Sustained cortical and subcortical neuromodulation induced by electrical tongue stimulation

ALSUntangled #75: Portable neuromodulation stimulator therapy

Spurred by patient interest, ALSUntangled herein examines the potential of the Portable Neuromodulation Stimulator (PoNS™) in treating amyotrophic lateral sclerosis (ALS). The PoNS™ device, FDA-approved for the treatment of gait deficits in adult patients with multiple sclerosis, utilizes translingual neurostimulation to stimulate trigeminal and facial nerves via the tongue, aiming to induce neuroplastic changes. While there are early, promising data for PoNS treatment to improve gait and balance in multiple sclerosis, stroke, and traumatic brain injury, no pre-clinical or clinical studies have been performed in ALS. Although reasonably safe, high costs and prescription requirements will limit PoNS accessibility. At this time, due to the lack of ALS-relevant data, we cannot endorse the use of PoNS as an ALS treatment.

Central effects of trigeminal electrical stimulation

This is a review of the literature on the main neuromodulation techniques, focusing on the possibility of introducing sensory threshold ULFTENS into them. Electro neuromodulation techniques have been in use for many years as promising methods of therapy for cognitive and emotional disorders. One of the most widely used forms of stimulation for orofacial pain is transcutaneous trigeminal stimulation on three levels: supraorbital area, dorsal surface of the tongue, and anterior skin area of the tragus. The purpose of this review is to trigger interest on using dental ULFTENS as an additional trigeminal neurostimulation and neuromodulation technique in the context of TMD. In particular, we point out the possibility of using ULFTENS at a lower activation level than that required to trigger a muscle contraction that is capable of triggering effects at the level of the autonomic nervous system, with extreme ease of execution and few side effects.

Cognitive Functions following Trigeminal Neuromodulation

Vast scientific effort in recent years have been focused on the search for effective and safe treatments for cognitive decline. In this regard, non-invasive neuromodulation has gained increasing attention for its reported effectiveness in promoting the recovery of multiple cognitive domains after central nervous system damage. In this short review, we discuss the available evidence supporting a possible cognitive effect of trigeminal nerve stimulation (TNS). In particular, we ask that, while TNS has been widely and successfully used in the treatment of various neuropsychiatric conditions, as far as research in the cognitive field is concerned, where does TNS stand? The trigeminal nerve is the largest cranial nerve, conveying the sensory information from the face to the trigeminal sensory nuclei, and from there to the thalamus and up to the somatosensory cortex. On these bases, a bottom-up mechanism has been proposed, positing that TNS-induced modulation of the brainstem noradrenergic system may affect the function of the brain networks involved in cognition. Nevertheless, despite the promising theories, to date, the use of TNS for cognitive empowering and/or cognitive decline treatment has several challenges ahead of it, mainly due to little uniformity of the stimulation protocols. However, as the field continues to grow, standardization of practice will allow for data comparisons across studies, leading to optimized protocols targeting specific brain circuitries, which may, in turn, influence cognition in a designed manner.

Clinical characteristics of visual motion hypersensitivity: a systematic review

This qualitative systematic review presents an overview of the state of the research relating to visual motion hypersensitivity (VMH) and offers a reference tool for future studies in the field. The study set out to identify and collate articles investigating risk groups with aberrant responses to visual motion as compared to healthy control groups, presenting evidence for risk factors associated with visual motion hypersensitivity. Data were synthesized into the state of the research and analyzed in the context of the clinical characteristics of each risk factor. Literature searches were performed on Medline Ovid, EMBASE, Web of Science, and Cinahl, identifying a total of 586 studies of which 54 were finally included. Original articles published between the dates of commencement for each database and 19th January 2021 were included. JBI critical appraisal tools were implemented for each corresponding article type. In total, the following number of studies was identified for each respective risk factor: age (n = 6), migraines (n = 8), concussions (n = 8), vestibular disorders (n = 13), psychiatric conditions (n = 5), and Parkinson's disease (n = 5). Several studies described VMH as the primary concern (n = 6), though these primarily included patients with vestibulopathies. There were considerable differences in the nomenclature employed to describe VMH, depending largely on the investigating group. An overview of investigated risk factors and their evaluation methods was presented in a Sankey diagram. Posturography was the most implemented methodology but due to diverse measurements meta-analyses were not possible. One may however note that while the easily implemented Vestibular Ocular Motor Screening (VOMS) was designed for concussed patients, it may prove useful for other risk groups.

Real world evidence of improved attention and cognition during physical therapy paired with neuromodulation: a brain vital signs study

Background

Non-invasive neuromodulation using translingual neurostimulation (TLNS) has been shown to advance rehabilitation outcomes, particularly when paired with physical therapy (PT). Together with motor gains, patient-reported observations of incidental improvements in cognitive function have been noted. Both studies in healthy individuals and case reports in clinical populations have linked TLNS to improvements in attention-related cognitive processes. We investigated if the use of combined TLNS/PT would translate to changes in objective neurophysiological cognitive measures in a real-world clinical sample of patients from two separate rehabilitation clinics.

Methods

Brain vital signs were derived from event-related potentials (ERPs), specifically auditory sensation (N100), basic attention (P300), and cognitive processing (N400). Additional analyses explored the attention-related N200 response given prior evidence of attention effects from TLNS/PT. The real-world patient sample included a diverse clinical group spanning from mild-to-moderate traumatic brain injury (TBI), stroke, Multiple Sclerosis (MS), Parkinson's Disease (PD), and other neurological conditions. Patient data were also acquired from a standard clinical measure of cognition for comparison.

Results

Results showed significant N100 variation between baseline and endpoint following TLNS/PT treatment, with further examination showing condition-specific significant improvements in attention processing (i.e., N100 and N200). Additionally, CogBAT composite scores increased significantly from baseline to endpoint.

Discussion

The current study highlighted real-world neuromodulation improvements in neurophysiological correlates of attention. Overall, the real-world findings support the concept of neuromodulation-related improvements extending beyond physical therapy to include potential attention benefits for cognitive rehabilitation.

Association between characteristics of swallowing-related muscles and trunk muscle mass

Swallowing function is associated with systemic factors. Whether trunk or appendicular skeletal muscle mass is a better indicator of swallowing-related muscle characteristics in community-dwelling older adults is not clear. Hence, we investigated the association between the characteristics of swallowing-related muscles (e.g., mass and quality) and trunk muscle mass. Community-dwelling older adults aged ≥ 65 years (n = 141; men: n = 45, women: n = 96) were recruited for this cross-sectional observational study via a health survey conducted in 2018. Trunk muscle mass index (TMI) and appendicular skeletal muscle mass index (SMI) were measured using bioelectrical impedance analysis. Cross-sectional areas (CSAs) and echo intensity (EI) of the geniohyoid muscle (GHM) and tongue were evaluated using an ultrasonic diagnostic apparatus. Multiple regression analysis was used to examine the relationship of the characteristics of swallowing-related muscle with TMI and SMI. Multiple regression analysis showed that CSA of the GHM was positively associated with both TMI (B = 24.9, p < 0.001) and SMI (B = 13.7, p = 0.002). EIs of swallowing-related muscles were not associated with TMI and SMI. Trunk muscle mass was associated with swallowing-related muscle mass and not muscle quality. The results of this study shed light on the elucidation of association of dysphagia with TMI and SMI.

Translingual neurostimulation combined with physical therapy to improve walking and balance in multiple sclerosis (NeuroMSTraLS): Study protocol for a randomized controlled trial

INTRODUCTION

Physical rehabilitation restores lost function and promotes brain plasticity in people with Multiple Sclerosis (MS). Research groups worldwide are testing the therapeutic effects of combining non-invasive neuromodulation with physical therapy (PT) to further improve functional outcomes in neurological disorders but with mixed results. Whether such devices enhance function is not clear. We present the rationale and study design for a randomized controlled trial evaluating if there is additional benefit to the synergistic pairing of translingual neurostimulation (TLNS) with PT to improve walking and balance in MS.

METHODS AND ANALYSIS

A parallel group [PT + TLNS or PT + Sham], quadruple-blinded, randomized controlled trial. Participants (N = 52) with gait and balance deficits due to relapsing-remitting or progressive MS, who are between 18 and 70 years of age, will be recruited through patient registries in Newfoundland & Labrador and Saskatchewan, Canada. All participants will receive 14 weeks of PT while wearing either a TLNS or sham device. Dynamic Gait Index is the primary outcome. Secondary outcomes include fast walking speed, subjective ratings of fatigue, MS impact, and quality of life. Outcomes are assessed at baseline (Pre), after 14 weeks of therapy (Post), and 26 weeks (Follow Up). We employ multiple methods to ensure treatment fidelity including activity and device use monitoring. Primary and secondary outcomes will be analyzed using linear mixed-effect models. We will control for baseline score and site to test the effects of Time (Post vs. Follow-Up), Group and the Group x Time interaction as fixed effects. A random intercept of participant will account for the repeated measures in the Time variable. Participants must complete the Post testing to be included in the analysis.

ETHICS AND DISSEMINATION

The Human Research Ethics Boards in Newfoundland & Labrador (HREB#2021.085) & Saskatchewan (HREB Bio 2578) approved the protocol. Dissemination avenues include peer-reviewed journals, conferences and patient-oriented communications.

Trigeminal electrical stimulation with ULFTENS of the dorsal anterior mucosal surface of the tongue: Effects on Heart Rate Variability (HRV)

BACKGROUND

Trigeminal electrical stimulation of the dorsal anterior mucosal surface of the tongue has demonstrated its efficacy in a variety of neurological disorders in which anatomical or functional alterations are present. The pathogenesis of such disorders is often linked to altered arousal circuits, and the benefits of tongue stimulation are attributed to the rebalancing of this system. Dental ULFTENS shows efficacy in acting on the muscular, autonomic system and control of the descending pathways that modulate pain. It is administered at the skin level in the area anterior to the tragus and not on the mucosal surface of the tongue. The use of this stimulation technique at the tongue level could have new applications and clinical results if it were able to reduce the activity of arousal circuits.

MATERIAL AND METHOD

A new intraoral device allowed electrical stimulation of the dorsal anterior mucosa of the tongue in 32 healthy young women. The effects on HRV were monitored by photoplethysmographic wave (PPG) and compared with a control group. The HRV parameters studied were RMSSD, HF, LF, LF/HF, REC, DET.

RESULTS

The group of stimulated subjects showed a significant change in some of the HRV parameters that was maintained even in the epoch after the end of electrical stimulation. This effect can be considered as a vagal activation and a change of HRV trend. The control group of unstimulated subjects showed an opposite trend. There were no undesirable or annoying effects of stimulation.

CONCLUSION

Stimulation of the dorsal anterior (trigeminal) mucosal surface of the tongue with ULFTENS applied with an intraoral device was shown to be able to increase HRV.

Improvement in Gait and Participation in a Child with Angelman Syndrome after Translingual Neurostimulation Associated with Goal-Oriented Therapy: A Case Report

Angelman syndrome is a genetic neurobehavioral syndrome characterized by motor and cognitive developmental delay, with a severe reduction in activity and participation. Treatments are limited and the effects of rehabilitation have not been studied. We report on the progress made by a 7-year-old boy with Angelman syndrome following an innovative synergic intervention involving translingual neurostimulation (TLNS) and goal-oriented rehabilitation to improve gait. The parents were interviewed regarding the child’s abilities and participation level and three-dimensional gait analysis was performed before and after the 4-week intervention (five days per week, 4 h per day) and 6 months later. Spatiotemporal and kinematic gait variables improved considerably at 4 weeks, with a reduction in lower limb agonist-antagonist co-contractions, and a large increase in walking distance (from 500 m to 2 km). The child’s engagement and ability to perform activities of daily living improved, as well as several functions not targeted by the intervention. Six months after cessation of the intervention, improvements were partially sustained. The rapid and considerable improvement in motor ability was likely due to potentiation of the rehabilitation by the TLNS. Further studies are required to understand the mechanisms underlying this effect and to determine if it is generalizable to other children with similar disorders.

Retention Effects of Long-Term Balance Training with Vibrotactile Sensory Augmentation in Healthy Older Adults

Vibrotactile sensory augmentation (SA) decreases postural sway during real-time use; however, limited studies have investigated the long-term effects of training with SA. This study assessed the retention effects of long-term balance training with and without vibrotactile SA among community-dwelling healthy older adults, and explored brain-related changes due to training with SA. Sixteen participants were randomly assigned to the experimental group (EG) or control group (CG), and trained in their homes for eight weeks using smart-phone balance trainers. The EG received vibrotactile SA. Balance performance was assessed before, and one week, one month, and six months after training. Functional MRI (fMRI) was recorded before and one week after training for four participants who received vestibular stimulation. Both groups demonstrated significant improvement of SOT composite and MiniBESTest scores, and increased vestibular reliance. Only the EG maintained a minimal detectable change of 8 points in SOT scores six months post-training and greater improvements than the CG in MiniBESTest scores one month post-training. The fMRI results revealed a shift from activation in the vestibular cortex pre-training to increased activity in the brainstem and cerebellum post-training. These findings showed that additional balance improvements were maintained for up to six months post-training with vibrotactile SA for community-dwelling healthy older adults.

The role of electrical stimulation for rehabilitation and regeneration after spinal cord injury

Electrical stimulation is used to elicit muscle contraction and can be utilized for neurorehabilitation following spinal cord injury when paired with voluntary motor training. This technology is now an important therapeutic intervention that results in improvement in motor function in patients with spinal cord injuries. The purpose of this review is to summarize the various forms of electrical stimulation technology that exist and their applications. Furthermore, this paper addresses the potential future of the technology.

Translingual neural stimulation affects resting-state functional connectivity in mild-moderate traumatic brain injury

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) can lead to movement and balance deficits. In addition to physical therapy, brain-based neurorehabilitation efforts have begun to show promise in improving these deficits. The present study investigated the effectiveness of translingual neural stimulation (TLNS) on patients with mild-to-moderate TBI (mmTBI) and related brain connectivity using a resting-state functional connectivity (RSFC) approach.

METHODS

Resting-state images with 5-min on GE750 3T scanner were acquired from nine participants with mmTBI. Paired t-test was used for calculating changes in RSFC and behavioral scores before and after the TLNS intervention. The balance and movement performances related to mmTBI were evaluated by Sensory Organization Test (SOT) and Dynamic Gait Index (DGI).

RESULTS

Compared to pre-TLNS intervention, significant behavioral changes in SOT and DGI were observed. The analysis revealed increased RSFC between the left postcentral gyrus and left inferior parietal lobule and left Brodmann Area 40, as well as the increased RSFC between the right culmen and right declive, indicating changes due to TLNS treatment. However, there were no correlations between the sensory/somatomotor (or visual or cerebellar) network and SOT/DGI behavioral performance.

CONCLUSIONS

Although the limited sample size may have led to lack of significant correlations with functional assessments, these results provide preliminary evidence that TLNS in conjunction with physical therapy can induce brain plasticity in TBI patients with balance and movement deficits.

Non-Instrumental Test for the Evaluation of Tongue Function

The tongue undergoes various negative adaptations in the presence of local or systemic pathologies, adversely its behavior within the body context. Tongue assessments to correctly diagnose its functions are carried out using instrumentation, such as ultrasonography, magnetic resonance imaging, electromyography and different intraoral devices (swallowing, strength, posture, phonesis). Currently, there is no dynamic non-instrumental test in the scientific literature to highlight any lingual dysfunctions. The article describes a non-instrumental test for the assessment of lingual function in the body context, to obtain preliminary information on the quality of the neurological activities of the tongue, with respect to the balance and muscle strength that the patient expresses. The text briefly reviews the anatomy of the tongue and describes a clinical case to better understand how to use this test. Further studies will be needed for the validation of the test.

A Missing Voice: The Lingual Complex and Osteopathic Manual Medicine in the Context of Five Osteopathic Models

The five osteopathic models recognized by the American Association of Colleges of Osteopathic Medicine guide clinicians in the evaluation and therapeutic choice which must be the most appropriate concerning the patient's needs. Skeletal muscles represent an important interpretation, such as screening and treatment, on which these models are based. A muscle district that is not considered by the usual osteopathic practice is the tongue. The lingual complex has numerous functions, both local and systemic; it can adapt negatively in the presence of pathology, just as it can influence the body system in a non-physiological manner if it is a source of dysfunctions. This paper, the first of its kind in the panorama of scientific literature, briefly reviews the anatomy and neurophysiology of the tongue, trying to highlight the logic and the need to insert this muscle in the context of the five osteopathic models. The clinician's goal is to restore the patient's homeostasis, and we believe that this task is more concrete if the patient is approached after understanding all the contractile districts, including the tongue.

Portable neuromodulation induces neuroplasticity to re-activate motor function recovery from brain injury: a high-density MEG case study

BACKGROUND

In a recent high-profile case study, we used functional magnetic resonance imaging (fMRI) to monitor improvements in motor function related to neuroplasticity following rehabilitation for severe traumatic brain injury (TBI). The findings demonstrated that motor function improvements can occur years beyond current established limits. The current study extends the functional imaging investigation to characterize neuromodulation effects on neuroplasticity to further push the limits.

METHODS

Canadian Soldier Captain (retired) Trevor Greene (TG) survived a severe open-TBI when attacked with an axe during a 2006 combat tour in Afghanistan. TG has since continued intensive daily rehabilitation to recover motor function, experiencing an extended plateau using conventional physical therapy. To overcome this plateau, we paired translingual neurostimulation (TLNS) with the continuing rehabilitation program.

RESULTS

Combining TLNS with rehabilitation resulted in demonstrable clinical improvements along with corresponding changes in movement evoked electro-encephalography (EEG) activity. High-density magneto-encephalography (MEG) characterized cortical activation changes in corresponding beta frequency range (27 Hz). MEG activation changes corresponded with reduced interhemispheric inhibition in the post-central gyri regions together with increased right superior/middle frontal activation suggesting large scale network level changes.

CONCLUSIONS

The findings provide valuable insight into the potential importance of non-invasive neuromodulation to enhance neuroplasticity mechanisms for recovery beyond the perceived limits of rehabilitation.

Relationship between tongue pressure and back muscle strength in healthy elderly individuals

BACKGROUND

Aging is associated with a decrease in muscle mass and strength in swallowing muscles, as well as in whole-body muscles. A decrease in tongue pressure (TP) is related with whole-body function, and the trunk, including abdominal and back muscles, forms the core of the body. However, the direct relationship between TP and trunk muscle strength remains unclear.

AIMS

To clarify the association between back muscle strength, an indicator of trunk muscle strength, and TP in healthy elderly individuals.

METHODS

In all, 112 healthy community-dwelling individuals aged ≥ 60 years (men: 35, median age 74.0; women: 77, median age 69.0) were included. Body mass index (BMI), TP, and back muscle strength (BMS) were measured. Tooth loss pattern was evaluated by the Eichner classification. Participants were divided into two groups based on the median of the BMS and classified into three groups based on the Eichner index (Eichner A, B, and C). The effects of BMS and occlusal support on TP were analyzed.

RESULTS

In the low BMS group, there was a significant difference in TP between the Eichner B and Eichner C (p = 0.017) groups. However, in the high BMS group, occlusal support did not affect TP. Moreover, the explanatory factors for TP were BMS (β = 0.373, p = 0.001) and the Eichner index (β = 0.190, p = 0.036).

CONCLUSIONS

TP was correlated more with BMS than aging and occlusal support in healthy elderly individuals. This study indicated that the clinical evaluation of the whole body is important when assessing oral and swallowing function.

Brain Vital Signs Detect Information Processing Differences When Neuromodulation Is Used During Cognitive Skills Training

Background: Neuromodulation through translingual neurostimulation (TLNS) has been shown to initiate long-lasting processes of neuronal reorganization with a variety of outcomes (i.e., neuroplasticity). Non-invasive TLNS is increasingly accessible through the Portable Neuromodulation Stimulator (PoNS^®), a medical device that delivers electrical stimulation to the tongue to activate the trigeminal (V) and facial (VII) cranial nerves. Anecdotal reports from previous clinical studies have suggested incidental improvements in cognitive function. To objectively explore this observation, we examined TLNS-related effects on the semantic N400 brain vital sign cognitive response during cognitive skills training in healthy individuals. Methods: Thirty-seven healthy volunteers were randomized to receive simultaneous TLNS (treatment) or no TLNS (control) while undergoing cognitive skills training. Cognitive training was conducted for two 20-min sessions (morning and afternoon/evening) over 3 consecutive days. Brain vital signs were evaluated at baseline, Day 1, and Day 3. Analyses focused on cognitive processing as measured by N400 changes in amplitude and latency. Results: Over the 3-day course of cognitive training, the N400 amplitude decreased significantly in the control group due to habituation (p = 0.028). In contrast, there was no significant change in the TLNS treatment group. Conclusion: TLNS led to a sustained N400 response during cognitive skills training, as measured by the brain's vital signs framework. The study findings suggest differential learning effects due to neuromodulation, consistent with increased attention and cognitive vigilance.

Brain Vital Signs Detect Cognitive Improvements During Combined Physical Therapy and Neuromodulation in Rehabilitation From Severe Traumatic Brain Injury: A Case Report

Using a longitudinal case study design, we have tracked the recovery of motor function following severe traumatic brain injury (TBI) through a multimodal neuroimaging approach. In 2006, Canadian Soldier Captain (retired) Trevor Greene (TG) was attacked with an axe to the head while on tour in Afghanistan. TG continues intensive daily rehabilitation, which recently included the integration of physical therapy (PT) with neuromodulation using translingual neurostimulation (TLNS) to facilitate neuroplasticity. Recent findings with PT + TLNS demonstrated that recovery of motor function occurred beyond conventional time limits, currently extending past 14-years post-injury. To investigate whether PT + TLNS similarly resulted in associated cognitive function improvements, we examined event-related potentials (ERPs) with the brain vital signs framework. In parallel with motor function improvements, brain vital signs detected significant increases in basic attention (as measured by P300 response amplitude) and cognitive processing (as measured by contextual N400 response amplitude). These objective cognitive improvements corresponded with TG's self-reported improvements, including a noteworthy and consistent reduction in ongoing symptoms of post-traumatic stress disorder (PTSD). The findings provide valuable insight into the potential importance of non-invasive neuromodulation in cognitive rehabilitation, in addition to initial indications for physical rehabilitation.

A Review of the Evidence and Current Applications of Portable Translingual Neurostimulation Technology

OBJECTIVES

Translingual neurostimulation (TLNS) with adjunct physical rehabilitation is used to treat balance and gait deficits in several chronic neurological conditions. The purpose of this review is to summarize and appraise the evidence currently available on the portable TLNS device and to assess its potential clinical application.

MATERIALS AND METHODS

In this narrative review, MEDLINE, EMBASE, Web of Science, and Google Scholar were searched for primary research investigating the use of portable TLNS devices on any neurologic condition. Data were extracted, reviewed, and appraised with respect to study design, conduct, and reporting.

RESULTS

Five randomized controlled trials (RCTs), three quasi-experimental trials, and seven case reports/series were found. Most studies demonstrated improvements in balance and gait deficits secondary to traumatic brain injury and multiple sclerosis, but evidence is also present to a lesser degree for stroke and balance disorder patients. In these studies, the feasibility and safety of TLNS have been convincingly demonstrated. Functional magnetic resonance studies have also suggested a plausible neuroplastic therapeutic mechanism. However, the efficacy of TLNS remains unclear due to bias and confounding within studies, and heterogeneity of results between studies.

CONCLUSIONS

TLNS is a promising treatment modality for various chronic neurological conditions that are often refractory to conventional therapy. However, TLNS technology remains largely investigational as high-quality RCTs are still required to elucidate efficacy, optimal dosages, necessary treatment durations, and treatment durability. Further research to develop an appropriate control group is needed for scientifically valid comparisons of TLNS.

Electrical stimulation of cranial nerves in cognition and disease

The cranial nerves are the pathways through which environmental information (sensation) is directly communicated to the brain, leading to perception, and giving rise to higher cognition. Because cranial nerves determine and modulate brain function, invasive and non-invasive cranial nerve electrical stimulation methods have applications in the clinical, behavioral, and cognitive domains. Among other neuromodulation approaches such as peripheral, transcranial and deep brain stimulation, cranial nerve stimulation is unique in allowing axon pathway-specific engagement of brain circuits, including thalamo-cortical networks. In this review we amalgamate relevant knowledge of 1) cranial nerve anatomy and biophysics; 2) evidence of the modulatory effects of cranial nerves on cognition; 3) clinical and behavioral outcomes of cranial nerve stimulation; and 4) biomarkers of nerve target engagement including physiology, electroencephalography, neuroimaging, and behavioral metrics. Existing non-invasive stimulation methods cannot feasibly activate the axons of only individual cranial nerves. Even with invasive stimulation methods, selective targeting of one nerve fiber type requires nuance since each nerve is composed of functionally distinct axon-types that differentially branch and can anastomose onto other nerves. None-the-less, precisely controlling stimulation parameters can aid in affecting distinct sets of axons, thus supporting specific actions on cognition and behavior. To this end, a rubric for reproducible dose-response stimulation parameters is defined here. Given that afferent cranial nerve axons project directly to the brain, targeting structures (e.g. thalamus, cortex) that are critical nodes in higher order brain networks, potent effects on cognition are plausible. We propose an intervention design framework based on driving cranial nerve pathways in targeted brain circuits, which are in turn linked to specific higher cognitive processes. State-of-the-art current flow models that are used to explain and design cranial-nerve-activating stimulation technology require multi-scale detail that includes: gross anatomy; skull foramina and superficial tissue layers; and precise nerve morphology. Detailed simulations also predict that some non-invasive electrical or magnetic stimulation approaches that do not intend to modulate cranial nerves per se, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), may also modulate activity of specific cranial nerves. Much prior cranial nerve stimulation work was conceptually limited to the production of sensory perception, with individual titration of intensity based on the level of perception and tolerability. However, disregarding sensory emulation allows consideration of temporal stimulation patterns (axon recruitment) that modulate the tone of cortical networks independent of sensory cortices, without necessarily titrating perception. For example, leveraging the role of the thalamus as a gatekeeper for information to the cerebral cortex, preventing or enhancing the passage of specific information depending on the behavioral state. We show that properly parameterized computational models at multiple scales are needed to rationally optimize neuromodulation that target sets of cranial nerves, determining which and how specific brain circuitries are modulated, which can in turn influence cognition in a designed manner.

A Prospective, Multicenter Study to Assess the Safety and Efficacy of Translingual Neurostimulation Plus Physical Therapy for the Treatment of a Chronic Balance Deficit Due to Mild‐to‐Moderate Traumatic Brain Injury

Objectives

Materials and Methods

Results

Conclusions

Sensory Neuromodulation

We describe a model of neurological disease based on dysfunctional brain oscillators. This is not a new model, but it is not one that is widely appreciated by clinicians. The value of this model lies in the predictions it makes and the utility it provides in translational applications, in particular for neuromodulation devices. Specifically, we provide a perspective on devices that provide input to sensory receptors and thus stimulate endogenous sensory networks. Current forms of clinically applied neuromodulation, including devices such as (implanted) deep brain stimulators (DBS) and various, noninvasive methods such as transcranial magnetic stimulation (TMS) and transcranial current methods (tACS, tDCS), have been studied extensively. The potential strength of neuromodulation of a sensory organ is access to the same pathways that natural environmental stimuli use and, importantly, the modulatory signal will be transformed as it travels through the brain, allowing the modulation input to be consistent with regional neuronal dynamics. We present specific examples of devices that rely on sensory neuromodulation and evaluate the translational potential of these approaches. We argue that sensory neuromodulation is well suited to, ideally, repair dysfunctional brain oscillators, thus providing a broad therapeutic approach for neurological diseases.

Human translingual neurostimulation alters resting brain activity in high-density EEG

BACKGROUND

Despite growing evidence of a critical link between neuromodulation technologies and neuroplastic recovery, the underlying mechanisms of these technologies remain elusive.

OBJECTIVE

To investigate physiological evidence of central nervous system (CNS) changes in humans during translingual neurostimulation (TLNS).

METHODS

We used high-density electroencephalography (EEG) to measure changes in resting brain activity before, during, and after high frequency (HF) and low frequency (LF) TLNS.

RESULTS

Wavelet power analysis around Cz and microstate analysis revealed significant changes after 20 min of stimulation compared to baseline. A secondary effect of exposure order was also identified, indicating a differential neuromodulatory influence of HF TLNS relative to LF TLNS on alpha and theta signal power.

CONCLUSIONS

These results further our understanding of the effects of TLNS on underlying resting brain activity, which in the long-term may contribute to the critical link between clinical effect and changes in brain activity.

The Anatomical Relationships of the Tongue with the Body System

The tongue plays a fundamental role in several body functions such as swallowing, breathing, speaking, and chewing. Its action is not confined to the oral cavity, but it affects lower limb muscle strength and posture. The tongue is an organ that has an autocrine/paracrine mechanism of action to synthesize different substances to interact with the whole body; according to a line of thought, it is also an extension of the enteric system. The aim of this study was to review the functions of the tongue and its anatomical association with the body system. According to the authors' knowledge, this is the first scientific article focusing on the tongue in a systemic context. In a clinical evaluation, connections with the tongue should be considered to optimize the clinical examination of the tongue and therefore enhance rehabilitation programs and therapeutic results.

Potential Mechanisms of Sensory Augmentation Systems on Human Balance Control

Numerous studies have demonstrated the real-time use of visual, vibrotactile, auditory, and multimodal sensory augmentation technologies for reducing postural sway during static tasks and improving balance during dynamic tasks. The mechanism by which sensory augmentation information is processed and used by the CNS is not well understood. The dominant hypothesis, which has not been supported by rigorous experimental evidence, posits that observed reductions in postural sway are due to sensory reweighting: feedback of body motion provides the CNS with a correlate to the inputs from its intact sensory channels (e.g., vision, proprioception), so individuals receiving sensory augmentation learn to increasingly depend on these intact systems. Other possible mechanisms for observed postural sway reductions include: cognition (processing of sensory augmentation information is solely cognitive with no selective adjustment of sensory weights by the CNS), “sixth” sense (CNS interprets sensory augmentation information as a new and distinct sensory channel), context-specific adaptation (new sensorimotor program is developed through repeated interaction with the device and accessible only when the device is used), and combined volitional and non-volitional responses. This critical review summarizes the reported sensory augmentation findings spanning postural control models, clinical rehabilitation, laboratory-based real-time usage, and neuroimaging to critically evaluate each of the aforementioned mechanistic theories. Cognition and sensory re-weighting are identified as two mechanisms supported by the existing literature.

The role of sensory augmentation for people with vestibular deficits: Real-time balance aid and/or rehabilitation device?

This narrative review highlights findings from the sensory augmentation field for people with vestibular deficits and addresses the outstanding questions that are critical to the translation of this technology into clinical and/or personal use. Prior research has demonstrated that the real-time use of visual, vibrotactile, auditory, and multimodal sensory augmentation technologies can improve balance during static and dynamic stance tasks within a laboratory setting. However, its application in improving gait requires additional investigation, as does its efficacy as a rehabilitation device for people with vestibular deficits. In some locomotor studies involving sensory augmentation, gait velocity decreased and secondary task performance worsened, and subjects negatively altered their segmental control strategies when cues were provided following short training sessions. A further question is whether the retention and/or carry-over effects of training with a sensory augmentation technology exceed the retention and/or carry-over effects of training alone, thereby supporting its use as a rehabilitation device. Preliminary results suggest that there are short-term improvements in balance performance following a small number of training sessions with a sensory augmentation device. Long-term clinical and home-based controlled training studies are needed. It is hypothesized that sensory augmentation provides people with vestibular deficits with additional sensory input to promote central compensation during a specific exercise/activity; however, research is needed to substantiate this theory. Major obstacles standing in the way of its use for these critical applications include determining exercise/activity specific feedback parameters and dosage strategies. This paper summarizes the reported findings that support sensory augmentation as a balance aid and rehabilitation device, but does not critically examine efficacy or the quality of the research methods used in the reviewed studies.

Noninvasive tongue stimulation combined with intensive cognitive and physical rehabilitation induces neuroplastic changes in patients with multiple sclerosis: A multimodal neuroimaging study

BACKGROUND

Multiple sclerosis (MS) patients have central nervous system (CNS) lesions that may impede cognitive and sensorimotor function. Few rehabilitative therapies are available.

OBJECTIVES

The objective of this paper is to study effects of noninvasive tongue stimulation using the Portable Neuromodulation Stimulator (PoNS™) combined with intensive cognitive and physical rehabilitation on working memory, gait, balance and concomitant changes in the brain.

METHODS

Fourteen MS patients, seven each in an active and a sham stimulation group, participated. Participants received intensive physical therapy and working memory training for 14 weeks. Functional magnetic resonance imaging (fMRI) using motor imagery and working-memory tasks were completed prior to and following therapy, as were sensory organization tests (SOT), motor performance measures, and neuropsychological assessment.

RESULTS

On the SOT, the active group showed significant improvement from baseline. fMRI revealed significant blood oxygen level-dependent signal changes in the left primary motor cortex for the Active Group, while the sham group had increased activity in bilateral premotor cortices. All individuals improved on working-memory tasks, but only the active group showed increased dorsolateral prefrontal cortex activity.

CONCLUSIONS

In this cohort of MS patients, the results suggest that PoNS stimulation can enhance motor performance and working memory while also driving neuroplasticity. Further studies are warranted to explore these findings.

Case report: post-stroke interventional BCI rehabilitation in an individual with preexisting sensorineural disability

Therapies involving new technologies such as brain-computer interfaces (BCI) are being studied to determine their potential for interventional rehabilitation after acute events such as stroke produce lasting impairments. While studies have examined the use of BCI devices by individuals with disabilities, many such devices are intended to address a specific limitation and have been studied when this limitation or disability is present in isolation. Little is known about the therapeutic potential of these devices for individuals with multiple disabilities with an acquired impairment overlaid on a secondary long-standing disability. We describe a case in which a male patient with congenital deafness suffered a right pontine ischemic stroke, resulting in persistent weakness of his left hand and arm. This patient volunteer completed four baseline assessments beginning at 4 months after stroke onset and subsequently underwent 6 weeks of interventional rehabilitation therapy using a closed-loop neurofeedback BCI device with visual, functional electrical stimulation, and tongue stimulation feedback modalities. Additional assessments were conducted at the midpoint of therapy, upon completion of therapy, and 1 month after completing all BCI therapy. Anatomical and functional MRI scans were obtained at each assessment, along with behavioral measures including the Stroke Impact Scale (SIS) and the Action Research Arm Test (ARAT). Clinically significant improvements in behavioral measures were noted over the course of BCI therapy, with more than 10 point gains in both the ARAT scores and scores for the SIS hand function domain. Neuroimaging during finger tapping of the impaired hand also showed changes in brain activation patterns associated with BCI therapy. This case study demonstrates the potential for individuals who have preexisting disability or possible atypical brain organization to learn to use a BCI system that may confer some rehabilitative benefit.

Feasibility of sensory tongue stimulation combined with task-specific therapy in people with spinal cord injury: a case study

Background

Previous evidence suggests the effects of task-specific therapy can be further enhanced when sensory stimulation is combined with motor practice. Sensory tongue stimulation is thought to facilitate activation of regions in the brain that are important for balance and gait. Improvements in balance and gait have significant implications for functional mobility for people with incomplete spinal cord injury (iSCI). The aim of this case study was to evaluate the feasibility of a lab- and home-based program combining sensory tongue stimulation with balance and gait training on functional outcomes in people with iSCI.

Methods

Two male participants (S1 and S2) with chronic motor iSCI completed 12 weeks of balance and gait training (3 lab and 2 home based sessions per week) combined with sensory tongue stimulation using the Portable Neuromodulation Stimulator (PoNS). Laboratory based training involved 20 minutes of standing balance with eyes closed and 30 minutes of body-weight support treadmill walking. Home based sessions consisted of balancing with eyes open and walking with parallel bars or a walker for up to 20 minutes each. Subjects continued daily at-home training for an additional 12 weeks as follow-up.

Results

Both subjects were able to complete a minimum of 83% of the training sessions. Standing balance with eyes closed increased from 0.2 to 4.0 minutes and 0.0 to 0.2 minutes for S1 and S2, respectively. Balance confidence also improved at follow-up after the home-based program. Over ground walking speed improved by 0.14 m/s for S1 and 0.07 m/s for S2, and skilled walking function improved by 60% and 21% for S1 and S2, respectively.

Conclusions

Sensory tongue stimulation combined with task-specific training may be a feasible method for improving balance and gait in people with iSCI. Our findings warrant further controlled studies to determine the added benefits of sensory tongue stimulation to rehabilitation training.

Systematic review and meta-analysis of noninvasive cranial nerve neuromodulation for nervous system disorders

OBJECTIVE

To systematically review the medical literature and comprehensively summarize clinical research done on rehabilitation with a novel portable and noninvasive electrical stimulation device called the cranial nerve noninvasive neuromodulator in patients suffering from nervous system disorders.

DATA SOURCES

PubMed, MEDLINE, and Cochrane Database of Systematic Reviews from 1966 to March 2013.

STUDY SELECTION

Studies were included if they recruited adult patients with peripheral and central nervous system disorders, were treated with the cranial nerve noninvasive neuromodulator device, and were assessed with objective measures of function.

DATA EXTRACTION

After title and abstract screening of potential articles, full texts were independently reviewed to identify articles that met inclusion criteria.

DATA SYNTHESIS

The search identified 12 publications: 5 were critically reviewed, and of these 5, 2 were combined in a meta-analysis. There were no randomized controlled studies identified, and the meta-analysis was based on pre-post studies. Most of the patients were individuals with a chronic balance dysfunction. The pooled results demonstrated significant improvements in the dynamic gait index postintervention with a mean difference of 3.45 (95% confidence interval, 1.75-5.15; P<.001), Activities-specific Balance Confidence scale with a mean difference of 16.65 (95% confidence interval, 7.65-25.47; P<.001), and Dizziness Handicap Inventory with improvements of -26.07 (95% confidence interval, -35.78 to -16.35; P<.001). Included studies suffered from small sample sizes, lack of randomization, absence of blinding, use of referral populations, and variability in treatment schedules and follow-up rates.

CONCLUSIONS

Given these limitations, the results of the meta-analysis must be interpreted cautiously. Further investigation using rigorous randomized controlled trials is needed to evaluate this promising rehabilitation tool for nervous system disorders.

Non-invasive neuromodulation to improve gait in chronic multiple sclerosis: a randomized double blind controlled pilot trial

BACKGROUND

This study sought to examine the effect of targeted physical therapy with and without cranial nerve non-invasive neuromodulation (CN-NINM), on the walking ability of people with MS who exhibited a dysfunctional gait. We hypothesized that subjects who received electrical stimulation would have greater improvement than those who had a control device after a 14-week intervention. Gait disturbance is a common problem for people with multiple sclerosis (MS). Current management may include exercise, pharmacology, functional electrical stimulation, compensatory strategies, use of assistive devices, and implanted electrical devices. We have developed an effective rehabilitative strategy using neuromodulation of the cranial nerves via electrical stimulation of the tongue to enhance the plasticity of the brain.

METHODS

The study is a within-subject blinded randomized control design. Twenty chronic MS subjects with an identified gait disturbance were assigned to either an active or control group. Both groups completed a 14-week intervention program using a standardized combination of exercise and a device that provided electrical stimulation to the tongue. Those in the active group received electrical stimulation on the tongue that they could perceive. Those in the control group used a device that did not provide a physiologically significant stimulus and was not perceivable. Subjects were assessed with the Dynamic Gait Index (DGI).

RESULTS

The DGI scores improved for both groups. There were significant between-group differences, with the active group showing statistically greater improvement than the control group mean.

CONCLUSION

People with MS demonstrated improved gait with CN-NINM training in a pilot randomized controlled trial. This study suggests that tongue-based neurostimulation may amplify the benefits of exercise for improving gait in people with chronic MS.

Improving the motor skill of children with posterior fossa syndrome: a case series

Children who receive treatment for medulloblastoma have a high survival rate, but also a high likelihood of developing posterior fossa syndrome, a condition that includes devastating balance and motor problems. This case series used 2 novel neuromodulation devices in conjunction with an intensive physical therapy intervention for 2 children who were 5 years post tumor treatment with a diagnosis of posterior fossa syndrome. Pre- and postclinical measures, in addition to magnetoencephalography brain imaging, describe positive behavioral and neuroplastic changes resulting from the intervention. The positive outcomes in these cases suggest that further study is needed using neuromodulatory devices and long-term rehabilitation in children with balance and movement disorders resulting from cancer treatment.

Short-term retention effect of rehabilitation using head position-based electrotactile feedback to the tongue: influence of vestibular loss and old-age

Our objective was to evaluate whether the severity of vestibular loss and old-age (>65) affect a patient's ability to benefit from training using head-position based, tongue-placed electrotactile feedback. Seventy-one chronic dizzy patients, who had reached a plateau with their conventional rehabilitation, followed six 1-h training sessions during 4 consecutive days (once on days 1 and 4, twice on days 2 and 3). They presented bilateral vestibular areflexia (BVA), bilateral vestibular losses (BVL), unilateral vestibular areflexia or unilateral vestibular losses and were divided into two age-subgroups (≤65 and >65). Posturographic assessments were performed without the device, 4h before and after the training. Patients were tested with eyes opened and eyes closed (EC) on static and dynamic (passively tilting) platforms. The studied posturographic scores improved significantly, especially under test conditions restricting either visual or somatosensory input. This 4-h retention effect was greater in older compared to younger patients and was proportional to the degree of vestibular loss, patients with increased vestibular losses showing greater improvements. In bilateral patients, who constantly fell under dynamic-EC condition at the baseline, the therapy effect was expressed by disappearance of falls in BVL and significant prolongation in time-to-fall in BVA subgroups. Globally, our data showed that short training with head-position based, tongue-placed electrotactile biofeedback improves balance in chronic vestibulopathic patients some 16.74% beyond that achieved with standard balance physiotherapy. Further studies with longer use of this biofeedback are needed to investigate whether this approach could have long-lasting retention effect on balance and quality of life.

Altered connectivity of the balance processing network after tongue stimulation in balance-impaired individuals

Some individuals with balance impairment have hypersensitivity of the motion-sensitive visual cortices (hMT+) compared to healthy controls. Previous work showed that electrical tongue stimulation can reduce the exaggerated postural sway induced by optic flow in this subject population and decrease the hypersensitive response of hMT+. Additionally, a region within the brainstem (BS), likely containing the vestibular and trigeminal nuclei, showed increased optic flow-induced activity after tongue stimulation. The aim of this study was to understand how the modulation induced by tongue stimulation affects the balance-processing network as a whole and how modulation of BS structures can influence cortical activity. Four volumes of interest, discovered in a general linear model analysis, constitute major contributors to the balance-processing network. These regions were entered into a dynamic causal modeling analysis to map the network and measure any connection or topology changes due to the stimulation. Balance-impaired individuals had downregulated response of the primary visual cortex (V1) to visual stimuli but upregulated modulation of the connection between V1 and hMT+ by visual motion compared to healthy controls (p ≤ 1E-5). This upregulation was decreased to near-normal levels after stimulation. Additionally, the region within the BS showed increased response to visual motion after stimulation compared to both prestimulation and controls. Stimulation to the tongue enters the central nervous system at the BS but likely propagates to the cortex through supramodal information transfer. We present a model to explain these brain responses that utilizes an anatomically present, but functionally dormant pathway of information flow within the processing network.

The tongue display unit (TDU) for electrotactile spatiotemporal pattern presentation

The Tongue Display Unit (TDU) is a 144-channel programmable pulse generator that delivers dc-balanced voltage pulses suitable for electrotactile (electrocutaneous) stimulation of the anterior-dorsal tongue, through a matrix of surface electrodes. This article reviews the theory of operation and a design overview of the TDU, as well as selected applications. These include sensory substitution, tactile information display and neurorehabilitation via induced neuroplasticity.

Tongue-based biofeedback for balance in stroke: results of an 8-week pilot study

OBJECTIVE

To assess balance recovery and quality of life after tongue-placed electrotactile biofeedback training in patients with stroke.

DESIGN

Prospective multicenter research design.

SETTING

Outpatient rehabilitation clinics.

PARTICIPANTS

Patients (N=29) with chronic stroke.

INTERVENTIONS

Patients were administered 1 week of therapy plus 7 weeks of home exercise using a novel tongue based biofeedback balance device.

MAIN OUTCOME MEASURES

The Berg Balance Scale (BBS), Timed Up and Go (TUG), Activities-Specific Balance Confidence (ABC) Scale, Dynamic Gait Index (DGI), and Stroke Impact Scale (SIS) were performed before and after the intervention on all subjects.

RESULTS

There were statistically and clinically significant improvements from baseline to posttest in results for the BBS, DGI, TUG, ABC Scale, and some SIS domains (Mobility, Activities of Daily Living/Instrumental Activities of Daily Living, Social, Physical, Recovery domains). Average BBS score increased from 35.9 to 41.6 (P<.001), and DGI score, from 11.1 to 13.7 (P<.001). Time to complete the TUG decreased from 24.7 to 20.7 seconds (P=.002). Including the BBS, DGI, TUG, and ABC Scale, 27 subjects improved beyond the minimal detectable change with 95% certainty (MDC-95) or minimal clinically important difference (MCID) in at least 1 outcome and 3 subjects improved beyond the MDC-95 or MCID in all outcomes.

CONCLUSIONS

Electrotactile biofeedback seems to be a promising integrative method to balance training. A future randomized controlled study is needed.

Electrical tongue stimulation normalizes activity within the motion-sensitive brain network in balance-impaired subjects as revealed by group independent component analysis

Multivariate analysis of functional magnetic resonance imaging (fMRI) data allows investigations into network behavior beyond simple activations of individual regions. We apply group independent component analysis to fMRI data collected in a previous study looking at the sustained neuromodulatory effects of electrical tongue stimulation in balance-impaired individuals. Twelve subjects with balance disorders viewed optic flow in an fMRI scanner before and after 5 days of electrical tongue stimulation. Nine healthy controls also viewed the visual stimuli but did not receive any stimulation. Multiple regression of the 47 estimated components found two that were modulated by the visual stimuli. Component 7, comprised primarily of the primary visual cortex (V1), responded to all visual stimuli and showed no difference in task-related activity between the healthy controls and the balance-impaired subjects before or after stimulation. Component 11 responded only to motion in the visual field and contained multiple cortical and subcortical regions involved in processing information pertinent to balance. Two-sample t-tests of the calculated signal change revealed that the task-related activity of this network is greater in balance-impaired subjects compared with controls before stimulation (p=0.02), but that this network hypersensitivity decreases after electrical tongue stimulation (p=0.001).

High-resolution fMRI detects neuromodulation of individual brainstem nuclei by electrical tongue stimulation in balance-impaired individuals

High-resolution functional magnetic resonance imaging (fMRI) can be used to precisely identify blood oxygen level dependent (BOLD) activation of small structures within the brainstem not accessible with standard fMRI. A previous study identified a region within the pons exhibiting sustained neuromodulation due to electrical tongue stimulation, but was unable to precisely identify the neuronal structure involved. For this study, high-resolution images of neural activity induced by optic flow were acquired in nine healthy controls and nine individuals with balance dysfunction before and after information-free tongue stimulation. Subjects viewed optic flow videos to activate the structures of interest. Sub-millimeter in-plane voxels of structures within the posterior fossa were acquired using a restricted field of view. Whole-brain functional imaging verified that global activation patterns due to optic flow were consistent with previous studies. Optic flow activated the visual association cortices, the vestibular nuclei, and the superior colliculus, as well as multiple regions within the cerebellum. The anterior cingulate cortex showed decreased activity after stimulation, while a region within the pons had increased post-stimulation activity. These observations suggest the pontine region is the trigeminal nucleus and that tongue stimulation interfaces with the balance-processing network within the pons. This high-resolution imaging allows detection of activity within individual brainstem nuclei not possible using standard resolution imaging.