shape how this therapy is used.

Deep Brain Stimulation Programming 2.0: Future Perspectives for Target Identification and Adaptive Closed Loop Stimulation

Deep brain stimulation has developed into an established treatment for movement disorders and is being actively investigated for numerous other neurological as well as psychiatric disorders. An accurate electrode placement in the target area and the effective programming of DBS devices are considered the most important factors for the individual outcome. Recent research in humans highlights the relevance of widespread networks connected to specific DBS targets. Improving the targeting of anatomical and functional networks involved in the generation of pathological neural activity will improve the clinical DBS effect and limit side-effects. Here, we offer a comprehensive overview over the latest research on target structures and targeting strategies in DBS. In addition, we provide a detailed synopsis of novel technologies that will support DBS programming and parameter selection in the future, with a particular focus on closed-loop stimulation and associated biofeedback signals.

A Neuroethics Framework for the Australian Brain Initiative

Neuroethics is central to the Australian Brain Initiative's aim to sustain a thriving and responsible neurotechnology industry. Diverse and inclusive community and stakeholder engagement and a trans-disciplinary approach to neuroethics will be key to the success of the Australian Brain Initiative.

Interleaving Stimulation in Parkinson's Disease, Tremor, and Dystonia

BACKGROUND/AIMS

Interleaving stimulation (ILS) in deep brain stimulation (DBS) provides individualized stimulation of 2 contacts delivered in alternating order. Currently, limited information on the utility of ILS exists. The aims of this study were to determine the practical applications and outcomes of ILS DBS in Parkinson's disease (PD), tremor, and dystonia.

METHODS

We performed a single-center, unblinded, retrospective chart review of all patients with DBS attempted on ILS at our referral center assessing for rationale and outcomes.

RESULTS

Fifty patients (PD, n = 27; tremor, n = 7; dystonia, n = 16 patients) tried ILS for 2 rationales: management of adverse effects (n = 29) and to improve clinical efficacy (n = 21). A total of 19 patients demonstrated improvement with ILS for adverse effect management predominately for the treatment of dyskinesias (n = 12). In the vast majority of dyskinetic patients, a contact added into the rostral zona incerta with ILS was performed. Nine out of 21 patients demonstrated improved clinical efficacy with ILS with all 6 PD patients who tried ILS for this rationale demonstrating benefit.

CONCLUSIONS

In PD, ILS provided benefits for dyskinesias and parkinsonism, with minimal improvement of other adverse effects. In tremor and dystonia, marginal effects in terms of mitigation of adverse effects and improvement of clinical outcomes were evident.

Deep brain stimulation in Tourette's syndrome: evidence to date

Tourette's syndrome (TS) is a neurodevelopmental disorder that comprises vocal and motor tics associated with a high frequency of psychiatric comorbidities, which has an important impact on quality of life. The onset is mainly in childhood and the symptoms can either fade away or require pharmacological therapies associated with cognitive-behavior therapies. In rare cases, patients experience severe and disabling symptoms refractory to conventional treatments. In these cases, deep brain stimulation (DBS) can be considered as an interesting and effective option for symptomatic control. DBS has been studied in numerous trials as a therapy for movement disorders, and currently positive data supports that DBS is partially effective in reducing the motor and non-motor symptoms of TS. The average response, mostly from case series and prospective cohorts and only a few controlled studies, is around 40% improvement on tic severity scales. The ventromedial thalamus has been the preferred target, but more recently the globus pallidus internus has also gained some notoriety. The mechanism by which DBS is effective on tics and other symptoms in TS is not yet understood. As refractory TS is not common, even reference centers have difficulties in performing large controlled trials. However, studies that reproduce the current results in larger and multicenter randomized controlled trials to improve our knowledge so as to support the best target and stimulation settings are still lacking. This article will discuss the selection of the candidates, DBS targets and mechanisms on TS, and clinical evidence to date reviewing current literature about the use of DBS in the treatment of TS.

Deep brain stimulation: potential for neuroprotection

Over the last two decades there has been an exponential rise in the number of patients receiving deep brain stimulation (DBS) to manage debilitating neurological symptoms in conditions such as Parkinson's disease, essential tremor, and dystonia. Novel applications of DBS continue to emerge including treatment of various psychiatric conditions (e.g. obsessive-compulsive disorder, major depression) and cognitive disorders such as Alzheimer's disease. Despite widening therapeutic applications, our understanding of the mechanisms underlying DBS remains limited. In addition to modulation of local and network-wide neuronal activity, growing evidence suggests that DBS may also have important neuroprotective effects in the brain by limiting synaptic dysfunction and neuronal loss in neurodegenerative disorders. In this review, we consider evidence from preclinical and clinical studies of DBS in Parkinson's disease, Alzheimer's disease, and epilepsy that suggest chronic stimulation has the potential to mitigate neuronal loss and disease progression.

Alternating Thalamic Deep Brain Stimulation for Essential Tremor: A Trial to Reduce Habituation

Background

DBS in the ventral intermediate nucleus (VIM) of the thalamus has been a revolutionary treatment for patients with essential tremor (ET) by reducing tremor. Unfortunately, some patients develop habituation to DBS and thus experience reduced efficacy and loss of tremor control. There are no standardized methods of addressing habituation to DBS. We propose alternating stimulation patterns as a way to reduce habituation.

Methods

This was a randomized, placebo-controlled trial for patients with VIM DBS for ET. Patients were randomized to either experimental treatment arm of alternating stimulation patterns on a weekly basis or standard care arm of continuous stimulation settings for 12 weeks. Primary outcome was change in the performance subscale of The Essential Tremor Rating Assessment Scale (TETRAS), which was performed at initial visit and 12-week follow-up. Secondary outcome included change in the activities of daily living subscale of TETRAS.

Results

Twenty-two patients were enrolled in the trial, and 16 were analyzed at follow-up. Experimental treatment subjects displayed sustained tremor control compared to standard care, as measured by the change in TETRAS performance subscale (-0.6 vs. 6.7 point change, respectively) with a 7.3 difference between the arms (P = 0.006).

Conclusion

Alternating stimulation patterns on a weekly basis for ET patients with VIM DBS reduced habituation in this pilot study. This study suggests that exposure to different stimulation groups may maintain better tremor control compared to constant stimulation parameters.

Decisions about deep brain stimulation therapy in Parkinson's disease

Parkinson's disease can be treated surgically in patients who present with motor complications such as fluctuations and dyskinesias, or medically-refractory disabling tremor. In this review, a group of specialists formulated suggestions for a preoperative evaluation protocol after reviewing the literature published up to October 2017. In this protocol, eligibility and ineligibility criteria for surgical treatment were suggested, as well as procedures that should be carried out before the multidisciplinary therapeutic decisions. The review emphasizes the need to establish "DBS teams", with professionals dedicated specifically to this area. Finally, surgical target selection (subthalamic nucleus or globus pallidus internus) is discussed briefly, weighing the pros and cons of each target.

Targeting the hot spot in a patient with essential tremor and Parkinson's disease: Tractography matters

INTRODUCTION

Thalamic ventralis intermedius deep brain stimulation (VIM-DBS) is generally effective in treating refractory tremor in Parkinson's disease (PD) and in essential tremor (ET), but some patients do not respond well due to side effects or from loss of the effect of stimulation over time. The caudal zona incerta (ZI) has emerged as a promising target in ET, and the effects of ZI-DBS on PD tremor are less studied. Here, we describe a rare situation in which both ET and PD coexist in a 72-year-old male referred for ZI-DBS due to refractory tremor. The aim of this study was to evaluate whether there was a difference in the area stimulated to improve each type of tremor and whether tractography could improve and predict motor outcome.

METHODS

Two months after the surgery, in order to define which of the cathodes was the most effective towards improving the tremor and parkinsonian symptoms, a double-blinded, monopolar evaluation was conducted on both hemispheres separately. Once the best contact and parameters were defined, the volume of tissue activation (VTA) was represented spatially for each type of tremor and, finally, the image model was fused with the tractography.

RESULTS

For both types of tremor, the hot spot stimulated region achieved the dentato-rubro-thalamic tract (DRTT) at the higher fiber density region. The DRTT fibers were asymmetrical between the right and left hemispheres.

CONCLUSION

Regardless of the type of tremor, DRTT can be the most effective region for stimulation. Tractography should be considered when planning the surgical target since the DRTT is not always symmetrical, and the reconstruction of the VTA together with the tractography can greatly improve the DBS programming, and, probably, the patient's outcome to the stimulation.

Deep Brain Stimulation and L-DOPA Therapy: Concepts of Action and Clinical Applications in Parkinson's Disease

L-DOPA is still the most effective pharmacological therapy for the treatment of motor symptoms in Parkinson's disease (PD) almost four decades after it was first used. Deep brain stimulation (DBS) is a safe and highly effective treatment option in patients with PD. Even though a clear understanding of the mechanisms of both treatment methods is yet to be obtained, the combination of both treatments is the most effective standard evidenced-based therapy to date. Recent studies have demonstrated that DBS is a therapy option even in the early course of the disease, when first complications arise despite a rigorous adjustment of the pharmacological treatment. The unique feature of this therapeutic approach is the ability to preferentially modulate specific brain networks through the choice of stimulation site. The clinical effects have been unequivocally confirmed in recent studies; however, the impact of DBS and the supplementary effect of L-DOPA on the neuronal network are not yet fully understood. In this review, we present emerging data on the presumable mechanisms of DBS in patients with PD and discuss the pathophysiological similarities and differences in the effects of DBS in comparison to dopaminergic medication. Targeted, selective modulation of brain networks by DBS and pharmacodynamic effects of L-DOPA therapy on the central nervous system are presented. Moreover, we outline the perioperative algorithms for PD patients before and directly after the implantation of DBS electrodes and strategies for the reduction of side effects and optimization of motor and non-motor symptoms.

Mathematical Modeling for Description of Oscillation Suppression Induced by Deep Brain Stimulation

A mathematical modeling for description of oscillation suppression by deep brain stimulation (DBS) is explored in this paper. High-frequency DBS introduced to the basal ganglia network can suppress pathological neural oscillations that occur in the Parkinsonian state. However, selecting appropriate stimulation parameters remains a challenging issue due to the limited understanding of the underlying mechanisms of the Parkinsonian state and its control. In this paper, we use a describing function analysis to provide an intuitive way to select the optimal stimulation parameters based on a biologically plausible computational model of the Parkinsonian neural network. By the stability analysis using the describing function method, effective DBS parameter regions for inhibiting the pathological oscillations can be predicted. Additionally, it is also found that a novel sinusoidal-shaped DBS may become an alternative stimulation pattern and expends less energy, but with a different mechanism. This paper provides new insight into the possible mechanisms underlying DBS and a prediction of optimal DBS parameter settings, and even suggests how to select novel DBS wave patterns for the treatment of movement disorders, such as Parkinson's disease.

Exploiting interfacial phenomena in organic bioelectronics: Conformable devices for bidirectional communication with living systems

A novel fully organic bioelectronic device is presented and validated as electronic transducer and current stimulator for brain implants. The device integrates polymeric electrodes made of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on paper thin foils, resulting in a high surface-to-volume ratio architecture that exhibits high sensitivity to interfacial ionic transport phenomena. The prototyping technique herein presented yields devices for the bidirectional communication with biological systems whose dimensionality can be controlled according to the desired application. Transduction of ultra-low local-field potentials and delivery of voltage pulse-trains alike those used in deep-brain stimulation are herein assessed, paving the way towards novel theranostic strategies for the treatment of Parkinson's Disease and other severe neurodegenerative and/or traumatic pathologies of the central nervous system.

Locally stable brain states predict suppression of epileptic activity by enhanced cognitive effort

Cognitive effort is known to play a role in healthy brain state organization, but little is known about its effects on pathological brain dynamics. When cortical stimulation is used to map functional brain areas prior to surgery, a common unwanted side effect is the appearance of afterdischarges (ADs), epileptiform and potentially epileptogenic discharges that can progress to a clinical seizure. It is therefore desirable to suppress this activity. Here, we analyze electrocorticography recordings from 15 patients with epilepsy. We show that a cognitive intervention in the form of asking an arithmetic question can be effective in suppressing ADs, but that its effectiveness is dependent upon the brain state at the time of intervention. By applying novel techniques from network analysis to quantify brain states, we find that the spatial organization of ADs with respect to coherent brain regions relates to the success of the cognitive intervention: if ADs are mainly localized within a single stable brain region, a cognitive intervention is likely to suppress the ADs. These findings show that cognitive effort is a useful tactic to modify unstable pathological activity associated with epilepsy, and suggest that the success of therapeutic interventions to alter activity may depend on an individual's brain state at the time of intervention.

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Cognitive intervention in the form of an arithmetic question can sometimes stop epileptic afterdischarges

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Brain states are measured through community structure of functional brain networks

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Success of intervention depends on spatial relationship between afterdischarge network and brain state

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Dynamic community detection is used to assess community stability

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If the afterdischarge network is in a strong, stable community, the cognitive intervention likely stops the afterdischarges

Thalamic Deep Brain Stimulation for Essential Tremor Also Reduces Voice Tremor

OBJECTIVE

Voice tremor is a common feature of essential tremor (ET) that is difficult to treat medically and significantly affects quality of life. Deep brain stimulation (DBS) of the ventral intermediate nucleus (Vim) of the thalamus is effective in improving contralateral distal limb tremor and has been shown in limited studies to affect voice tremor. Our objective was to retrospectively evaluate whether Vim-DBS used to treat patients with essential motor tremor also effectively treated underlying concurrent voice tremor and assess whether particular lead locations were favorable for treating vocal tremor.

MATERIALS AND METHODS

In this retrospective cohort study, patients had unilateral or bilateral lead placement and were monitored for up to 12 months. We used the Fahn-Tolosa-Marin (FTM) subscore to assess vocal tremor. Changes in vocal tremor before and after stimulation and over several sessions were assessed.

RESULTS

Of the 77 patients who met the inclusion criteria and were treated for essential tremor, 20 (26%) patients had vocal tremor prior to stimulation. Active Vim-DBS decreased the amplitude of voice tremor by 80% (p < 0.001). The mean FTM score as 1.24 pre-operation, 1.08 post-implantation (consistent with a lesion effect), and 0.25 with stimulation. The effect magnitude was maintained at last follow-up with slight improvement over time (p < 0.05). Unilateral and bilateral stimulation resulted in similar degrees of tremor reduction. A model of the centroid of stimulation showed that Vim thalamic stimulation that is more anterior on average yielded better voice tremor control, significantly so on the left side (p < 0.05). Additionally, there was improvement in head, tongue, and face tremor scores (p < 0.05).

CONCLUSIONS

Unilateral and bilateral Vim-DBS targeted to treat the motor component of essential tremor also dramatically decreased the amplitude of voice tremor in this group of patients, suggesting a potential benefit of this treatment for affected patients.

DBS Programming: An Evolving Approach for Patients with Parkinson's Disease

Deep brain stimulation (DBS) surgery is a well-established therapy for control of motor symptoms in Parkinson's disease. Despite an appropriate targeting and an accurate placement of DBS lead, a thorough and efficient programming is critical for a successful clinical outcome. DBS programming is a time consuming and laborious manual process. The current approach involves use of general guidelines involving determination of the lead type, electrode configuration, impedance check, and battery check. However there are no validated and well-established programming protocols. In this review, we will discuss the current practice and the recent advances in DBS programming including the use of interleaving, fractionated current, directional steering of current, and the use of novel DBS pulses. These technological improvements are focused on achieving a more efficient control of clinical symptoms with the least possible side effects. Other promising advances include the introduction of computer guided programming which will likely impact the efficiency of programming for the clinicians and the possibility of remote Internet based programming which will improve access to DBS care for the patients.

Directional DBS increases side-effect thresholds-A prospective, double-blind trial

OBJECTIVE

The objective of this study was to investigate whether directional deep brain stimulation (DBS) of the subthalamic nucleus in Parkinson's disease (PD) offers increased therapeutic windows, side-effect thresholds, and clinical benefit.

METHODS

In 10 patients, 20 monopolar reviews were conducted in a prospective, randomized, double-blind design to identify the best stimulation directions and compare them to conventional circular DBS regarding side-effect thresholds, motor improvement, and therapeutic window. In addition, circular and best-directional DBS were directly compared in a short-term crossover. Motor outcome was also assessed after an open-label follow-up of 3 to 6 months.

RESULTS

Stimulation in the individual best direction resulted in significantly larger therapeutic windows, higher side-effect thresholds, and more improvement in hand rotation than circular DBS. Rigidity and finger tapping did not respond differentially to the stimulation conditions. There was no difference in motor efficacy or stimulation amplitudes between directional and circular DBS in the short-term crossover. Follow-up evaluations 3 to 6 months after implantation revealed improvements in motor outcome and medication reduction comparable to other DBS studies with a majority of patients remaining with a directional setting.

CONCLUSION

Directional DBS can increase side-effect thresholds while achieving clinical benefit comparable to conventional DBS. Whether directional DBS improves long-term clinical outcome needs to be investigated in the future. © 2017 International Parkinson and Movement Disorder Society.

Comparing functional MRI protocols for small, iron-rich basal ganglia nuclei such as the subthalamic nucleus at 7 T and 3 T

The basal ganglia (BG) form a network of subcortical nuclei. Functional magnetic resonance imaging (fMRI) in the BG could provide insight in its functioning and the underlying mechanisms of Deep Brain Stimulation (DBS). However, fMRI of the BG with high specificity is challenging, because the nuclei are small and variable in their anatomical location. High resolution fMRI at field strengths of 7 Tesla (T) could help resolve these challenges to some extent. A set of MR protocols was developed for functional imaging of the BG nuclei at 3 T and 7 T. The protocols were validated using a stop-signal reaction task (Logan et al. []: J Exp Psychol: Human Percept Perform 10:276-291). Compared with sub-millimeter 7 T fMRI protocols aimed at cortex, a reduction of echo time and spatial resolution was strictly necessary to obtain robust Blood Oxygen Level Dependent (BOLD) sensitivity in the BG. An fMRI protocol at 3 T with identical resolution to the 7 T showed no robust BOLD sensitivity in any of the BG nuclei. The results suggest that the subthalamic nucleus, as well as the substantia nigra, red nucleus, and the internal and external parts of the globus pallidus show increased activation in failed stop trials compared with successful stop and go trials. Hum Brain Mapp 38:3226-3248, 2017. © 2017 Wiley Periodicals, Inc.

What Do Medical Students Know about Deep Brain Stimulation?

BACKGROUND

Deep brain stimulation (DBS) is an established therapy for movement disorders. It is currently under investigation in neuropsychiatric disorders. Neurophobia is a common phenomenon that might have a negative impact in medical education. Little is known about medical students' knowledge about DBS when they enter university and what they learn about it during their medical formation.

METHODS

A 10-item questionnaire was designed. Questions addressed indications for DBS, costs of DBS, complications, the percentage of Parkinson disease (PD) patients who might profit from DBS, etc. Students at Hannover Medical School were asked to complete the questionnaire in the preclinical study period and in the last year of the study.

RESULTS

Comparing the "early group" (204 students) and the "advanced group" (162 students), there was a significant gain of knowledge. More common disorders such as PD and tremor were known to be indications for DBS. Knowledge about the impact of DBS on specific symptoms in PD and about DBS targets was limited in both groups.

CONCLUSIONS

DBS is partly known among medical students in the preclinical phase with a gain of knowledge during further study. Future studies on this topic addressing general practitioners as neurologists are needed to better understand why knowledge on DBS is still limited.

Subthalamic nucleus deep brain stimulation on motor-symptoms of Parkinson's disease: Focus on neurochemistry

Deep brain stimulation (DBS) has become a standard therapy for Parkinson's disease (PD) and it is also currently under investigation for other neurological and psychiatric disorders. Although many scientific, clinical and ethical issues are still unresolved, DBS delivered into the subthalamic nucleus (STN) has improved the quality of life of several thousands of patients. The mechanisms underlying STN-DBS have been debated extensively in several reviews; less investigated are the biochemical consequences, which are still under scrutiny. Crucial and only partially understood, for instance, are the complex interplays occurring between STN-DBS and levodopa (LD)-centred therapy in the post-surgery follow-up. The main goal of this review is to address the question of whether an improved motor control, based on STN-DBS therapy, is also achieved through the additional modulation of other neurotransmitters, such as noradrenaline (NA) and serotonin (5-HT). A critical issue is to understand not only acute DBS-mediated effects, but also chronic changes, such as those involving cyclic nucleotides, capable of modulating circuit plasticity. The present article will discuss the neurochemical changes promoted by STN-DBS and will document the main results obtained in microdialysis studies. Furthermore, we will also examine the preliminary achievements of voltammetry applied to humans, and discuss new hypothetical investigational routes, taking into account novel players such as glia, or subcortical regions such as the pedunculopontine (PPN) area. Our further understanding of specific changes in brain chemistry promoted by STN-DBS would further disseminate its utilisation, at any stage of disease, avoiding an irreversible lesioning approach.

In vivo Exploration of the Connectivity between the Subthalamic Nucleus and the Globus Pallidus in the Human Brain Using Multi-Fiber Tractography

The basal ganglia is part of a complex system of neuronal circuits that play a key role in the integration and execution of motor, cognitive and emotional function in the human brain. Parkinson’s disease is a progressive neurological disorder of the motor circuit characterized by tremor, rigidity, and slowness of movement. Deep brain stimulation (DBS) of the subthalamic nucleus and the globus pallidus pars interna provides an efficient treatment to reduce symptoms and levodopa-induced side effects in Parkinson’s disease patients. While the underlying mechanism of action of DBS is still unknown, the potential modulation of white matter tracts connecting the surgical targets has become an active area of research. With the introduction of advanced diffusion MRI acquisition sequences and sophisticated post-processing techniques, the architecture of the human brain white matter can be explored in vivo. The goal of this study is to investigate the white matter connectivity between the subthalamic nucleus and the globus pallidus. Two multi-fiber tractography methods were used to reconstruct pallido-subthalamic, subthalamo-pallidal and pyramidal fibers in five healthy subjects datasets of the Human Connectome Project. The anatomical accuracy of the tracts was assessed by four judges with expertise in neuroanatomy, functional neurosurgery, and diffusion MRI. The variability among subjects was evaluated based on the fractional anisotropy and mean diffusivity of the tracts. Both multi-fiber approaches enabled the detection of complex fiber architecture in the basal ganglia. The qualitative evaluation by experts showed that the identified tracts were in agreement with the expected anatomy. Tract-derived measurements demonstrated relatively low variability among subjects. False-negative tracts demonstrated the current limitations of both methods for clinical decision-making. Multi-fiber tractography methods combined with state-of-the-art diffusion MRI data have the potential to help identify white matter tracts connecting DBS targets in functional neurosurgery intervention.

Deep brain stimulation for childhood dystonia: Is 'where' as important as in 'whom'?

Deep brain stimulation (DBS) has become a mainstay of dystonia management in adulthood. Typically targeting electrode placement in the GPi, sustained improvement in dystonic symptoms are anticipated in adults with isolated genetic dystonias. Dystonia in childhood is more commonly a symptomatic condition, with dystonia frequently expressed on the background of a structurally abnormal brain. Outcomes following DBS in this setting are much more variable, the reasons for which have yet to be elucidated. Much of the focus on improving outcomes following DBS in dystonia management has been on the importance of patient selection, with, until recently, little discussion of the choice of target. In this review, we advance the argument that patient selection for DBS in childhood cannot be made separate from the choice of target nuclei. The anatomy of common DBS targets is considered, and factors influencing their choice for electrode insertion are discussed. We propose an "ABC" for DBS in childhood dystonia is proposed: Appropriate Child selected; Best nuclei chosen for electrode insertion; Correct position within that nucleus.

Cortico-Striatal-Thalamic Loop Circuits of the Salience Network: A Central Pathway in Psychiatric Disease and Treatment

The salience network (SN) plays a central role in cognitive control by integrating sensory input to guide attention, attend to motivationally salient stimuli and recruit appropriate functional brain-behavior networks to modulate behavior. Mounting evidence suggests that disturbances in SN function underlie abnormalities in cognitive control and may be a common etiology underlying many psychiatric disorders. Such functional and anatomical abnormalities have been recently apparent in studies and meta-analyses of psychiatric illness using functional magnetic resonance imaging (fMRI) and voxel-based morphometry (VBM). Of particular importance, abnormal structure and function in major cortical nodes of the SN, the dorsal anterior cingulate cortex (dACC) and anterior insula (AI), have been observed as a common neurobiological substrate across a broad spectrum of psychiatric disorders. In addition to cortical nodes of the SN, the network’s associated subcortical structures, including the dorsal striatum, mediodorsal thalamus and dopaminergic brainstem nuclei, comprise a discrete regulatory loop circuit. The SN’s cortico-striato-thalamo-cortical loop increasingly appears to be central to mechanisms of cognitive control, as well as to a broad spectrum of psychiatric illnesses and their available treatments. Functional imbalances within the SN loop appear to impair cognitive control, and specifically may impair self-regulation of cognition, behavior and emotion, thereby leading to symptoms of psychiatric illness. Furthermore, treating such psychiatric illnesses using invasive or non-invasive brain stimulation techniques appears to modulate SN cortical-subcortical loop integrity, and these effects may be central to the therapeutic mechanisms of brain stimulation treatments in many psychiatric illnesses. Here, we review clinical and experimental evidence for abnormalities in SN cortico-striatal-thalamic loop circuits in major depression, substance use disorders (SUD), anxiety disorders, schizophrenia and eating disorders (ED). We also review emergent therapeutic evidence that novel invasive and non-invasive brain stimulation treatments may exert therapeutic effects by normalizing abnormalities in the SN loop, thereby restoring the capacity for cognitive control. Finally, we consider a series of promising directions for future investigations on the role of SN cortico-striatal-thalamic loop circuits in the pathophysiology and treatment of psychiatric disorders.

Proceedings of the Fourth Annual Deep Brain Stimulation Think Tank: A Review of Emerging Issues and Technologies

This paper provides an overview of current progress in the technological advances and the use of deep brain stimulation (DBS) to treat neurological and neuropsychiatric disorders, as presented by participants of the Fourth Annual DBS Think Tank, which was convened in March 2016 in conjunction with the Center for Movement Disorders and Neurorestoration at the University of Florida, Gainesveille FL, USA. The Think Tank discussions first focused on policy and advocacy in DBS research and clinical practice, formation of registries, and issues involving the use of DBS in the treatment of Tourette Syndrome. Next, advances in the use of neuroimaging and electrochemical markers to enhance DBS specificity were addressed. Updates on ongoing use and developments of DBS for the treatment of Parkinson's disease, essential tremor, Alzheimer's disease, depression, post-traumatic stress disorder, obesity, addiction were presented, and progress toward innovation(s) in closed-loop applications were discussed. Each section of these proceedings provides updates and highlights of new information as presented at this year's international Think Tank, with a view toward current and near future advancement of the field.

Synapse engineering: A new level of brain modulation

Brain modulation is a powerful approach to study brain function in vivo. Tremendous progress had been made by controlling brain activity with different brain modulation tools. Synapse is the more fundamental functional unit of brain. In theory, synapse engineering could modulate brain function more precisely. However this had not been possible until recently. Our review provides a brief introduction of various brain modulation methods, and elaborates on a recently developed synapse-engineering tool. This technique allows modulation of specific synapses in vivo for the first time and has been used to clarify the causal role of synaptic plasticity in learning and memory. We also discuss its potentials for further development.