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Opsoclonus refers to saccadic oscillations without an intersaccadic interval occurring in multiple planes. Opsoclonus mostly indicates dysfunction of the brainstem or cerebellum. We report opsoclonus induced by horizontal head-shaking without other signs of brainstem or cerebellar dysfunction in two patients with vestibular migraine (VM). The development of opsoclonus after horizontal head-shaking indicates unstable or hyperactive neural circuits between the excitatory and inhibitory saccadic premotor burst neurons in these patients with VM. [ABSTRACT FROM AUTHOR]

Differentiation of spinocerebellar ataxia type 17 (SCA17) from Huntington's disease (HD) is often challenging since they share the clinical features of chorea, parkinsonism, and dystonia. The ocular motor findings remain to be elucidated in SCA17, and may help differentiating SCA17 from HD. We retrospectively compared the ocular motor findings of 11 patients with SCA17 with those of 10 patients with HD. In SCA17, abnormal ocular motor findings included impaired smooth pursuit (9/11, 82%), dysmetric saccades (9/11, 82%), central positional nystagmus (CPN, 7/11, 64%), abnormal head-impulse tests (4/11, 36%), and horizontal gaze-evoked nystagmus (GEN, 3/11, 27%). Among these, CPN was more frequently observed in SCA17 than in HD (7/11 (64%) vs. 0/10 (0%), p = 0.004) while saccadic slowing was more frequently observed in HD than in SCA17 (8/10 (80%) vs. 2/11 (18%), p = 0.009). Of six patients with follow-up evaluation, five later developed bilateral saccadic hypermetria (n = 4), GEN (n = 1), CPN (n = 1), bilaterally abnormal smooth pursuit (n = 1), and hyperactive head-impulse responses (n = 1) along with a clinical decline. Ocular motor abnormalities can be utilized as a diagnostic marker for differentiation of SCA17 from HD as well as a surrogate marker for clinical decline in SCA17. [ABSTRACT FROM AUTHOR]

The mechanism of vestibular syncope, the syncope occurring during the vertigo attacks, remains uncertain. This study aims to clarify the mechanism of vestibular syncope by pursuing the function of vestibular system in cardiovascular autonomic control and by defining neuro-hemodynamic changes in vestibular syncope. By integrating the velocity-storage (VS) circuit in the brainstem and cerebellum, we propose that the vestibular syncope develops as a result of dyssynergia of the vestibulosympathetic and baroreflexes in which centrally estimated downward inertial acceleration during the vertigo attacks acts as a trigger. Recognition of the vestibular disorders as a possible cause of syncope would allow proper managements for prevention of further syncope and related complications in patients with vestibular disorders. [ABSTRACT FROM AUTHOR]

Hyperventilation changes the extracellular pH modulating many central pathologies, such as tremor. The questions that remain unanswered are the following: (1) Hyperventilation modulates which aspects of the oscillations? (2) Whether the effects of hyperventilation are instantaneous and the recovery is rapid and complete? Here we study the effects of hyperventilation on eye oscillations in the syndrome of oculopalatal tremor (OPT), a disease model affecting the inferior olive and cerebellar system. These regions are commonly involved in the pathogenesis of many movement disorders. The focus on the ocular motor system also allows access to the well-known physiology and precise measurement techniques. We found that hyperventilation causes modest but insignificant changes in the intensity of oscillation displacement (i.e., how large the eye excursions are) and velocity (i.e., how fast do the eyes move during oscillations). We found the robust increase in the randomness of the oscillatory waveform during hyperventilation and it instantaneously reverts to the baseline after hyperventilation. The subsequent analysis classified the oscillations according to their waveform shape and randomness into different clusters. The hyperventilation substantially changed the cluster type in 60% of the subjects, but it reverted to the pre-hyperventilation cluster at the conclusion of the hyperventilation. In summary, hyperventilation instantaneously affects the randomness of the oscillatory waveforms but there are less substantial effects on the intensity. The deficits reverse immediately at the end of the hyperventilation. [ABSTRACT FROM AUTHOR]

We report atypical opsoclonus in a patient with multiple system atrophy and propose a mechanism based on the patterns of modulation by visual, vestibular, and saccadic and vergence stimulation. Firstly, the 6-Hz opsoclonus mostly in the vertical plane occurred only after the development of downbeat nystagmus in darkness without visual fixation. Even after a substantial build-up, visual suppression of the opsoclonus was immediate and complete. Furthermore, the latency for re-emergence of opsoclonus in darkness was greater when the duration of preceding visual fixation was longer. Secondly, the effect of preceding downbeat nystagmus on the development of opsoclonus was evaluated by changing the head position. The opsoclonus did not occur in the supine position when the downbeat nystagmus was absent. After horizontal head shaking, the opsoclonus in the vertical plane gradually evolved into horizontal plane and resumed its vertical direction again after vertical head shaking. Thirdly, any opsoclonus was not triggered by imaginary saccades in the supine position. Lastly, combined vergence and saccadic eye movements during the Müller paradigm did not induce opsoclonus. From these findings of modulation, we suggest that the opsoclonus observed in our patient was invoked by vestibular signals. When the function of the omnipause neurons and saccadic system was impaired, the centrally mediated vestibular eye velocity signals may activate the saccadic system to generate opsoclonus. These atypical patterns of opsoclonus, distinct from the classic opsoclonus frequently observed in para-neoplastic or para-infectious disorders, may be an unrevealing sign of degenerative brainstem or cerebellar disorders. [ABSTRACT FROM AUTHOR]

We investigated the vestibular perception of position, velocity, and time (duration) in humans with rotational stimuli including low velocities and small amplitudes. The participants were categorized into young, middle, and old age groups, and each consisted of 10 subjects. Position perception was assessed after yaw rotations ranged from 30 to 180° in both clockwise and counterclockwise directions. For each position, the rotation was delivered at two or more different velocities ranging from 15 to 120°/s. Position perception tended to underestimate the actual position and was similar during the slow and fast rotations. However, the trends of underestimation disappeared in the old age group. Velocity perception was evaluated by forcing the selection of the faster direction in each pair of rotations toward two positions (30° and 60°) with velocity differences from 0 to 20°/s. Velocity discrimination was similar between the rotation amplitudes or among the age groups. For duration perception, participants chose the rotation of longer duration for three test paradigms with different amplitudes (small vs. large) and durations (short vs. long) of rotation. The accuracy of discriminating duration was similar across the test paradigms or age groups, but the precision was lower in the older group and altered significantly according to the test paradigm. In conclusion, vestibular perception can be assessed using rotations of low velocities and small amplitudes. The perception of position and duration is affected by aging. The precision of duration perception can be influenced by the interactions between the amplitude and duration of motion. [ABSTRACT FROM AUTHOR]

Paroxysmal positional nystagmus frequently occurs in lesions involving the cerebellum, and has been ascribed to disinhibition and enhanced canal signals during positioning due to cerebellar dysfunction. This study aims to elucidate the mechanism of central positional nystagmus (CPN) by determining the effects of baclofen on the intensity of paroxysmal positional downbeat nystagmus due to central lesions. Fifteen patients with paroxysmal downbeat CPN were subjected to manual straight head-hanging before administration of baclofen, while taking baclofen 30 mg per day for at least one week, and two weeks after discontinuation of baclofen. The maximum slow phase velocity (SPV) and time constant (TC) of the induced paroxysmal downbeat CPN were analyzed. The positional vertigo was evaluated using an 11-point numerical rating scale (0 to 10) in 9 patients. After treatment with baclofen, the median of the maximum SPV of paroxysmal downbeat CPN decreased from 30.1°/s [interquartile range (IQR) = 19.6—39.0°/s] to 15.2°/s (IQR = 11.2—22.0°/s, Wilcoxon signed rank test, p < 0.001) with the median decrement ratio at 40.2% (IQR = 28.2—50.6%). After discontinuation of baclofen, the maximum SPV re-increased to 24.6°/s (IQR = 13.1—34.4°/s, Wilcoxon signed rank test, p = 0.001) with the median increment ratio at 23.5% (IQR = 5.2—87.9%). In contrast, the TCs of paroxysmal downbeat CPN remained unchanged at approximately 3.0 s throughout the evaluation. The positional vertigo also decreased with the medication (Wilcoxon signed rank test, p = 0.020), and remained unchanged even after discontinuation of medication (Wilcoxon signed rank test, p = 0.737). The results of this study support the prior presumption that paroxysmal CPN is caused by enhanced responses of the semicircular canals during positioning due to cerebellar disinhibition. Baclofen may be tried in symptomatic patients with paroxysmal CPN. [ABSTRACT FROM AUTHOR]

Two vestibular signals, rotational and inertial cues, converge for the perception of complex motion. However, how vestibular perception is built on neuronal behaviors and decision-making processes, especially during the simultaneous presentation of rotational and inertial cues, has yet to be elucidated in humans. In this study, we analyzed the perceptual responses of 20 participants after pairwise rotational experiments, comprised of four control and four test sessions. In both control and test sessions, participants underwent clockwise and counterclockwise rotations in head-down and head-up positions. The difference between the control and test sessions was the head re-orientation relative to gravity after rotations, thereby providing only rotational cues in the control sessions and both rotational and inertial cues in the test sessions. The accuracy of perceptual responses was calculated by comparing the direction of rotational and inertial cues acquired from participants with that predicted by the velocity-storage model. The results showed that the accuracy of rotational perception ranged from 80 to 95% in the four control sessions but significantly decreased to 35 to 75% in the four test sessions. The accuracy of inertial perception in the test sessions ranged from 50 to 70%. The accuracy of rotational perception improved with repetitive exposure to the simultaneous presentation of both rotational and inertial cues, while the accuracy of inertial perception remained steady. The results suggested a significant interaction between rotational and inertial perception and implied that vestibular perception acquired in patients with vestibular disorders are potentially inaccurate. [ABSTRACT FROM AUTHOR]