Journal of Vestibular Research

This is a study of Subjective Visual Vertical (SVV) perception during acute attacks of Ménière's disease (MD) with comparative evaluation of concurrent nystagmus. We studied 21 patients with unilateral MD during the acute phase and 7 days later. Of the nine patients with an initial attack of MD, seven had an alteration of SVV perception and of these, three indicated a match with canal functional signs, while four patients showed an opposite trend of SVV perception relative to the spontaneous nystagmus. Nine of the 12 patients with definite MD had a pathological SVV perception always in correspondence with the same type of canal event. At 1-week control, no patient with an initial MD attack had alteration of SVV perception, whereas 5 patients with definite MD presented a pathological SVV perception toward the affected side. In the course of acute attacks of unilateral MD, clinical manifestations may include otolithic involvement and this may have an opposite trend compared to concomitant canal signs, especially during initial attacks. This behavior allows us to distinguish clinical signs of maculo-canal "correspondence" and "dissociation" with a significant prevalence of the second indication in those subjects with an initial MD attack.

Vestibulo-Ocular Reflex (VOR) abnormalities in cerebellar ataxias are a matter of renewed interest. We have previously reported vestibular areflexia in a group of Yemenite-Jews with Spinocerebellar Ataxia Type 3 (SCA3) who had clear bilateral pathological horizontal Head Impulse Test (HIT). The objective of this study was to evaluate the VOR of ten SCA3 patients who have variable bedside HIT responses by recording their eye movements using magnetic search coils and to correlate these results with their clinical and genetic data. Eight out of the ten patients have abnormal horizontal HIT detected by both clinical bedside examination and laboratory tests. Results of bedside HIT testing were significantly correlated with the VOR gain recorded using magnetic search coils. No significant correlations were found between VOR gain and other clinical or genetic data. Our study confirms the presence of defective VOR in SCA3 patients and corroborates the useful of the HIT as a reliable bedside test for diagnosis of VOR deficits.

The goal of this study was to assess the effect of amplitude and frequency predictability on the performance of the translational vestibulo-ocular reflex (tVOR). Eye movements were recorded in 5 subjects during continuous vertical translation that consisted of a series of segments with: 1) 3 amplitudes at constant frequency (2 Hz) or 2) 3 different frequencies (1.6, 2, 2.5 Hz). Stimulus changes were presented in a pseudo-random order. We found that there was little change in the tVOR immediately after an unexpected stimulus change, as if eye velocity were being driven more by an expectation based on previous steady-state motion than by current head translation. For amplitude transitions, only about 30% of the eventual response change was seen in the first half cycle. Similarly, a sudden change in translation frequency did not appear in eye velocity for 70 ms, compared to a 8 ms lag during similar yaw rotation. Finally, after a sudden large decrease in frequency, the eyes continued to track at the original higher frequency, resulting initially in an anti-compensatory tVOR acceleration. Our results elucidate further the complexity of the tVOR and show that motion prediction based on prior experience plays an important role in its response.

Vertigo and vigorous horizontal spontaneous nystagmus in a presenting patient is usually taken to indicate unilaterally reduced horizontal canal function. However here we report results which question that presumption. In three such patients with an acute vestibular syndrome, complete testing of all peripheral vestibular sense organs using new tests of canal and otolith function (vHIT and VEMPs) showed that semicircular canal function was normal, but that there were unilateral otolithic deficits which probably caused their acute syndrome.

Most of our knowledge concerning central vestibular pathways is derived from animal studies while evidence of the functional importance and localization of these pathways in humans is less well defined. The termination of these pathways at the thalamic level in humans is even less known. In this review we summarize the findings concerning the central subcortical vestibular pathways in humans and the role of these structures in the central vestibular system with regard to anatomical localization and function. Also, we review the role of the thalamus in the pathogenesis of higher order sensory deficits such as spatial neglect, pusher syndrome or thalamic astasia and the correlation of these phenomena with findings of a vestibular tone imbalance at the thalamic level.

By highlighting thalamic structures involved in vestibular signal processing and relating the different nomenclatures we hope to provide a base for future studies on thalamic sensory signal processing.

A growing body of clinical and epidemiological evidence supports a specific relationship between vestibular symptoms and migraine. Without a biomarker or complete understanding of pathophysiology, diagnosis of vestibular migraine (VM) currently depends upon symptoms in two dimensions: episodic vestibular symptoms temporally related to migraine symptoms. The Bárány Society and the International Headache Society have recently developed consensus diagnostic criteria. However, many issues remain unsettled, including the type, duration, and timing of vestibular symptoms related to headache that should be required for diagnosing VM. This paper focuses on the challenging third dimension of comorbidity, a frequent cause of diagnostic uncertainty that may confound clinical application and research validation of VM criteria. Several other neurotologic conditions occur more frequently in migraineurs than controls, including benign paroxysmal positional vertigo, Ménière's disease, and motion sickness. Patients with VM also have high rates of chronic subjective dizziness, which may be associated with anxious, introverted temperaments that can affect clinical presentation and treatment response. Broadly inclusive studies of well-characterized patients with other neurotologic and psychiatric comorbidities are needed to fully understand how vestibular symptoms and migraine interact in order to truly validate vestibular migraine, distill its essential features, define its boundaries, and characterize overlapping comorbidities.

Atypical variants of benign paroxysmal positional vertigo (BPPV) are often encountered and frequently confusing. The authors present a hypothetical framework that accounts for all classical patterns of BPPV and several unusual variants such as BPPV without nystagmus, BPPV with downbeat nystagmus and BPPV with paradoxically direction-changing nystagmus. The authors introduce new concepts, such as “ipsicanal switch” and “horizontal short arm canalolithiasis” and suggest that their use may improve diagnosis and treatment in everyday clinical practice. The possible consequences of saccular otoconia detachment are reviewed according to the literature.

During gaze shifts, humans can use visual, vestibular, and proprioceptive feedback, as well as feedforward mechanisms, for stabilization against active and passive head movements. The contributions of feedforward and sensory feedback control, and the role of the cerebellum, are still under debate. To quantify these contributions, we increased the head moment of inertia in three groups (ten healthy, five chronic vestibular-loss and nine cerebellar-ataxia patients) while they performed large gaze shifts to flashed targets in darkness. This induces undesired head oscillations. Consequently, both active (desired) and passive (undesired) head movements had to be compensated for to stabilize gaze. All groups compensated for active and passive head movements, vestibular-loss patients less than the other groups (P < 0.001, passive/active compensatory gains: vestibular-loss 0.23 ± 0.09/0.43 ± 0.12, healthy 0.80 ± 0.17/0.83 ± 0.15, cerebellar-ataxia 0.68 ± 0.17/0.77 ± 0.30, mean ± SD). The compensation gain ratio against passive and active movements was smaller than one in vestibular-loss patients (0.54 ± 0.10, P=0.001). Healthy and cerebellar-ataxia patients did not differ in active and passive compensation. In summary, vestibular-loss patients can better stabilize gaze against active than against passive head movements. Therefore, feedforward mechanisms substantially contribute to gaze stabilization. Proprioception alone is not sufficient (gain 0.2). Stabilization against active and passive head movements was not impaired in our cerebellar ataxia patients.

Fear of heights is elicited by a glance into an abyss. However, the visual exploration behavior of fearful subjects at height has not been analyzed yet. We investigated eye- and head movements, i.e. visual exploration behavior, of subjects susceptible to fear of heights during exposure to a visual cliff. The movements of eyes and head were recorded in 19 subjects susceptible to fear of heights and 18 controls while standing still on an emergency balcony 20 meters above ground level for periods of 30 seconds. Participants wore mobile, infrared eye-tracking goggles with inertial sensors for recording head movements. Susceptibles exhibited fewer and smaller-amplitude eye-in-head saccades with fixations of longer duration. Spontaneous head movements were reduced by 49% in susceptibles with a significantly lower mean absolute angular velocity (5.3°/s vs. 10.4°/s), and all three dimensions (yaw, pitch and roll) were equally affected. Gaze-in-space – which indicates exploration by coordinated eye-head movements – covered a smaller total area of the visual scene (explored horizontal angle: 19° vs. 32°, vertical: 9° vs. 17°). We hypothesize that the susceptibles suppress eye and head movements to alleviate fear of heights. However, this behavior has the potential disadvantage of impairing the visual stabilization of postural balance.

Diagnosis of central vestibulopathy remains a challenge when it is associated with peripheral vestibular dysfunction because neurotological findings from peripheral vestibulopathy may overshadow those from central vestibular involvements. To define the characteristics of disorders involving both peripheral and central vestibular structures, we classified the combined vestibulopathies into four types according to their vestibular manifestations, and describe a typical case in each subtype. Infarction involving the territory of anterior inferior cerebellar artery is the most common cause of acute unilateral cases, whereas tumors involving the cerebellopontine angle should be of prime suspicion in patients with chronic unilateral ones. Wernicke encephalopathy was most common in patients with acute bilateral combined vestibulopathy while degenerative disorders should be considered in chronic bilateral ones. Since the head impulse test (HIT) is mostly positive in combined vestibulopathy, signs of central vestibular dysfunction other than negative HIT should be sought carefully even in patients with obvious clinical or laboratory features of peripheral vestibulopathy.

Functional imaging, lesion studies and behavioural observations suggest that vestibular processing is lateralised to the non-dominant hemisphere. Moreover, disruption of interhemispheric balance via inhibition of left parietal cortex using transcranial direct current stimulation (tDCS) has been associated with an asymmetric suppression of the vestibulo-ocular reflex (VOR). However, the mechanism by which the VOR was modulated remains unknown. In this paper we review the literature on non-invasive brain stimulation techniques which have been used to probe vestibular function over the last decade. In addition, we investigate the mechanisms whereby tDCS may modulate VOR, e.g. by acting upon pursuit, VOR suppression mechanisms or direct VOR modulation. We applied bi-hemispheric parietal tDCS in 11 healthy subjects and only observed significant effects on VOR gain (tdcs * condition p=0.041) – namely a trend for VOR gain increase with right anodal/left cathodal stimulation, and a decrease with right cathodal/left anodal stimulation. Hence, we suggest that the modulation of the VOR observed both here and in previous reports, is directly caused by top-down cortical control of the VOR as a result of disruption to interhemispheric balance, likely parietal.

The head impulse test (HIT) is nowadays recognized as the gold standard for clinical testing of the angular vestibulo-ocular reflex (VOR). By imposing unpredictable, abrupt head rotations in canal pairs' planes it aims at unveiling the dysfunction of the semicircular canal towards which the head is rotated based on Ewald's II law. Functional testing of the VOR aims at assessing the ability of the reflex to stabilize gaze in space and thus allow clear vision during head movements. The HIT device (HITD) approach exploits impulsive head rotations spawning a range of angular accelerations while requiring subjects to identify optotypes briefly displayed on a screen. Here we also recorded eye movements, so that the evaluation of the individual subject is based both on the VOR gain and on the percentage of correct answers with respect to a population of controls. Here we used the HITD to study 14 patients suffering from vestibular neuritis and 7 of those were re-tested after three months. We found that the HITD was able to unveil the ipsilesional deficit and the contralesional impairment, together with the improvement in the follow-up test.