Non-Invasive Neuromodulation Using Time-Varying Caloric Vestibular Stimulation

Cognition in vestibular disorders: state of the field, challenges, and priorities for the future

Vestibular disorders are prevalent and debilitating conditions of the inner ear and brain which affect balance, coordination, and the integration of multisensory inputs. A growing body of research has linked vestibular disorders to cognitive problems, most notably attention, visuospatial perception, spatial memory, and executive function. However, the mechanistic bases of these cognitive sequelae remain poorly defined, and there is a gap between our theoretical understanding of vestibular cognitive dysfunction, and how best to identify and manage this within clinical practice. This article takes stock of these shortcomings and provides recommendations and priorities for healthcare professionals who assess and treat vestibular disorders, and for researchers developing cognitive models and rehabilitation interventions. We highlight the importance of multidisciplinary collaboration for developing and evaluating clinically relevant theoretical models of vestibular cognition, to advance research and treatment.

Time-varying caloric vestibular stimulation for the treatment of neurodegenerative disease

Time-varying caloric vestibular stimulation (tvCVS) is a new form of non-invasive neuromodulation similar to, but different from, diagnostic caloric vestibular stimulation (CVS). Using a non-invasive, solid-state delivery device, tvCVS has been successfully used in a human clinical trial with Parkinson’s disease (PD) subjects. Additionally, the effects of tvCVS on brain activation have been studied in healthy human subjects using transcranial Doppler sonography (TCD) and functional magnetic resonance imaging (BOLD fMRI). A novel finding in the TCD and fMRI studies was the induction of cerebral blood flow velocity (CBFv) oscillations. How such oscillations might lead to the observed clinical effects seen in PD subjects will be discussed. Enabling studies of tvCVS with rodents is an attractive goal in support of explorations of the mechanism of action. Male Wistar rats were used in a proof-of-concept study described herein. Rats were anesthetized (isoflurane) and ventilated for the duration of the tvCVS runs. Time-varying thermal stimuli were administered using a digital temperature controller to modulate Peltier-type heater/cooler devices. Blunt ear bars conveyed the thermal stimulus to the external ear canals of the rats. Different thermal waveform combinations were evaluated for evidence of successful induction of the CVS effect. It was found that bilateral triangular thermal waveforms could induce oscillations in CBFv both during and after the application of tvCVS. These oscillations were similar to, but different from those observed in awake human subjects. The establishment of a viable animal model for the study of tvCVS will augment ongoing clinical investigations of this new form of neuromodulation in patients with neurodegenerative disease.

Vestibular Sensory Conflict During Postural Control, Freezing of Gait, and Falls in Parkinson's Disease

BACKGROUND

The vestibular system has been implicated in the pathophysiology of episodic motor impairments in Parkinson's disease (PD), but specific evidence remains lacking.

OBJECTIVE

We investigated the relationship between the presence of freezing of gait and falls and postural failure during the performance on Romberg test condition 4 in patients with PD.

METHODS

Modified Romberg sensory conflict test, fall, and freezing-of-gait assessments were performed in 92 patients with PD (70 males/22 females; mean age, 67.6 ± 7.4 years; Hoehn and Yahr stage, 2.4 ± 0.6; mean Montreal Cognitive Assessment, 26.4 ± 2.8).

RESULTS

Failure during Romberg condition 4 was present in 33 patients (35.9%). Patients who failed the Romberg condition 4 were older and had more severe motor and cognitive impairments than those without. About 84.6% of all patients with freezing of gait had failure during Romberg condition 4, whereas 13.4% of patients with freezing of gait had normal performance (χ²  = 15.6; P < 0.0001). Multiple logistic regression analysis showed that the regressor effect of Romberg condition 4 test failure for the presence of freezing of gait (Wald χ²  = 5.0; P = 0.026) remained significant after accounting for the degree of severity of parkinsonian motor ratings (Wald χ²  = 6.2; P = 0.013), age (Wald χ²  = 0.3; P = 0.59), and cognition (Wald χ²  = 0.3; P = 0.75; total model: Wald χ²  = 16.1; P < 0.0001). Patients with PD who failed the Romberg condition 4 (45.5%) did not have a statistically significant difference in frequency of patients with falls compared with patients with PD without abnormal performance (30.5%; χ²  = 2.1; P = 0.15).

CONCLUSIONS

The presence of deficient vestibular processing may have specific pathophysiological relevance for freezing of gait, but not falls, in PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cholinergic brain network deficits associated with vestibular sensory conflict deficits in Parkinson's disease: correlation with postural and gait deficits

To examine regional cerebral vesicular acetylcholine transporter (VAChT) ligand [¹⁸F]fluoroethoxybenzovesamicol ([¹⁸F]-FEOBV) PET binding in Parkinson' disease (PD) patients with and without vestibular sensory conflict deficits (VSCD). To examine associations between VSCD-associated cholinergic brain deficits and postural instability and gait difficulties (PIGD). PD persons (M70/F22; mean age 67.6 ± 7.4 years) completed clinical assessments for imbalance, falls, freezing of gait (FoG), modified Romberg sensory conflict testing, and underwent VAChT PET. Volumes of interest (VOI)-based analyses included detailed thalamic and cerebellar parcellations. VSCD-associated VAChT VOI selection used stepwise logistic regression analysis. Vesicular monoamine transporter type 2 (VMAT2) [¹¹C]dihydrotetrabenazine (DTBZ) PET imaging was available in 54 patients. Analyses of covariance were performed to compare VSCD-associated cholinergic deficits between patients with and without PIGD motor features while accounting for confounders. PET sampling passed acceptance criteria in 73 patients. This data-driven analysis identified cholinergic deficits in five brain VOIs associating with the presence of VSCD: medial geniculate nucleus (MGN) (P < 0.0001), para-hippocampal gyrus (P = 0.0043), inferior nucleus of the pulvinar (P = 0.047), fusiform gyrus (P = 0.035) and the amygdala (P = 0.019). Composite VSCD-associated [¹⁸F]FEOBV-binding deficits in these 5 regions were significantly lower in patients with imbalance (- 8.3%, F = 6.5, P = 0.015; total model: F = 5.1, P = 0.0008), falls (- 6.9%, F = 4.9, P = 0.03; total model F = 4.7, P = 0.0015), and FoG (- 14.2%, F = 9.0, P = 0.0043; total model F = 5.8, P = 0.0003), independent of age, duration of disease, gender and nigrostriatal dopaminergic losses. Post hoc analysis using MGN VAChT binding as the single cholinergic VOI demonstrated similar significant associations with imbalance, falls and FoG. VSCD-associated cholinergic network changes localize to distinct structures involved in multi-sensory, in particular vestibular, and multimodal cognitive and motor integration brain regions. Relative clinical effects of VSCD-associated cholinergic network deficits were largest for FoG followed by postural imbalance and falls. The MGN was the most significant region identified.

Cholinergic system changes in Parkinson's disease: emerging therapeutic approaches

In patients with Parkinson's disease, heterogeneous cholinergic system changes can occur in different brain regions. These changes correlate with a range of clinical features, both motor and non-motor, that are refractory to dopaminergic therapy, and can be conceptualised within a systems-level framework in which nodal deficits can produce circuit dysfunctions. The topographies of cholinergic changes overlap with neural circuitries involved in sleep and cognitive, motor, visuo-auditory perceptual, and autonomic functions. Cholinergic deficits within cognition network hubs predict cognitive deficits better than do total brain cholinergic changes. Postural instability and gait difficulties are associated with cholinergic system changes in thalamic, caudate, limbic, neocortical, and cerebellar nodes. Cholinergic system deficits can involve also peripheral organs. Hypercholinergic activity of mesopontine cholinergic neurons in people with isolated rapid eye movement (REM) sleep behaviour disorder, as well as in the hippocampi of cognitively normal patients with Parkinson's disease, suggests early compensation during the prodromal and early stages of Parkinson's disease. Novel pharmacological and neurostimulation approaches could target the cholinergic system to treat motor and non-motor features of Parkinson's disease.

Mild Therapeutic Hypothermia and Putative Mechanisms of Hair Cell Survival in the Cochlea

Significance: Sensorineural hearing loss has significant implications for quality of life and risk for comorbidities such as cognitive decline. Noise and ototoxic drugs represent two common risk factors for acquired hearing loss that are potentially preventable. Recent Advances: Numerous otoprotection strategies have been postulated over the past four decades with primary targets of upstream redox pathways. More recently, the application of mild therapeutic hypothermia (TH) has shown promise for otoprotection for multiple forms of acquired hearing loss. Critical Issues: Systemic antioxidant therapy may have limited application for certain ototoxic drugs with a therapeutic effect on redox pathways and diminished efficacy of the primary drug's therapeutic function (e.g., cisplatin for tumors). Future Directions: Mild TH likely targets multiple mechanisms, contributing to otoprotection, including slowed metabolics, reduced oxidative stress, and involvement of cold shock proteins. Further work is needed to identify the mechanisms of mild TH at play for various forms of acquired hearing loss.

The Acute Effects of Time-Varying Caloric Vestibular Stimulation as Assessed With fMRI

We describe preliminary results from the application of time-varying caloric vestibular stimulation (tvCVS) to volunteers during a continuous blood oxygen level dependent (BOLD) functional MRI (fMRI) acquisition, recording baseline, during-tvCVS and post-tvCVS epochs. The modifications necessary to enable the use of this novel device in a 3-Tesla magnetic field are discussed. Independent component analysis (ICA) was used as a model-free method to highlight spatially and temporally coherent brain networks. The ICA results are consistent with tvCVS induction being mediated principally by thermoconvection in the vestibular labyrinth and not by direct thermal effects. The activation of hub networks identified by ICA is consistent with the concept of sensory neuromodulation, which posits that a modulatory signal introduced to a sensory organ is able to traverse the regions innervated (directly and indirectly) by that organ, while being transformed so as to be “matched” to regional neuronal dynamics. The data suggest that regional neurovascular coupling and a systemic cerebral blood flow component account for the BOLD contrast observed. The ability to modulate cerebral hemodynamics is of significant interest. The implications of these initial findings for the use of tvCVS therapeutically are discussed.

Caloric and galvanic vestibular stimulation for the treatment of Parkinson's disease: rationale and prospects

Introduction: Deeply embedded within the inner ear, the sensory organs of the vestibular system are exquisitely sensitive to the orientation and movement of the head. This information constrains aspects of autonomic reflex control as well as higher-level processes involved in cognition and affect. The anatomical pathways that underline these functional interactions project to many cortical and sub-cortical brain areas, and the question arises as to whether they can be therapeutically harnessed.Areas covered: The body of work reviewed here indicates that the controlled application of galvanic or thermal current to the vestibular end-organs can modulate activity throughout the ascending vestibular network and, under appropriate conditions, reduce motor and non-motor symptoms associated with Parkinson's disease, a disease of growing prevalence and continued unmet clinical need.Expert opinion: The appeal of vestibular stimulation in Parkinson's disease is underpinned by its noninvasive nature, favorable safety profile, and capacity for home-based administration. Clinical adoption now rests on the demonstration of cost-effectiveness and on the commercial availability of suitable devices, many of which are only permitted for research use or lack functionality. Dose optimization and mechanisms-of-action studies are also needed, along with a broader awareness amongst physicians of its therapeutic potential.

Non-Pharmacological Approaches to Headaches: Non-Invasive Neuromodulation, Nutraceuticals, and Behavioral Approaches

Significant side effects or drug interactions can make pharmacological management of headache disorders very difficult. Non-conventional and non-pharmacological treatments are becoming increasingly used to overcome these issues. In particular, non-invasive neuromodulation, nutraceuticals, and behavioral approaches are well tolerated and indicated for specific patient categories such as adolescents and pregnant women. This paper aims to present the main approaches reported in the literature in the management of headache disorders. We therefore reviewed the available literature published between 2010 and 2020 and performed a narrative presentation for each of the three categories (non-invasive neuromodulation, nutraceuticals, and behavioral therapies). Regarding non-invasive neuromodulation, we selected transcranial magnetic stimulation, supraorbital nerve stimulation, transcranial direct current stimulation, non-invasive vagal nerve stimulation, and caloric vestibular stimulation. For nutraceuticals, we selected Feverfew, Butterbur, Riboflavin, Magnesium, and Coenzyme Q10. Finally, for behavioral approaches, we selected biofeedback, cognitive behavioral therapy, relaxation techniques, mindfulness-based therapy, and acceptance and commitment therapy. These approaches are increasingly seen as a valid treatment option in headache management, especially for patients with medication overuse or contraindications to drug treatment. However, further investigations are needed to consider the effectiveness of these approaches also with respect to the long-term effects.

Noninvasive Neuromodulation in Migraine

PURPOSE OF REVIEW

The past two decades has seen an influx of noninvasive neuromodulation devices aimed at treatment of various primary headache disorders, including cluster headache and migraine. This narrative review is to summarize the current options in noninvasive neuromodulation in migraine.

RECENT FINDINGS

A variety of noninvasive neuromodulation devices have been FDA cleared and marketed for use in migraine, including single-pulse transcranial magnetic stimulation (sTMS), noninvasive vagal nerve stimulators (nVNS), and external trigeminal nerve stimulators (eTNS). Newer devices include peripheral electrical stimulation devices (PES), caloric stimulation, and others. Each has varying levels of evidence supporting its use in migraine, tolerability profiles, and access issues. Noninvasive neuromodulation devices can be beneficial when used in patients with migraine, with minimal side effects. As more devices are developed, approved, and marketed in the future, rigorous research on efficacy and safety remain a top priority.

Peripheral Neuromodulation for the Management of Headache

Context

Neuromodulation is an expanding field of study for headache treatment to reduce pain by targeting structures within the nervous system that are commonly involved in headache pathophysiology, such as the vagus nerve (VNS), occipital nerves, or sphenopalatine ganglion (SPG) for stimulation. Pharmaceutical medical therapies for abortive and prophylactic treatment, such as triptans, NSAIDs, beta-blockers, TCAs, and antiepileptics, are effective for some individuals, but the role that technology plays in investigating other therapeutic modalities is essential. Peripheral neuromodulation has gained popularity and FDA approval for use in treating certain headaches and migraine headache conditions, particularly in those who are refractory to treatment. Early trials found FDA approved neurostimulatory implant devices, including Cephaly and SpringTMS, improved patient-oriented outcomes with reductions in headaches per month (frequency) and severity.

Evidence Acquisition

This was a narrative review. The sources for this review are as follows: Searching on PubMed, Google Scholar, Medline, and ScienceDirect from 1990 - 2019 using keywords: Peripheral Neuromodulation, Headache, vagus nerve, occipital nerves, sphenopalatine ganglion.

Results

The first noninvasive neurostimulator device approved for migraine treatment was the Cefaly device, an external trigeminal nerve stimulation device (e-TNS) that transcutaneously excites the supratrochlear and supraorbital branches of the ophthalmic nerve. The second noninvasive neurostimulation device receiving FDA approval was the single-pulse transcranial magnetic stimulator, SpringTMS, positioned at the occiput to treat migraine with aura. GammaCore is a handheld transcutaneous vagal nerve stimulator applied directly to the neck at home by the patient for treatment of cluster headache (CH) and migraine. Several other devices are in development for the treatment of headaches and target headache evolution at different levels and inputs. The Scion device is a caloric vestibular stimulator (CVS) which interfaces with the user through a set of small cones resting in the ear canal on either side and held in place by modified over-ear headphones. The pulsante SPG Microstimulator is a patient-controlled device implanted in the patient’s upper jaw via an hour-long oral procedure to target the sphenopalatine ganglion. The occipital nerve stimulator (ONS) is an invasive neuromodulation device for headache treatment that consists of an implanted pulse generator on the chest wall connected to a subcutaneous lead with 4 - 8 electrodes that is tunneled the occiput.

Conclusions

The aim of this review is to provide a comprehensive overview of the efficacy, preliminary outcomes, and limitations of neurostimulatory implants available for use in the US and those pending further development.

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.

The disappearing hand: vestibular stimulation does not improve hand localisation

Background

Bodily self-consciousness depends on the coherent integration of sensory information. In addition to visual and somatosensory information processing, vestibular contributions have been proposed and investigated. Vestibular information seems especially important for self-location, but remains difficult to study.

Methods

This randomised controlled experiment used the MIRAGE multisensory illusion box to induce a conflict between the visually- and proprioceptively-encoded position of one hand. Over time, the perceived location of the hand slowly shifts, due to the fact that proprioceptive input is progressively weighted more heavily than the visual input. We hypothesised that left cold caloric vestibular stimulation (CVS) augments this shift in hand localisation.

Results

The results from 24 healthy participants do not support our hypothesis: CVS had no effect on the estimations with which the perceived position of the hand shifted from the visually- to the proprioceptively-encoded position. Participants were more likely to report that their hand was 'no longer there' after CVS. Taken together, neither the physical nor the subjective data provide evidence for vestibular enhanced self-location.

Caloric vestibular stimulation for the management of motor and non-motor symptoms in parkinson's disease: Intention-to-treat data

This report provides data related to the safety and effectiveness of repeated time-varying caloric vestibular stimulation (CVS) as a treatment for motor and non-motor features of Parkinson's disease (PD). Forty-six subjects receiving stable anti-Parkinsonian therapy were randomized to active (n = 23) or placebo (n = 23) treatment arms. Subjects self-administered CVS twice-daily over a period of 8 weeks at home via a portable, pre-programmed, solid-state ThermoNeuroModulation (TNM™) device delivering continually-varying thermal waveforms through aluminium ear-probes mounted on a wearable headset. Change scores from baseline to end of treatment and to a 1-month follow-up were determined using standardized clinical measures. The data presented here report sample demographics, detailed safety data and the statistical outcomes from the intention-to-treat and modified intention-to-treat analyses. These data supplement findings of the main per protocol analysis reported in the allied article entitled, 'Caloric Vestibular Stimulation for the Management of Motor and Non-Motor Symptoms in Parkinson's Disease' Wilkinson et al.

A new era in headache treatment

Primary headache disorders, such as migraine and cluster headache, are common and often debilitating. When preventive therapy is needed, several oral medications are used. Patients tend to have poor adherence and persistence on their preventive therapy. The introduction of treatments blocking calcitonin gene-related peptide (CGRP) is anticipated to begin a new era in migraine preventive treatment. In addition, non-triptan serotonin receptor agonists, newer delivery systems for older therapies, and innovative devices represent other exciting advances in acute and preventive migraine and cluster treatment and shall also be discussed in this review.

An Update on Non-Pharmacological Neuromodulation for the Acute and Preventive Treatment of Migraine

OBJECTIVE

To review current neuromodulation treatments available for migraine therapy, both in the acute and preventive setting.

METHODS

The published literature was reviewed for studies reporting the effects of different neuromodulation strategies in migraine with and without aura. The use of non-invasive: single pulse transcranial magnetic stimulation, non-invasive vagal nerve stimulation, supraorbital nerve stimulation, and transcranial direct current stimulation, as well as invasive methods such as occipital nerve stimulation and sphenopalatine ganglion stimulation, are assessed.

RESULTS

The available evidence shows that non-invasive techniques represent promising treatment strategies, whereas an invasive approach should only be used where patients are refractory to other preventives, including non-invasive methods.

CONCLUSIONS

Neuromodulation is emerging as an exciting approach to migraine therapy, especially in the context of failure of commonly used medicines or for patients who do not tolerate common side effects. More studies with appropriate blinding strategies are needed to confirm the results of these new treatment opportunities.