Vestibular Control Research Articles

Centre of pressure velocity shows impairments in NCAA Division I athletes six months post-concussion during standing balance

ABSTRACT Sport-related concussion return to play (RTP) decisions are largely based on the resolution of self-reported symptoms and neurocognitive function. Some evaluators also incorporate balance; however, an objective approach to balance that can detect effects beyond the acute condition is warranted. The purpose of this study is to examine linear measures of biomechanical balance up to 6 months post-concussion, and to present preliminary diagnostic thresholds useful for RTP. Each concussed athlete participated in instrumented standing balance tasks at 4 timepoints post-concussion. The measures from concussed athletes were compared to the sport-matched non-concussed athlete group at each timepoint. Centre of pressure (COP) mediolateral (ML) velocity in double-leg stance on a hard surface discriminated well between non-concussed and concussed athletes. COP anterior-posterior (AP) velocity in tandem stance on foam showed sensitivity to concussion. Sixty per cent of athletes at 6 months post-concussion did not recover to within the proposed COP ML velocity threshold in double-leg stance on a hard surface. Seventy-one per cent of athletes at 6 months post-concussion did not recover to within the COP AP velocity threshold in tandem stance on foam. This lack of recovery potentially indicates vestibular and motor control impairments long past the typical period of RTP.

P85 Head motion predictability explains phase- and speed-dependent suppression of vestibular balance control during walking

P85 Head motion predictability explains phase- and speed-dependent suppression of vestibular balance control during walking

Head motion predictability explains activity-dependent suppression of vestibular balance control

Vestibular balance control is dynamically weighted during locomotion. This might result from a selective suppression of vestibular inputs in favor of a feed-forward balance regulation based on locomotor efference copies. The feasibility of such a feed-forward mechanism should however critically depend on the predictability of head movements (HMP) during locomotion. To test this, we studied in 10 healthy subjects the differential impact of a stochastic vestibular stimulation (SVS) on body sway (center-of-pressure, COP) during standing and walking at different speeds and compared it to activity-dependent changes in HMP. SVS-COP coupling was determined by correlation analysis in frequency and time domains. HMP was quantified as the proportion of head motion variance that can be explained by the average head trajectory across the locomotor cycle. SVS-COP coupling decreased from standing to walking and further dropped with faster locomotion. Correspondingly, HMP increased with faster locomotion. Furthermore, SVS-COP coupling depended on the gait-cycle-phase with peaks corresponding to periods of least HMP. These findings support the assumption that during stereotyped human self-motion, locomotor efference copies selectively replace vestibular cues, similar to what was previously observed in animal models.

Impact of lian gong on the quality of life of individuals with dizziness in primary care.

ABSTRACTOBJECTIVE To assess the effects of the lian gong practice as a rehabilitation strategy in primary health care on the quality of life and functional capacity of people with dizziness.METHODS Randomized controlled clinical trial. Thirty-six people, who were complaining of dizziness or vertigo without the presence of central signs and were referred by the physician of primary health care participated in the study. The individuals were randomly allocated to the three experimental conditions: lian gong group (n = 11), vestibular rehabilitation group (n = 11) and control group (n = 14). The interventions were weekly, in group, with duration of 12 sessions. The participants were evaluated before and after the intervention regarding quality of life by the 36-Item Short Form Health Survey and the functional capacity by the Short Physical Performance Battery.RESULTS The scores of all domains of the Short Form Health Survey increased after intervention in the lian gong group. This variation was higher than that observed in the control group for the domains functional capacity, limitation by physical aspects and general health status, and also higher than that found after the intervention in the Vestibular Rehabilitation Group regarding pain. No differences were found in the Short Physical Performance Battery.CONCLUSIONS Based on the results presented, lian gong improves the quality of life of individuals with dizziness, without altering the functional capacity.

Towards Using the Instrumented Timed Up-and-Go Test for Screening of Sensory System Performance for Balance Control in Older Adults.

Background: Decreasing performance of the sensory systems’ for balance control, including the visual, somatosensory and vestibular system, is associated with increased fall risk in older adults. A smartphone-based version of the Timed Up-and-Go (mTUG) may allow screening sensory balance impairments through mTUG subphases. The association between mTUG subphases and sensory system performance is examined. Methods: Functional mobility of forty-one community-dwelling older adults (>55 years) was measured using a validated mTUG. Duration of mTUG and its subphases ‘sit-to-walk’, ‘walking’, ‘turning’, ‘turn-to-sit’ and ‘sit-down’ were extracted. Sensory systems’ performance was quantified by validated posturography during standing (30 s) under different conditions. Visual, somatosensory and vestibular control ratios (CR) were calculated from posturography and correlated with mTUG subphases. Results: Vestibular CR correlated with mTUG total time (r = 0.54; p < 0.01), subphases ‘walking’ (r = 0.56; p < 0.01), and ‘turning’ (r = 0.43; p = 0.01). Somatosensory CR correlated with mTUG total time (r = 0.52; p = 0.01), subphases ‘walking’ (r = 0.52; p < 0.01) and ‘turning’ (r = 0.44; p < 0.01). Conclusions: Supporting the proposed approach, results indicate an association between specific mTUG subphases and sensory system performance. mTUG subphases ‘walking’ and ‘turning’ may allow screening for sensory system deterioration. This is a first step towards an objective, detailed and expeditious balance control assessment, however needing validation in a larger study.

Static monocular visual cues can decrease the vestibular-evoked balance response at low frequencies

BackgroundThe balance system continually integrates and processes diverse sensorimotor cues to maintain upright posture. Yet, little is known about how monocular visual cues may modulate the vestibular control of standing balance. Research questionTo determine how visual cues, specifically monocular vision, modulate the vestibular-evoked myogenic and whole-body balance response. MethodsSeventeen (12 female) healthy subjects (age: 24.8 ± 5.3years) were exposed to a random, continuous electrical vestibular stimulation (EVS) signal (±3.5 mA, 0–20 Hz). Subjects stood quietly during four experimental (no vision, non-dominant eye, dominant eye, binocular) conditions. The EVS-medial-lateral ground reaction force (ML GRF) acting on the body and EVS-medial gastrocnemius electromyography (EMG, bilateral) responses were evaluated in the frequency (coherence) and time (cumulant density) domains. ResultsCoherence was increased for no vision compared to binocular, dominant eye, and non-dominant eye visual cues, respectively, with the most pronounced increases occurring at lower frequencies. For cumulant density, the EVS-ML GRF medium-latency peak amplitude was increased 45, 26 and 18% with no vision compared to binocular, dominant eye and non-dominant eye visual cues, respectively (p < .05). The EVS-EMG medium-latency peak amplitude during no vision was greater than binocular (p < .05) for both gastrocnemii, but binocular and dominant eye monocular vision was not different (p > .05). The EVS-ML GRF and EVS-EMG (right medial gastrocnemius) medium-latency peak amplitude was greater for non-dominant eye monocular vision compared to binocular vision (p < .05). SignificanceMonocular visual cues, at least for the dominant eye, can depress the vestibular-evoked balance response at low frequencies akin to binocular vision with limited differences exhibited between dominant and non-dominant eye.

Vestibular dysfunction as cortical damage with amyotrophic lateral sclerosis

BackgroundCortical damage in areas such as the frontal lobe is reported in amyotrophic lateral sclerosis (ALS). However, aside from executive dysfunction, the pathological significance of this cortical damage has yet to be clarified. The present study investigated the effects of cortical damage on vestibular function in ALS. MethodsSubjects comprised 18 ALS patients and 18 age- and sex-matched healthy controls. Cold air caloric stimulation was performed in all subjects to induce vestibular nystagmus, which was analysed to evaluate vestibular function. Visual suppression testing to investigate the suppressive effects of visual stimuli on vestibular nystagmus was expressed as suppression rate (SR, %). Executive function was tested using the frontal assessment battery (FAB). ResultsSuppression rate and FAB score were significantly lower in the ALS group than in the control group (p < 0.01 each). A positive correlation was also observed between SR and FAB score (R = 0.65, p = 0.023). ConclusionVisual suppression testing showed significant damage to the central nervous system vestibular control mechanisms, which utilize visual information in the ALS group and a positive correlation between SR and FAB score suggest a relationship between frontal lobe damage and impaired vestibular control. A simple vestibular function test may be useful as a tool to objectively monitor the progression of cerebral lesions in ALS.

Sinusoidal Transcranial Direct Current Versus Galvanic Vestibular Stimulation for Treatment of Lateropulsion Poststroke

ObjectiveTo compare the effects of Transcranial Direct Current Stimulation (tDCS) versus Galvanic Vestibular Stimulation (GVS) on Lateropulsion following stroke. MethodsPatients with Stroke and Burke Lateropulsion Scale (BLS) scores greater than or equal to 2 gave informed consent to receive sinusoidal 1 Hz DC (0-2 mA) anodal stimulation over the affected parietal cortex versus similar GVS with ipsilesional mastoidal anode. Seated haptic center of pressure (COP-X) was measured using an AMTI analog-to-digital forceplate. An inclinometer (Biopac ) measured lateral thoracic tilt. COP-X Power Spectra were analyzed over 3 frequency intervals: 0-.3 Hz, .3-1 Hz, and 1-3 Hz. ResultsSix males/4 females age 66 ± 9.5 standard deviation with admission BLS scores of 5.4 ± 3.7 within 8.6 ± 8.1 days poststroke were enrolled. COP-X medial-lateral speed increased for both the tDCS and the GVS protocols compared to sham condition. Fourier Analysis of COP-X velocity for 0-.3 Hz responses showed a significant increase for tDCS stimulation. The .3-1 Hz responses for the tDCS condition were decreased from baseline. Lateral thoracic tilt showed significant improvement for tDCS compared to Sham stimulation at 10 minutes and for GVS versus Sham at 15 minutes. DiscussionAnodal tDCS over the ipsilesional PIVC increases low frequency postural responses usually attributed to visual control with down regulation of median frequency vestibular responses, biasing postural control toward more dependence on visual as opposed to vestibular control. Conclusions2 mA sinusoidal 1 Hz anodal tDCS over the ipsi-lesional PIVC or similar ipsi-lesional anodal GVS improve Lateropulsion following stroke.

Down regulation of vestibular balance stabilizing mechanisms to enable transition between motor states

The neural control of transition between posture and movement encompasses the regulation of reflex-stabilizing mechanisms to enable motion. Optimal feedback theory suggests that such transitions require the disengagement of one motor control policy before the implementation of another. To test this possibility, we investigated the continuity of the vestibular control of balance during transitions between quiet standing and locomotion and between two standing postures. Healthy subjects initiated and terminated locomotion or shifted the distribution of their weight between their feet, while exposed to electrical vestibular stimuli (EVS). The relationship between EVS and ground reaction forces was quantified using time-frequency analyses. Discontinuities corresponding to null coherence periods were observed preceding the onset of movement initiation and during the step preceding locomotion termination. These results show humans interrupt the vestibular balance stabilizing mechanisms to transition between motor states, suggesting a discrete change between motor control policies, as predicted by optimal feedback theory.

Susceptibility to Fear of Heights in Bilateral Vestibulopathy and Other Disorders of Vertigo and Balance.

Aims: To determine the susceptibility to visual height intolerance (vHI) in patients with acquired bilateral vestibulopathy (BVP). The question was whether postural instability in BVP, which is partially compensated for by visual substitution of the impaired vestibular control of balance, leads to an increased susceptibility. This is of particular importance since fear of heights is dependent on body posture, and visual control of balance at heights can no longer substitute vestibular input. For comparison susceptibility to vHI was determined in patients with other vestibular or functional disorders.Methods: A total of 150 patients aged 18 or above who had been referred to the German Center for Vertigo and Balance Disorders and diagnosed to have BVP were surveyed with a standardized questionnaire by specifically trained neurological professionals. Further, 481 patients with other vestibular or functional disorders were included.Results: Susceptibility to vHI was reported by 29% (32 % in females, 25% in males) of the patients with BVP. Patients with vHI were slightly younger (67 vs. 71 years). Seventy percent of those with vHI reported avoidance of climbing, hiking, stairs, darkness, cycling or swimming (84% of those without vHI). Mean age for onset of vHI was 40 years. Susceptibility to vHI was higher in patients with other vertigo disorders than in those with BVP: 64% in those with phobic postural vertigo, 61% in vestibular migraine, 56% in vestibular paroxysmia, 54% in benign paroxysmal positional vertigo, 49% in unilateral vestibulopathy and 48% in Menière's disease.Conclusions: The susceptibility to vHI in BVP was not higher than that of the general population (28%).This allows two explanations that need not be alternatives but contribute to each other: (1) Patients with a bilateral peripheral vestibular deficit largely avoid exposure to heights because of their postural instability. (2) The irrational anxiety to fall from heights triggers increased susceptibility to vHI, not the objective postural instability. However, patients with BVP do not exhibit increased comorbid anxiety disorders. This view is supported by the significantly increased susceptibility to vHI in other vestibular syndromes, which are characterized by an increased comorbidity of anxiety disorders.

Differential effects of vision upon the accuracy and precision of vestibular-evoked balance responses.

Key points Effective balance control requires the transformation of vestibular signals from head‐ to foot‐centred coordinates in order to move the body in an appropriate direction.This transformation process has previously been studied by analysing the directional accuracy of the averaged sway response to multiple electrical vestibular stimuli (EVS).Here we studied trial‐by‐trial variability of EVS responses to measure any changes in directional precision which may be masked by the averaging process.We found that vision increased directional variability without influencing the mean sway direction, demonstrating that response accuracy and precision are dissociable.These results emphasise the importance of single trial analysis in determining the efficacy of vestibular control of balance. Vestibular information must be transformed from head‐ to‐foot‐centred coordinates for balance control. This transformation process has previously been investigated using electrical vestibular stimulation (EVS), which evokes a sway response fixed in head coordinates. The craniocentric nature of the response has been demonstrated by analysing average responses to multiple stimuli. This approach misses any trial‐by‐trial variability which would reflect poor balance control. Here we performed single‐trial analysis to measure this directional variability (precision), and compared this to mean performance (accuracy). We determined the effect of vision upon both parameters. Standing volunteers adopted various head orientations (0, ±30 and ±60 deg yaw) while EVS‐evoked response direction was determined from ground reaction force vectors. As previously reported, mean force direction was orientated towards the anodal ear, and rotated in line with head yaw. Although vision caused a ∼50% reduction in response magnitude, it had no influence on the direction of the mean sway response, indicating that accuracy was unaffected. However, individual trial analysis revealed up to 30% increases in directional variability with the eyes open. This increase was inversely correlated with the size of the force response. The paradoxical observation that vision reduces the precision of the balance response may be explained by a multi‐sensory integration process. As additional veridical sensory information becomes available, this lessens the relative contribution of vestibular input, causing a simultaneous reduction in both the magnitude and the precision of the response to EVS. Our novel approach demonstrates the importance of single‐trial analysis in revealing the efficacy of vestibular reflexes.

The vestibulomyogenic balance response is elevated following high-intensity lengthening contractions of the lower limb

The purpose was to investigate whether exercise-induced muscle weakness of the plantar and dorsiflexors through high-intensity lengthening contractions increases the vestibulomyogenic balance response. Nine males (∼25 years) participated in three experimental testing days to evaluate the vestibular control of standing balance and neuromuscular function of the plantar and dorsiflexors pre- and post (30 min, and 1 and 7 days) high-intensity lengthening plantar and dorsiflexions. To evaluate the vestibular-evoked balance response, participants stood quietly on a force plate while exposed to continuous, random electrical vestibular stimulation (EVS) for two 90-s trials. Relationships between EVS-antero-posterior (AP) forces and EVS-medial gastrocnemius electromyography (EMG) were estimated in the frequency domain (i.e., coherence). Weakness of the right plantar and dorsiflexors were assessed using maximal voluntary contraction (MVC) torque. The lengthening contractions induced a 13 and 24% reduction in plantar and dorsiflexor MVC torque, respectively (p < 0.05) of the exercised leg, which did not recover by 1 day post. The EVS-EMG coherence increased over a range of frequencies up to 7 days post compared to pre-lengthening contractions. Conversely, EVS-AP forces coherence exhibited limited changes. The greater EVS-EMG coherence post exercise-induced muscle weakness may be a compensatory mechanism to maintain the whole-body vestibular-evoked balance response when muscle strength is reduced.

Vestibular-Evoked Responses Indicate a Functional Role for Intrinsic Foot Muscles During Standing Balance

Maintaining standing balance involves multisensory processing and integration to produce dynamic motor responses. Electrical vestibular stimulation (EVS) delivered over the mastoid processes can be used to explore the vestibular control of balance. The purpose of this study was to determine whether intrinsic foot muscles exhibit vestibular-evoked balance responses and to characterize the traits associated with these responses. Electromyography (EMG) of the abductor hallucis (AH), abductor digiti minimi (ADM) and medial gastrocnemius (MG) and anterior–posterior (AP) forces were sampled while quietly standing participants were subjected to a random continuous EVS signal (peak-to-peak amplitude = ±3 mA). The relationship between EVS input and motor output was characterized in both the frequency (coherence) and time (cumulant density) domains. When head orientation was rotated in yaw from left to right, the biphasic cumulant density function was inverted for all muscle (EVS–EMG) and whole-body (EVS–AP forces) balance responses. When vision was occluded, the EVS–EMG and EVS–AP forces coherence function amplitude increased at low frequencies (<2 Hz) and was accompanied by a heightened medium-latency peak amplitude for all muscles as well as the whole-body balance response (AP forces) compared to when static visual cues were present. The enhanced coherence amplitudes at lower frequencies may highlight a mechanism for the increase in postural sway from vision to occluded vision. The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing.

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.

The role of insula-cerebellum connection underlying aversive regulation with acupuncture.

Acupuncture at pericardium 6 (PC6) shows a consistently positive efficacy in nausea response suggested by consensus expert guidelines. Nausea encompasses aversive symptom as well as strong emotional components. Disgust is a subjective emotion of uneasy commonly accompanying with a physiological response that is accompanied by strong visceral sensations (e.g., nausea). Understanding the brain circuitry by which acupuncture influences the disgust emotion may further elucidate the modulation effect of acupuncture on aversive experience. In the present study, a well-established aversive conditioning model on healthy subjects was combined with acupuncture intervention at PC6, as well as different acupoints (both local PC7 and distant GB37) as separate controls, to investigate the brain network involved aversive regulation with acupuncture; 48 healthy subjects were enrolled and randomized into four parallel groups: group 1 received disgust-induced (DI) stimuli only; groups 2, 3, and 4 received acupuncture at three single acupoints separately prior to the DI. Disgust sensations were rated at baseline and following disgust stimuli. Acupuncture PC6 can induce significant attenuations in disgust sensations than that of no intervention and acupuncture at other acupoints. Neuroimaging further showed that increased causal interaction strength between the cerebellum (nodulus) and insula can predict greater attenuations in aversive experiences. We also found evidence for radical reorganizations of local stronger casual interaction patterns to disgust-induced brain responses targeted by acupuncture at different acupoints. This study provided the brain substrate for acupuncture on aversion modulation. The coupling between the cerebellum (nodulus) and insula supported interoception system and vestibular control which provided the specific neural basis.

Vestibular dysfunction and glycemic control in diabetes mellitus: Is there a correlation?

Objectives: The aim of this study is to evaluate and find the proportion of patients with Type-II diabetes mellitus (DM) with sensorineural hearing loss (SNHL) and vestibular dysfunction (VD) and association with glycemic control. Materials and Methods: An observational cross-sectional study was carried out in 100 patients (age group: 30–60 years) diagnosed with Type-II DM coming to the outpatient department of our Rural Tertiary Care Teaching Hospital, fulfilling the inclusion criteria. Prior approval of the Institutional Ethics Committee and written informed consent was obtained. All patients were subjected to investigations to assess their diabetes control, hearing, and vestibular function. The findings were subjected to statistical analysis. Results: Out of 100 patients, 62 were male and 38 were female between the age group of 30 and 60 years. The mean hemoglobin A1c (HbA1c) level was 9.16 ± 2.4. The patients were divided into three groups depending on HbA1c level, to denote control, good (≤7%), moderate (>7, ≤12%), and poor (>12%). There were a total of 69 patients with SNHL and 70 patients with VD. SNHL was present in 57.6% of good control group, 66.1% of moderate control group, and 100% of poor control group. Analysis with Chi-square test for correlation between glycemic control and SNHL was statistically significant. Out of the 70 patients with VD, 51.4% had right vestibulopathy, 41.4% had left vestibulopathy, and 7.2% had a bilateral vestibulopathy. Twenty-two patients had benign paroxysmal positional vertigo. VD was present in 42.3% of good control group, 74.5% of moderate control group, and 100% of poor control group. Chi-square test was statistically significant. Conclusion: There is a significant association between Type II DM, and SNHL and VD, especially with worsening of glycemic control. Screening for these debilities should be a part of the routine workup of a diabetic patient. VD is a potential cause for imbalance and vertigo in DM.

Co-ordination of the upper and lower limbs for vestibular control of balance.

Key points When standing and holding an earth‐fixed object, galvanic vestibular stimulation (GVS) can evoke upper limb responses to maintain balance.In the present study, we determined how these responses are affected by grip context (no contact, light grip and firm grip), as well as how they are co‐ordinated with the lower limbs to maintain balance.When GVS was applied during firm grip, hand and ground reaction forces were generated.The directions of these force vectors were co‐ordinated such that the overall body sway response was always aligned with the inter‐aural axis (i.e. craniocentric).When GVS was applied during light grip (< 1 N), hand forces were secondary to body movement, suggesting that the arm performed a mostly passive role.These results demonstrate that a minimum level of grip is required before the upper limb becomes active in balance control and also that the upper and lower limbs co‐ordinate for an appropriate whole‐body sway response. Vestibular stimulation can evoke responses in the arm when it is used for balance. In the present study, we determined how these responses are affected by grip context, as well as how they are co‐ordinated with the rest of the body. Galvanic vestibular stimulation (GVS) was used to evoke balance responses under three conditions of manual contact with an earth‐fixed object: no contact, light grip (< 1 N) (LG) and firm grip (FG). As grip progressed along this continuum, we observed an increase in GVS‐evoked hand force, with a simultaneous reduction in ground reaction force (GRF) through the feet. During LG, hand force was secondary to the GVS‐evoked body sway response, indicating that the arm performed a mostly passive role. By contrast, during FG, the arm became actively involved in driving body sway, as revealed by an early force impulse in the opposite direction to that seen in LG. We then examined how the direction of this active hand vector was co‐ordinated with the lower limbs. Consistent with previous findings on sway anisotropy, FG skewed the direction of the GVS‐evoked GRF vector towards the axis of baseline postural instability. However, this was effectively cancelled by the hand force vector, such that the whole‐body sway response remained aligned with the inter‐aural axis, maintaining the craniocentric principle. These results show that a minimum level of grip is necessary before the upper limb plays an active role in vestibular‐evoked balance responses. Furthermore, they demonstrate that upper and lower‐limb forces are co‐ordinated to produce an appropriate whole‐body sway response.

The effect of fear of falling on vestibular feedback control of balance.

Vestibular sensation contributes to cervical‐head stabilization and fall prevention. To what extent fear of falling influences the associated vestibular feedback processes is currently undetermined. We used galanic vestibular stimulation (GVS) to induce vestibular reflexes while participants stood at ground level and on a narrow walkway at 3.85 m height to induce fear of falling. Fear was confirmed by questionnaires and elevated skin conductance. Full‐body kinematics was measured to differentiate the whole‐body centre of mass response (CoM) into component parts (cervical, axial trunk, appendicular short latency, and medium latency). We studied the effect of fear of falling on each component to discern their underlying mechanisms. Statistical parametric mapping analysis provided sensitive discrimination of early GVS and height effects. Kinematic analysis revealed responses at 1 mA stimulation previously believed marginal through EMG and force plate analysis. The GVS response comprised a rapid, anode‐directed cervical‐head acceleration, a short‐latency cathode‐directed acceleration (cathodal buckling) of lower extremities and pelvis, an anode‐directed upper thorax acceleration, and subsequently a medium‐latency anode‐directed acceleration of all body parts. At height, head and upper thorax early acceleration were unaltered, however, short‐latency lower extremity acceleration was increased. The effect of height on balance was a decreased duration and increased rate of change in the CoM acceleration pattern. These results demonstrate that fear modifies vestibular control of balance, whereas cervical‐head stabilization is governed by different mechanisms unaffected by fear of falling. The mechanical pattern of cathodal buckling and its modulation by fear of falling both support the hypothesis that short‐latency responses contribute to regulate balance.

Orthodontic Metallic Lingual Brackets: The Dark Side of the Moon of Bond Failures?

Lingual orthodontics, among both young and adult patients, increased in popularity during last years. The purposes of the present investigation were to evaluate the shear bond strength (SBS) values and Adhesive Remnant Index (ARI) scores of different lingual brackets compared with a vestibular control bracket. One hundred bovine teeth were extracted and embedded in resin blocks. Four different lingual brackets (Idea, Leone; STB, Ormco; TTR, RMO; 2D, Forestadent) and a vestibular control bracket (Victory, 3M) were bonded to the bovine enamel surfaces and subsequently shear tested to failure utilizing a Universal Testing Machine. SBS values were measured. A microscopic evaluation was performed to obtain ARI scores. Statistical analysis was performed at a statistically significant level of p < 0.05 to determine significant differences in SBS values and ARI Scores. No statistically significant variations in SBS were reported among the different groups. Conversely, significant differences were shown in ARI scores among the various groups. Clinical relevance of the present study is that orthodontists can expect similar resistance to debonding forces from lingual appliances as with vestibular brackets.

The internal representation of head orientation differs for conscious perception and balance control.

We tested perceived head-on-feet orientation and the direction of vestibular-evoked balance responses in passively and actively held head-turned postures. The direction of vestibular-evoked balance responses was not aligned with perceived head-on-feet orientation while maintaining prolonged passively held head-turned postures. Furthermore, static visual cues of head-on-feet orientation did not update the estimate of head posture for the balance controller. A prolonged actively held head-turned posture did not elicit a rotation in the direction of the vestibular-evoked balance response despite a significant rotation in perceived angular head posture. It is proposed that conscious perception of head posture and the transformation of vestibular signals for standing balance relying on this head posture are not dependent on the same internal representation. Rather, the balance system may operate under its own sensorimotor principles, which are partly independent from perception. Vestibular signals used for balance control must be integrated with other sensorimotor cues to allow transformation of descending signals according to an internal representation of body configuration. We explored two alternative models of sensorimotor integration that propose (1) a single internal representation of head-on-feet orientation is responsible for perceived postural orientation and standing balance or (2) conscious perception and balance control are driven by separate internal representations. During three experiments, participants stood quietly while passively or actively maintaining a prolonged head-turned posture (>10min). Throughout the trials, participants intermittently reported their perceived head angular position, and subsequently electrical vestibular stimuli were delivered to elicit whole-body balance responses. Visual recalibration of head-on-feet posture was used to determine whether static visual cues are used to update the internal representation of body configuration for perceived orientation and standing balance. All three experiments involved situations in which the vestibular-evoked balance response was not orthogonal to perceived head-on-feet orientation, regardless of the visual information provided. For prolonged head-turned postures, balance responses consistent with actual head-on-feet posture occurred only during the active condition. Our results indicate that conscious perception of head-on-feet posture and vestibular control of balance do not rely on the same internal representation, but instead treat sensorimotor cues in parallel and may arrive at different conclusions regarding head-on-feet posture. The balance system appears to bypass static visual cues of postural orientation and mainly use other sensorimotor signals of head-on-feet position to transform vestibular signals of head motion, a mechanism appropriate for most daily activities.