Invasive and Noninvasive Brain Stimulation in Parkinson's Disease: Clinical Effects and Future Perspectives

Repetitive transcranial magnetic stimulation improves cognition, depression, and walking ability in patients with Parkinson's disease: a meta-analysis

OBJECTIVE

To evaluate the efficacy of repetitive transcranial magnetic stimulation (rTMS) on cognitive function, depression, and walking ability in patients with Parkinson's disease.

METHODS

A comprehensive search was conducted in PubMed, Web of Science, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Database (CBM), VIP Database, and Wanfang Database. Randomized controlled trials (RCTs) on rTMS treatment in Parkinson's disease patients were retrieved, covering the period from the inception of each database to July 2024. The quality of the included studies was assessed using the Cochrane risk of bias tool. Two researchers independently screened the literature, extracted data, and assessed the risk of bias in the studies. Data synthesis and analysis were performed using RevMan 5.4 and Stata 17.0 software.

RESULTS

A total of 15 studies were included. The meta-analysis revealed that rTMS significantly improved the MOCA score (MD = 2.98, 95% CI 2.08, 3.88, P = 0.000), TUGT score (SMD=-0.72, 95% CI -1.43, 0.00, P = 0.048), FOG-Q score (SMD=-0.54, 95% CI -0.97, -0.11, P = 0.01), and UPDRS-III score (SMD=-0.66, 95% CI -0.84, -0.47, P = 0.000) in Parkinson's disease patients, and also alleviated depressive symptoms as measured by the HAMD (SMD=-0.43, 95% CI -0.72, -0.13, P = 0.004).

CONCLUSIONS

rTMS can improve cognitive function, depressive symptoms, and walking ability in patients with Parkinson's disease.

Effects of non-invasive brain stimulation over the supplementary motor area on motor function in Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Motor dysfunction profoundly affects individuals with Parkinson's disease (PD). Non-invasive brain stimulation (NIBS) targeting the supplementary motor area (SMA), a critical region for movement-related processing, offers a promising approach to enhance motor function for PD.

OBJECTIVE

This systematic review and meta-analysis aims to evaluate the efficacy of NIBS over the SMA (SMA-NIBS) in alleviating motor symptoms in PD.

METHODS

We conducted literature searches in MEDLINE, EMBASE, Physiotherapy Evidence Database, Web of Science, the Chinese National Knowledge Infrastructure, and Scopus. The meta-analysis utilized an inverse variance method and a random-effects model. Subgroup analyses were performed based on stimulation types (e.g., TMS and tDCS), stimulation protocols (e.g., facilitatory and inhibitory stimulation), and medication status during stimulation.

RESULTS

Twenty randomized control trials involving 442 individuals with PD were included. Compared to sham stimulation, SMA-NIBS significantly improved motor function as measured by the motor section of Unified Parkinson's Disease Rating Scale (UPDRS-III) (mean differences [MD]: -3.45, 95 % confidence interval [CI]: -5.65 to -1.26). Subgroup analysis revealed that only TMS (MD: -3.62, 95%CI: -6.15 to -1.08), not tDCS (MD: -2.47, 95 % CI: -5.03 to 0.08), has significant effect on motor function. Both facilitatory (MD: -2.59, 95 % CI: -3.37 to -1.82) and inhibitory stimulation (MD: -4.98, 95 % CI: -9.29 to -0.66) significantly improved the UPDRS-III score. Effectiveness was observed only during ON medication. Statistically significant effects of SMA-NIBS were reported on Freezing of Gait Questionnaire, not timed up and go test and walking speed.

CONCLUSION

SMA-NIBS is a promising approach to enhance motor function in PD.

Exploring Magnetic and Electrical Brain Stimulation in Parkinsonian Dyskinetic Monkeys

BACKGROUND

Parkinson's disease (PD) chronic L-Dopa treatment often triggers motor complications, such as L-Dopa-induced dyskinesias (LID). LID are reported to be associated with abnormal glutamatergic activity between the striatum and primary motor cortex (M1), resulting in M1 hyperactivation. Beneficial noninvasive brain stimulation (NIBS) paradigms were reported to normalize glutamatergic activity. The objective of the present study was thus to set up a NIBS paradigm in parkinsonian monkeys to investigate motor behavior under basal conditions and with L-Dopa treatment-inducing dyskinesias.

METHODS

Motor behavior was investigated in five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) dyskinetic female Macaca fascicularis monkey models of PD, allowing us to monitor the administration of NIBS and drugs. NIBS used were inhibitory protocols, that is, cathodal transcranial direct current stimulation (c-tDCS) and continuous theta-burst stimulation (cTBS). A procedure of three weeks was developed to progressively acclimate animals to the experimental conditions, equipment and noise of c-tDCS and cTBS before stimulating them with either vehicle or L-Dopa.

RESULTS

One session of c-tDCS with L-Dopa yielded no effect, whereas five sessions briefly reduced LID but decreased the duration of L-Dopa anti-PD effects. cTBS alone improved (decreased) parkinsonian scores as compared to sham stimulation or vehicle alone. Two sessions of cTBS with L-Dopa decreased LID without affecting L-Dopa anti-PD effects.

CONCLUSION

This is the first study testing c-tDCS and cTBS on the motor behavior of MPTP dyskinetic monkeys. As compared to medicated patients, MPTP monkeys offer the opportunity to evaluate NIBS after-effects in drug-free and LID conditions, which are critical in the search for new PD treatment.

Assessment of noninvasive brain stimulation interventions in Parkinson's disease: a systematic review and network meta-analysis

A network meta-analysis of randomized controlled trials was conducted to compare and rank the effectiveness of various noninvasive brain stimulation (NIBS) for Parkinson's disease (PD). We searched PubMed, Web of Science, Cochrane Library, Embase, China National Knowledge Infrastructure (CNKI), Wanfang Database, China Science and Technology Journal Database (VIP), and Chinese Biomedical Literature Service System (SinoMed) databases from the date of database inception to April 30th, 2024. Two researchers independently screened studies of NIBS treatment in patients with PD based on inclusion and exclusion criteria. Two researchers independently performed data extraction of the included studies using an Excel spreadsheet and assessed the quality of the literature according to the Cochrane Risk of Bias Assessment Tool (RoB2). Network meta-analysis was performed in StataMP 17.0. A total of 28 studies involving 1628 PD patients were included. The results showed that HF-rTMS over the SMA (SMD = - 2.01; 95% CI [- 2.87, - 1.15]), HF-rTMS over the M1 and DLPFC (SMD = - 1.80; 95% CI [- 2.90, - 0.70]), HF-rTMS over the M1 (SMD = - 1.10; 95% CI [- 1.55, - 0.65]), a-tDCS over the DLPFC (SMD = - 1.08; 95% CI [- 1.90, - 0.27]), HF-rTMS over the M1 and PFC (SMD = - 0.92; 95% CI [- 1.71, - 0.14]), LF-rTMS over the M1 (SMD = - 0.72; 95% CI [- 1.17, - 0.28]), and HF-rTMS over the DLPFC (SMD = - 0.70; 95% CI [- 1.21, - 0.19]) were significantly improved motor function compared with sham stimulation. The SUCRA three highest ranked were HF-rTMS over the SMA (95.1%), HF-rTMS over the M1 and DLPFC (89.6%), and HF-rTMS over the M1 (73.0%). In terms of enhanced cognitive function, HF-rTMS over the DLPFC (SMD = 0.80; 95% CI [0.03,1.56]) was significantly better than sham stimulation. The SUCRA three most highly ranked were a-tDCS over the M1 (69.8%), c-tDCS over the DLPFC (66.9%), and iTBS over the DLPFC (65.3%). HF-rTMS over the M1 (SMD = - 1.43; 95% CI [- 2.26, - 0.61]) and HF-rTMS over the DLPFC (SMD = - 0.79; 95% CI [- 1.45, - 0.12)]) significantly improved depression. The SUCRA three highest ranked were HF-rTMS over the M1 (94.1%), LF-rTMS over the M1 (71.8%), and HF-rTMS over the DLPFC (69.0%). HF-rTMS over the SMA may be the best option for improving motor symptoms in PD patients. a-tDCS and HF-rTMS over the M1 may be the NIBS with the most significant effects on cognition and depression, separately.Trial registration: International Prospective Register of Systematic Review, PROSPERO (CRD42023456088).

TDCS for parkinson's disease disease-related pain: A randomized trial

OBJECTIVE

To evaluate the effects of transcranial direct current stimulation (tDCS) on Parkinson's disease (PD)-related pain.

METHODS

This triple-blind randomized controlled trial included twenty-two patients (age range 38-85, 10 male) with PD-related pain. Eleven subjects received ten sessions of 20 minutes tDCS over the primary motor cortex contralateral to pain at 2 mA intensity. Eleven subjects received sham stimulation. Outcome measures included changes in the Kinǵs Parkinsońs Pain Scale (KPPS), Brief Pain Inventory (BPI), widespread mechanical hyperalgesia (WMH), temporal summation of pain (TS), and conditioned pain modulation (CPM).

RESULTS

Significant differences were found in KPPS between groups favoring the active-tDCS group compared to the sham-tDCS group at 15-days follow-up (p = 0.014) but not at 2 days post-intervention (p = 0.059). The active-group showed significant improvements over the sham-group after 15 days (p = 0.017). Significant changes were found in CPM between groups in favor of active-tDCS group at 2 days post-intervention (p = 0.002) and at 15 days (p = 0.017). No meaningful differences were observed in BPI or TS.

CONCLUSIONS

tDCS of the primary motor cortex alleviates perceived PD-related pain, reduces pain sensitization, and enhances descending pain inhibition.

SIGNIFICANCE

This is the first study to test and demonstrate the use of tDCS for improving PD-related pain.

Objective clinical registration of tremor, bradykinesia, and rigidity during awake stereotactic neurosurgery: a scoping review

Tremor, bradykinesia, and rigidity are incapacitating motor symptoms that can be suppressed with stereotactic neurosurgical treatment like deep brain stimulation (DBS) and ablative surgery (e.g., thalamotomy, pallidotomy). Traditionally, clinicians rely on clinical rating scales for intraoperative evaluation of these motor symptoms during awake stereotactic neurosurgery. However, these clinical scales have a relatively high inter-rater variability and rely on experienced raters. Therefore, objective registration (e.g., using movement sensors) is a reasonable extension for intraoperative assessment of tremor, bradykinesia, and rigidity. The main goal of this scoping review is to provide an overview of electronic motor measurements during awake stereotactic neurosurgery. The protocol was based on the PRISMA extension for scoping reviews. After a systematic database search (PubMed, Embase, and Web of Science), articles were screened for relevance. Hundred-and-three articles were subject to detailed screening. Key clinical and technical information was extracted. The inclusion criteria encompassed use of electronic motor measurements during stereotactic neurosurgery performed under local anesthesia. Twenty-three articles were included. These studies had various objectives, including correlating sensor-based outcome measures to clinical scores, identifying optimal DBS electrode positions, and translating clinical assessments to objective assessments. The studies were highly heterogeneous in device choice, sensor location, measurement protocol, design, outcome measures, and data analysis. This review shows that intraoperative quantification of motor symptoms is still limited by variable signal analysis techniques and lacking standardized measurement protocols. However, electronic motor measurements can complement visual evaluations and provide objective confirmation of correct placement of the DBS electrode and/or lesioning. On the long term, this might benefit patient outcomes and provide reliable outcome measures in scientific research.

Cellular excitability and ns-pulsed electric fields: Potential involvement of lipid oxidation in the action potential activation

Recent studies showed that nanosecond pulsed electric fields (nsPEFs) can activate voltage-gated ion channels (VGICs) and trigger action potentials (APs) in excitable cells. Under physiological conditions, VGICs' activation takes place on time scales of the order 10-100 µs. These time scales are considerably longer than the applied pulse duration, thus activation of VGICs by nsPEFs remains puzzling and there is no clear consensus on the mechanisms involved. Here we propose that changes in local electrical properties of the cell membrane due to lipid oxidation might be implicated in AP activation. We first use MD simulations of model lipid bilayers with increasing concentration of primary and secondary lipid oxidation products and demonstrate that oxidation not only increases the bilayer conductance, but also the bilayer capacitance. Equipped with MD-based characterization of electrical properties of oxidized bilayers, we then resort to AP modelling at the cell level with Hodgkin-Huxley-type models. We confirm that a local change in membrane properties, particularly the increase in membrane conductance, due to formation of oxidized membrane lesions can be high enough to trigger an AP, even when no external stimulus is applied. However, excessive accumulation of oxidized lesions (or other conductive defects) can lead to altered cell excitability.

The Application of Deep Brain Stimulation for Parkinson's Disease on the Motor Pathway: A Bibliometric Analysis across 10 Years

BACKGROUND AND OBJECTIVE

Since its initial report by James Parkinson in 1817, Parkinson's disease (PD) has remained a central subject of research and clinical advancement. The disease is estimated to affect approximately 1% of adults aged 60 and above. Deep brain stimulation, emerging as an alternative therapy for end-stage cases, has offered a lifeline to numerous patients. This review aimed to analyze publications pertaining to the impact of deep brain stimulation on the motor pathway in patients with PD over the last decade.

METHODS

Data were obtained from the Web of Science Core Collection through the library of Huazhong University of Science and Technology (China). The search strategy encompassed the following keywords: "deep brain stimulation", "Parkinson's disease", "motor pathway", and "human", from January 1, 2012, to December 1, 2022. Additionally, this review visualized the findings using the Citespace software.

RESULTS

The results indicated that the United States, the United Kingdom, Germany, and China were the primary contributors to this research field. University College London, Capital Medical University, and Maastricht University were the top 3 research institutions in the research area. Tom Foltynie ranked first with 6 publications, and the journals of Brain and Brain Stimulation published the greatest number of relevant articles. The prevailing research focal points in this domain, as determined by keywords "burst analysis", "encompassed neuronal activity", "nucleus", "hyper direct pathway", etc. CONCLUSION: This study has provided a new perspective through bibliometric analysis of the deep brain stimulation therapy for treating patients with PD, which can shed light on future research to advance our comprehension of this particular field of study.

Research hotspots and trends of transcranial magnetic stimulation in Parkinson's disease: a bibliometric analysis

Background

Transcranial magnetic stimulation (TMS), as a non-invasive neuromodulation technique, has been widely used in the treatment of Parkinson's disease (PD). The increasing application of TMS has promoted an increasing number of clinical studies. In this paper, a bibliometric analysis of existing studies was conducted to reveal current research hotspots and guide future research directions.

Method

Relevant articles and reviews were obtained from the Science Citation Index Expanded of Web of Science Core Collection database. Data related to publications, countries, institutions, authors, journals, citations, and keywords in the studies included in the review were systematically analyzed using VOSviewer 1.6.18 and Citespace 6.2.4 software.

Result

A total of 1,894 papers on the topic of TMS in PD between 1991 and 2022 were analyzed and visualized to identify research hotspots and trends in the field. The number of annual publications in this field of study has increased gradually over the past 30 years, with the number of annual publications peaking in 2022 (n = 150). In terms of publications and total citations, countries, institutions, and authors from North America and Western Europe were found to make significant contributions to the field. The current hotspot focuses on the effectiveness of TMS for PD in different stimulation modes or different stimulated brain regions. The keyword analysis indicates that the latest research is oriented to the mechanism study of TMS for motor symptoms in PD, and the non-motor symptoms are also receiving more attention.

Conclusion

Our study offers insights into the current hotspots and emerging trends of TMS in the rehabilitation of PD. These findings may serve as a guide for future research and the application of TMS for PD.

Motor function improvement and acceptability of non-invasive brain stimulation in patients with Parkinson's disease: a Bayesian network analysis

Background

Parkinson's disease (PD) is a neurodegenerative disorder defined by progressive motor and non-motor symptoms. Currently, the pro-cognitive effects of transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) are well-supported in previous literatures. However, controversy surrounding the optimal therapeutic target for motor symptom improvement remains.

Objective

This network meta-analysis (NMA) was conducted to comprehensively evaluate the optimal strategy to use rTMS and tDCS to improve motor symptoms in PD.

Methods

We searched PubMed, Embase, and Cochrane electronic databases for eligible randomized controlled studies (RCTs). The primary outcome was the changes of Unified Parkinson's Disease Rating Scale (UPDRS) part III score, the secondary outcomes were Time Up and Go Test (TUGT) time, and Freezing of Gait Questionnaire (FOGQ) score. The safety outcome was indicated by device-related adverse events (AEs).

Result

We enrolled 28 studies that investigated various strategies, including high-frequency rTMS (HFrTMS), low-frequency rTMS (LFrTMS), anodal tDCS (AtDCS), AtDCS_ cathode tDCS (CtDCS), HFrTMS_LFrTMS, and Sham control groups. Both HFrTMS (short-term: mean difference (MD) -5.21, 95% credible interval (CrI) -9.26 to -1.23, long-term: MD -4.74, 95% CrI -6.45 to -3.05), and LFrTMS (long-term: MD -4.83, 95% CrI -6.42 to -3.26) were effective in improving UPDRS-III score compared with Sham stimulation. For TUGT time, HFrTMS (short-term: MD -2.04, 95% CrI -3.26 to -0.8, long-term: MD -2.66, 95% CrI -3.55 to -1.77), and AtDCS (short-term: MD -0.8, 95% CrI -1.26 to -0.34, long-term: MD -0.69, 95% CrI -1.31 to -0.08) produced a significant difference compared to Sham stimulation. However, no statistical difference was found in FOGQ score among the various groups. According to the surface under curve ranking area, HFrTMS ranked first in short-term UPDRS-III score (0.77), short-term (0.82), and long-term (0.84) TUGT time, and short-term FOGQ score (0.73). With respect to the safety outcomes, all strategies indicated few and self-limiting AEs.

Conclusion

HFrTMS may be the optimal non-invasive brain stimulation (NIBS) intervention to improve motor function in patients with PD while NIBS has generally been well tolerated. However, further studies focusing on the clinical outcomes resulting from the different combined schedules of tDCS and rTMS are required.

Systematic review registration

https://inplasy.com/inplasy-2023-4-0087/, identifier: 202340087.

Current evidence, clinical applications, and future directions of transcranial magnetic stimulation as a treatment for ischemic stroke

Transcranial magnetic stimulation (TMS) is a non-invasive brain neurostimulation technique that can be used as one of the adjunctive treatment techniques for neurological recovery after stroke. Animal studies have shown that TMS treatment of rats with middle cerebral artery occlusion (MCAO) model reduced cerebral infarct volume and improved neurological dysfunction in model rats. In addition, clinical case reports have also shown that TMS treatment has positive neuroprotective effects in stroke patients, improving a variety of post-stroke neurological deficits such as motor function, swallowing, cognitive function, speech function, central post-stroke pain, spasticity, and other post-stroke sequelae. However, even though numerous studies have shown a neuroprotective effect of TMS in stroke patients, its possible neuroprotective mechanism is not clear. Therefore, in this review, we describe the potential mechanisms of TMS to improve neurological function in terms of neurogenesis, angiogenesis, anti-inflammation, antioxidant, and anti-apoptosis, and provide insight into the current clinical application of TMS in multiple neurological dysfunctions in stroke. Finally, some of the current challenges faced by TMS are summarized and some suggestions for its future research directions are made.

Cross-Frequency Coupling and Intelligent Neuromodulation

Cross-frequency coupling (CFC) reflects (nonlinear) interactions between signals of different frequencies. Evidence from both patient and healthy participant studies suggests that CFC plays an essential role in neuronal computation, interregional interaction, and disease pathophysiology. The present review discusses methodological advances and challenges in the computation of CFC with particular emphasis on potential solutions to spurious coupling, inferring intrinsic rhythms in a targeted frequency band, and causal interferences. We specifically focus on the literature exploring CFC in the context of cognition/memory tasks, sleep, and neurological disorders, such as Alzheimer's disease, epilepsy, and Parkinson's disease. Furthermore, we highlight the implication of CFC in the context and for the optimization of invasive and noninvasive neuromodulation and rehabilitation. Mainly, CFC could support advancing the understanding of the neurophysiology of cognition and motor control, serve as a biomarker for disease symptoms, and leverage the optimization of therapeutic interventions, e.g., closed-loop brain stimulation. Despite the evident advantages of CFC as an investigative and translational tool in neuroscience, further methodological improvements are required to facilitate practical and correct use in cyborg and bionic systems in the field.

Chaotic dynamics of the Hénon map and neuronal input-output: A comparison with neurophysiological data

In this study, the Hénon map was analyzed using quantifiers from information theory in order to compare its dynamics to experimental data from brain regions known to exhibit chaotic behavior. The goal was to investigate the potential of the Hénon map as a model for replicating chaotic brain dynamics in the treatment of Parkinson's and epilepsy patients. The dynamic properties of the Hénon map were compared with data from the subthalamic nucleus, the medial frontal cortex, and a q-DG model of neuronal input-output with easy numerical implementation to simulate the local behavior of a population. Using information theory tools, Shannon entropy, statistical complexity, and Fisher's information were analyzed, taking into account the causality of the time series. For this purpose, different windows over the time series were considered. The findings revealed that neither the Hénon map nor the q-DG model could perfectly replicate the dynamics of the brain regions studied. However, with careful consideration of the parameters, scales, and sampling used, they were able to model some characteristics of neural activity. According to these results, normal neural dynamics in the subthalamic nucleus region may present a more complex spectrum within the complexity-entropy causality plane that cannot be represented by chaotic models alone. The dynamic behavior observed in these systems using these tools is highly dependent on the studied temporal scale. As the size of the sample studied increases, the dynamics of the Hénon map become increasingly different from those of biological and artificial neural systems.

Transcranial direct current electrical stimulation in combination with aerobic exercise: A pilot study in post-COVID-19 systemic autoimmune rheumatic patients

BACKGROUND

Systemic autoimmune rheumatic diseases (SARDs) are a group of diseases with multiorgan involvement and a high prevalence of chronic pain and fatigue. Patients with SARDs and post-coronavirus disease 2019 (COVID-19) syndrome experience aggravation of symptoms. In this context, it is essential to establish strategies to reduce chronic pain and fatigue and improve quality of life.

AIM

To assess the efficacy of transcranial direct current stimulation (tDCS) for the treatment of fatigue and pain-associated post-COVID-19 syndrome in patients with SARDs.

METHODS

This study included nine patients with different types of SARDs. All patients had reverse transcription-polymerase chain reaction (RT-PCR) test confirmed COVID-19 as well as significant, persistent fatigue and pain that began to worsen after infection. Anodal tDCS was administered in five daily sessions (2mA, 20 min). Concomitantly, patients were involved in aerobic exercise program. All participants were evaluated using specific questionnaires and strength assessment by handgrip and physical function by timed-up-and-go test and sit-to-stand test at baseline (within one week before tDCS protocol), and one week after tDCS protocol. During all procedures, the patients’ treatments remained unchanged.

RESULTS

The sample comprised eight women and one man with a mean age of 48.7 ± 9.6 years. After the tDCS protocol, pain and fatigue significantly improved on the visual analog scale (P < 0.05). The physical function also improved 9.5 ± 2.7 vs 6.8 ± 0.8 (P = 0.001) for timed-up-go-test and 10.3 ± 3.7 vs 15.1 ± 4.0 (P = 0.037) for sit-to-stand test. None of the patients experienced any adverse events.

CONCLUSION

The present study showed that tDCS in combination with aerobic exercise was effective in improving physical function, and reducing fatigue/pain in SARDs patients with post-COVID-19 syndrome.

New insight into brain disease therapy: nanomedicines-crossing blood-brain barrier and extracellular space for drug delivery

INTRODUCTION

Brain diseases including brain tumor, Alzheimer's disease, Parkinson's disease, etc. are difficult to treat. The blood-brain barrier (BBB) is a major obstacle for drug delivery into the brain. Although nano-package and receptor-mediated delivery of nanomedicine markedly increases BBB penetration, it yet did not extensively improve clinical cure rate. Recently, brain extracellular space (ECS) and interstitial fluid (ISF) drainage in ECS have been found to determine whether a drug dissolved in ISF can reach its target cells. Notably, an increase in tortuosity of ECS associated with slower ISF drainage induced by the accumulated harmful substances, such as: amyloid-beta (Aβ), α-synuclein, and metabolic wastes, causes drug delivery failure.

AREAS COVERED

The methods of nano-package and receptor-mediated drug delivery and the penetration efficacy of nanomedicines across BBB and ECS are assessed.

EXPERT OPINION

Invasive delivering drug via ECS and noninvasive near-infrared photo-sensitive nanomedicines may provide a promising benefit to patients with brain disease.

Neuroprotection and Non-Invasive Brain Stimulation: Facts or Fiction?

Non-Invasive Brain Stimulation (NIBS) techniques, such as transcranial Direct Current Stimulation (tDCS) and repetitive Magnetic Transcranial Stimulation (rTMS), are well-known non-pharmacological approaches to improve both motor and non-motor symptoms in patients with neurodegenerative disorders. Their use is of particular interest especially for the treatment of cognitive impairment in Alzheimer's Disease (AD), as well as axial disturbances in Parkinson's (PD), where conventional pharmacological therapies show very mild and short-lasting effects. However, their ability to interfere with disease progression over time is not well understood; recent evidence suggests that NIBS may have a neuroprotective effect, thus slowing disease progression and modulating the aggregation state of pathological proteins. In this narrative review, we gather current knowledge about neuroprotection and NIBS in neurodegenerative diseases (i.e., PD and AD), just mentioning the few results related to stroke. As further matter of debate, we discuss similarities and differences with Deep Brain Stimulation (DBS)-induced neuroprotective effects, and highlight possible future directions for ongoing clinical studies.

Efficacy of repetitive transcranial magnetic stimulation in Parkinson's disease: A systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive form of brain stimulation that positively regulates the motor and non-motor symptoms of Parkinson's disease (PD). Although, most reviews and meta-analysis have shown that rTMS intervention is effective in treating motor symptoms and depression, very few have used randomised controlled trials (RCTs) to analyse the efficacy of this intervention in PD. We aimed to review RCTs of rTMS in patients with PD to assess the efficacy of rTMS on motor and non-motor function in patients with PD.

METHODS

In this systematic review and meta-analysis, we searched PubMed, MEDLINE and Web of Science databases for RCTs on rTMS in PD published between January 1, 1988 to January 1, 2022. Eligible studies included sham-controlled RCTs that used rTMS stimulation for motor or non-motor symptoms in PD. RCTs not focusing on the efficacy of rTMS in PD were excluded. Summary data were extracting from those RCTs by two investigators independently. We then calculated standardised mean difference with random-effect models. The main outcome included motor and non-motor examination of scales that were used in PD motor or non-motor assessment. This study was registered with PROSPERO, CRD42022329633.

FINDINGS

Fourteen studies with 469 patients met the criteria for our meta-analysis. Twelve eligible studies with 381 patients were pooled to analyse the efficacy of rTMS on motor function improvement. The effect size on motor scale scores was 0.51 (P < 0.0001) and were not distinctly heterogeneous (I² = 29%). Five eligible studies with 202 patients were collected to evaluate antidepressant-like effects. The effect size on depression scale scores was 0.42 (P = 0.004), and were not distinctly heterogeneous (I² = 25%), indicating a significant anti-depressive effect (P = 0.004). The results suggest that high-frequency of rTMS on primary motor cortex (M1) is effective in improving motor symptoms; while the dorsolateral prefrontal cortex (DLPFC) may be a potentially effective area in alleviating depressive symptom.

INTERPRETATION

The findings suggest that rTMS could be used as a possible adjuvant therapy for PD mainly to improve motor symptoms, but could have potential efficacy on depressive symptoms of PD. However, further investigation is needed.

FUNDING

The National Natural Science Foundation of China (NO: 81873777, 82071414), Initiated Foundation of Zhujiang Hospital (NO: 02020318005), Scientific Research Foundation of Guangzhou (NO: 202206010005), and Science and Technology Program of Guangdong of China (NO: 2020A0505100037).

Impacts of stimulus parameters and configurations on motor cortex direct electrical stimulation using intrinsic optical imaging: a pilot study

Background

Motor cortex stimulation applied as a clinical treatment for neuropathic disorders for decades. With stimulation electrodes placed directly on the cortical surface, this neuromodulation method provides higher spatial resolution than other non-invasive therapies. Yet, the therapeutic effects reported were not in conformity with different syndromes. One of the main issues is that the stimulation parameters are always determined by clinical experience. The lack of understanding about how the stimulation current propagates in the cortex and various stimulation parameters and configurations obstruct the development of this method.

Methods

In this study, we investigated the effect of different stimulation configurations on cortical responses to motor cortical stimulations using intrinsic optical imaging.

Results

Our results showed that the cortical activation of electrical stimulation is not only related to the current density but also related to the propagation distance. Besides, stimulation configurations also affect the propagation of the stimulation current.

Conclusions

All these results provide preliminary experimental evidence for parameter and electrode configuration optimizations.

Neuroprotective Effects of Intermittent Theta Burst Stimulation in Parkinson’s Disease (NET-PD): A Study Protocol for a Delayed-Start Randomized Double-Blind Sham-Controlled Trial

Background: As a typical high-disability neurodegenerative disease, Parkinson’s disease (PD) progresses variably, and patients who are clinically insensitive to dopaminergic therapy and whose symptoms fail to improve are commonly observed. As a result, achieving early neuron protection is critical. Methods/Design: The NET-PD study is a 2-year prospective single-center, double-blind, multi-arm, delayed-start, sham-controlled clinical trial assessing the long-term neuroprotective effect of intermittent theta burst stimulation (iTBS) in PD patients. Patients diagnosed with PD, aged 50–80, Hoehn–Yahr stage ≤4, and who maintain medication stability during the study will be enrolled. Clinical assessment and multi-modal markers are used to clarify the clinical improvement and dynamic neuronal changes in PD patients. With a standard deviation of 2, a test level of 0.05, a dropout rate of 10%, and a degree of certainty of 0.9, 60 PD patients are required for this study. Results: The NET-PD project was funded in March 2022, data collection began in July 2022, and is currently in the recruitment phase with two PD patients already enrolled. Data collection is expected to be completed in June 2024. The results are expected for publication in December 2024. Discussion: Previous research has demonstrated a rudimentary method for assessing and delaying PD progression in clinical medication trials. The NET-PD study adopts a rigorous methodology and specific disease-modifying designs to demonstrate the neuroprotective effect of iTBS on PD and investigate the potential mechanism of iTBS in regulating brain and motor functions. We hope to provide supposition for the subsequent exploration of diverse neuroprotection methods.

Action and emotion perception in Parkinson's disease: A neuroimaging meta-analysis

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The neural substrates for action and emotion perception deficits in PD are still unclear.

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We addressed this issue via coordinate-based meta-analyses of previous fMRI data.

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PD patients exhibit decreased response in the basal ganglia.

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PD patients exhibit a trend toward decreased response in the parietal areas.

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PD patients exhibit a trend toward increased activation in the posterior cerebellum.

Patients with Parkinson disease (PD) may show impairments in the social perception. Whether these deficits have been consistently reported, it remains to be clarified which brain alterations subtend them. To this aim, we conducted a neuroimaging meta-analysis to compare the brain activity during social perception in patients with PD versus healthy controls. Our results show that PD patients exhibit a significantly decreased response in the basal ganglia (putamen and pallidum) and a trend toward decreased activity in the mirror system, particularly in the left parietal cortex (inferior parietal lobule and intraparietal sulcus). This reduced activation may be tied to a disruption of cognitive resonance mechanisms and may thus constitute the basis of impaired others’ representations underlying action and emotion perception. We also found increased activation in the posterior cerebellum in PD, although only in a within-group analysis and not in comparison with healthy controls. This cerebellar activation may reflect compensatory mechanisms, an aspect that deserves further investigation. We discuss the clinical implications of our findings for the development of novel social skill training programs for PD patients.

Chiropractic care of Parkinson's disease and deformity

Parkinson's disease (PD) is a progressive neurological disease characterized by muscle stiffness, tremor, slowness of movement, and difficulties with posture and walking. Muscle and joint pain are frequent non-motor symptoms of PD. Pain associated with PD is mainly caused by a combination of truncal dystonia, stooped posture, and muscle rigidity. However, PD deformities were rarely discussed in the literature. A 68-year-old Asian female with PD treated with Levodopa for six years complained of progressive neck pain, contractures, and subluxation of both hands in the last two years. A positron emission tomography (PET) scan revealed decreased rostrocaudal gradient uptake in both posterior putamen. After 9 months of multimodal chiropractic rehabilitation, the patient had significant improvement in symptoms, including pain resolution as per the numeric rating scale and physical and mental improvement as per the PD questionnaire. Radiographic measurement showed significantly improved postural alignment and stability. Measurement of joint motion and angles showed an improvement in hand deformity. Although PD is a neurodegenerative disease that is not curable, multimodal rehabilitation may improve neurological and musculoskeletal functions by inducing proprioceptive balance, motor strength, and joint movement. The current study may illustrate multimodal rehabilitation addressing orthopedic deformity associated with symptoms in a PD patient.

The understanding of Parkinson's disease through genetics and new therapies

INTRODUCTION

Parkinson's disease is one of the progressive neurodegenerative diseases from which people suffer for years. The mechanism of this disease is associated with a decrease in the number of dopaminergic neurons in the substantia nigra (SN) while Lewy bodies are still present. As a result, both motor-ridity, tremor, and bradykinesia-and non-motor symptoms such as anxiety and depression. Nowadays, it is well known that the cause behind Parkinson's disease is mainly environmental changes, genetic susceptibility, and toxins. Unfortunately, there is no cure for the disease but treatments. The replacement of lost neurons, α-synuclein and apomorphine, is currently being studied for new therapies. This article focuses on history, mechanism, factors causing Parkinson's disease as well as future therapies for the cure of the diseases.

METHODOLOGY

Data were collected from medical journals published on PubMed, The Lancet, Cells, and Nature Reviews Neurology databases with a predefined search strategy. All articles considering new therapies for Parkinson's disease were considered.

RESULTS

The pathophysiology of Parkinson's disease is currently reasonably understood. However, there is no definitive cure so all the treatments focus mainly on reducing or limiting the symptoms. Current treatment studies focus on genetics, replacing lost neurons, α-synuclein and apomorphine.

CONCLUSION

Parkinson's disease is the most common movement disorder worldwide because of the loss of dopaminergic neurons in the substantia nigra. Its symptoms include motor dysfunctions such as rigidity, tremor, and bradykinesia and non-motor dysfunctions such as anxiety and depression. Through genetics, environmental changes and toxins analysis, it is now known that future new therapies are working on replacing lost neurons, α-synuclein and apomorphine.

Intraoperative Quantification of MDS-UPDRS Tremor Measurements Using 3D Accelerometry: A Pilot Study

The most frequently used method for evaluating tremor in Parkinson’s disease (PD) is currently the internationally standardized Movement Disorder Society—Unified PD Rating Scale (MDS-UPDRS). However, the MDS-UPDRS is associated with limitations, such as its inherent subjectivity and reliance on experienced raters. Objective motor measurements using accelerometry may overcome the shortcomings of visually scored scales. Therefore, the current study focuses on translating the MDS-UPDRS tremor tests into an objective scoring method using 3D accelerometry. An algorithm to measure and classify tremor according to MDS-UPDRS criteria is proposed. For this study, 28 PD patients undergoing neurosurgical treatment and 26 healthy control subjects were included. Both groups underwent MDS-UPDRS tests to rate tremor severity, while accelerometric measurements were performed at the index fingers. All measurements were performed in an off-medication state. Quantitative measures were calculated from the 3D acceleration data, such as tremor amplitude and area-under-the-curve of power in the 4−6 Hz range. Agreement between MDS-UPDRS tremor scores and objective accelerometric scores was investigated. The trends were consistent with the logarithmic relationship between tremor amplitude and MDS-UPDRS score reported in previous studies. The accelerometric scores showed a substantial concordance (>69.6%) with the MDS-UPDRS ratings. However, accelerometric kinetic tremor measures poorly associated with the given MDS-UPDRS scores (R2 < 0.3), mainly due to the noise between 4 and 6 Hz found in the healthy controls. This study shows that MDS-UDPRS tremor tests can be translated to objective accelerometric measurements. However, discrepancies were found between accelerometric kinetic tremor measures and MDS-UDPRS ratings. This technology has the potential to reduce rater dependency of MDS-UPDRS measurements and allow more objective intraoperative monitoring of tremor.

Transcranial Magnetic Stimulation for the Neurological Patient: Scientific Principles and Applications

Non-invasive brain stimulation has been increasingly recognized for its potential as an investigational, diagnostic and therapeutic tool across the clinical neurosciences. Transcranial magnetic stimulation (TMS) is a non-invasive method of focal neuromodulation. Diagnostically, TMS can be used to probe cortical excitability and plasticity, as well as for functional mapping. Therapeutically, depending on the pattern employed, TMS can either facilitate or inhibit stimulated cortex potentially modulating maladaptive physiology through its effects on neuroplasticity. Despite this potential, applications of TMS in neurology have only been approved for diagnostic clinical neurophysiology, pre-surgical mapping of motor and language cortex, and the treatment of migraines. In this article, we discuss the principles of TMS and its clinical applications in neurology, including experimental applications in stroke rehabilitation, seizures, autism spectrum disorder, neurodegenerative disorders, movement disorders, tinnitus, chronic pain and functional neurological disorder. To promote increased cross-talk across neurology and psychiatry, we also succinctly review the TMS literature for the treatment of major depression and obsessive compulsive disorder. Overall, we argue that larger clinical trials that are better informed by circuit-level biomarkers and pathophysiological models will lead to an expansion of the application of TMS for patients cared for by neurologists.

Cortical oscillatory dysfunction in Parkinson disease during movement activation and inhibition

Response activation and inhibition are functions fundamental to executive control that are disrupted in Parkinson disease (PD). We used magnetoencephalography to examine event related changes in oscillatory power amplitude, peak latency and frequency in cortical networks subserving these functions and identified abnormalities associated with PD. Participants (N = 18 PD, 18 control) performed a cue/target task that required initiation of an un-cued movement (activation) or inhibition of a cued movement. Reaction times were variable but similar across groups. Task related responses in gamma, alpha, and beta power were found across cortical networks including motor cortex, supplementary and pre- supplementary motor cortex, posterior parietal cortex, prefrontal cortex and anterior cingulate. PD-related changes in power and latency were noted most frequently in the beta band, however, abnormal power and delayed peak latency in the alpha band in the pre-supplementary motor area was suggestive of a compensatory mechanism. PD peak power was delayed in pre-supplementary motor area, motor cortex, and medial frontal gyrus only for activation, which is consistent with deficits in un-cued (as opposed to cued) movement initiation characteristic of PD.

Temporal Interference (TI) Stimulation Boosts Functional Connectivity in Human Motor Cortex: A Comparison Study with Transcranial Direct Current Stimulation (tDCS)

Temporal interference (TI) could stimulate deep motor cortex and induce movement without affecting the overlying cortex in previous mouse studies. However, there is still lack of evidence on potential TI effects in human studies. To fill this gap, we collected resting-state functional magnetic resonance imaging data on 40 healthy young participants both before and during TI stimulation on the left primary motor cortex (M1). We also chose a widely used simulation approach (tDCS) as a baseline condition. In the stimulation session, participants were randomly allocated to 2 mA TI or tDCS for 20 minutes. We used a seed-based whole brain correlation analysis method to quantify the strength of functional connectivity among different brain regions. Our results showed that both TI and tDCS significantly boosted functional connection strength between M1 and secondary motor cortex (premotor cortex and supplementary motor cortex). This is the first time to demonstrate substantial stimulation effect of TI in the human brain.

Target Selection for Magnetic Resonance-Guided Focused Ultrasound in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a common, progressive, and incurable neurodegenerative disease. Pharmacological treatment is the first-line therapy for PD, including carbidopa-levodopa, dopamine agonists. However, some patients respond poorly to medication. For these patients, functional neurosurgical treatment is an important option. Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel, minimally invasive surgical option for patients refractory to drugs. Currently, several important anatomical structures can be targeted by MRgFUS in the treatment of PD. However, there is no uniform standard for target selection. This review summarizes the clinical studies on MRgFUS for PD, focusing on the relationship between different treatment targets and the relieved symptoms, to help clinicians determine the ideal therapeutic target for individual patients. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 4.

Noninvasive neuromodulation in Parkinson's disease: Neuroplasticity implication and therapeutic perspectives

Noninvasive brain stimulation techniques can be used to study in vivo the changes of cortical activity and plasticity in subjects with Parkinson's disease (PD). Also, an increasing number of studies have suggested a potential therapeutic effect of these techniques. High-frequency repetitive transcranial magnetic stimulation (rTMS) and anodal transcranial direct current stimulation (tDCS) represent the most used stimulation paradigms to treat motor and nonmotor symptoms of PD. Both techniques can enhance cortical activity, compensating for its reduction related to subcortical dysfunction in PD. However, the use of suboptimal stimulation parameters can lead to therapeutic failure. Clinical studies are warranted to clarify in PD the additional effects of these stimulation techniques on pharmacologic and neurorehabilitation treatments.

Using Transcranial Electrical Stimulation in Audiological Practice: The Gaps to Be Filled

The effects of transcranial electrical stimulation (tES) approaches have been widely studied for many decades in the motor field, and are well known to have a significant and consistent impact on the rehabilitation of people with motor deficits. Consequently, it can be asked whether tES could also be an effective tool for targeting and modulating plasticity in the sensory field for therapeutic purposes. Specifically, could potentiating sensitivity at the central level with tES help to compensate for sensory loss? The present review examines evidence of the impact of tES on cortical auditory excitability and its corresponding influence on auditory processing, and in particular on hearing rehabilitation. Overall, data strongly suggest that tES approaches can be an effective tool for modulating auditory plasticity. However, its specific impact on auditory processing requires further investigation before it can be considered for therapeutic purposes. Indeed, while it is clear that electrical stimulation has an effect on cortical excitability and overall auditory abilities, the directionality of these effects is puzzling. The knowledge gaps that will need to be filled are discussed.

Neurophysiological Predictors of Response to Medication in Parkinson's Disease

Background: Although dopaminergic medication has been the foundation of Parkinson's disease (PD) therapy for decades, sensitive and specific therapeutic response biomarkers that allow for better treatment optimization are lacking. Objective: We tested whether the features of Transcranial Magnetic Stimulation-based neurophysiological measures taken off-medication are associated with dopaminergic medication-induced clinical effects. Method: Motor cortex excitability [short-latency intracortical inhibition (SICI), intracortical facilitation (ICF), short-latency afferent inhibition (SAI), and input-output (IO) curve], and plasticity [paired associative stimulation (PAS) protocol] neurophysiological measures were examined in 23 PD patients off-medication. Clinical features were quantified by the motor section of the Unified Parkinson's Disease Scale (total score and lateralized total, bradykinesia, and rigidity sub-scores), and the differences between measures off-medication and on-medication (following the usual morning dose), were determined. Total daily dopaminergic medication dose (expressed as levodopa equivalent daily dose-LEDD), was also determined. Results: SICI significantly correlated with changes in lateralized UPDRS motor and bradykinesia sub-scores, suggesting that patients with stronger basal intracortical inhibition benefit more from dopaminergic treatment than patients with weaker intracortical inhibition. Also, ICF significantly negatively correlated with LEDD, suggesting that patients with stronger intracortical facilitation require less dopaminergic medication to achieve optimal therapeutic benefit. Both associations were independent of disease severity and duration. Conclusions: The results suggest variability of (patho) physiological phenotypes related to intracortical inhibitory and facilitatory mechanisms determining clinical response to dopaminergic medication in PD. Measures of intracortical excitability may help predict patients' response to dopaminergic therapy, thus potentially providing a background for developing personalized therapy in PD.

Multisite non-invasive brain stimulation in Parkinson's disease: A scoping review

BACKGROUND:

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by cardinal motor symptoms in addition to cognitive impairment. New insights concerning multisite non-invasive brain stimulation effects have been gained, which can now be used to develop innovative treatment approaches.

OBJECTIVE:

Map the researchs involving multisite non-invasive brain stimulation in PD, synthesize the available evidence and discuss future directions.

METHODS:

The databases PubMed, PsycINFO, CINAHL, LILACS and The Cochrane Library were searched from inception until April 2020, without restrictions on the date of publication or the language in which it was published. The reviewers worked in pairs and sequentially evaluated the titles, abstracts and then the full text of all publications identified as potentially relevant.

RESULTS:

Twelve articles met the inclusion criteria. The target brain regions included mainly the combination of a motor and a frontal area, such as stimulation of the primary motor córtex associated with the dorsolateral prefrontal cortex. Most of the trials showed that this modality was only more effective for the motor component, or for the cognitive and/or non-motor, separately.

CONCLUSIONS:

Despite the results being encouraging for the use of the multisite aproach, the indication for PD management should be carried out with caution and deserves scientific deepening.

Transcranial direct current stimulation provides no clinically important benefits over walking training for improving walking in Parkinson's disease: a systematic review

QUESTIONS

Does walking training combined with transcranial direct current stimulation (tDCS) improve walking (ie, speed, cadence and step length) and reduce falls and freezing, compared with no/sham intervention, in people with Parkinson's disease? Is walking training combined with tDCS superior to walking training alone? Are any benefits carried over to social participation and/or maintained beyond the intervention period?

DESIGN

A systematic review with meta-analyses of randomised clinical trials.

PARTICIPANTS

Ambulatory adults with a clinical diagnosis of Parkinson's disease.

INTERVENTION

tDCS combined with walking training.

OUTCOME MEASURES

Primary outcomes were walking speed, cadence and step length. Secondary outcomes were number of falls, fear of falling, freezing of gait and social participation.

RESULTS

Five trials involving 117 participants were included. The mean PEDro score of the included trials was 8 out of 10. Participants undertook training for 30 to 60 minutes, two to three times per week, on average for 4 weeks. Moderate-quality evidence indicated that the addition of tDCS to walking training produced negligible additional benefit over the effect of walking training alone on walking speed (MD -0.01 m/s, 95% CI -0.05 to 0.04), step length (MD 1.2 cm, 95% CI -1.2 to 3.5) or cadence (MD -3 steps/minute, 95% CI -6 to 1). No evidence was identified with which to estimate the effect of the addition of tDCS to walking training on freezing of gait, falls and social participation.

CONCLUSION

The addition of tDCS to walking training provided no clinically important benefits on walking in ambulatory people with Parkinson's disease.

REGISTRATION

PROSPERO CRD42020162908.

Potential Non-invasive Brain Stimulation Targets to Alleviate Freezing of Gait in Parkinson's Disease

Freezing of gait (FOG) is a common motor symptom in Parkinson's disease (PD). Although FOG reduces quality of life, affects mobility and increases the risk of falls, there are little to no effective treatments to alleviate FOG. Non-invasive brain stimulation (NIBS) has recently yielded attention as a potential treatment to reduce FOG symptoms however, stimulation parameters and protocols remain inconsistent and require further research. Specifically, targets for stimulation require careful review. Thus, with current neuroimaging and neuro-electrophysiological evidence, we consider potential cortical targets thought to be involved in the pathophysiology of FOG according to the Interference model, and within reach of NIBS. We note that the primary motor cortex, the supplementary motor area and the dorsolateral prefrontal cortex have already drawn attention as NIBS targets for FOG, but based on neuroimaging evidence the premotor cortex, the medial prefrontal cortex, the cerebellum, and more particularly, the posterior parietal cortex should be considered as potential regions for stimulation. We also discuss different methodological considerations, such as stimulation type, medication state, and hemisphere to target, and future perspectives for NIBS protocols in FOG.

Energy-Efficient Integrated Circuit Solutions Toward Miniaturized Closed-Loop Neural Interface Systems

Miniaturized implantable devices play a crucial role in neural interfaces by monitoring and modulating neural activities on the peripheral and central nervous systems. Research efforts toward a compact wireless closed-loop system stimulating the nerve automatically according to the user's condition have been maintained. These systems have several advantages over open-loop stimulation systems such as reduction in both power consumption and side effects of continuous stimulation. Furthermore, a compact and wireless device consuming low energy alleviates foreign body reactions and risk of frequent surgical operations. Unfortunately, however, the miniaturized closed-loop neural interface system induces several hardware design challenges such as neural activity recording with severe stimulation artifact, real-time stimulation artifact removal, and energy-efficient wireless power delivery. Here, we will review recent approaches toward the miniaturized closed-loop neural interface system with integrated circuit (IC) techniques.

Medical Devices for Tremor Suppression: Current Status and Future Directions

Tremors are the most prevalent movement disorder that interferes with the patient’s daily living, and physical activities, ultimately leading to a reduced quality of life. Due to the pathophysiology of tremor, developing effective pharmacotherapies, which are only suboptimal in the management of tremor, has many challenges. Thus, a range of therapies are necessary in managing this progressive, aging-associated disorder. Surgical interventions such as deep brain stimulation are able to provide durable tremor control. However, due to high costs, patient and practitioner preference, and perceived high risks, their utilization is minimized. Medical devices are placed in a unique position to bridge this gap between lifestyle interventions, pharmacotherapies, and surgical treatments to provide safe and effective tremor suppression. Herein, we review the mechanisms of action, safety and efficacy profiles, and clinical applications of different medical devices that are currently available or have been previously investigated for tremor suppression. These devices are primarily noninvasive, which can be a beneficial addition to the patient’s existing pharmacotherapy and/or lifestyle intervention.

Image-based biophysical modeling predicts cortical potentials evoked with subthalamic deep brain stimulation

BACKGROUND

Subthalamic deep brain stimulation (DBS) is an effective surgical treatment for Parkinson's disease and continues to advance technologically with an enormous parameter space. As such, in-silico DBS modeling systems have become common tools for research and development, but their underlying methods have yet to be standardized and validated.

OBJECTIVE

Evaluate the accuracy of patient-specific estimates of neural pathway activations in the subthalamic region against intracranial, cortical evoked potential (EP) recordings.

METHODS

Pathway activations were modeled in eleven patients using the latest advances in connectomic modeling of subthalamic DBS, focusing on the hyperdirect pathway (HDP) and corticospinal/bulbar tract (CSBT) for their relevance in human research studies. Correlations between pathway activations and respective EP amplitudes were quantified.

RESULTS

Good model performance required accurate lead localization and image fusions, as well as appropriate selection of fiber diameter in the biophysical model. While optimal model parameters varied across patients, good performance could be achieved using a global set of parameters that explained 60% and 73% of electrophysiologic activations of CSBT and HDP, respectively. Moreover, restricted models fit to only EP amplitudes of eight standard (monopolar and bipolar) electrode configurations were able to extrapolate variation in EP amplitudes across other directional electrode configurations and stimulation parameters, with no significant reduction in model performance across the cohort.

CONCLUSIONS

Our findings demonstrate that connectomic models of DBS with sufficient anatomical and electrical details can predict recruitment dynamics of white matter. These results will help to define connectomic modeling standards for preoperative surgical targeting and postoperative patient programming applications.

Effect of skin conductivity on the electric field induced by transcranial stimulation techniques in different head models

This study aims at quantifying the effect that using different skin conductivity values has on the estimation of the electric (E)-field distribution induced by transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in the brain of two anatomical models. The induced E-field was calculated with numerical simulations inside MIDA and Duke models, assigning to the skin a conductivity value estimated from a multi-layered skin model and three values taken from literature. The effect of skin conductivity variations on the local E-field induced by tDCS in the brain was up to 70%. In TMS, minor local differences, in the order of 20%, were obtained in regions of interest for the onset of possible side effects. Results suggested that an accurate model of the skin is necessary in all numerical studies that aim at precisely estimating the E-field induced during TMS and tDCS applications. This also highlights the importance of further experimental studies on human skin characterization, especially at low frequencies.

New Approaches Based on Non-Invasive Brain Stimulation and Mental Representation Techniques Targeting Pain in Parkinson's Disease Patients: Two Study Protocols for Two Randomized Controlled Trials

Pain is an under-reported but prevalent symptom in Parkinson’s Disease (PD), impacting patients’ quality of life. Both pain and PD conditions cause cortical excitability reduction and non-invasive brain stimulation. Mental representation techniques are thought to be able to counteract it, also resulting effectively in chronic pain conditions. We aim to conduct two independent studies in order to evaluate the efficacy of transcranial direct current stimulation (tDCS) and mental representation protocol in the management of pain in PD patients during the ON state: (1) tDCS over the Primary Motor Cortex (M1); and (2) Action Observation (AO) and Motor Imagery (MI) training through a Brain-Computer Interface (BCI) using Virtual Reality (AO + MI-BCI). Both studies will include 32 subjects in a longitudinal prospective parallel randomized controlled trial design under different blinding conditions. The main outcomes will be score changes in King’s Parkinson’s Disease Pain Scale, Brief Pain Inventory, Temporal Summation, Conditioned Pain Modulation, and Pain Pressure Threshold. Assessment will be performed pre-intervention, post-intervention, and 15 days post-intervention, in both ON and OFF states.

Non-invasive brain stimulation for Parkinson's disease: Clinical evidence, latest concepts and future goals: A systematic review

Parkinson's disease (PD) is becoming a major public-health issue in an aging population. Available approaches to treat advanced PD still have limitations; new therapies are needed. The non-invasive brain stimulation (NIBS) may offer a complementary approach to treat advanced PD by personalized stimulation. Although NIBS is not as effective as the gold-standard levodopa, recent randomized controlled trials show promising outcomes in the treatment of PD symptoms. Nevertheless, only a few NIBS-stimulation paradigms have shown to improve PD's symptoms. Current clinical recommendations based on the level of evidence are reported in Table 1 through Table 3. Furthermore, novel technological advances hold promise and may soon enable the non-invasive stimulation of deeper brain structures for longer periods.

Transcranial random noise stimulation over the primary motor cortex in PD-MCI patients: a crossover, randomized, sham-controlled study

Mild cognitive impairment (MCI) is a very common non-motor feature of Parkinson’s disease (PD) and the non-amnestic single-domain is the most frequent subtype. Transcranial random noise stimulation (tRNS) is a non-invasive technique, which is capable of enhancing cortical excitability. As the main contributor to voluntary movement control, the primary motor cortex (M1) has been recently reported to be involved in higher cognitive functioning. The aim of this study is to evaluate the effects of tRNS applied over M1 in PD-MCI patients in cognitive and motor tasks. Ten PD-MCI patients, diagnosed according to the Movement Disorder Society, Level II criteria for MCI, underwent active (real) and placebo (sham) tRNS single sessions, at least 1 week apart. Patients underwent cognitive (Digit Span Forward and Backward, Digit Symbol, Visual Search, Letter Fluency, Stroop Test) and motor assessments (Unified Parkinson’s Disease Rating Scale [UPDRS-ME], specific timed trials for bradykinesia, 10-m walk and Timed up and go tests) before and after each session. A significant improvement in motor ability (UPDRS-ME and lateralized scores, ps from 0.049 to 0.003) was observed after real versus sham tRNS. On the contrary, no significant differences were found in other motor tasks and cognitive assessment both after real and sham stimulations. These results confirm that tRNS is a safe and effective tool for improving motor functioning in PD-MCI. Future studies using a multisession tRNS applied over multitargeted brain areas (i.e., dorsolateral prefrontal cortex and M1) are required to clarify the role of tRNS regarding rehabilitative intervention in PD.

Enhancing rehabilitation and functional recovery after brain and spinal cord trauma with electrical neuromodulation

PURPOSE OF REVIEW

This review discusses recent advances in the rehabilitation of motor deficits after traumatic brain injury (TBI) and spinal cord injury (SCI) using neuromodulatory techniques.

RECENT FINDINGS

Neurorehabilitation is currently the only treatment option for long-term improvement of motor functions that can be offered to patients with TBI or SCI. Major advances have been made in recent years in both preclinical and clinical rehabilitation. Activity-dependent plasticity of neuronal connections and circuits is considered key for successful recovery of motor functions, and great therapeutic potential is attributed to the combination of high-intensity training with electrical neuromodulation. First clinical case reports have demonstrated that repetitive training enabled or enhanced by electrical spinal cord stimulation can yield substantial improvements in motor function. Described achievements include regaining of overground walking capacity, independent standing and stepping, and improved pinch strength that recovered even years after injury.

SUMMARY

Promising treatment options have emerged from research in recent years using neurostimulation to enable or enhance intense training. However, characterizing long-term benefits and side-effects in clinical trials and identifying patient subsets who can benefit are crucial. Regaining lost motor function remains challenging.

Feasibility of Transcranial Direct Current Stimulation in Patients with Deep Brain Stimulation: a Case Report

Although deep brain stimulation (DBS) has been reported to be effective to ameliorate motor and non-motor dysfunctions, freezing of gait (FoG) is often resistant to DBS in patients with Parkinson's disease (PD). Transcranial direct current stimulation (tDCS) has been reported as an alternative therapeutic strategy to ameliorate FoG in PD patients. In this case report, we describe the effects of cumulative tDCS over the primary motor cortex of the lower leg to reduce FoG in 2 cases of PD patients with DBS. Two PD patients who had undergone DBS of the subthalamic nucleus visited the rehabilitation medicine department for refractory FoG. Each patient received cumulative tDCS over the primary motor cortex of the lower leg over to reduce FoG. Neither patient required change in dose of dopaminergic medication during the tDCS period nor a significant side effect during and after tDCS. Although the FoG-questionnaire (FoG-Q) in case 1 showed no change after 10 tDCS treatments, the patient in case 2 reported a significant improvement of FoG-Q from 11 to 3 after 5 days of tDCS. We present the safety and feasibility of tDCS in PD patients with DBS who showed refractory FoG.

Computational modelling of the long-term effects of brain stimulation on the local and global structural connectivity of epileptic patients

Computational studies of the influence of different network parameters on the dynamic and topological network effects of brain stimulation can enhance our understanding of different outcomes between individuals. In this study, a brain stimulation session along with the subsequent post-stimulation brain activity is simulated for a period of one day using a network of modified Wilson-Cowan oscillators coupled according to diffusion imaging based structural connectivity. We use this computational model to examine how differences in the inter-region connectivity and the excitability of stimulated regions at the time of stimulation can affect post-stimulation behaviours. Our findings indicate that the initial inter-region connectivity can heavily affect the changes that stimulation induces in the connectivity of the network. Moreover, differences in the excitability of the stimulated regions seem to lead to different post-stimulation connectivity changes across the model network, including on the internal connectivity of non-stimulated regions.