Noisy galvanic vestibular stimulation (nGVS) has been shown to improve postural control. However, the focus has been on the vestibular system, failing to account for other sensory inputs. The aim of the present study was thus to examine the relative impact of the various sensory feedback sources on the improvement of postural control following nGVS in older adults. Fourty-seven participants (20 controls; 27 older adults) were recruited for this study. Participants performed the modified clinical test of sensory integration as part of the postural control assessment. Older adults received an nGVS or sham stimulation which was compared to their baseline measurements and to an optimal performance (control group comprised of young adults). Results suggest that the nGVS-induced improvement of postural control in older individuals is significant only in conditions where visual and somatosensory feedback were hindered.The data also suggest that improvements in these conditions is more significant in individuals with reduced vestibular feedback. The study confirms the potential impact of nGVS for the rehabilitation of balance difficulties in the elderly population, most particularly in conditions with less reliable somatosensory and visual inputs. nGVS effects are thus modulated by sensory feedback with a dominant effect of somatosensory and visual sensory cues.

The vestibular system has been shown to play a role in the integration of spatial sensory information. For instance, vestibular perturbations induce significant shifts in spatial tactile tasks, but results have been contradictory regarding auditory modality. This observation may be because some of the previous vestibular stimulation methods (i.e., stochastic GVS) did not reliably induce a self-motion effect. This study aims to evaluate the importance of directional illusory motion on auditory localization mechanism, using direct current GVS. Twenty young healthy participants performed a sound localization task under earphones with 9 positions in the azimuth plane divided into three quadrants 7Left (45°;− 30°;− 20°), Center (− 10°;0°;10°), and Right (20°;30°;45)]. Participants were asked to verbally identify the exact position of the sound source under 3 conditions: (1) Without GVS (2) GVS with anode on the right mastoid (3) GVS with anode on the left mastoid. Results were analyzed using the non-parametric Friedman test and Wilcoxon rank-sum post-hoc test with a Bonferroni correction applied to account for multiple comparisons. Compared to baseline, left anodal stimulation caused a greater error ratio for sounds in all quadrants. Moreover, for sounds in the right quadrant, a significantly greater error ratio was observed for anode left compared to the anode right condition. Right anodal condition caused a greater error ratio for sounds in the left and the center quadrants compared to the baseline condition. This study demonstrates for the first time, that sound source localization can be influenced by direct current GVS and is modulated according to the anode position.

In contrast to the large body of findings confirming the influence of auditory cues on body perception and movement-related activity, the influence of body representation on spatial hearing remains essentially unexplored. Here, we use a disorientation task to assess whether a change in the body's orientation in space could lead to an illusory shift in the localization of a sound source. While most of the participants were initially able to locate the sound source with great precision, they all made substantial errors in judging the position of the same sound source following the body orientation-altering task. These results demonstrate that a change in body orientation can have a significant impact on the auditory processes underlying sound localization. The illusory errors not only confirm the strong connection between the auditory system and the representation of the body in space but also raise questions about the importance of hearing in determining spatial position.

The influence of multisensory integration on spatial hearing has received more attention in recent years. Notably, incongruent sensory inputs can bias auditory spatial processing. Here, we present a protocol for producing an illusory shift in the localization of a sound source by inducing an unconscious shift in the representation of the body in space. We describe steps for screening participants and evaluating vestibular and hearing abilities. We then detail procedures for performing auditory localization tasks both with and without disorientation.For complete details on the use and execution of this protocol, please refer to Paromov et al.1

BackgroundThe video head impulse test (vHIT) is vital in clinical setting for assessing vestibulo-ocular reflex (VOR) function in patients of all ages. However, how normal aging influence VOR gain and catch-up saccades remains unclear, thus leading to confusion in interpretation of vHIT results.ObjectiveThis study aims to compare VOR gain and saccades parameters (frequency, amplitude, and latency) between younger and older adults, while maintaining head velocity and acceleration within the same range.MethodsA total of 24 younger and 24 older adults performed horizontal vHIT tests (ICS Impulse, Otometrics, Denmark). Gain and saccades were analyzed using a custom MATLAB script. Three VOR gain algorithms were compared: Area under the curve (AUC), instantaneous gain, and regression gain.ResultsIn our sample, no significant differences in the VOR gains were observed between younger and older adults using any of the algorithms. Compared to younger adults, older adults had saccades that were significantly more frequent, of greater amplitude, and of shorter latencies. However, a larger sample size is needed to confirm the lack of aging effect on VOR gains.ConclusionsThe absence of significant effects of aging on VOR gain in vHIT demonstrates that all three gain algorithms should provide similar values for patients across all ages in clinical practice. The results suggest that small saccades in older adults are unrelated to head impulse parameters, and the mechanisms behind this increase in saccades with normal aging remain to be explored.

There is growing evidence linking hearing impairments and the deterioration of postural stability in older adults. To our knowledge, however, no study to date has investigated the effect of age-related hearing loss on the sensory reweighting process during postural control. In the absence of data, much is unknown about the possible mechanisms, both deleterious and compensatory, that could underly the deterioration of postural control following hearing loss in the elderly. The aim of this study was to empirically examine sensory reweighting for postural control in older adults with age-related hearing loss as compared to older adults with normal hearing. The center of pressure of all participants was recorded using a force platform and the modified clinical test of sensory interaction and balance protocol. The results suggest that individuals with age-related hearing loss displayed increased somatosensory reliance relative to normal hearing younger adults. This increased reliance on somatosensory input does not appear to be effective in mitigating the loss of postural control, probably due to the concomitant deterioration of tactile and proprioceptive sensitivity and acuity associated with aging. Beyond helping to further define the role of auditory perception in postural control, these results further the understanding of sensory-related mechanisms associated with postural instability in older adults.

BACKGROUND:Falls are a major health concern with potentially dramatic consequences for people over 65 years of age. One crucial determinant in the risk of falls in older adults is postural control, a complex process that requires the contribution of different sensory modalities, namely visual, vestibular, auditory, and somatosensory. While there are well-established methods to screen for age-related vision, hearing, tactile, and vestibular impairments, there are very few widely available methods to screen for somatosensory function, but studies indicate that ankle audiometry (vibration thresholds) using a common B-71 bone vibrator can serve that purpose. To date, unfortunately, this technique has received little attention as a tool to measure postural instability in older adults. PURPOSE:The objective of the present study was to examine postural control in older adults with and without degradation of the somatosensory functions, as determined with ankle audiometry. RESEARCH DESIGN:This was standard group comparison. STUDY SAMPLE:In total, 36 healthy elderly aged between 65 and 80 years old were divided into two groups (low vibration threshold [n = 18] and high vibration threshold [n = 18]). DATA COLLECTION AND ANALYSIS:Standard audiometry, video head impulse test, vibration thresholds (big toe, ankle, and tibia), and static postural control task using a force platform were performed. RESULTS:Greater postural instability in participants with higher (worse) vibration thresholds as compared with participants with lower (better) vibration thresholds was observed even though both groups were comparable on hearing threshold and vestibular function. CONCLUSION:The results indicate that performing a simple vibration threshold evaluation, using a clinically available B-71 with a cut-off value of 42 dB hearing loss, could be an effective, fast, and easy-to-use procedure for detecting people at risk of falls.

Long-term dance training is known to improve postural control, especially in challenging postural tasks. However, the effect of dance training on the vestibulo-ocular reflex (VOR) has yet to be properly assessed. This study directly investigated whether VOR parameters are influenced by long-term dance training by testing dancers and controls using the video head impulse test. VOR gains using two of the most common methods (area ratio and instantaneous gains), latency and amplitude of the first saccade, if applicable, were computed. Results revealed a larger VOR gain as measured by area gain and instantaneous gain at 40 ms specifically for left-head impulses, but not right-head impulses. No significant differences in saccade frequency, amplitude, or latency were observed between groups. These differences appear to stem from a modified eye-to-head relationship during high-velocity head impulses in dancers. More specifically, the dancers' eyes lead head movement during passively applied head impulses, which result in higher VOR gain.NEW & NOTEWORTHY This study demonstrates, for the first time, that long-term dance training results in a nonlinear relationship between eye and head velocity within the first milliseconds following passive head impulse. The data also suggest a larger VOR gain in dancers. This finding suggests that dance training may modify eye-head relationship in passive high-frequency head movements. This is of particular interest for vestibular rehabilitation.

BACKGROUND:Cervical Vestibular Evoked Myogenic Potentials (cVEMP) is an electromyogenic measure commonly used in clinic to assess saccule function. The main parameters are peak-peak amplitude and interaural asymmetry ratio (IAR). Several non-vestibular factors may influence these parameters. Notably, a greater EMG contraction level prior to stimulation leads to an increased amplitude. As aging impacts both vestibular structures and muscle propreties, it is still a matter of debate whether the decrease in cVEMP amplitude observed in normal aging is due to EMG differences prior to stimulation or to the effect of aging on the sacculo-collic reflex pathway. At the clinical level, understanding the effect of aging on the relationship between EMG activity and cVEMP response (amplitude, asymmetry ratio) and the effect of normalization is crucial to improving the categorization of healthy versus pathological responses.OBJECTIVE:To investigate whether normalization modifies cVEMP amplitude and asymmetry ratios differently in younger and older heatlhy adults.METHOD:cVEMP recordings were conducted in 42 normal healthy participants divided in two age groups: younger (n = 29): mean = 22.79 years old SD = 1.66; and older (n = 13): mean = 69.00 years old SD = 3.61. Air-conducted cVEMP were recorded using Eclipse (Interacoustics, Denmark). The stimulus was a 95 dBnHL tone burst (500 Hz) with rise, plateau and fall time of 1 ms. cVEMP were recorded only when EMG levels were between 50μV and 150μV, using the Eclipse (Interacoustic, Denmark) monitoring system.RESULTS:No significant differences were observed for prestimulus EMG levels between younger and older participants (F(1,83) = 1.13, p = 0.291). However, significant differences between groups were observed for raw cVEMP amplitude (F(1,83) = 14.78; p < 0.001) and corrected cVEMP amplitude (F(1,83) = 21.85; p < 0.0001). A significant positive linear relationship between prestimulus EMG contraction level (RMS) and raw cVEMP amplitude was observed in younger participants (r2 = 0.234; p < 0.001), but not in older adults (r2 = -0.0144; p = 0.056). Finally, no significant differences between younger and older participants were observed for raw amplitude asymmetry ratios (F(1,41) = 0.124, p = 0.726) or normalized asymmetry ratios (F(1,41) = 0.726, p = 0.508).CONCLUSION:Our results suggest that when EMG is monitored and activation of the SCM is sufficient, the observed decline in cVEMP amplitude with normal aging does not seem to be caused by EMG differences and is therefore likely due to the known histopathological modifications of the vestibular system that occurs with normal aging.

Recent evidences suggest that binaural vestibular stimulation affects tactile temporal processing. However, it remains difficult to determine the physiological mechanisms supporting the vestibular–somatosensory interactions observed during a TOJ task. Controlling the activation of the right or left vestibular system separately could allow to better understand the physiological bases of these findings and reconcile previous studies. The objective of the present study was to examine tactile temporal processing using a temporal order judgment task following selective stimulation of the right and left vestibular system with bi-thermal caloric vestibular stimulation (CVS). A total of 24 right-handed participants received bi-thermal CVS either in the right ear (n = 12) or the left ear (n = 12). Participants held vibrators in both hands which delivered a signal temporally separated by a variable asynchrony. Participants had to report the hand where the vibration was perceived first. The task was performed in three different CVS conditions: (1) baseline, (2) warm CVS, and (3) cold CVS. Analysis of the logistics curve parameters—just noticeable difference (JND) and point of subjective simultaneity (PSS)—for each participant in each CVS conditions revealed an increase in JND greater following warm CVS. A significant increase in JND following warm CVS was measured bilaterally. However, cold CVS increased JND only when CVS was applied in the left ear, but not in the right ear. Finally, no influence of CVS on PSS was observed.

It has been well established that eye movements have an impact on balance, and it has been hypothesized that extraocular oculomotor signals could play a significant role in this effect. Unfortunately, this hypothesis could not be confirmed as the previous methodology did not allow for the independent assessment of the differential effects of visual and oculomotor stimulation. The objective of the present study is to examine the impact of motor movements of the eyes without visual stimulation on balance. Static postural control, a prerequisite for balance, was assessed using a force platform in 20 participants. They were asked either to remain still without moving or to make movements of the tongue or eyes at a rate of two cycles per second. Movements were monitored using electrophysiological recordings. Each of the conditions was performed with eyes open and with eyes closed. Significant changes in postural control were observed due to eye movements when the eyes were open, but no significant differences were found between the conditions when the eyes were closed. The results confirm that the visual system provides important spatial cues for balance, allowing the body to be better positioned in space, and reject the possibility that extraocular signals are directly involved in postural stability.

The brain of deaf people is definitely not just deaf, and we have to reconsider what we know about the impact of hearing loss on brain development in light of comorbid vestibular impairments.

This study aimed at better understanding the neurochemistry underlying transcranial magnetic stimulation (TMS) and magnetic resonance spectroscopy (MRS) measurements as it pertains to GABAergic activity following administration of allosteric GABAA receptor agonist lorazepam. Seventeen healthy adults (8 females, 26.0 ± 5.4 years old) participated in a double-blind, crossover, placebo-controlled study, where participants underwent TMS and MRS two hours after drug intake (placebo or lorazepam; 2.5 mg). Neuronavigated TMS measures reflecting cortical inhibition and excitation were obtained in the left primary motor cortex. Sensorimotor cortex and occipital cortex MRS data were acquired using a 3T scanner with a MEGA-PRESS sequence, allowing water-referenced [GABA] and [Glx] (glutamate + glutamine) quantification. Lorazepam administration decreased occipital [GABA], decreased motor cortex excitability and increased GABAA-receptor mediated motor cortex inhibition (short intracortical inhibition (SICI)). Lorazepam intake did not modulate sensorimotor [GABA] and TMS measures of intra-cortical facilitation, long-interval cortical inhibition, cortical silent period, and resting motor threshold. Furthermore, higher sensorimotor [GABA] was associated with higher cortical inhibition (SICI) following lorazepam administration, suggesting that baseline sensorimotor [GABA] may be valuable in predicting pharmacological or neuromodulatory treatment response. Finally, the differential effects of lorazepam on MRS and TMS measures, with respect to GABA, support the idea that TMS measures of cortical inhibition reflect synaptic GABAergic phasic inhibitory activity while MRS reflects extrasynaptic GABA.

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

Previous studies have reported an important relationship between increasing age, vestibular impairment, and increased risk of falls. Recently, noisy galvanic vestibular stimulation (nGVS) has been shown to improve postural control in older adults during and potentially following stimulation. However, this effect of nGVS in older adults has not been examined in interaction with the integrity of the vestibular function. We aimed at determining the effect of nGVS on postural control in older adults with and without vestibular impairment and examining the sustained effect of nGVS as compared with a sham stimulation. Thirty-six older adults were assigned to the nGVS group (n = 24) or the sham group (n = 12). In the nGVS group, 12 participants had normal vestibular function and 12 had vestibular impairment. Static postural control was assessed prior to stimulation, during stimulation, and immediately following 30 min of nGVS. Results showed that nGVS induced a significant improvement in sway velocity (P < 0.001) and path length (P < 0.001) compared with sham stimulation. Furthermore, nGVS induced a significantly greater improvement of sway velocity (P < 0.05) and path length (P < 0.05) in older adults with vestibular impairment compared with older adults with normal vestibular function. Improvements in sway velocity (P < 0.001) and path length (P < 0.001) induced by nGVS were sustained immediately following stimulation. These findings suggest that nGVS improves postural control in older adults, and that the effect of nGVS varies depending on the integrity of the vestibular function. Results also show that nGVS effect on postural control, compared with a sham stimulation, can be sustained after the end of stimulation. NEW & NOTEWORTHY The present study is the first study to investigate the impact of vestibular function on the improvement of postural control induced by nGVS in older adults and to compare the improvement of postural control of older adults with and without vestibular impairment. Our results also suggest that nGVS is beneficial for all older adults, and even more for those with a vestibular impairment. Therefore, it could be an approach to reduce falls.

Mental imagery can induce audiovisual integration, but whether it can induce interactions in other modalities remains uncertain. It has been demonstrated that audiomotor interaction can be generated following training, but whether such audiomotor interaction can be induced by auditory imagery training remains unknown. The present study aims at determining whether auditory mental imagery could induce a multimodal association with postural control. We examined static postural control in the presence of a frequency-modulated sound in three groups of participants, prior to and following a short period of training designed to create an association between auditory mental imagery of sounds and postural swaying. Results suggest that mental imagery impacted performance, as a significant decrease in postural control was observed in the experimental group following mental imagery training. Results of the control groups confirmed that the effect of mental imagery was not due to response bias, but to a significant multimodal interaction following training. These findings are in accordance with previous studies suggesting that mental imagery stimuli can interact with perceptual stimuli of a different sensory modality and lead to multisensory integration. The results also confirm that audiomotor interaction can be generated a mental imagery training. However, the full extent of mental imagery influence on multimodal interaction remains to be determined.

Subconcussive hits to the head and physical fitness both have been associated with alterations in white matter (WM) microstructure in partly overlapping areas of the brain. The aim of the present study was to determine whether WM damage associated with repeated exposure to subconcussive hits to the head in university level contact sports athletes is modulated by high levels of fitness. To this end, 72 students were recruited: 24 athletes practicing a varsity contact sport (A-CS), 24 athletes practicing a varsity non-contact sport (A-NCS), and 24 healthy non-athletes (NA). Participants underwent a magnetic resonance imaging session that included diffusion-weighted imaging. Between-groups, statistical analyses were performed with diffusion tensor imaging measures extracted by tractometry of sections of the corpus callosum and the corticospinal tract. Most significant effects were found in A-NCS who exhibited higher fractional anisotropy (FA) values than A-CS in almost all segments of the corpus callosum and in the corticospinal tract. The A-NCS also showed higher FA compared with NA in the anterior regions of the corpus callosum and the corticospinal tracts. No group difference was found between the A-CS and the NA groups. These data suggest that repeated subconcussive hits to the head lead to anisotropic changes in the WM that may counteract the beneficial effects associated with high levels of fitness.

Functional neuroimaging studies have demonstrated that following deafness, auditory regions can respond to tactile stimuli. However, research to date has not conclusively demonstrated the behavioral correlates of these functional changes, with most studies showing normal-like tactile capabilities in the deaf. It has recently been suggested that more cognitive and complex tactile processes, such as music perception, could help to uncover superior tactile capabilities in the deaf. Indeed, following deafness music seems to be perceived through vibration, but the extent to which they can perceive musical features though the tactile modality remains undetermined. The goal of this study was to investigate tactile identification of musical emotion in the deaf. Participants had to rate melodies based on their emotional perception. Stimuli were presented through an haptic glove. Data suggest that deaf and control participants were comparable in the identification of three of the four emotions tested (sad, fear/threat, peacefulness). However and most importantly, for the simplest emotion (happiness), significant differences emerged between groups, suggesting an improved tactile identification of musical emotion in the deaf. Results support the hypothesis that brain plasticity following deafness can lead to improved complex tactile ability.

Musicians are better at processing sensory information and at integrating multisensory information in detection and discrimination tasks, but whether these enhanced abilities extend to more complex processes is still unknown. Emotional appeal is a crucial part of musical experience, but whether musicians can better identify emotions in music throughout different sensory modalities has yet to be determined. The goal of the present study was to investigate the auditory, tactile and audiotactile identification of emotions in musicians. Melodies expressing happiness, sadness, fear/threat, and peacefulness were played and participants had to rate each excerpt on a 10-point scale for each of the four emotions. Stimuli were presented through headphones and/or a glove with haptic audio exciters. The data suggest that musicians and control are comparable in the identification of the most basic (happiness and sadness) emotions. However, in the most difficult unisensory identification conditions (fear/threat and peacefulness), significant differences emerge between groups, suggesting that musical training enhances the identification of emotions, in both the auditory and tactile domains. These results support the hypothesis that musical training has an impact at all hierarchical levels of sensory and cognitive processing.

Plusieurs études ont révélé l’impact de la stimulation vestibulaire galvanique (SVG) sur le contrôle postural. Par contre, ses effets à long terme et l’influence de paramètres de stimulation, telle la densité du courant de la SVG, demeure méconnus. Les objectifs de cette étude sont d’examiner : – l’effet à long terme de la SVG sur le contrôle postural en comparaison à un placebo ; – l’influence de la densité du courant. Soixante-quatre sujets ont participé à deux examens. Dans la première expérience, 28 participants ont reçu une SVG ou un placebo pendant 30 minutes. Une tâche de contrôle postural a été effectuée avant la stimulation, après la stimulation et 1h post-stimulation. Lors d’une seconde expérience, 36 autres participants ont été assignés soit à l’un des deux groupes de SVG (35 cm2 ; 3 cm2) ou au groupe contrôle. Le contrôle postural a été évalué avant la stimulation et après la stimulation. Mis en commun, les résultats des études suggèrent que l’amélioration du contrôle postural est dépendante de la densité de courant appliqué lors de la SVG. Par contre, les données ne permettent pas de confirmer son impact à long terme. Les données révèlent l’importance d’une condition contrôle et l’influence de la densité du courant sur le contrôle postural lors de l’application de la SVG. D’autres études sont nécessaires pour examiner l’influence de d’autres variables, tel que l’état de la fonction vestibulaire, sur l’effet de la SVG à court et à long terme.