Balance control: looking forwards to feedforward.
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Adaptation, Physiological↗
Biomedical subjects
Adolfo M Bronstein
Publications and source records attributed to Adolfo M Bronstein.
Self-initiated gait increases susceptibility to the moving platform after-effect.
Walking onto a stationary platform previously experienced as moving results in a large forward sway, despite awareness of the changing context. This after-effect demonstrates aberrant motor prediction. Here, we compared after-effect magnitude when gait initiation was either externally triggered or self-initiated. Both participant groups adapted their walking speed similarly when walking onto the moving platform. When it was kept stationary however, after-effect magnitude was more than doubled in the self-initiated group. We attribute this to a stronger association made between the action (gait initiation) and its consequence (platform movement) when the action is initiated by oneself. This increased sense of agency reduces the ability to switch off the acquired motor response when it is no longer appropriate.
Adult↗
Cardio-respiratory responses evoked by transient linear acceleration.
INTRODUCTION: Predictive control of the responses to re-orientating stimuli and its interaction with vestibular signals may be an important factor in protecting against spatial disorientation. Here we evaluated the influence of stimulus predictability on the cardio-respiratory responses to transient fore-aft linear accelerations. METHODS: There were 13 normal subjects and 6 patients with bilateral loss of vestibular function who were exposed to linear acceleration of +0.26 Gx peak while seated upright and restrained on a motorized bogie. Accelerations were: (1) 'unpredictable', triggered by the experimenter either at the end of expiration or at the end of inspiration; or (2) 'predictable', triggered by the subjects pressing a button. The two conditions included false trials when nothing would happen. Respiratory frequency, electrocardiogram, and trunk acceleration were recorded. RESULTS: For unpredictable accelerations, in all subjects, the RR interval decreased within the first to second beat after acceleration onset. In normal subjects this decrease was maintained or more evident during the third, fourth, or fifth heart beat after onset. Cardiac responses were not significantly different when acceleration was triggered at the end of inspiration or at the end of expiration. Self-triggered acceleration also provoked prolonged, but attenuated, heart rate responses in healthy subjects, while responses were absent in the patients. All subjects responded with a consistent rapid inspiration to the onset of acceleration, whether predictable or not. DISCUSSION: A vestibulo-cardiac response is evoked by transient linear acceleration, independently from the phase of the breathing cycle and from the predictability of the stimulus. A vestibular signal of motion appears to be required to produce a prolonged increase in heart rate.
Acceleration↗
Systemic autoantibodies against discrete inner ear compartments in bilateral vestibular loss.
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Animals↗
Clinical grand round: a rapidly progressive pyramidal and extrapyramidal syndrome with a supranuclear gaze palsy.
The case history of a patient with a rapidly progressive spastic tetraparesis, pseudobulbar palsy, supranuclear gaze palsy, and extrapyramidal signs is presented. The patient died 17 months after symptom onset, and the differential diagnosis and pathological findings are reviewed.
Basal Ganglia Diseases↗
The effects of vestibular system lesions on autonomic regulation: observations, mechanisms, and clinical implications.
The loss of labyrinthine inputs in patients or animal models has been demonstrated to affect autonomic regulation. Considerable evidence suggests that vestibular-autonomic responses serve to adjust blood pressure and respiratory activity during movement and postural alterations. However, following peripheral vestibular lesions, compensation rapidly occurs, such that autonomic disturbances are not readily evident in patients with chronic labyrinthine dysfunction. This manuscript summarizes the evidence suggesting that vestibular inputs influence autonomic regulation, but that cardiovascular and respiratory responses linked to movement recover quickly subsequent to the loss of labyrinthine signals. In addition, the clinical implications of dysfunction of vestibulo-autonomic reflexes are described. Furthermore, the mechanisms potentially responsible for the return of the ability to produce posturally-related adjustments in blood pressure and respiration following vestibular lesions are discussed. In particular, evidence that somatosensory signals can replace labyrinthine inputs to vestibular nucleus neurons that participate in autonomic regulation is provided.
Animals↗
Effectiveness of primary care-based vestibular rehabilitation for chronic dizziness.
BACKGROUND: Dizziness is a very common symptom and is usually managed in primary care. Vestibular rehabilitation for dizziness is a simple treatment that may be suitable for primary care delivery, but its effectiveness has not yet been determined. OBJECTIVE: To evaluate the effectiveness of nurse-delivered vestibular rehabilitation in primary care for patients with chronic dizziness. DESIGN: Single-blind randomized, controlled trial. SETTING: 20 general practices in southern England. PATIENTS: 170 adult patients with chronic dizziness who were randomly assigned to vestibular rehabilitation (n = 83) or usual medical care (n = 87). INTERVENTION: Each patient received one 30- to 40-minute appointment with a primary care nurse. The nurse taught the patient exercises to be carried out daily at home, with the support of a treatment booklet. MEASUREMENTS: Primary outcome measures were baseline, 3-month, and 6-month assessment of self-reported spontaneous and provoked symptoms of dizziness, dizziness-related quality of life, and objective measurement of postural stability with eyes open and eyes closed. RESULTS: At 3 months, improvement on all primary outcome measures in the vestibular rehabilitation group was significantly greater than in the usual medical care group; this improvement was maintained at 6 months. Of 83 treated patients, 56 (67%) reported clinically significant improvement compared with 33 of 87 (38%) usual care patients (relative risk, 1.78 [95% CI, 1.31 to 2.42]). LIMITATIONS: Psychological elements of the therapy may have contributed to outcomes, and the treatment may be effective only for well-motivated patients. CONCLUSIONS: Vestibular rehabilitation delivered by nurses in general practice improves symptoms, postural stability, and dizziness-related handicap in patients with chronic dizziness.
Chronic Disease↗
Is uric acid implicated in benign paroxysmal positional vertigo?
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Adult↗
Vision and vertigo: some visual aspects of vestibular disorders.
This review deals with two syndromes, oscillopsia and visual vertigo. Oscillopsia is the illusion of oscillation of the visual surroundings. For diagnosis purposes one should ask, when does the oscillopsia occur? If oscillopsia is only present during head (or whole body) movements, the likely underlying cause is a bilateral defect in the vestibulo-ocular reflex (VOR). The more common causes are post meningitic vestibular damage, gentamicin ototoxicity or bilateral idiopathic vestibular failure. When oscillopsia develops after specific head positions, it is usually due to a positional nystagmus, usually the result of brainstem-cerebellar disease. When the oscillopsia is largely unrelated to head movements, one should ask, is it fairly constant or is it in attacks (paroxysmal)? If the oscillopsia is constant it is usually due to the presence of a clinically observable nystagmus; the most common is downbeat nystagmus but the most visually disabling is pendular nystagmus. If the oscillopsia comes in brief attacks it is usually due to a paroxysmal nystagmus as observed in irritative VIII nerve and brainstem lesions. However, the most common cause of paroxysmal oscillopsia is a non organic condition called voluntary nystagmus. Treatment of oscillopsia is often pharmacological but disappointing; the best chance of success is carbamazepine for paroxysmal disorders secondary to structural vestibular nerve/nuclear lesions.Visual vertigo should not be confused with oscillopsia. It can be defined as dizziness provoked by visual environments with large size (full field) repetitive or moving visual patterns. Patients with visual vertigo report discomfort in supermarkets and when viewing movement of large visual objects, eg crowds, traffic, clouds or foliage. Visual vertigo is present in many patients with a history of a peripheral vestibular disorder, particularly those who are visually dependent (ie subjects who use vision preferentially for postural and space orientation control). Patients with visual vertigo benefit from the addition to their standard vestibular rehabilitation of optic flow (optokinetic) stimuli and exercises involving visuo-vestibular conflict.
Head Movements↗
Simulator based rehabilitation in refractory dizziness.
UNLABELLED: Patients with chronic vestibular symptoms are common in neurological practice but the most effective treatment remains an open question. The purpose of our study was to conduct a controlled, between-group comparison of patients' responses to a customised exercise regime (Group C, for customised) versus treatment additionally incorporating simulator based desensitisation exposure (Group S, for simulator) integrating whole-body or visual environment rotators. Forty chronic peripheral vestibular patients who had previously undergone conventional vestibular rehabilitation without notable improvement were randomly assigned into Group C or S. Individuals attended therapy sessions twice weekly for eight weeks and were provided with a customised home programme. Response to treatment was assessed at four-week intervals with dynamic posturography, vestibular time constants, and questionnaires concerning symptoms, symptom-triggers and emotional status. At final assessment posturography and subjective scores had significantly improved for both groups, although Group S showed greater improvement. A statistically significant improvement for visual vertigo symptom scores was noted only for Group S (p < 0.01; total improvement 53.5 %). Anxiety and depression levels significantly decreased for both groups; improvements were significantly correlated particularly to improvements in visual vertigo (SCQ) (p < 0.01; r = 0.53 and r = 0.57, respectively). Significant differences were noted between groups (p = 0.02) for posturography scores. Vestibular time constants showed no notable change in either group. CONCLUSIONS: Both groups improved but exposure to simulator motion gave overall better results. These effects were also observed in psychological symptoms and partly relate to simulator effects on visual vertigo symptoms. Visual motion and visuo-vestibular conflict situations should be incorporated in the rehabilitation of patients with refractory dizziness.
Adult↗
A new paradigm to investigate the roles of head and eye movements in the coordination of whole-body movements.
Although previous studies have demonstrated the existence of coordinated eye and head movements during gaze shifts, none has studied the temporal and spatial characteristics of the various body segments during gaze transfers that require whole body movements. Without this information it is not possible to determine the extent of the interaction between the oculomotor control system and the motor control systems responsible for moving other body parts. Presented here is a detailed analysis of the timing and kinematic characteristics of participants' ( N = 5) eye, head, upper body and feet during rotation of their body to align with light cues positioned at eccentric locations (45, 90, and 135 degrees, left and right of centre). For all rotation amplitudes there was a clear sequence of body segment orientation (eye, head, upper body and feet) consistent with previous studies of locomotor steering and significant correlations between the onset latency times of the eyes and all body segments. There were also significant correlations between temporally aligned kinematic profiles of the feet and the eye in space for all movement amplitudes. The extent of correlation was significantly lower for displacement profiles of the feet versus head and of the feet versus upper body. These findings demonstrate substantial eye-foot coordination during a novel whole-body rotation paradigm and provide evidence that the output of the motor systems responsible for moving the feet is heavily influenced by the motor systems responsible for generating and coordinating eye and head movements to peripheral targets.
Adult↗
The integration of multiple proprioceptive information: effect of ankle tendon vibration on postural responses to platform tilt.
Previous studies have looked at co-processing of multiple proprioceptive inputs but few have investigated the effect of separate dynamic and tonic predominantly proprioceptive disruptions applied concurrently at the same segment. The purpose of the present study was to investigate how simultaneous ankle tendon vibration, a tonic stimulus, with a dynamic toes-up (TU) or toes-down (TD) platform perturbation (1) affects postural stability and (2) influences the adaptation process. Sixteen normal subjects (ten male, six female, mean age 26 +/- 4.8 years) stood blindfolded on a moving platform with vibrators attached bilaterally over the Achilles tendons. Participants were tested in quiet stance (QS), and with five successive TU and TD tilts. All tests were conducted both with (QS+V, TU+V, TD+V) and without vibration. Centre of pressure (CoP) displacements and pitch angular trunk velocity were recorded. Results for QS+V showed a significant 1.02-cm backward CoP displacement (P<0.01) and a significant increase in trunk velocity (peak-to-peak amplitude, P<0.05; SD of trunk velocity, P<0.05). TU+V resulted in a non-significant increase of maximum backwards CoP displacement when compared to TU alone. In addition, no notable effect of vibration on other measures of CoP (pre-tilt position, SD and area of sway) and trunk velocity (peak-to-peak, SD and area of sway) indicates that TU+V does not introduce significantly greater instability compared to tilt alone. In the TD condition, vibration was found to be a stabilising influence, causing a significant shift of the mean pre-tilt position 0.85 cm backwards (P<0.01) and a substantial decrease in the area of forward CoP displacement (P<0.01). However, maximum forwards CoP displacement and trunk velocity measures were not significantly altered during TD+V. Furthermore, in neither TU nor TD was the time-course or pattern of adaptation disrupted by the additional application of vibration. In conclusion, although vibration significantly affects postural measures when applied in isolation, this finding does not hold when it is applied in combination with a more dynamic stimulus. Instead it seems that once postural stability has been disrupted the central nervous system can rapidly assess information from a weaker tonic input and utilise or suppress it appropriately, depending on its effect towards overall postural control. It can be concluded that postural responses to the concurrent application of different predominantly proprioceptive stimuli are dependent upon the type of stimulus and the ability of the central nervous system to rapidly assess and re-weigh available sensory inputs.
Adaptation, Physiological↗
Effect of semicircular canal stimulation on the perception of the visual vertical.
UNLABELLED: The subjective visual vertical (SVV) is usually considered a measure of otolith function. Herewith we investigate the influence of semicircular canal (SCC) stimulation on the SVV by rotating normal subjects in yaw about an earth-vertical axis, with velocity steps of +/- 90 degrees /s, for 60 s. SVV was assessed by setting an illuminated line to perceived earth vertical in darkness, during a per- and postrotary period. Four head positions were tested: upright, 30 degrees backward (chin up) or forward, and approximately 40 degrees forward from upright. During head upright/backward conditions, a significant SVV tilt (P < 0.01) in the direction opposite to rotation was found that reversed during postrotary responses. The rotationally induced SVV tilt had a time constant of decay of approximately 30 s. Rotation with the head 30 degrees forward did not affect SVV, whereas the 40 degrees forward tilt caused a direction reversal of SVV responses compared with head upright/backward. Spearman correlation values (Rho) between individual SCC efficiencies in different head positions and mean SVV tilts were 0.79 for posterior, 0.34 for anterior, and - 0.80 for horizontal SCCs. Three-dimensional video-oculography showed that SVV and torsional eye position measurements were highly correlated (0.83) and in the direction opposite to the slow phase torsional vestibuloocular reflex. IN CONCLUSION: 1) during yaw axis rotation without reorientation of the head with respect to gravity, the SVV is influenced by SCC stimulation; 2) this effect is mediated by the vertical SCCs, particularly the posterior SCCs; 3) rotationally induced SVV changes are due to torsional ocular tilt; 4) SVV and ocular tilts occur in the "anticompensatory," fast phase direction of the torsional nystagmus; and 5) clinically, abnormal SVV tilts cannot be considered a specific indication of otolith system dysfunction.
Acceleration↗
Influence of target size on vertical gaze palsy in a pathologically proven case of progressive supranuclear palsy.
We document a new oculomotor phenomenon in a patient with pathologically proven progressive supranuclear gaze palsy (PSP), namely that vertical gaze excursion improves with larger pursuit targets. We used computerised video-oculography during vertical smooth pursuit eye movements (SPEM) of circular targets of diameter 0.16 degrees and 16 degrees, sinusoidally oscillating at 0.08 Hz (peak-to-peak amplitude 49 degrees). Increasing target size improved vertical gaze excursion from 10 degrees to 25 degrees. There was no concomitant increase in slow phase eye velocity. The findings could be explained by a potentiation of the position control mechanism of pursuit by target size due to increased activation of brainstem pursuit-optokinetic pathways and to higher order attentional mechanisms. This observation may be useful in the clinical assessment of PSP patients with severe neck rigidity in whom the doll's head-eye manoeuvre cannot be performed by comparing the degree of vertical gaze palsy during smooth pursuit testing between at least two differently sized targets and observing whether there is a larger excursion in response to a large target such as a newspaper.
Aged↗
Visual motion detection in patients with absent vestibular function.
Labyrinthine defective subjects (LDS) experience oscillopsia during head movements due to the absence of the vestibulo-ocular reflex (VOR). The purpose of this study was to compare horizontal and vertical visual motion detection in LDS during (i) body-stationary and (ii) horizontal whole-body oscillation conditions. Twelve LDS and controls detected the onset of drift direction of a grating that moved with accelerating velocity. Thresholds were raised in the patient group in both conditions. The loss of the VOR per se cannot explain raised thresholds in the body-stationary condition nor during whole-body (horizontal) oscillation with vertical grating motion. Findings indicate changes in visual processing that make LDS less sensitive to visual motion. It is postulated that these changes are due to adaptive mechanisms involved to reduce oscillopsia.
Adult↗
Benign paroxysmal positional vertigo: some recent advances.
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Diagnosis, Differential↗