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.

Long-term course of orthostatic tremor in serial posturographic measurement.

OBJECTIVE: Primary orthostatic tremor (OT) is a rare neurological disease of unknown pathophysiology characterized by a high-frequency tremor mainly of the legs when standing. The aim of this study was to examine its long-term course by subjective estimation and objective recording by serial posturography and to obtain further standardized epidemiological and clinical data on patients with OT. METHODS: A clinical cohort of 37 patients with the diagnosis of primary OT was screened for this longitudinal follow-up study. Eighteen patients consented to participate. During study visit all patients underwent a standardized neurological examination and completed subjective scales and scores. Posturographic recordings at follow-up were compared to prior clinical posturographic measurements in 15 cases. RESULTS: In our cohort the mean duration of symptoms was 14.1 ± 6.8 years. Subjectively, 78% of patients reported progression of the disease. Posturographic data (5.4 ± 4.0 years) revealed a significant increase of the total sway path (standing on firm ground with eyes open) from 2.4 ± 1.3 to 3.4 ± 1.4 m/min (p = 0.022) and of the total root mean square values from 9.8 ± 4.3 to 12.4 ± 4.8 mm (p = 0.028). None of these observations are explained by aging of the patients. Mean frequency of the tremor did not change over time (14.7 ± 1.9 Hz vs. 14.9 ± 2.0 Hz at follow-up). Clinically, most patients had signs of cerebellar dysfunction and a substantial portion also showed proprioceptive deficits in the long-term course. CONCLUSIONS: This long-term follow-up study indicates, that primary OT is a progressive disorder. Furthermore, the clinical observation of cerebellar dysfunction in most OT patients in the long-term course might indicate an important role of the cerebellum in its pathophysiology.

Appraisal of the signal-to-noise-ratio of uni- and bipolar recordings of ocular vestibular evoked myogenic potentials.

Ocular vestibular evoked myogenic potentials (oVEMPs) are a non-invasive method to investigate otolith function mediated via the superior vestibular nerve. However, the herein used recordings and protocols may alter within different studies. In particular the diverging use of electrode configuration regarding polarity or even electrode position varies across studies. Therefore, a systematic analysis and appraisal of the different electrode configuration seems mandatory. In this study we compared the quality of uni- and bipolar recordings based on the signal to noise ratio (SNR). We recoded oVEMPs using a uni- and bipolar electrode configuration simultaneously and compared the recorded amplitudes and latencies and calculated the SNR. The amplitudes recorded by the unipolar configurations were significantly (p < 0.01) increased compared to the bipolar configuration. However, the SNR of the bipolar setup was significantly better (p < 0.05) when compared to the unipolar setup. Additionally, we estimated a transfer function that enabled a comparison of uni- and bipolar recordings. To conclude, the variety of setups used for oVEMP recording hinder a comparison of results and unipolar electrode configurations have clear disadvantages.

Disturbed vestibular-neck interaction in cerebellar disease.

Cerebellar dysfunction results in ataxia including postural deficits. Evidence from animal experiments suggests convergence of vestibular and neck-position related inputs in cerebellar midline structures. We investigated 20 ambulatory patients with cerebellar disease for disturbed postural control using posturography during static lateral head turns. Binaural bipolar sine-wave galvanic vestibular stimulation (GVS) was used to evoke specific body movements. The Klockgether clinical score was used to assess the severity of cerebellar dysfunction (4-17 of maximal 35 points). In 12 healthy controls and seven lightly affected patients (score <8), GVS elicited physiologic alternating body sway in the head-frontal plane in seven head-on-trunk positions (0°; 30°, 45° and 60° left and right). Body sway turning with head excursion was progressively attenuated or abolished in more severely affected patients (scores 9-17; r = 0.57, p = 0.008). With most severe impairment, body sway was always in the body-frontal plane irrespective of head turn. A simple clinical test with walking under maximal head turn and closed eyes correlated with posturography data (r = 0.87, p < 0.001) and with Klockgether scores (r = 0.71, p < 0.001). Thus in cerebellar disease, head on trunk position can have a pronounced effect on postural control.

Inadequate interaction between open- and closed-loop postural control in phobic postural vertigo.

Phobic postural vertigo (PPV) is characterized by a subjective dizziness and postural imbalance. Changes in postural control strategy may cause the disturbed postural performance in PPV. A better understanding of the mechanisms behind this change in strategy is required to improve the diagnostic tools and therapeutic options for this prevalent disorder. Here we apply stabilogram diffusion analysis (SDA) to examine the characteristics and modes of interaction of open- and closed-loop processes that make up the postural control scheme in PPV. Twenty patients with PPV and 20 age-matched healthy controls were recorded on a stabilometer platform with eyes open and with eyes closed. Spatio-temporal changes of the center of pressure (CoP) displacement were analyzed by means of SDA and complementary CoP amplitude measures. (1) Open-loop control mechanisms in PPV were disturbed because of a higher diffusion activity (p < 0.001). (2) The interaction of open- and closed-loop processes was altered in that the sensory feedback threshold of the system was lowered (p = 0.010). These two changes were comparable to those observed in healthy subjects during more demanding balance conditions such as standing with eyes closed. These data indicate that subjective imbalance in PPV is associated with characteristic changes in the coordination of open- and closed-loop mechanisms of postural control. Patients with PPV use sensory feedback inadequately during undisturbed stance, and this impairs postural performance. These changes are compatible with higher levels of anti-gravity muscle activity and co-contraction during the conscious concentration on control of postural stability.

Postural imbalance and falls in PSP correlate with functional pathology of the thalamus.

OBJECTIVE: To determine how postural imbalance and falls are related to regional cerebral glucose metabolism (PET) and functional activation of the cerebral postural network (fMRI) in patients with progressive supranuclear palsy (PSP). METHODS: Sixteen patients with PSP, who had self-monitored their frequency of falls, underwent a standardized clinical assessment, posturographic measurement of balance during modified sensory input, and a resting [¹8F]FDG-PET. In addition, patients performed an fMRI paradigm using mental imagery of standing. Results were compared to healthy controls (n = 16). RESULTS: The frequency of falls/month in patients (range 1-40) correlated with total PSP rating score (r = 0.90). Total sway path in PSP significantly correlated with frequency of falls, especially during modulated sensory input (eyes open: r = 0.62, eyes closed: r = 0.67, eyes open/head extended: r = 0.84, eyes open/foam-padded platform: r = 0.87). Higher sway path values and frequency of falls were associated with decreased regional glucose metabolism (rCGM) in the thalamus (sway path: r = -0.80, falls: r = -0.64) and increased rCGM in the precentral gyrus (sway path: r = 0.79, falls: r = 0.64). Mental imagery of standing during fMRI revealed a reduced activation of the mesencephalic brainstem tegmentum and the thalamus in patients with postural imbalance and falls. CONCLUSIONS: The new and clinically relevant finding of this study is that imbalance and falls in PSP are closely associated with thalamic dysfunction. Deficits in thalamic postural control get most evident when balance is assessed during modified sensory input. The results are consistent with the hypothesis that reduced thalamic activation via the ascending brainstem projections may cause postural imbalance in PSP.

The effect of nicotine on perceptual, ocular motor, postural, and vegetative functions at rest and in motion.

Nicotine has wellknown, unpleasant side effects, e.g., transient dizziness, nausea, and nicotine-induced nystagmus (NIN). To investigate factors influencing these effects, we addressed three questions: (1) Is the intensity of dizziness, nausea, NIN, and unsteadiness dependent on nicotine dosage? (2) Does the intensity of perceptual, ocular motor, vegetative effects, and postural imbalance correlate? (3) Do visual or vestibular motion stimuli produce and/or aggravate distressing dizziness and nausea? Sixty healthy non-smokers or occasional smokers participated; 40 were tested once before and six times after application of a nicotine nasal spray in doses of 1 mg or 2 mg with or without motion stimulation; 20 received a placebo nasal spray. Plasma nicotine concentrations were significantly related to nicotine dosage. Dizziness, nausea, NIN, and unsteadiness also depended on the nicotine dosage (p < 0.01).Nicotine blood concentration was a better predictor for the temporal dependence of nystagmus than nicotine dosage. Dizziness correlated highly with nausea (R = 0.63, p < 0.001). The degree of nicotine-induced nausea significantly correlated with postural imbalance. The time course of postural sway differed according to nicotine dosage and gender: for women, there was no clear relationship between sway magnitude and nicotine dosage, while men showed increased sway with higher dosage. Motion stimulation increased nicotine-induced dizziness and nausea, but did not significantly influence NIN or postural imbalance. Our data support the view that all measured adverse effects reflect dose-dependent nicotine-induced vestibular dysfunction. Additional motion stimulation aggravates dizziness and nausea, i.e., nicotine increases sensitivity to motion sickness.

[The electrical stimulation bicycle: a neuroprosthesis for the everyday use of paraplegic patients]. / Das Elektrostimulationsfahrrad als Neuroprothese. Querschnittgelähmte Patienten mit dem Fahrrad unterwegs.

Until recently, few patients with complete paraplegia could walk or stand with the help of functional electrical stimulation (FES) of the leg muscles regularly at home. In comparison, FES cycling with an adapted tricycle is easy to put into practice because the legs remain connected to the pedals and through the use of a tricycle or stationary bicycle, the balancing problems of the patient recedes into the background. In the first German feasibility studies for paraplegic cycling, eleven completely paraplegic patients have been tested so far. The goal is to make FES cycling a daily activity in the lives of as many patients as possible.

[Paraplegic cycling using functional electrical stimulation. Experimental and model-based study of power output]. / Fahrradfahren Querschnittgelähmter mittels funktioneller Elektrostimulation. Eine experimentelle und modellbasierte Untersuchung der Leistungsabgabe.

Cycling using functional electrical stimulation offers paraplegics the possibility of muscle and cardiovascular training as well as the chance for independent locomotion. To investigate whether this method might be suitable for a large group of paraplegics, the first German feasibility study of functional electrical stimulation (FES) cycling with seven paraplegic patients was started at the beginning of 2003. Even at the beginning of the study, and without training, these patients were able to drive distances of 0.5-1.6 km. To stimulate cardiovascular adaptation processes in the case of FES ergometer training or to cover useful distances in the case of FES cycling, a minimum amount of generated mechanical output power is required, which as a rule cannot be achieved yet. In this study, we point out two particular aspects of FES cycling, which impair power output: prolonged fatigue mode and viscous joint friction of the paraplegic FES cyclist. We discuss current possibilities for increasing output power and endurance.

Treatment of downbeat nystagmus with 3,4-diaminopyridine: a placebo-controlled study.

BACKGROUND: Several drugs that primarily act on gamma-aminobutyrate or muscarinic receptors have been used to treat downbeat nystagmus (DBN) syndrome despite their having only moderate success and causing several side effects that limit their effectiveness. These drugs were tested under the assumption that DBN was caused by a disinhibition of a physiologic inhibitory cerebellar input on vestibular nuclei. OBJECTIVE: To evaluate the effects of a single dose of the potassium channel blocker 3,4-diaminopyridine (3,4-DAP), which is known to increase the excitability of Purkinje cells, on DBN in a prospective, placebo-controlled, double-blind study with a crossover design. METHODS: Seventeen patients with DBN due to cerebellar atrophy (5), infarction (3), Arnold-Chiari malformation (1), or unknown etiology (8) were included in the study (1 of 18 patients had to be excluded). Mean peak slow-phase velocity (PSPV) was measured before and 30 minutes after randomized ingestion of 20 mg of 3,4-DAP or placebo orally; at least 1 week later, the treatments were switched. RESULTS: 3,4-DAP reduced mean PSPV of DBN from 7.2 +/- 4.2 degrees /s (mean +/- SD) before treatment to 3.1 +/- 2.5 degrees/s 30 minutes after ingestion of the 3,4-DAP (p < 0.001, two-way analysis of variance). Placebo had no measurable effect. In 10 of 17 subjects, the mean PSPV decreased by >50% and in 12 of 17 by >40%. In parallel, the subjects had less oscillopsia and felt more stable while standing and walking. Nine of the subjects continued to take the drug with success. Except for transient minor perioral or digital paresthesia reported by three subjects and nausea and headache reported by one, no other side effects were observed. CONCLUSIONS: In this study, the authors demonstrated that a single dose of 3,4-DAP significantly improved DBN. In view of animal studies reporting that micromolar concentrations of 4-aminopyridine increased the excitability of Purkinje cells, it is suggested that the efficacy of 3,4-DAP may be due to an increase of the physiologic inhibitory influence of the vestibulocerebellum on the vestibular nuclei.

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Patients with somatoform phobic postural vertigo: the more difficult the balance task, the better the balance performance.

The objective was to test, whether the increased body sway activity, shown in patients with phobic postural vertigo (PPV) in a previous posturographic study, impairs postural balance during demanding balance tasks. In 17 patients with PPV and 15 normal subjects body sway was analyzed for two standing positions on a foam rubber-padded posturographic platform with the eyes open or closed: (a) normal upright stance, (b) tandem stance. During normal upright stance patients showed an increase in body sway activity between 0.1 and 19 Hz and in sway path values for lateral and fore/aft directions. During the most difficult balance task, i.e. tandem stance with the eyes closed, body sway activity and sway path values did not differ between patients and controls. Objective balance skills were not impaired in patients with PPV during balance tasks at the limits of postural control.

Increased body sway at 3.5-8 Hz in patients with phobic postural vertigo.

Postural sway during upright stance was analyzed in 12 patients with phobic postural vertigo (PPV) and in 12 age-matched healthy volunteers. Recordings were made under different conditions (with the eyes open or closed): when standing on a foam rubber pad with the head upright, turned 30 degrees to the right or left, or during 1 Hz horizontal head oscillations. Sway analysis included calculation of sway path, of root mean square values of sway and of the power spectrum of sway in fore/aft and lateral directions. There was a significant increase in sway activity in the 3.53-8 Hz frequency band in patients with PPV. This did not impair objective postural stability. Increase in higher frequency sway activity may simply reflect a change in postural strategy rather than a sensorimotor dysfunction. The patients' conscious control of stance may augment co-activation of anti-gravity muscles, a strategy applied by normal subjects when performing demanding balancing tasks.

Can short-latency vestibulospinal reflexes in lower leg muscles be elicited by tapping the head?

A gentle tap on the forehead evoked short-latency motor responses in the sternocleidomastoid muscle, which may be vestibulocollic reflexes with characteristics similar to those elicited by clicks. We tested this paradigm in subjects standing upright, in order to determine the differential effects of taps on the forehead on the patterns and latencies of spinal stretch and vestibulospinal reflexes, which are important for postural control. Taps on the forehead elicited short-latency inhibitory electromyographic responses in both gastrocnemius muscles with a mean latency of 48.3 +/- 3.1 ms (onset) to 98.3 +/- 6.3 ms (end). Taps on the sternum elicited similar responses from the gastrocnemius muscles, indicating that vestibular stimulation is not essential for eliciting these responses. Both responses may play a role in predetermining the strategy for correcting body perturbations. The actual reflex is probably elicited by somatosensory input from the neck, which converges with vestibular input for the multisensory control of posture.

Postural stability differentiates "lower body" from idiopathic parkinsonism.

INTRODUCTION: Patients with an akinetic Parkinson syndrome of the lower extremities and a poor response to L-DOPA have been described as "lower body Parkinsonism" (LBP). These patients are characterized by frequent fallings and poor balance. METHODS: We have studied body sway with static (force platform) and dynamic (Equitest) posturography in 11 LBP patients, 6 of them revealing deep white matter lesions on MRI and 10 patients with advanced Parkinson's disease (PD) and compared performance with 30 age-matched controls. RESULTS: When standing on a fixed support the postural performance of both patient groups lay within the normal range. The balance of LBP patients worsened in the static testing in the conditions "eyes open on foam" (p < 0.05) and "eyes closed on foam" (p < 0.0006, of 11 patients falling), whereas the balance of PD patients deteriorated only with "eyes closed on foam" (p < 0.05). Dynamic posturography confirmed these results in 6 different sensory conditions, clearly distinguishing the more unstable LBP patients from PD patients during "standing, eyes closed, foot support sway referenced" (p < 0.005). CONCLUSION: We conclude, that postural adjustments in LBP patients are more disturbed than those in PD patients and posturography can be an additional tool for the differential diagnosis of Parkinson syndromes with gait disorders.

Dependence of visual stabilization of postural sway on the cortical magnification factor of restricted visual fields.

Monocular visual stabilization of fore-aft and lateral body sway was tested posturographically in normal subjects (wearing visual field blinds) as a function of visual field size and location of the visual field on the central or peripheral retina. Body sway applied to a force- measuring platform is less with central (foveal) vision when central and peripheral visual fields have the same area. If, however, the peripheral field size is corrected by the cortical magnification factor of the retina in the primary cortex, body sway is stabilized by the peripheral retina to the same extent. Thus, there is no functional specialization of central and peripheral retina with respect to balance control. Visual stabilization of upright stance is a function of field size and cortical representation of the retina. The central and the peripheral retina have different thresholds to detect motion; this was surprisingly not reflected in measurements of normal fore-aft and lateral body sway.