Galvanic vestibular stimulation speeds visual memory recall

Impact of repetitive home-based galvanic vestibular stimulation on cognitive skills in healthy older adults

The human vestibular system is adversely affected by the aging process. Recent evidence indicates that vestibular information and cognitive functions are related, suggesting that age-related vestibular loss may contribute to cognitive impairment. In this study, we aimed to investigate the effects of repetitive, home-based galvanic vestibular stimulation (GVS) on cognitive functions in healthy older adults. Twenty-one participants (age = 64.66 ± 2.97 years, 12 females) were randomly allocated to either a home-based GVS or an active control group. The GVS intervention lasted 20 min per session, five times a week, for two weeks (10 sessions). Cognitive functions were assessed before and after the intervention using the Stroop Test, Trail Making Test A&B, and Dual-Task (digit recall and paper-pencil tracking test). Our findings revealed a significant group-by-time interaction effect for the tracking accuracy (F(1,18) = 7.713, p = 0.012, η p2 = 0.30), with only the home-based GVS group showing significant improvement (t = -2.544, p = 0.029). The proposed home-based GVS protocol offers a promising non-pharmacological avenue for enhancing visuospatial ability in healthy older adults. Further research is needed to investigate the effects of different GVS protocols on various cognitive functions, particularly in older individuals with different health conditions.

Appropriate Vestibular Stimulation in Children and Adolescents-A Prerequisite for Normal Cognitive, Motor Development and Bodily Homeostasis-A Review

The structural development of the vestibular part of the inner ear is completed by birth but its central connections continue to develop until adolescence. Their development is dependent on vestibular stimulation-vestibular experience. Studies have shown that vestibular function, modulated by experience and epigenetic factors, is not solely an instrument for body position regulation, navigation, and stabilization of the head and images but also influences cognition, emotion, the autonomous nervous system and hormones. To emphasize the importance of appropriate vestibular stimulation, we present a literature review of its effect on bodily homeostasis, cognition and emotion.

Additive Sensory Noise Effects on Operator Performance in a Lunar Landing Simulation

INTRODUCTION: Adding noise to a system to improve a weak signal's detectability is known as stochastic resonance (SR). SR has been shown to improve sensory perception and cognitive performance in certain individuals, but it is unknown whether this performance improvement can translate to meaningful macrocognitive enhancements in performance for complex, operational tasks.OBJECTIVE: We investigated human operator performance in a lunar landing simulation while applying auditory white noise and/or noisy galvanic vestibular stimulation.METHODS: We measured performance (N = 16 subjects) while completing simulation trials in our Aerospace Research Simulator. Trials were completed with and without the influence of auditory white noise, noisy galvanic vestibular stimulation, and both simultaneously in a multimodal fashion. Performance was observed holistically and across subdimensions of the task, which included flight skill and perception. Subjective mental workload was collected after completing four trials in each treatment.RESULTS: We did not find broad operator improvement under the influence of noise, but a significant interaction was identified between subject and noise treatment, indicating that some subjects were impacted by additive noise. We also found significant interactions between subject and noise treatment in performance subdimensions of flight skill and perception. We found no significant main effects on mental workload.CONCLUSIONS: This study investigated the utility of using additive sensory noise to induce SR for complex tasks. While SR has been shown to improve aspects of performance, our results suggest additive noise does not yield operational performance changes for a broad population, but specific individuals may be affected.Sherman SO, Shen Y-Y, Gutierrez-Mendoza D, Schlittenhart M, Watson C, Clark TK, Anderson AP. Additive sensory noise effects on operator performance in a lunar landing simulation. Aerosp Med Hum Perform. 2023; 94(10):770-779.

Optimal Design of Galvanic Vestibular Stimulation for Patients with Vestibulopathy and Cerebellar Disorders

OBJECTIVES

Galvanic vestibular stimulation (GVS) has shown positive outcomes in various neurological and psychiatric disorders, such as enhancing postural balance and cognitive functions. In order to expedite the practical application of GVS in clinical settings, our objective was to determine the best GVS parameters for patients with vestibulopathy and cerebellar disorders using optimal design calculation.

METHODS

A total of 31 patients (26 males, mean age 57.03 ± 14.75 years, age range 22-82 years) with either unilateral or bilateral vestibulopathy (n = 18) or cerebellar ataxia (n = 13) were enrolled in the study. The GVS intervention included three parameters, waveform (sinusoidal, direct current [DC], and noisy), amplitude (0.4, 0.8, and 1.2 mA), and duration of stimulation (5 and 30 min), resulting in a total of 18 GVS intervention modes as input variables. To evaluate the effectiveness of GVS, clinical vertigo and gait assessments were conducted using the Dizziness Visual Analogue Scale (D-VAS), Activities-specific Balance Confidence Scale (ABC), and Scale for Assessment and Rating of Ataxia (SARA) as output variables. Optimal design and local sensitivity analysis were employed to determine the most optimal GVS modes.

RESULTS

Patients with unilateral vestibulopathy experienced the most favorable results with either noisy or sinusoidal GVS at 0.4 mA amplitude for 30 min, followed by DC GVS at 0.8 mA amplitude for 5 min. Noisy GVS at 0.8 or 0.4 mA amplitude for 30 min demonstrated the most beneficial effects in patients with bilateral vestibulopathy. For patients with cerebellar ataxia, the optimal choices were noisy GVS with 0.8 or 0.4 mA amplitude for 5 or 30 min.

CONCLUSIONS

This study is the first to utilize design optimization methods to identify the GVS stimulation parameters that are tailored to individual-specific characteristics of dizziness and imbalance. A sensitivity analysis was carried out along with the optimal design to offset the constraints of a limited sample size, resulting in the identification of the most efficient GVS modes for patients suffering from vestibular and cerebellar disorders.

High-current galvanic vestibular stimulation impairs working memory span, but not other executive functions

Patients with peripheral vestibular dysfunction (PVD) suffer not only from physical problems such as imbalance or vertigo but also from neuropsychological difficulties, including executive deficits. However, it is unclear whether the PVD directly causes executive problems. To examine the causal vestibular influence on executive functions, we induced either high-current (2 mA), low-current (0.8 mA), or sham current (0 mA) galvanic vestibular stimulation (GVS) in 79 healthy participants. Participants solved three tasks, measuring the core executive components (working memory, inhibition, cognitive flexibility) before and during GVS. High-current GVS impaired working memory span, but not inhibition and cognitive flexibility performance. Low-current GVS did not influence executive performance. Results indicate a causal vestibular influence on working memory span. Joint cortical areas of vestibular and working memory processing are discussed. Since high-current GVS in healthy participants serves as a model for an artificial vestibular dysfunction, our results could improve the diagnostics and therapy of patients with PVD.

Training augmentation using additive sensory noise in a lunar rover navigation task

Background

The uncertain environments of future space missions means that astronauts will need to acquire new skills rapidly; thus, a non-invasive method to enhance learning of complex tasks is desirable. Stochastic resonance (SR) is a phenomenon where adding noise improves the throughput of a weak signal. SR has been shown to improve perception and cognitive performance in certain individuals. However, the learning of operational tasks and behavioral health effects of repeated noise exposure aimed to elicit SR are unknown.

Objective

We evaluated the long-term impacts and acceptability of repeated auditory white noise (AWN) and/or noisy galvanic vestibular stimulation (nGVS) on operational learning and behavioral health.

Methods

Subjects (n = 24) participated in a time longitudinal experiment to access learning and behavioral health. Subjects were assigned to one of our four treatments: sham, AWN (55 dB SPL), nGVS (0.5 mA), and their combination to create a multi-modal SR (MMSR) condition. To assess the effects of additive noise on learning, these treatments were administered continuously during a lunar rover simulation in virtual reality. To assess behavioral health, subjects completed daily, subjective questionnaires related to their mood, sleep, stress, and their perceived acceptance of noise stimulation.

Results

We found that subjects learned the lunar rover task over time, as shown by significantly lower power required for the rover to complete traverses (p < 0.005) and increased object identification accuracy in the environment (p = 0.05), but this was not influenced by additive SR noise (p = 0.58). We found no influence of noise on mood or stress following stimulation (p > 0.09). We found marginally significant longitudinal effects of noise on behavioral health (p = 0.06) as measured by strain and sleep. We found slight differences in stimulation acceptability between treatment groups, and notably nGVS was found to be more distracting than sham (p = 0.006).

Conclusion

Our results suggest that repeatedly administering sensory noise does not improve long-term operational learning performance or affect behavioral health. We also find that repetitive noise administration is acceptable in this context. While additive noise does not improve performance in this paradigm, if it were used for other contexts, it appears acceptable without negative longitudinal effects.

Effects of additive sensory noise on cognition

Background

Adding noise to a system to improve a weak signal's throughput is known as stochastic resonance (SR). SR has been shown to improve sensory perception. Some limited research shows noise can also improve higher order processing, such as working memory, but it is unknown whether SR can broadly improve cognition.

Objective

We investigated cognitive performance while applying auditory white noise (AWN) and/or noisy galvanic vestibular stimulation (nGVS).

Methods

We measured cognitive performance (n = 13 subjects) while completing seven tasks in the cognition test battery (CTB). Cognition was assessed with and without the influence of AWN, nGVS, and both simultaneously. Performance in speed, accuracy, and efficiency was observed. A subjective questionnaire regarding preference for working in noisy environments was collected.

Results

We did not find broad cognitive performance improvement under the influence of noise (p > 0.1). However, a significant interaction was found between subject and noise condition for accuracy (p = 0.023), indicating that some subjects exhibited cognitive changes with the addition of noise. Across all metrics, noisy environment preference may trend to be a potential indicator of whether subjects will exhibit SR cognitive benefits with a significant predictor in efficiency (p = 0.048).

Conclusion

This study investigated using additive sensory noise to induce SR in overall cognition. Our results suggest that using noise to improve cognition is not applicable for a broad population; however, the effect of noise differs across individuals. Further, subjective questionnaires may be a means to identify which individuals are sensitive to SR cognitive benefits, but further investigation is needed.

Thresholds for vestibular and cutaneous perception and oculomotor response induced by galvanic vestibular stimulation

Objectives

In this study, the specific threshold intensities and response characteristics of galvanic vestibular stimulation (GVS) on vestibular (conscious) and cutaneous (detrimental) perception as well as oculomotor nystagmus (reflex) were determined.

Methods

The threshold intensities for vestibular and cutaneous perception and oculomotor response induced by GVS were determined in 25 right-handed healthy subjects (32.6 ± 7.2 years of age; 56% female). The subjects were seated upright, and eye movements were recorded while a direct GVS current was applied with paradigms of cathode on the right and anode on the left (CRAL) and also cathode on the left and anode on the right (CLAR).

Results

Subjects experienced dizziness, sense of spinning, or fall tendency, which was more frequently directed to the cathode (76%) than the anode (24%, p < 0.001, chi-square one-variable test) at mean current greater than 0.98 ± 0.29 mA (mean vestibular threshold). The current also triggered a more frequent mild tingling sensation at the cathode (56%) than the anode (30%) or on both sides (14%; p = 0.001, chi-square one-variable test) when above the mean cutaneous threshold of 0.9 ± 0.29 mA. Above the mean oculomotor threshold of 1.61 ± 0.35 mA, combined horizontal and torsional nystagmus was more frequent toward the cathode (86%) than toward the anode (p < 0.001, chi-square one-variable test). The mean oculomotor threshold was significantly higher than both the vestibular (p < 0.001, Mann–Whitney U-test) and cutaneous (p < 0.001, Mann–Whitney U-test) thresholds, which were comparable (p = 0.317, Mann–Whitney U-test). There was no significant disparity in these specific thresholds between the two GVS paradigms. The vestibular threshold was significantly higher in males than in females [1 (0.5–1.25) mA vs. 0.75 (0.625–1.125) mA, Z = −2.241, p = 0.025, Mann–Whitney U-test]. However, the thresholds of cutaneous perception and oculomotor response did not differ by sex.

Conclusion

The findings indicate that thresholds for vestibular and somatosensory perception are lower than the oculomotor threshold. Therefore, a strategy to reduce GVS current intensity to the level of vestibular or somatosensory perception threshold could elicit beneficial vestibular effects while avoiding undesirable effects such as oculomotor consequences.

The rehabilitation of object agnosia and prosopagnosia: A systematic review

BACKGROUND

Agnosia for objects is often overlooked in neuropsychology, especially with respect to rehabilitation. Prosopagnosia has been studied more extensively, yet there have been few attempts at training it. The lack of training protocols may partially be accounted for by their relatively low incidence and specificity to sensory modality. However, finding effective rehabilitations for such deficits may help to reduce their impact on the social and psychological functioning of individuals.

OBJECTIVE

Our aim in this study was to provide clinicians and researchers with useful information with which to conduct new studies on the rehabilitation of object agnosia and prosopagnosia. To accomplish this, we performed a systematic and comprehensive review of the effect of neuropsychological rehabilitation on visual object and prosopagnosia.

METHODS

The Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines were followed. In addition, the Single-Case Experimental Design (SCED) and the Critical Appraisal Skills Programme (CASP) scales were used to assess the quality of reporting.

RESULTS

Seven articles regarding object agnosia, eight articles describing treatments for prosopagnosia, and two articles describing treatments for both deficits were included.

CONCLUSIONS

In the light of the studies reviewed, treatments based on analysis of parts seem effective for object agnosia, while prosopagnosia appears to benefit most from treatments relying on holistic/configural processing. However, more attempts at rehabilitation of face and object agnosia are needed to clarify the mechanisms of these processes and possible rehabilitations. Moreover, a publication bias could mask a broader attempt to find effective treatments for visual agnosia and leaving out studies that are potentially more informative.

Frequency-Specific Effects of Galvanic Vestibular Stimulation on Response-Time Performance in Parkinson's Disease

Background: Galvanic vestibular stimulation (GVS) is being increasingly explored as a non-invasive brain stimulation technique to treat symptoms in Parkinson's disease (PD). To date, behavioral GVS effects in PD have been explored with only two stimulus types, direct current and random noise (RN). The interaction between GVS effects and anti-parkinsonian medication is unknown. In the present study, we designed multisine (ms) stimuli and investigated the effects of ms and RN GVS on motor response time. In comparison to the RN stimulus, the ms stimuli contained sinusoidal components only at a set of desired frequencies and the phases were optimized to improve participants' comfort. We hypothesized GVS motor effects were a function of stimulation frequency, and specifically, that band-limited ms-GVS would result in better motor performance than conventionally used broadband RN-GVS.

Materials and Methods: Eighteen PD patients (PDMOFF/PDMON: off-/on-levodopa medication) and 20 healthy controls (HC) performed a simple reaction time task while receiving sub-threshold GVS. Each participant underwent nine stimulation conditions: off-stimulation, RN (4–200 Hz), ms-θ (4–8 Hz), ms-α (8–13 Hz), ms-β (13–30 Hz), ms-γ (30–50 Hz), ms-h1 (50–100 Hz), ms-h2 (100–150 Hz), and ms-h3 (150–200 Hz).

Results: The ms-γ resulted in shorter response time (RPT) in both PDMOFF and HC groups compared with the RN. In addition, the RPT of the PDMOFF group decreased during the ms-β while the RPT of the HC group decreased during the ms-α, ms-h1, ms-h2, and ms-h3. There was considerable inter-subject variability in the optimum stimulus type, although the frequency range tended to fall within 8–100 Hz. Levodopa medication significantly reduced the baseline RPT of the PD patients. In contrast to the off-medication state, GVS did not significantly change RPT of the PD patients in the on-medication state.

Conclusions: Using band-limited ms-GVS, we demonstrated that the GVS frequency for the best RPT varied considerably across participants and was >30 Hz for half of the PDMOFF patients. Moreover, dopaminergic medication was found to influence GVS effects in PD patients. Our results indicate the common “one-size-fits-all” RN approach is suboptimal for PD, and therefore personalized stimuli aiming to address this variability is warranted to improve GVS effects.

Galvanic Vestibular Stimulation Improves Spatial Cognition After Unilateral Labyrinthectomy in Mice

Objectives: To investigate the deficits of spatial memory and navigation from unilateral vestibular deafferentation (UVD) and to determine the efficacy of galvanic vestibular stimulation (GVS) for recovery from these deficits using a mouse model of unilateral labyrinthectomy (UL).

Methods: Thirty-six male C57BL/6 mice were allocated into three groups that comprise a control group and two experimental groups, UVD with (GVS group) and without GVS intervention (non-GVS group). In the experimental groups, we assessed the locomotor and cognitive behavioral function before (baseline) and 3, 7, and 14 days after surgical UL, using the open field (OF), Y maze, and Morris water maze (MWM) tests. In the GVS group, the stimulations were applied for 30 min daily from postoperative day (POD) 0–4 via the electrodes inserted subcutaneously close to both bony labyrinths.

Results: Locomotion and spatial cognition were significantly impaired in the mice with UVD non-GVS group compared to the control group. GVS significantly accelerated recovery of locomotion compared to the control and non-GVS groups on PODs 3 (p < 0.001) and 7 (p < 0.05, Kruskal–Wallis and Mann–Whitney U tests) in the OF and Y maze tests. The mice in the GVS group were better in spatial working memory assessed with spontaneous alternation performance and spatial reference memory assessed with place recognition during the Y maze test than those in the non-GVS group on POD 3 (p < 0.001). In addition, the recovery of long-term spatial navigation deficits during the MWM, as indicated by the escape latency and the probe trial, was significantly better in the GVS group than in the non-GVS group 2 weeks after UVD (p < 0.01).

Conclusions: UVD impairs spatial memory, navigation, and motor coordination. GVS accelerated recoveries in short- and long-term spatial memory and navigation, as well as locomotor function in mice with UVD, and may be applied to the patients with acute unilateral vestibular failure.

Galvanic Vestibular Stimulation influences risk-taking behaviour

Risk-taking behaviour is an essential aspect of our interactions with the environment. Here we investigated whether vestibular inputs influence behavioural measurement of risk-taking propensity. We have combined bipolar Galvanic Vestibular Stimulation (GVS) with a well-known and established risk-taking behaviour task, namely the Balloon Analogue Risk Task (BART). A sham stimulation was used to control for non-specific effects. Left-anodal and right-cathodal GVS (L-GVS), which preferentially activates the vestibular projections in the right hemisphere, decreased the willingness to take risk during the BART compared with right-anodal and left-cathodal GVS (R-GVS), which activates the left hemisphere. This proved a specific vestibular effect which depends on GVS polarity. Conversely, no generic vestibular effect, defined as the adjusted average of L-GVS and R-GVS conditions compared to sham, emerged, excluding non-specific vestibular effects. Our results confirmed recent findings of a vestibular contribution to decision-making and strategy control behaviour. We suggest that the vestibular-mediated balancing of risk seeking behaviour is an important element of the brain's capacity to adapt to the environment.

Therapies to Restore Consciousness in Patients with Severe Brain Injuries: A Gap Analysis and Future Directions

Background/Objective

For patients with disorders of consciousness (DoC) and their families, the search for new therapies has been a source of hope and frustration. Almost all clinical trials in patients with DoC have been limited by small sample sizes, lack of placebo groups, and use of heterogeneous outcome measures. As a result, few therapies have strong evidence to support their use; amantadine is the only therapy recommended by current clinical guidelines, specifically for patients with DoC caused by severe traumatic brain injury. To foster and advance development of consciousness-promoting therapies for patients with DoC, the Curing Coma Campaign convened a Coma Science Work Group to perform a gap analysis.

Methods

We consider five classes of therapies: (1) pharmacologic; (2) electromagnetic; (3) mechanical; (4) sensory; and (5) regenerative. For each class of therapy, we summarize the state of the science, identify gaps in knowledge, and suggest future directions for therapy development.

Results

Knowledge gaps in all five therapeutic classes can be attributed to the lack of: (1) a unifying conceptual framework for evaluating therapeutic mechanisms of action; (2) large-scale randomized controlled trials; and (3) pharmacodynamic biomarkers that measure subclinical therapeutic effects in early-phase trials. To address these gaps, we propose a precision medicine approach in which clinical trials selectively enroll patients based upon their physiological receptivity to targeted therapies, and therapeutic effects are measured by complementary behavioral, neuroimaging, and electrophysiologic endpoints.

Conclusions

This personalized approach can be realized through rigorous clinical trial design and international collaboration, both of which will be essential for advancing the development of new therapies and ultimately improving the lives of patients with DoC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12028-021-01227-y.

Galvanic Vestibular Stimulation Improves Subnetwork Interactions in Parkinson's Disease

Background

Activating vestibular afferents via galvanic vestibular stimulation (GVS) has been recently shown to have a number of complex motor effects in Parkinson's disease (PD), but the basis of these improvements is unclear. The evaluation of network-level connectivity changes may provide us with greater insights into the mechanisms of GVS efficacy.

Objective

To test the effects of different GVS stimuli on brain subnetwork interactions in both health control (HC) and PD groups using fMRI.

Methods

FMRI data were collected for all participants at baseline (resting state) and under noisy, 1 Hz sinusoidal, and 70-200 Hz multisine GVS. All stimuli were given below sensory threshold, blinding subjects to stimulation. The subnetworks of 15 healthy controls and 27 PD subjects (on medication) were identified in their native space, and their subnetwork interactions were estimated by nonnegative canonical correlation analysis. We then determined if the inferred subnetwork interaction changes were affected by disease and stimulus type and if the stimulus-dependent GVS effects were influenced by demographic features.

Results

At baseline, interactions with the visual-cerebellar network were significantly decreased in the PD group. Sinusoidal and multisine GVS improved (i.e., made values approaching those seen in HC) subnetwork interactions more effectively than noisy GVS stimuli overall. Worsening disease severity, apathy, depression, impaired cognitive function, and increasing age all limited the beneficial effects of GVS.

Conclusions

Vestibular stimulation has widespread system-level brain influences and can improve subnetwork interactions in PD in a stimulus-dependent manner, with the magnitude of such effects associating with demographics and disease status.

Assessing head acceleration to identify a motor threshold to galvanic vestibular stimulation

Galvanic vestibular stimulation (GVS) is used to assess vestibular system function, but vestibulospinal responses can exhibit variability depending on protocols or intensities used. Here, we measured head acceleration in healthy subjects to identify an objective motor threshold on which to base GVS intensity when assessing standing postural responses. Thirteen healthy right-handed subjects stood on a force platform, eyes closed, and head facing forward. An accelerometer was placed on the vertex to detect head acceleration, and electromyography activity of the right soleus was recorded. GVS (200 ms; current steps 0.5, from 1 mA to 4 mA) was applied in a binaural and bipolar configuration. 1) GVS induced a biphasic accelerometer response at a latency of 15 ms. Based on response amplitude, we constructed a recruitment curve for all participants and determined the motor threshold. In parallel, the method of limits was used to devise a more rapid approach to determine motor threshold. 2) We observed significant differences between motor threshold based on a recruitment curve and all perceptual thresholds reported either by the subject (sensation of movement) or a standing experimenter observing the participant (perception of movement). No significant difference was observed between the motor threshold based on the method of limits and perceptual thresholds of movement. 3) Using orthogonal polynomial contrasts, we observed a linear progression between multiples of the objective motor threshold (0.5, 0.75, 1, 1.5× motor threshold) and the 95% confidence ellipse area, the first peak of center of pressure displacement velocity, and the short and medium latency responses in the soleus. Hence, an objective motor threshold for GVS based on head acceleration was identified in standing participants and a recruitment curve could be constructed for all participants. These novel approaches could enable better understanding of changes in the vestibular system in different conditions or over time.NEW & NOTEWORTHY Galvanic vestibular stimulation (GVS) has been used to assess the vestibular system, but the significant interindividual variability in the responses makes it difficult to quantitatively compare them between individuals or conditions. Using an accelerometer to quantify head movement induced by GVS, we were able to determine an objective motor threshold and construct a recruitment curve for all participants. These methods could help assess changes in the vestibular system under different conditions.

Cortical Effects of Noisy Galvanic Vestibular Stimulation Using Functional Near-Infrared Spectroscopy

Noisy galvanic vestibular stimulation (nGVS) can improve different motor, sensory, and cognitive behaviors. However, it is unclear how this stimulation affects brain activity to facilitate these improvements. Functional near-infrared spectroscopy (fNIRS) is inexpensive, portable, and less prone to motion artifacts than other neuroimaging technology. Thus, fNIRS has the potential to provide insight into how nGVS affects cortical activity during a variety of natural behaviors. Here we sought to: (1) determine if fNIRS can detect cortical changes in oxygenated (HbO) and deoxygenated (HbR) hemoglobin with application of subthreshold nGVS, and (2) determine how subthreshold nGVS affects this fNIRS-derived hemodynamic response. A total of twelve healthy participants received nGVS and sham stimulation during a seated, resting-state paradigm. To determine whether nGVS altered activity in select cortical regions of interest (BA40, BA39), we compared differences between nGVS and sham HbO and HbR concentrations. We found a greater HbR response during nGVS compared to sham stimulation in left BA40, a region previously associated with vestibular processing, and with all left hemisphere channels combined (p < 0.05). We did not detect differences in HbO responses for any region during nGVS (p > 0.05). Our results suggest that fNIRS may be suitable for understanding the cortical effects of nGVS.

The potential of noisy galvanic vestibular stimulation for optimizing and assisting human performance

Noisy galvanic vestibular stimulation (nGVS) is an emerging non-invasive brain stimulation technique. It involves applying alternating currents of different frequencies and amplitudes presented in a random, or noisy, manner through electrodes on the mastoid bones behind the ears. Because it directly activates vestibular hair cells and afferents and has an indirect effect on a variety of brain regions, it has the potential to impact many different functions. The objective of this review is twofold: (1) to review how nGVS affects motor, sensory, and cognitive performance in healthy adults; and (2) to discuss potential clinical applications of nGVS. First, we introduce the technique. We then describe the regions receiving and processing vestibular information. Next, we discuss the effects of nGVS on motor, sensory, and cognitive function in healthy adults. Subsequently, we outline its potential clinical applications. Finally, we highlight other electrical stimulation technologies and discuss why nGVS offers an alternative or complementary approach. Overall, nGVS appears promising for optimizing human performance and as an assistive technology, though further research is required.

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.

Vestibular cognition: State-of-the-art and future directions

Vestibular information has been traditionally considered as a specialized input for basic orienting behaviours, such as oculo-motor adjustments, postural control and gaze orientation. However, in the past two decades a widespread vestibular network in the human brain has been identified, that goes far beyond the low-level reflex circuits emphasized by earlier work. Because this vestibular cortical network is so widely distributed, it could, in principle, impact multiple neurocognitive functions in health and disease. This paper focuses on the relations between vestibular input, vestibular networks, and vestibular interventions by providing the authors' personal viewpoint on the state-of-the-art of vestibular cognitive neuropsychology, and its potential relevance for neurorehabilitation.

Vestibular-guided visual search

The amnesic symptoms that accompany vestibular dysfunction point to a functional relationship between the vestibular and visual memory systems. However, little is known about the underpinning cognitive processes. As a starting point, we sought evidence for a type of cross-modal interaction commonly observed between other sensory modalities in which the identification of a target (in this case, visual) is facilitated if earlier coupled to a unique, temporally coincident stimulus from another sensory domain (in this case, vestibular). Participants first performed a visual detection task in which stimuli appeared at random locations within a computerised grid. Unknown to participants, the onset of one particular stimulus was accompanied by a brief, sub-sensory pulse of galvanic vestibular stimulation (GVS). Across two visual search experiments, both old and new targets were identified faster when presented in the grid location at which the GVS-paired visual stimulus had appeared in the earlier detection task. This location advantage appeared to be based on relative rather than absolute spatial co-ordinates since the effect held when the search grid was rotated 90°. Together these findings indicate that when individuals return to a familiar visual scene (here, a 2D grid), visual judgements are facilitated when targets appear at a location previously associated with a unique, task-irrelevant vestibular cue. This novel case of multisensory interplay has broader implications for understanding how vestibular signals inform cognitive processes and helps constrain the growing therapeutic application of GVS.

Effects of Noisy Galvanic Vestibular Stimulation During a Bimanual Tracking Robotic Task

Background

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve motor performance in people with and without disabilities. Previous investigations on the use of nGVS to improve upper-limb motor performance have focused on unimanual fine motor movements, nevertheless, bimanual gross movements are also essential for conducting activities of daily living and can be affected as a result of cerebral dysfunction. Consequently, in this study we investigated the effects of nGVS on bimanual gross motor performance.

Methods

Twelve healthy participants completed a visuomotor task in which they performed bimanual upper-limb movements using two robots. During the task, participants tracked a target that oscillated following a sinusoidal amplitude-modulated trajectory. In half of the trials, participants received subthreshold nGVS, in the other half, they received sham stimulation. Primary outcome measure: percent improvement in root mean square error (RMSE) between the target’s and cursors’ trajectories. Secondary outcome measures: percent improvement in lag between the cursors and target; and percent improvement in RMSE between the cursors’ trajectories. A post-test questionnaire was administered to evaluate the experience of participants.

Results

Tracking error was not affected by nGVS: left −2.6(5.5)%, p = 0.128; right −0.9(6.2)%, p = 0.639; nor was bimanual coordination −1.5(9.6)%, p = 0.590. When comparing if one hand was affected more than the other, we did not find a statistically significant difference (−1.7(3.3)%, p = 0.098). Similar results were found for the lag. Questionnaire results indicated that the robotic devices did not limit participants’ movements, did not make participants feel unsafe, nor were they difficult to control. Furthermore, participants did not feel unsafe with the nGVS device, nor did they report any discomfort due to nGVS.

Conclusion

Results suggest that nGVS applied to people without disabilities do not affect bimanual gross motor performance. However, as this was the first study to investigate such effects, stimulation parameters were based on previous unimanual fine motor studies. Future studies should investigate optimal stimulation parameters for improving upper-limb gross motor performance. Overall, participants felt safe using the robotic devices and receiving the noisy electrical stimulation. As such, a similar setup could potentially be employed for subsequent studies investigating the relation between upper-limb performance and nGVS.

Noisy galvanic vestibular stimulation modulates spatial memory in young healthy adults

Hippocampal and striatal circuits play important roles in spatial navigation. These regions integrate environmental information and receive intrinsic afferent inputs from the vestibular system. Past research indicates that galvanic vestibular stimulation (GVS) is a non-invasive technique that modulates hippocampal and striatal activities. There are also evidences for enhanced motor and cognitive functions through GVS. This study extends previous research to investigate whether noisy GVS may improve hippocampal- and striatal-associated aspects of spatial navigation performance. Using a virtual navigation task, we examined effects of noisy GVS on spatial learning and memory. To probe the participants’ sensitivity to hippocampal- or striatal-associated spatial information, we either enlarged the virtual environment’s boundary or replaced an intra-environmental location cue, respectively. Noisy GVS or sham stimulation was applied online during the learning phase in a within-subject crossover design. The results showed that noisy GVS enhanced spatial learning and the sensitivity foremost to hippocampal-dependent spatial information both in males and females. Individual differences in spatial working memory capacity moderated the effects of GVS, with individuals with lower capacity benefitting more from the stimulation. Furthermore, sex-related differences in GVS effects on the two forms of spatial representations may reflect differences between males and females in preferred spatial strategies.

Investigation on the effect of noisy galvanic vestibular stimulation on fine motor skills during a visuomotor task in healthy participants

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve dynamic walking stability, affect postural responses, enhance balance in healthy subjects, and influence motor performance in individuals with Parkinson’s disease. Although the studies to fully characterize the effect of nGVS are still ongoing, stochastic resonance theory which states that the addition of noisy signal may enhance a weak sensory input signals transmission in a non-linear system may provide a possible explanation for the observed positive effects of nGVS. This study explores the effect of nGVS on fine tracking behavior in healthy subjects. Ten healthy participants performed a computer-based visuomotor task by controlling an object with a joystick to follow an amplitude-modulated signal path while simultaneously receiving a sham or pink noise nGVS. The stimulation was generated to have a zero-mean, linearly detrended 1/f-type power spectrum, Gaussian distribution within 0.1–10 Hz range, and a standard deviation (SD) set to 90% based on each participant’s cutaneous threshold value. Results show that simultaneous nGVS delivery statistically improved the tracking performance with a decreased root-mean-squared error of 5.71±6.20% (mean±SD), a decreased time delay of 11.88±9.66% (mean±SD), and an increased signal-to-noise ratio of 2.93% (median, interquartile range (IQR) 3.31%). This study showed evidence that nGVS may be beneficial in improving sensorimotor performance during a fine motor tracking task requiring fine wrist movement in healthy subjects. Further research with a more comprehensive subset of tasks is required to fully characterize the effects of nGVS on fine motor skills.

The Promise of Stochastic Resonance in Falls Prevention

Multisensory integration is essential for maintenance of motor and cognitive abilities, thereby ensuring normal function and personal autonomy. Balance control is challenged during senescence or in motor disorders, leading to potential falls. Increased uncertainty in sensory signals is caused by a number of factors including noise, defined as a random and persistent disturbance that reduces the clarity of information. Counter-intuitively, noise can be beneficial in some conditions. Stochastic resonance is a mechanism whereby a particular level of noise actually enhances the response of non-linear systems to weak sensory signals. Here we review the effects of stochastic resonance on sensory modalities and systems directly involved in balance control. We highlight its potential for improving sensorimotor performance as well as cognitive and autonomic functions. These promising results demonstrate that stochastic resonance represents a flexible and non-invasive technique that can be applied to different modalities simultaneously. Finally we point out its benefits for a variety of scenarios including in ambulant elderly, skilled movements, sports and to patients with sensorimotor or autonomic dysfunctions.

Effect of noisy galvanic vestibular stimulation in community-dwelling elderly people: a randomised controlled trial

Background

Balance disorders are a risk factor for falls in the elderly. Although noisy galvanic vestibular stimulation (nGVS) has been reported to improve balance in young people, randomised control trials targeting community-dwelling elderly people have not been conducted to date. We aimed to assess the influence of nGVS on COP sway in the open-eye standing posture among community-dwelling elderly people in a randomised controlled trial.

Methods

A randomised controlled trial of 32 community-dwelling elderly people randomly assigned to control (sham stimulation) and an nGVS groups. All participants underwent centre of pressure (COP) sway measurements while standing with open eyes at baseline and during stimulation. The control group underwent sham stimulation and the nGVS group underwent noise stimulation (0.4 mA; 0.1–640 Hz).

Results

In the nGVS group, sway path length, mediolateral mean velocity and anteroposterior mean velocity decreased during stimulation compared with baseline (P < 0.01). The effect of nGVS was large in participants with a high COP sway path length at baseline, but there was no significant difference in COP sway in the control group.

Conclusions

We conclude that nGVS decreases the COP sway path length and mean velocity of community-dwelling elderly people when standing with open eyes. This suggests that nGVS could be effective for treating balance dysfunction in the elderly.

Galvanic Vestibular Stimulation (GVS) Augments Deficient Pedunculopontine Nucleus (PPN) Connectivity in Mild Parkinson's Disease: fMRI Effects of Different Stimuli

Falls and balance difficulties remain a major source of morbidity in Parkinson's Disease (PD) and are stubbornly resistant to therapeutic interventions. The mechanisms of gait impairment in PD are incompletely understood but may involve changes in the Pedunculopontine Nucleus (PPN) and its associated connections. We utilized fMRI to explore the modulation of PPN connectivity by Galvanic Vestibular Stimulation (GVS) in healthy controls (n = 12) and PD subjects even without overt evidence of Freezing of Gait (FOG) while on medication (n = 23). We also investigated if the type of GVS stimuli (i.e., sinusoidal or stochastic) differentially affected connectivity. Approximate PPN regions were manually drawn on T1 weighted images and 58 other cortical and subcortical Regions of Interest (ROI) were obtained by automatic segmentation. All analyses were done in the native subject's space without spatial transformation to a common template. We first used Partial Least Squares (PLS) on a subject-by-subject basis to determine ROIs across subjects that covaried significantly with the voxels within the PPN ROI. We then performed functional connectivity analysis on the PPN-ROI connections. In control subjects, GVS did not have a significant effect on PPN connectivity. In PD subjects, baseline overall magnitude of PPN connectivity was negatively correlated with UPDRS scores (p < 0.05). Both noisy and sinusoidal GVS increased the overall magnitude of PPN connectivity (p = 6 × 10⁻⁵, 3 × 10⁻⁴, respectively) in PD, and increased connectivity with the left inferior parietal region, but had opposite effects on amygdala connectivity. Noisy stimuli selectively decreased connectivity with basal ganglia and cerebellar regions. Our results suggest that GVS can enhance deficient PPN connectivity seen in PD in a stimulus-dependent manner. This may provide a mechanism through which GVS assists balance in PD, and may provide a biomarker to develop individualized stimulus parameters.

Trigeminal, Visceral and Vestibular Inputs May Improve Cognitive Functions by Acting through the Locus Coeruleus and the Ascending Reticular Activating System: A New Hypothesis

It is known that sensory signals sustain the background discharge of the ascending reticular activating system (ARAS) which includes the noradrenergic locus coeruleus (LC) neurons and controls the level of attention and alertness. Moreover, LC neurons influence brain metabolic activity, gene expression and brain inflammatory processes. As a consequence of the sensory control of ARAS/LC, stimulation of a sensory channel may potential influence neuronal activity and trophic state all over the brain, supporting cognitive functions and exerting a neuroprotective action. On the other hand, an imbalance of the same input on the two sides may lead to an asymmetric hemispheric excitability, leading to an impairment in cognitive functions. Among the inputs that may drive LC neurons and ARAS, those arising from the trigeminal region, from visceral organs and, possibly, from the vestibular system seem to be particularly relevant in regulating their activity. The trigeminal, visceral and vestibular control of ARAS/LC activity may explain why these input signals: (1) affect sensorimotor and cognitive functions which are not directly related to their specific informational content; and (2) are effective in relieving the symptoms of some brain pathologies, thus prompting peripheral activation of these input systems as a complementary approach for the treatment of cognitive impairments and neurodegenerative disorders.

Galvanic Vestibular Stimulation (GVS) effects on impaired interhemispheric connectivity in Parkinson's Disease

Disrupted interhemispheric connectivity (IHC) is being increasingly recognized as a robust feature of a number of neurological diseases, including Parkinson's Disease (PD). We investigated whether or not Galvanic Vestibular Stimulation (GVS) - a proposed treatment for PD - affected IHC in 11 PD subjects (off medication). In order to avoid the confound of stimulation artifact disrupting the EEG, we investigated the immediate period (52 sec) after stimulation (72 sec) with noisy 1/f-type GVS stimuli. Partial Least Squares (PLS) regression was used to determine the subject-specific linear combination of EEG electrodes that maximized covariance between hemispheres and then computed coherence between the dominant PLS components. PD subjects had increased IHC <;~10 Hz and decreased IHC >13 Hz compared to 11 healthy, age-matched controls. After GVS in PD subjects, a significant increase in IHC was detected, especially above 30 Hz. We suggest that GVS may partially exert its beneficial effects in PD by "normalizing" impaired IHC.

Effects of galvanic vestibular stimulation on event related potentials

[Purpose] The purpose of this study was to examine the effects of galvanic vestibular stimulation on event-related potentials. [Subjects and Methods] Forty normal female adult subjects were randomly distributed to a galvanic vestibular stimulation application group (20 subjects) and sham group (20 subjects). For galvanic vestibular stimulation application, a positive electrode was applied to the right mastoid process, and a negative electrode was applied to the left mastoid process; simulation was applied for 10 minutes. A test was conducted on the N100 and P300 components of the event-related potentials before and after galvanic vestibular stimulation. [Results] The N100 latency showed statistically significant differences in interaction effects between time and group in the F3, F4, Fz, and Pz areas. The P300 latency showed the same results in the Fp1 and Fp2 areas, the N100 amplitude showed the same results in the Fp2, Fz, and Pz areas; and the P300 amplitude showed the same results in the Pz area. [Conclusion] These results suggest that galvanic vestibular stimulation may play a positive role in the N100 and P300 components of the event-related potentials of the cerebral cortex related to decision-making in matching words with images.

Comparing Auditory Noise Treatment with Stimulant Medication on Cognitive Task Performance in Children with Attention Deficit Hyperactivity Disorder: Results from a Pilot Study

Background: Recent research has shown that acoustic white noise (80 dB) can improve task performance in people with attention deficits and/or Attention Deficit Hyperactivity Disorder (ADHD). This is attributed to the phenomenon of stochastic resonance in which a certain amount of noise can improve performance in a brain that is not working at its optimum. We compare here the effect of noise exposure with the effect of stimulant medication on cognitive task performance in ADHD. The aim of the present study was to compare the effects of auditory noise exposure with stimulant medication for ADHD children on a cognitive test battery. A group of typically developed children (TDC) took the same tests as a comparison.

Methods: Twenty children with ADHD of combined or inattentive subtypes and twenty TDC matched for age and gender performed three different tests (word recall, spanboard and n-back task) during exposure to white noise (80 dB) and in a silent condition. The ADHD children were tested with and without central stimulant medication.

Results: In the spanboard- and the word recall tasks, but not in the 2-back task, white noise exposure led to significant improvements for both non-medicated and medicated ADHD children. No significant effects of medication were found on any of the three tasks.

Conclusion: This pilot study shows that exposure to white noise resulted in a task improvement that was larger than the one with stimulant medication thus opening up the possibility of using auditory noise as an alternative, non-pharmacological treatment of cognitive ADHD symptoms.

Noisy vestibular stimulation improves dynamic walking stability in bilateral vestibulopathy

OBJECTIVE

To examine the effects of imperceptible levels of white noise galvanic vestibular stimulation (nGVS) on dynamic walking stability in patients with bilateral vestibulopathy (BVP).

METHODS

Walking performance of 13 patients with confirmed BVP (mean age 50.1 ± 5.5 years) at slow, preferred, and fast speeds was examined during walking with zero-amplitude nGVS (sham trial) and nonzero-amplitude nGVS set to 80% of the individual cutaneous threshold for GVS (nGVS trial). Eight standard gait measures were analyzed: stride time, stride length, base of support, double support time percentage as well as the bilateral phase coordination index, and the coefficient of variation (CV) of stride time, stride length, and base of support.

RESULTS

Compared to the sham trial, nGVS improved stride time CV by 26.0% ± 8.4% (p < 0.041), stride length CV by 26.0% ± 7.7% (p < 0.029), base of support CV by 27.8% ± 2.9% (p < 0.037), and phase coordination index by 8.4% ± 8.8% (p < 0.013). The nGVS effects on walking performance were correlated with subjective ratings of walking balance (ρ = 0.79, p < 0.001). Effect of nGVS on walking stability was most pronounced during slow walking.

CONCLUSIONS

In patients with BVP, nGVS is effective in improving impaired gait performance, predominantly during slower walking speeds. It primarily targets the variability and bilateral coordination characteristics of the walking pattern, which are linked to dynamic walking stability. nGVS might present an effective treatment option to immediately improve walking performance and reduce the incidence of falls in patients with BVP.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that in patients with BVP, an imperceptible level of nGVS improves dynamic walking stability.

The Moving History of Vestibular Stimulation as a Therapeutic Intervention

Although the discovery and understanding of the function of the vestibular system date back only to the 19th century, strategies that involve vestibular stimulation were used long before to calm, soothe and even cure people. While such stimulation was classically achieved with various motion devices, like Cox's chair or Hallaran's swing, the development of caloric and galvanic vestibular stimulation has opened up new possibilities in the 20th century. With the increasing knowledge and recognition of vestibular contributions to various perceptual, motor, cognitive, and emotional processes, vestibular stimulation has been suggested as a powerful and non-invasive treatment for a range of psychiatric, neurological and neurodevelopmental conditions. Yet, the therapeutic interventions were, and still are, often not hypothesis-driven as broader theories remain scarce and underlying neurophysiological mechanisms are often vague. We aim to critically review the literature on vestibular stimulation as a form of therapy in various selected disorders and present its successes, expectations, and drawbacks from a historical perspective.

Stochastic resonance in the synaptic transmission between hair cells and vestibular primary afferents in development

The stochastic resonance (SR) is a phenomenon of nonlinear systems in which the addition of an intermediate level of noise improves the response of such system. Although SR has been studied in isolated hair cells and in the bullfrog sacculus, the occurrence of this phenomenon in the vestibular system in development is unknown. The purpose of the present study was to explore for the existence of SR via natural mechanical-stimulation in the hair cell-vestibular primary afferent transmission. In vitro experiments were performed on the posterior semicircular canal of the chicken inner ear during development. Our experiments showed that the signal-to-noise ratio of the afferent multiunit activity from E15 to P5 stages of development exhibited the SR phenomenon, which was characterized by an inverted U-like response as a function of the input noise level. The inverted U-like graphs of SR acquired their higher amplitude after the post-hatching stage of development. Blockage of the synaptic transmission with selective antagonists of the NMDA and AMPA/Kainate receptors abolished the SR of the afferent multiunit activity. Furthermore, computer simulations on a model of the hair cell - primary afferent synapse qualitatively reproduced this SR behavior and provided a possible explanation of how and where the SR could occur. These results demonstrate that a particular level of mechanical noise on the semicircular canals can improve the performance of the vestibular system in their peripheral sensory processing even during embryonic stages of development.

Noisy galvanic vestibular stimulation enhances spatial memory in cognitive impairment-induced by intracerebroventricular-streptozotocin administration

There are several anatomical connections between vestibular system and brain areas construct spatial memory. Since subliminal noisy galvanic vestibular stimulation (GVS) has been demonstrated to enhance some types of memory, we speculated that application of noisy GVS may improve spatial memory in a rat model of intracerebroventricular streptozotocin (ICV-STZ)-induced cognitive impairment. Moreover, we attempted to determine the effect of repeated exposure to GVS on spatial memory performance. The spatial memory was assessed using Morris water maze test. The groups received 1 (ICV-STZ/GVS-I) or 5 (ICV-STZ/GVS-II) sessions, each lasting 30 min, of low amplitude noisy GVS, or no GVS at all (Control, ICV-saline, ICV-STZ/noGVS). Hippocampal morphological changes investigated with cresyl violet staining and the immediate early gene product c-Fos, as a neuronal activity marker, was measured. Hippocampal c-Fos positive cells increased in both GVS stimulated groups. We observed significantly improved spatial performance only in ICV-STZ/GVS-II group. Histological evaluation showed normal density in ICV-STZ/GVS-II group whereas degeneration observed in ICV-STZ/GVS-I group similar to ICV-STZ/noGVS. The results showed the improvement of memory impairment after repeated exposure to GVS. This effect may be due in part to frequent activation of the vestibular neurons and the hippocampal regions connected to them. Our current study suggests the potential role of GVS as a practical method to combat cognitive decline induced by sporadic Alzheimer disease.

Differential effects of white noise in cognitive and perceptual tasks

Beneficial effects of noise on higher cognition have recently attracted attention. Hypothesizing an involvement of the mesolimbic dopamine system and its functional interactions with cortical areas, the current study aimed to demonstrate a facilitation of dopamine-dependent attentional and mnemonic functions by externally applying white noise in five behavioral experiments including a total sample of 167 healthy human subjects. During working memory, acoustic white noise impaired accuracy when presented during the maintenance period (Experiments 1-3). In a reward based long-term memory task, white noise accelerated perceptual judgments for scene images during encoding but left subsequent recognition memory unaffected (Experiment 4). In a modified Posner task (Experiment 5), the benefit due to white noise in attentional orienting correlated weakly with reward dependence, a personality trait that has been associated with the dopaminergic system. These results suggest that white noise has no general effect on cognitive functions. Instead, they indicate differential effects on perception and cognition depending on a variety of factors such as task demands and timing of white noise presentation.

Noise-Enhanced Vestibular Input Improves Dynamic Walking Stability in Healthy Subjects

BACKGROUND

White noise galvanic vestibular stimulation (GVS) is thought to enhance the sensitivity of vestibular organs.

OBJECTIVE

To examine the effects of noise-enhanced vestibular input on the walking performance in healthy subjects walking with eyes closed.

METHODS

Walking performance of 17 healthy subjects (mean age 28.8 ± 1.7 years) at slow, preferred, and fast speeds was examined during three different conditions: (1) walking with eyes open (EO) as baseline condition, (2) walking with eyes closed and sham noisy GVS (EC), and (3) walking with eyes closed and non-zero amplitude noisy GVS set to 80% of the individual sensory threshold for GVS (EC-GVS). Ten gait parameters were examined: stride time, stride length, base of support, swing time percentage, double support time percentage as well as gait asymmetry, bilateral phase coordination and the coefficient of variation (CV) of stride time, stride length and base of support.

RESULTS

Noisy GVS improved stride time CV by 36% (p < 0.034), stride length CV by 31% (p < 0.037), base of support CV by 14% (p < 0.009), and bilateral phase coordination by 23% (p < 0.034). The ameliorating effects of noisy GVS on locomotion function were primarily observable during slow walking speeds.

CONCLUSION

Noise-enhanced vestibular input is effective in improving locomotion function and is accompanied by a subjectively felt improvement of walking balance. It predominantly targets the variability and bilateral coordination characteristics of the walking pattern, which are critically linked to dynamic walking stability. Noisy GVS might present an effective treatment option to improve walking performance in patients with bilateral vestibular dysfunction.

Using low levels of stochastic vestibular stimulation to improve locomotor stability

Low levels of bipolar binaural white noise based imperceptible stochastic electrical stimulation to the vestibular system (stochastic vestibular stimulation, SVS) have been shown to improve stability during balance tasks in normal, healthy subjects by facilitating enhanced information transfer using stochastic resonance (SR) principles. We hypothesize that detection of time-critical sub-threshold sensory signals using low levels of bipolar binaural SVS based on SR principles will help improve stability of walking during support surface perturbations. In the current study 13 healthy subjects were exposed to short continuous support surface perturbations for 60 s while walking on a treadmill and simultaneously viewing perceptually matched linear optic flow. Low levels of bipolar binaural white noise based SVS were applied to the vestibular organs. Multiple trials of the treadmill locomotion test were performed with stimulation current levels varying in the range of 0–1500 μA, randomized across trials. The results show that subjects significantly improved their walking stability during support surface perturbations at stimulation levels with peak amplitude predominantly in the range of 100–500 μA consistent with the SR phenomenon. Additionally, objective perceptual motion thresholds were measured separately as estimates of internal noise while subjects sat on a chair with their eyes closed and received 1 Hz bipolar binaural sinusoidal electrical stimuli. The optimal improvement in walking stability was achieved on average with peak stimulation amplitudes of approximately 35% of perceptual motion threshold. This study shows the effectiveness of using low imperceptible levels of SVS to improve dynamic stability during walking on a laterally oscillating treadmill via the SR phenomenon.

Using Low Levels of Stochastic Vestibular Stimulation to Improve Balance Function

Low-level stochastic vestibular stimulation (SVS) has been associated with improved postural responses in the medio-lateral (ML) direction, but its effect in improving balance function in both the ML and anterior-posterior (AP) directions has not been studied. In this series of studies, the efficacy of applying low amplitude SVS in 0–30 Hz range between the mastoids in the ML direction on improving cross-planar balance function was investigated. Forty-five (45) subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in ML, AP and combined APML directions. Results show that binaural bipolar SVS given in the ML direction significantly improved balance performance with the peak of optimal stimulus amplitude predominantly in the range of 100–500 μA for all the three directions, exhibiting stochastic resonance (SR) phenomenon. Objective perceptual and body motion thresholds as estimates of internal noise while subjects sat on a chair with their eyes closed and were given 1 Hz bipolar binaural sinusoidal electrical stimuli were also measured. In general, there was no significant difference between estimates of perceptual and body motion thresholds. The average optimal SVS amplitude that improved balance performance (peak SVS amplitude normalized to perceptual threshold) was estimated to be 46% in ML, 53% in AP, and 50% in APML directions. A miniature patch-type SVS device may be useful to improve balance function in people with disabilities due to aging, Parkinson’s disease or in astronauts returning from long-duration space flight.

Effect of galvanic vestibular stimulation on movement-related cortical potential

[Purpose] This study examined the effects of galvanic vestibular stimulation on motion-related cortical potential. [Subjects and Methods] Fourty healthy female adult subjects each received galvanic vestibular stimulation or sham treatment. For galvanic vestibular stimulation, the anode and cathode were applied to the right and left mastoid processes, respectively, for 10 minutes. Motion-related cortical potential was tested pre- and post-treatment. To measure motion-related cortical potential, surface electromyography signals were generated by 50 thumb abductions with electrode application on the abductor pollicis brevis of the left (i.e., non-dominant) hand. [Results] The negative slope cortical potential on the C3 area (i.e., dominant hand) and cortical negative slope and motor potential on the C4 area (i.e., non-dominant hand) showed significant interaction effects. The galvanic vestibular stimulation group showed an increased negative slope amplitude in the C3 area, and increased negative slope and motor potential amplitudes in the C4 area compared to the sham group. [Conclusion] Galvanic vestibular stimulation increases the negative slope and motor potential amplitudes of the homonymous brain cortex area, which controls hand function and motion-related cortical potential, and the negative slope amplitude of the opposite cortical area, thus activating the brain areas for hand function.

Different effects of adding white noise on cognitive performance of sub-, normal and super-attentive school children

OBJECTIVES

Noise often has detrimental effects on performance. However, because of the phenomenon of stochastic resonance (SR), auditory white noise (WN) can alter the "signal to noise" ratio and improve performance. The Moderate Brain Arousal (MBA) model postulates different levels of internal "neural noise" in individuals with different attentional capacities. This in turn determines the particular WN level most beneficial in each individual case-with one level of WN facilitating poor attenders but hindering super-attentive children. The objective of the present study is to find out if added WN affects cognitive performance differently in children that differ in attention ability.

METHODS

Participants were teacher-rated super- (N = 25); normal- (N = 29) and sub-attentive (N = 36) children (aged 8 to 10 years). Two non-executive function (EF) tasks (a verbal episodic recall task and a delayed verbal recognition task) and two EF tasks (a visuo-spatial working memory test and a Go-NoGo task) were performed under three WN levels. The non-WN condition was only used to control for potential differences in background noise in the group testing situations.

RESULTS

There were different effects of WN on performance in the three groups-adding moderate WN worsened the performance of super-attentive children for both task types and improved EF performance in sub-attentive children. The normal-attentive children's performance was unaffected by WN exposure. The shift from moderate to high levels of WN had little further effect on performance in any group.

SIGNIFICANCE

The predicted differential effect of WN on performance was confirmed. However, the failure to find evidence for an inverted U function challenges current theories. Alternative explanations are discussed. We propose that WN therapy should be further investigated as a possible non-pharmacological treatment for inattention.

Effects of galvanic vestibular stimulation on visual memory recall and EEG

[Purpose] This study aimed to examine the effects of galvanic vestibular stimulation (GVS) on visual memory recall and EEG. [Subjects and Methods] In the present study, 42 adults were selected and divided equally into two groups of 21 adults, the GVS group and the Sham group. The error rate was calculated as a percentage based on the total number of errors in the answers to 24 questions after stimulation, while the reaction time was measured in intervals between the time the questions were asked and the time it took the subjects to answer the questions. EEG data were obtained by attaching electrodes to the Fz, Cz, and Pz points during the question and answer phase. [Results] The error rate showed statistically significant differences in the interaction involving the time of response and group. The reaction time showed no statistically significant differences in the interaction involving the time of response and group. When relative band power parameters were analyzed, alpha waves showed no statistically significant differences in the interaction involving the time of response and group, but only the Fz area of beta waves showed statistically significant differences in the interaction involving the time of response and group. [Conclusion] GVS may improve visual memory recall in relation to a flower, a person, an animal, or a building.

Face processing improvements in prosopagnosia: successes and failures over the last 50 years

Clinicians and researchers have widely believed that face processing cannot be improved in prosopagnosia. Though more than a dozen reported studies have attempted to enhance face processing in prosopagnosics over the last 50 years, evidence for effective treatment approaches has only begun to emerge. Here, we review the current literature on spontaneous recovery in acquired prosopagnosia (AP), as well as treatment attempts in acquired and developmental prosopagnosia (DP), differentiating between compensatory and remedial approaches. We find that for AP, rather than remedial methods, strategic compensatory training such as verbalizing distinctive facial features has shown to be the most effective approach (despite limited evidence of generalization). In children with DP, compensatory training has also shown some effectiveness. In adults with DP, two recent larger-scale studies, one using remedial training and another administering oxytocin, have demonstrated group-level improvements and evidence of generalization. These results suggest that DPs, perhaps because of their more intact face processing infrastructure, may benefit more from treatments targeting face processing than APs.

Caloric vestibular stimulation as a treatment for conversion disorder: a case report and medical hypothesis

Conversion disorder is a medical condition in which a person has paralysis, blindness, or other neurological symptoms that cannot be clearly explained physiologically. To date, there is neither specific nor conclusive treatment. In this paper, we draw together a number of disparate pieces of knowledge to propose a novel intervention to provide transient alleviation for this condition. As caloric vestibular stimulation has been demonstrated to modulate a variety of cognitive functions associated with brain activations, especially in the temporal-parietal cortex, anterior cingulate cortex, and insular cortex, there is evidence to assume an effect in specific mental disorders. Therefore, we go on to hypothesize that lateralized cold vestibular caloric stimulation will be effective in treating conversion disorder and we present provisional evidence from one patient that supports this conclusion. If our hypothesis is correct, this will be the first time in psychiatry and neurology that a clinically well-known mental disorder, long considered difficult to understand and to treat, is relieved by a simple or common, non-invasive medical procedure.

Spatial cognition, body representation and affective processes: the role of vestibular information beyond ocular reflexes and control of posture

A growing number of studies in humans demonstrate the involvement of vestibular information in tasks that are seemingly remote from well-known functions such as space constancy or postural control. In this review article we point out three emerging streams of research highlighting the importance of vestibular input: (1) Spatial Cognition: Modulation of vestibular signals can induce specific changes in spatial cognitive tasks like mental imagery and the processing of numbers. This has been shown in studies manipulating body orientation (changing the input from the otoliths), body rotation (changing the input from the semicircular canals), in clinical findings with vestibular patients, and in studies carried out in microgravity. There is also an effect in the reverse direction; top-down processes can affect perception of vestibular stimuli. (2) Body Representation: Numerous studies demonstrate that vestibular stimulation changes the representation of body parts, and sensitivity to tactile input or pain. Thus, the vestibular system plays an integral role in multisensory coordination of body representation. (3) Affective Processes and Disorders: Studies in psychiatric patients and patients with a vestibular disorder report a high comorbidity of vestibular dysfunctions and psychiatric symptoms. Recent studies investigated the beneficial effect of vestibular stimulation on psychiatric disorders, and how vestibular input can change mood and affect. These three emerging streams of research in vestibular science are-at least in part-associated with different neuronal core mechanisms. Spatial transformations draw on parietal areas, body representation is associated with somatosensory areas, and affective processes involve insular and cingulate cortices, all of which receive vestibular input. Even though a wide range of different vestibular cortical projection areas has been ascertained, their functionality still is scarcely understood.

Galvanic vestibular stimulation in hemi-spatial neglect

Hemi-spatial neglect is an attentional disorder in which the sufferer fails to acknowledge or respond to stimuli appearing in contralesional space. In recent years, it has become clear that a measurable reduction in contralesional neglect can occur during galvanic vestibular stimulation, a technique by which transmastoid, small amplitude current induces lateral, attentional shifts via asymmetric modulation of the left and right vestibular nerves. However, it remains unclear whether this reduction persists after stimulation is stopped. To estimate longevity of effect, we therefore conducted a double-blind, randomized, dose-response trial involving a group of stroke patients suffering from left-sided neglect (n = 52, mean age = 66 years). To determine whether repeated sessions of galvanic vestibular stimulation more effectively induce lasting relief than a single session, participants received 1, 5, or 10 sessions, each lasting 25 min, of sub-sensory, left-anodal right-cathodal noisy direct current (mean amplitude = 1 mA). Ninety five percent confidence intervals indicated that all three treatment arms showed a statistically significant improvement between the pre-stimulation baseline and the final day of stimulation on the primary outcome measure, the conventional tests of the Behavioral Inattention Test. More remarkably, this change (mean change = 28%, SD = 18) was still evident 1 month later. Secondary analyses indicated an allied increase of 20% in median Barthel Index (BI) score, a measure of functional capacity, in the absence of any adverse events or instances of participant non-compliance. Together these data suggest that galvanic vestibular stimulation, a simple, cheap technique suitable for home-based administration, may produce lasting reductions in neglect that are clinically important. Further protocol optimization is now needed ahead of a larger effectiveness study.