Transcranial Pulsed-Current Stimulation versus Transcranial Direct Current Stimulation in Patients with Disorders of Consciousness: A Pilot, Sham-Controlled Cross-Over Double-Blind Study

Cognitive and neurophysiological effects of bilateral tDCS neuromodulation in patients with minimally conscious state

The minimally conscious state (MCS) is a clinical condition characterized by severely reduced but present awareness of self and the environment. Transcranial direct current stimulation (tDCS) has shown promising potential. The aim of this quasi-randomised control study was to investigate the effects of bilateral of tDCS applied to the right and left dorsolateral prefrontal cortex (DLPFC) on neurophysiological and cognitive outcomes in 28 patients with MCS. Participants were quasi-randomly assigned to one of two groups: experimental group with tDCS over both DLPFC, and a control group, which received sham tDCS. Neurophysiological assessments included event-related potentials (ERPs) analysis (N200 and P300) and EEG beta band study. Clinical outcomes were measured using ad hoc psychometric battery, including Coma Recovery Scale-Revised (CRS-R), Levels of Cognitive Functioning Scale (LCFS), and Functional Independence Measure (FIM). The findings revealed a significant improvement in ERP latencies and increased beta band rhythms in the experimental group, indicating enhanced neural responsiveness to cognitive stimuli. Additionally, significant improvements were observed in clinical measures of awareness and functional capacity. These findings suggest that tDCS may represent a promising therapeutic option for enhancing both neurophysiological responses and cognitive functioning in patients with MCS.

Characterization of responders to transcranial direct current stimulation in disorders of consciousness: A retrospective study of 8 clinical trials

The treatment for patients with disorders of consciousness challenges researchers and clinicians. The stimulation of the left dorsolateral prefrontal cortex with transcranial direct current stimulation (tDCS) may enhance behavioral responsiveness of a subset of patients in a minimally conscious state, while having limited effects in unresponsive patients. However, heterogeneity in responses raises questions about the effectiveness of tDCS. Our objective was to explore the characteristics of responders to tDCS based on previously published RCTs and investigate the heterogeneity of treatment effect to better direct future tDCS studies towards patient profiles that appear to be more responsive to the treatment. We explored clinical and demographical differences between responders (i.e., recovery of a new sign of consciousness after active stimulation) and non-responder and the predictors of treatment response with a LASSO logistic regression. We included 131 patients (44 women, 61 traumatic brain injury, 90 minimally conscious, mean age 46.13 years [SD ​= ​16], median time since injury 12.84 months [IQR: 5.25-35.10]) of which 33 responded to tDCS. While 32 ​% of minimally conscious patients responded to tDCS (95%CI 0.24, 0.43), 10 ​% (95%CI 0.04, 0.25) of those unresponsive responded. The regression model, using diagnosis at baseline, Coma Recovery Scale-Revised Index at baseline, age, sex and time since injury correctly discriminated between tDCS responders and non-responders (area under the curve of 0.77). Our findings suggest that patients in minimally conscious state, with a better cognitive profile and longer TSI respond better to tDCS, making them better candidates for the treatment.

Neuromodulation and Disorders of Consciousness: Systematic Review and Pathophysiology

INTRODUCTION

Disorders of consciousness (DoC) represent a range of clinical states, affect hundreds of thousands of people in the United States, and have relatively poor outcomes. With few effective pharmacotherapies, neuromodulation has been investigated as an alternative for treating DoC. To summarize the available evidence, a systematic review of studies using various forms of neuromodulation to treat DoC was conducted.

MATERIALS AND METHODS

Adhering to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for systematic literature review, the PubMed, Scopus, and Web of Science databases were queried to identify articles published between 1990 and 2023 in which neuromodulation was used, usually in conjunction with pharmacologic intervention, to treat or reverse DoC in humans and animals. Records were excluded if DoC (eg, unresponsive wakefulness syndrome, minimally conscious state, etc) were not the primary clinical target.

RESULTS

A total of 69 studies (58 human, 11 animal) met the inclusion criteria for the systematic review, resulting in over 1000 patients and 150 animals studied in total. Most human studies investigated deep brain stimulation (n = 15), usually of the central thalamus, and transcranial magnetic stimulation (n = 18). Transcranial direct-current stimulation (n = 15) and spinal cord stimulation (n = 6) of the dorsal column also were represented. A few studies investigated low-intensity focused ultrasound (n = 2) and median nerve stimulation (n = 2). Animal studies included primate and murine models, with nine studies involving deep brain stimulation, one using ultrasound, and one using transcranial magnetic stimulation.

DISCUSSION

While clinical outcomes were mixed and possibly confounded by natural recovery or pharmacologic interventions, deep brain stimulation appeared to facilitate greater improvements in DoC than other modalities. However, repetitive transcranial magnetic stimulation also demonstrated clinical potential with much lower invasiveness.

Non-pharmacologic interventions in disorders of consciousness

Severely brain-injured patients with disorders of consciousness pose significant challenges in terms of management, particularly due to the limited therapeutic options available. Despite the potential for some patients to benefit from interventions even years after the injury, clinicians often lack clear and reliable treatment strategies to promote patient recovery. In response to this clinical need, the field of neuromodulation has emerged as a promising alternative to traditional pharmacologic therapies. Both invasive and noninvasive brain stimulation techniques offer diverse possibilities for restoring physiologic neural activity and enhancing functional network integrity in these complex neurological disorders. This chapter offers a comprehensive overview of current neuromodulation techniques, exploring their potential applications and analyzing the existing evidence for their efficacy. Specifically, we describe transcranial electrical stimulation, transcranial magnetic stimulation, deep brain stimulation, low-intensity focused ultrasound, vagal nerve stimulation (including transcutaneous methods), spinal cord stimulation, and median nerve stimulation. While certain approaches show promise for patients with disorders of consciousness, there remains a pressing need for large-scale interventional clinical trials that will play an essential role for elucidating the underlying mechanisms of recovery and for refining stimulation parameters. This, together with the development of tailored individual interventions will move the field forward and optimize therapeutic outcomes.

Cognitive Effects of Transcranial Direct Current Stimulation Plus Robotic Verticalization in Minimally Conscious State

BACKGROUND AND OBJECTIVES

Transcranial direct current stimulation (tDCS) is a non-invasive therapeutic method that modulates cortical excitability and shows promising results for treating disorders of consciousness (DoCs). Robotic verticalization training (RVT) has been shown to enhance motor and cognitive recovery. This study evaluates the effects of an innovative approach combining RVT with tDCS in individuals with DoCs.

METHODS

Twenty-four subjects with DoCs, particularly those with chronic minimally conscious state (MCS) due to vascular or traumatic brain injury, participated in a quasi-randomized study at the Neurorehabilitation Unit, IRCCS Neurolesi (Messina, Italy). Participants were divided into either a control group (CG) receiving RVT alone or an experimental group (EG) receiving combined tDCS and RVT. Both groups underwent treatments five times weekly for four weeks, with tDCS/sham sessions over the dorsolateral prefrontal cortex (DLPFC) lasting 20 min before Erigo training sessions, which lasted 45 min.

RESULTS

The findings indicate that combining tDCS with Erigo® Pro RTT could lead to greater improvements in cognitive functioning and P300 latency compared to the CG.

CONCLUSIONS

These results suggest that the integrated approach of tDCS with RVT could offer significant benefits for patients with MCS, highlighting its potential to enhance cognitive recovery, such as reducing P300 latency.

Modulation of brain activity in brain-injured patients with a disorder of consciousness in intensive care with repeated 10-Hz transcranial alternating current stimulation (tACS): a randomised controlled trial protocol

INTRODUCTION

Therapeutic interventions for disorders of consciousness lack consistency; evidence supports non-invasive brain stimulation, but few studies assess neuromodulation in acute-to-subacute brain-injured patients. This study aims to validate the feasibility and assess the effect of a multi-session transcranial alternating current stimulation (tACS) intervention in subacute brain-injured patients on recovery of consciousness, related brain oscillations and brain network dynamics.

METHODS AND ANALYSES

The study is comprised of two phases: a validation phase (n=12) and a randomised controlled trial (n=138). Both phases will be conducted in medically stable brain-injured adult patients (traumatic brain injury and hypoxic-ischaemic encephalopathy), with a Glasgow Coma Scale score ≤12 after continuous sedation withdrawal. Recruitment will occur at the intensive care unit of a Level 1 Trauma Centre in Montreal, Quebec, Canada. The intervention includes a 20 min 10 Hz tACS at 1 mA intensity or a sham session over parieto-occipital cortical sites, repeated over five consecutive days. The current's frequency targets alpha brain oscillations (8-13 Hz), known to be associated with consciousness. Resting-state electroencephalogram (EEG) will be recorded four times daily for five consecutive days: pre and post-intervention, at 60 and 120 min post-tACS. Two additional recordings will be included: 24 hours and 1-week post-protocol. Multimodal measures (blood samples, pupillometry, behavioural consciousness assessments (Coma Recovery Scale-revised), actigraphy measures) will be acquired from baseline up to 1 week after the stimulation. EEG signal analysis will focus on the alpha bandwidth (8-13 Hz) using spectral and functional network analyses. Phone assessments at 3, 6 and 12 months post-tACS, will measure long-term functional recovery, quality of life and caregivers' burden.

ETHICS AND DISSEMINATION

Ethical approval for this study has been granted by the Research Ethics Board of the CIUSSS du Nord-de-l'Île-de-Montréal (Project ID 2021-2279). The findings of this two-phase study will be submitted for publication in a peer-reviewed academic journal and submitted for presentation at conferences. The trial's results will be published on a public trial registry database (ClinicalTrials.gov).

TRIAL REGISTRATION NUMBER

NCT05833568.

An update on noninvasive neuromodulation in the treatment of patients with prolonged disorders of consciousness

BACKGROUND

With the improvement of emergency techniques, the survival rate of patients with severe brain injury has increased. However, this has also led to an annual increase in the number of patients with prolonged disorders of consciousness (pDoC). Hence, recovery of consciousness is an important part of treatment. With advancing techniques, noninvasive neuromodulation seems a promising intervention. The objective of this review was to summarize the latest techniques and provide the basis for protocols of noninvasive neuromodulations in pDoC.

METHODS

This review summarized the advances in noninvasive neuromodulation in the treatment of pDoC in the last 5 years.

RESULTS

Variable techniques of neuromodulation are used in pDoC. Transcranial ultrasonic stimulation (TUS) and transcutaneous auricular vagus nerve stimulation (taVNS) are very new techniques, while transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) are still the hotspots in pDoC. Median nerve electrical stimulation (MNS) has received little attention in the last 5 years.

CONCLUSIONS

Noninvasive neuromodulation is a valuable and promising technique to treat pDoC. Further studies are needed to determine a unified stimulus protocol to achieve optimal effects as well as safety.

Effectiveness of coma arousal therapy on patients with disorders of consciousness - A systematic review and meta-analysis

BACKGROUND

Disorders of consciousness (DOC) incorporate stages of awareness and arousal. Through coma arousal therapy sensory deprivation experienced by patients with DOC can be mitigated. Nevertheless, consensus concerning its effectiveness on these patients is still fractional.

PURPOSE

This review aims to investigate the effectiveness of coma arousal therapies on patients with DOC.

METHODS

A meta-analysis was performed by searching electronic databases using search terms, the studies investigating the effect of coma arousal therapy in patients with DOC using the Coma Recovery Scale-Revised and Glasgow Coma Scale as outcome measures were included. The risk of bias was assessed, using Cochrane and Joanna Briggs Institute critical appraisal tools. Further, analysis was conducted for the included studies.

RESULTS

Out of 260 studies, 45 trials were reviewed and assessed for bias, with 31 studies included for analysis. The analysis demonstrates a significant difference in pre- and post - sensory stimulation, vagus nerve stimulation, transcranial magnetic stimulation, and transcranial direct current stimulation. Sensory stimulation showed the greatest mean difference of -4.96; 95% CI = -5.76 to - 4.15. The patients who underwent intervention after 3 months of illness showed significant improvement.

CONCLUSION

The result shows that sensory stimulation, transcranial magnetic stimulation, and transcranial direct stimulation can improve behavioral outcomes of patients with DOC, wherein sensory stimulation is found to be more effective.

Transcranial pulsed current stimulation: A scoping review of the current literature on scope, nature, underlying mechanisms, and gaps

Transcranial pulsed current stimulation (tPCS) is a noninvasive brain stimulation technique that has aroused considerable attention in recent years. This review aims to provide an overview of the existing literature on tPCS, examine the scope and nature of previous research, investigate its underlying mechanisms, and identify gaps in the literature. Searching online databases resulted in 36 published tPCS studies from inception until May 2023. These studies were categorized into three groups: human studies on healthy individuals, human studies on clinical conditions, and animal studies. The findings suggest that tPCS has the potential to modulate brain excitability by entraining neural oscillations and utilizing stochastic resonance. However, the underlying mechanisms of tPCS are not yet fully understood and require further investigation. Furthermore, the included studies indicate that tPCS may have therapeutic potential for neurological diseases. However, before tPCS can be applied in clinical settings, a better understanding of its mechanisms is crucial. Hence, the tPCS studies were categorized into four types of research: basic, strategic, applied, and experimental research, to identify the nature of the literature and gaps. Analysis of these categories revealed that tPCS, with its diverse parameters, effects, and mechanisms, presents a wide range of research opportunities for future investigations.

Technological Modalities in the Assessment and Treatment of Disorders of Consciousness

Over the last 10 years, there have been rapid advances made in technologies that can be utilized in the diagnosis and treatment of patients with a disorder of consciousness (DoC). This article provides a comprehensive review of these modalities including the evidence supporting their potential use in DoC. This review specifically addresses diagnostic, non-invasive therapeutic, and invasive therapeutic technological modalities except for neuroimaging, which is discussed in another article. While technologic advances appear promising for both assessment and treatment of patients with a DoC, high-quality evidence supporting widespread clinical adoption remains limited.

Combined behavioral and EEG evidence for the 70 Hz frequency selection of short-term spinal cord stimulation in disorders of consciousness

OBJECTIVES

This study investigated the prognostic effect of electroencephalography (EEG) instant effects of single spinal cord stimulation (SCS) on clinical outcome in disorders of consciousness (DOC) and the time-dependent brain response during the recovery of consciousness prompted by SCS.

METHODS

Twenty three patients with DOC underwent short-term SCS (stSCS) implantation operation. Then, all patients received the postoperative EEG test including EEG record before (T1) and after (T2) single SCS session. Subsequently, 2 weeks stSCS treatment was performed and revised coma recovery scale (CRS-R) and EEG data were collected. Finally, they were classified into effective and ineffective groups at 3-month follow-up (T6).

RESULTS

The parietal-occipital (PO) connectivity and clustering coefficients (CC) in the beta band of the effective group at the 1 week after the treatment (T5) were found to be higher than preoperative assessment (T0). Correlation analysis showed that the change in beta CC at T1/T2 was correlated with the change in CRS-R at T0/T6. In addition, the change in PO connectivity and CC in the beta at T0/T5 were also correlated with the change in CRS-R at T0/T5.

CONCLUSION

SCS may facilitate the recovery of consciousness by enhancing local information interaction in posterior brain regions. And the recovery can be predicted by beta CC in the EEG test.

Swallowing dysfunctions in patients with disorders of consciousness: Evidence from neuroimaging data, assessment, and management

Following severe brain injuries, a subset of patients may remain in an altered state of consciousness; most of these patients require artificial feeding. Currently, a functional oral phase and the presence of exclusive oral feeding may constitute signs of consciousness. Additionally, the presence of pharyngo-laryngeal secretions, saliva aspiration, cough reflex and tracheostomy are related to the level of consciousness. However, the link between swallowing and consciousness is yet to be fully understood. The primary aim of this review is to establish a comprehensive overview of the relationship between an individual's conscious behaviour and swallowing (reflexive and voluntary). Previous studies of brain activation during volitional and non-volitional swallowing tasks in healthy subjects are also reviewed. We demonstrate that the areas activated by voluntary swallowing tasks (primary sensorimotor, cingulate, insula, premotor, supplementary motor, cerebellum, and operculum) are not specific to deglutitive function but are shared with other motor tasks and brain networks involved in consciousness. This review also outlines suitable assessment and treatment methods for dysphagic patients with disorders of consciousness. Finally, we propose that markers of swallowing could contribute to the development of novel diagnostic guidelines for patients with disorders of consciousness.

A Comparison of the Neuromodulation Effects of Frontal and Parietal Transcranial Direct Current Stimulation on Disorders of Consciousness

Frontal transcranial direct current stimulation (tDCS) and parietal tDCS are effective for treating disorders of consciousness (DoC); however, the relative efficacies of these techniques have yet to be determined. This paper compares the neuromodulation effects of frontal and parietal tDCS on DoC. Twenty patients with DoC were recruited and randomly assigned to two groups. One group received single-session frontal tDCS and single-session sham tDCS. The other group received single-session parietal tDCS and single-session sham tDCS. Before and after every tDCS session, we recorded coma recovery scale-revised (CRS-R) values and an electroencephalogram. CRS-R was also used to evaluate the state of consciousness at 9-12-month follow-up. Both single-session frontal and parietal tDCS caused significant changes in the genuine permutation cross-mutual information (G_PCMI) of local frontal and across brain regions (p < 0.05). Furthermore, the changes in G_PCMI values were significantly correlated to the CRS-R scores at 9-12-month follow-up after frontal and parietal tDCS (p < 0.05). The changes in G_PCMI and CRS-R scores were also correlated (p < 0.05). Both frontal tDCS and parietal tDCS exert neuromodulatory effects in DoC and induce significant changes in electrophysiology. G_PCMI can be used to evaluate the neuromodulation effects of tDCS.

Effect of non-invasive brain stimulation on conscious disorder in patients after brain injury: a network meta-analysis

OBJECTIVE

To systematically evaluate the rehabilitation effect of non-invasive brain stimulation (NIBS) on disorder of consciousness (DOC) after brain injury and compare the effects of different NIBSs.

METHODS

Randomized controlled trials (RCTs) on the effect of NIBS on DOC after brain injury were retrieved from the PubMed, Cochrane Library, Web of Science, CNKI, VIP, Wanfang Data, and CBM databases from inception to October 2022. The risk of bias and quality of the trials were assessed following the Cochrane Handbook of Systematic Reviews and the physiotherapy evidence database Jadad Scale. Statistical analysis was conducted with RevMan 5.4 and R Studio. This study was registered on PROSPERO (No. CRD42022371334).

RESULTS

A total of 28 articles were included involving 1118 patients. Meta-analysis showed that NIBS combined with routine rehabilitation had the highest effect than the routine rehabilitation and the sham NIBS combined with routine rehabilitation. The cumulative probability ranking results showed that the rTMS was best. The order of network meta-analysis with GCS (Glasgow Coma Scale) as the outcome index is rTMS combined with routine rehabilitation > tDCS combined with routine rehabilitation > routine rehabilitation > NIBS sham stimulation combined with routine rehabilitation. The order of network meta-analysis with CRS-R (Coma Recovery Scale-Revised) as the outcome index is rTMS combined with routine rehabilitation > tDCS combined with routine rehabilitation > NIBS sham stimulation combined with routine rehabilitation > routine rehabilitation. For patients with different conditions of DOC, the subgroup analysis results showed that rTMS improved the effect of patients with severe DOC better than those with unclear conditions of DOC, but the overall results of the two groups were not significantly different. On the contrary, the effect of tDCS on patients with DOC whose condition was not clear was better than that on patients with severe DOC, and the effect on patients with severe DOC was not significant (P > 0.05). In terms of safety, only 9 articles mentioned ADRs in the included literature, including 8 articles without ADRs, and 1 article with ADRs.

CONCLUSION

Based on the research results of various indicators, NIBS can improve DOC after brain injury, and the rTMS is the best. Limited by the number and the quality of literature, the above conclusions need more high-quality research to verify.

Effect of transcranial direct current stimulation for patients with disorders of consciousness: A systematic review and meta-analysis

Introduction

Transcranial direct current stimulation (tDCS) could potentially facilitate consciousness improvement in patients with disorders of consciousness (DOC). The aim of this study was to investigate the therapeutic efficacy of tDCS on consciousness recovery for patients with DOC.

Methods

Eight databases were systematically searched from their inception to June 2022. Quality of included studies were assessed using PEDro score and Cochrane's risk of bias assessment. All statistical analyses were performed using RevMan software. Seventeen studies with 618 patients were identified eligible for this study, and fifteen studies with sufficient data were pooled in the meta-analysis.

Results

The results of meta-analysis showed a significant effect on increasing GCS scores (MD = 1.73; 95% CI, 1.28-2.18; P < 0.01) and CRS-R scores (MD = 1.28; 95% CI = 0.56-2.00; P < 0.01) in favor of the real stimulation group as compared to sham. The results of subgroup analysis demonstrated that only more than 20 sessions of stimulation could significantly enhance the improvement of GCS scores and the CRS-R scores. Moreover, the effect of tDCS on CRS-R score improvement was predominant in patients with minimal conscious state (MCS) (MD = 1.84; 95% CI = 0.74-2.93; P < 0.01).

Conclusion

Anodal tDCS with sufficient stimulation doses appears to be an effective approach for patients with MCS, in terms of CRS-R scores.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022336958.

Effectiveness of transcranial direct current stimulation over dorsolateral prefrontal cortex in patients with prolonged disorders of consciousness: A systematic review and meta-analysis

Background

Transcranial direct current stimulation (tDCS) has been widely studied for treatment of patients with prolonged disorders of consciousness (PDOC). The dorsolateral prefrontal cortex (DLPFC) is a hot target for intervention, but some controversies remain.

Purpose

This review aimed to systematically investigate the therapeutic effects of DLPFC-anodal-tDCS for patients with PDOC through a meta-analysis approach.

Data sources

Searches for relevant articles available in English were conducted using EMBASE, Medline, Web of Science, EBSCO, and Cochrane Central Register of Controlled Trials from inception until March 26, 2022.

Study selection

All randomized parallel or cross-over controlled trials comparing the effect of intervention with active-tDCS and Sham-tDCS on Coma Recovery Scale Revised (CRS-R) score in individuals with PDOC were included.

Data extraction

Two authors independently extracted data, assessed the methodological quality, and rated each study.

Data synthesis

Ten randomized parallel or cross-over controlled trials were eligible for systematic review, and eight of the studies involving 165 individuals were identified as eligible for meta-analysis. Compared with Sham-tDCS, the use of anode-tDCS over DLPFC improved the CRS-R score (SMD = 0.71; 95% CI: 0.47–0.95, I² = 10%). Patients with PDOC classified as MCS and clinically diagnosed as CVA or TBI may benefit from anode-tDCS.

Limitations

Failure to evaluate the long-term effects and lack of quantitative analysis of neurological examination are the main limitations for the application of anode-tDCS.

Conclusions

Anodal-tDCS over the left DLPFC may be advantageous to the recovery of patients with MCS and clinically diagnosed with CVA or TBI. There is a lack of evidence to support the duration of the disease course will limit the performance of the treatment. Further studies are needed to explore the diversity of stimulation targets and help to improve the mesocircuit model.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=279391, identifier: CRD42022279391.

Brain Metabolic Connectivity Patterns in Patients with Prolonged Disorder of Consciousness after Hypoxic-Ischemic Injury: A Preliminary Study

Understanding the patterns of brain glucose metabolism and connectivity in hypoxic-ischemic encephalopathy (HIE) patients with prolonged disorders of consciousness (DOC) may be of positive significance to the accurate assessment of consciousness and the optimization of neuromodulation strategy. We retrospectively analyzed the brain glucose metabolism pattern and its correlation with clinical Coma Recovery Scale-Revised (CRS-R) score in six HIE patients with prolonged DOC who had undergone 18F-deoxyglucose brain positron emission tomography scanning (FDG-PET). We also compared the differences in global metabolic connectivity patterns and the characteristics of several brain networks between HIE patients and healthy controls (HC). The metabolism of multiple brain regions decreased significantly in HIE patients, and the degree of local metabolic preservation was correlated with CRS-R score. The internal metabolic connectivity of occipital lobe and limbic system in HIE patients decreased, and their metabolic connectivity with frontal lobe, parietal lobe and temporal lobe also decreased. The metabolic connectivity patterns of default mode network, dorsal attention network, salience network, executive control network and subcortex network of HIE also changed compared with HC. The present study suggested that pattern of cerebral glucose metabolism and network connectivity of HIE patients with prolonged DOC were significantly different from those of healthy people.