Journal of Vestibular Research - Volume 10, issue 1

Authors: Smith, Paul F.

Article Type: Research Article

Abstract: Aminoglycoside antibiotics are commonly prescribed throughout the world for the treatment of serious gram-negative bacterial infections. However, their use is limited by nephrotoxicity and ototoxicity. Although the traditional explanation for their ototoxicity in cochlear and vestibular hair cells has been the inhibition of mitochondrial protein synthesis, evidence is accumulating to suggest that many aminoglycosides cause excitotoxicity in hair cells as a result of their agonist action at the polyamine site on the N- methyl-D-aspartate (NMDA) receptor. The aim of this minireview is to summarise and critically evaluate this evidence and to consider the therapeutic implications of this hypothesis

Keywords: aminoglycoside antibiotics, ototoxicity, vestibulotoxicity, excitotoxicity, glutamate

DOI: 10.3233/VES-2000-10101

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 1-5, 2000

Authors: Cohen, Helen S.

Article Type: Research Article

Abstract: The goal of this study was to determine if people use vestibular information to keep track of their positions while walking through a simple course. Subjects were normals and patients with chronic peripheral vestibulopathies – each of whom were tested once – and patients with acoustic neuromas tested pre- operatively and one and three weeks post-operatively. Subjects walked over a straight course, 7.62 m, with their eyes open and then with their eyes closed. The time needed for task performance, the forward distance subjects walked before veering, and the lateral distance subjects veered from the straight ahead were recorded. The …angle of veering was then calculated. Normals were able to perform this task easily with eyes open or closed. With eyes closed pre-operative acoustic neuroma subjects walked significantly shorter distances before veering than normals but did not veer significantly more than normals or take longer than normals to perform the task. Chronic vestibulopathy subjects, by contrast, were significantly impaired compared to normals on all measures. With eyes open within a week after acoustic neuroma resection subjects could perform the task as well as normals. With eyes closed, however, post-operative subjects were impaired compared to their own pre-operative levels, but they had returned to their pre-operative levels at the second post-operative test. Ataxia was only weakly correlated to any measures and tumor size was not related to performance. These findings support the hypothesis that vestibular input is used for spatial orientation during active motion. Show more

Keywords: veering, spatial orientation, navigation, dead reckoning

DOI: 10.3233/VES-2000-10102

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 7-15, 2000

Authors: Ahn, Seung Cheol | Lee, Chae Yong | Kim, Dong Wook | Lee, Moo Hoo

Article Type: Research Article

Abstract: To investigate the short-term vestibular habituation, we performed the 4 successive velocity step tests on 28 volunteers, the peak velocity of which was 100 deg/sec with acceleration and deceleration of 100 deg / sec 2 . As the repeated rotations might alter the vestibulo-ocular reflex (VOR), sinusoidal rotations at a frequency of 0.16 Hz were also given before and after the 4 successive velocity step tests to investigate the changes of gain and phase of VOR. The 28 volunteers were divided into two groups, group I and II, according to their responses to repeated …rotations. In group I (25 subjects, mean age 23.7 year), the mean values of the slow cumulative eye position (SCEP), the time integral of eye velocity during nystagmus, was reduced after each trial of the 4-successive velocity step tests as follows; 403.4 ± 29 degree (1st trial), 346.2 ± 37 degree (2nd trial), 278.3 ± 33 degree (3rd trial) and 256.6 ± 36 degree (4th trial). The time constant of the nystagmus was also reduced as follows; 12.9 ± 0.78 second (1st trial), 12 ± 0.63 second (2nd trial), 9.7 ± 0.78 second (3rd trial) and 9.9 ± 0.54 second (4th trial). In group II (3 subjects, mean age 28.3 year), the mean values of SCEP gradually increased; 774.3 ± 135 degree (1st trial), 1127 ± 178 degree (2nd trial), 1096.3 ± 123.4 degree (3rd trial) and 1225.7 ± 199.7 degree (4th trial). The time constant of the nystagmus increased; 15.7 ± 2.7 second (1st trial), 22 ± 4.5 second (2nd trial), 22.3 ± 3.3 second (3rd trial) and 23.3 ± 5.7 second (4th trial). The gain of vestibulo-ocular reflex (VOR) induced by sinusoidal rotations at a frequency 0.16 Hz increased in both groups: 0.59 ± 0.03 to 0.78 ± 0.06 (group I) and 0.65 ± 0.07 to 1.15 ± 0.06 (group II). Phase changes were also observed. In group I, the phase was shifted from 0.6 ± 0.6 degree to − 0.40 ± 0.6 degree. In group II, the phase was shifted from 3.67 ± 1.86 degree to − 0.33 ± 0.33 degree. The repeated rotation did not induce a common nystagmic response in all subjects. Thus, person to person variations should be considered in short term vestibular habituation. Show more

Keywords: vestibular habituation, slow cumulative eye position (SCEP), gain, phase

DOI: 10.3233/VES-2000-10103

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 17-23, 2000

Authors: Formby, C. | Robinson, D.A.

Article Type: Research Article

Abstract: A protocol is described for measuring responses to a broadband (1–2 Hz) caloric step stimulus from which the vestibular ocular reflex (VOR) and adaptation time constants can be estimated. This novel stimulation is the caloric equivalent to a rotatory step of head acceleration. In this protocol, the ear is irrigated continuously for 5 min with water at a constant temperature. During the initial 2-min period of irrigation the subject is seated and leaning forward in a nonstimulable position (horizontal canals in a horizontal plane). This irrigation phase establishes a steady-state thermal gradient across the horizontal canal, effectively eliminating thermal dynamic …properties of the caloric transmission as a confounding factor. At the end of this phase, the subject is rapidly reclined to a stimulable position (horizontal canals in vertical plane) that elicits the VOR nystagmus response to an on-step of force on the cupula. Consistent with adaptation processes, the VOR response first increases and then declines gradually over the 2-min period that the step of force is maintained. Four minutes after the onset of irrigation, the subject is rapidly returned to the nonstimulable position (off-step), which is then maintained for a final 1 min. The response after the off-step, which releases the force on the cupula, reveals reversed after-nystagmus due to adaptation. Five subjects provided caloric step responses for 26 caloric temperature conditions spanning the range from 28.4 to 43.0 ∘ C. The resulting responses were fitted with an adaptation model similar to models applied to rotatory acceleration step responses. Estimates of the model parameters for robust caloric stimulation, including time constants for the VOR (18.3 sec) and for vestibular adaptation (153.2 sec), are considered in relation to corresponding values reported in the literature for rotatory and caloric vestibular stimulation. The results suggest that caloric step stimulation can be used successfully to probe VOR dynamics. Show more

Keywords: vestibular ocular reflex, caloric step stimulation, vestibular time constants, vestibular adaptation

DOI: 10.3233/VES-2000-10104

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 25-39, 2000

Authors: Paquet, Nicole | Watt, Douglas G.D. | Lefebvre, Luc

Article Type: Research Article

Abstract: A repetitive manoeuvre called torso rotation (TR) is known to temporarily reduce the gain of the horizontal vestibulo-ocular reflex by 10–15% consists of a series of rhythmical rotations of the eyes, head and upper body executed continuously for 30 minutes while standing. Our aim was to investigate whether TR affects the ability to hold the head in a fixed fore-aft position relative to space while walking on a treadmill with eyes closed. Ten healthy subjects stood in a carefully standardized position on a stationary treadmill. The treadmill started unexpectedly and ran for 4 s at 29 cm/s. The test stimulus …was a linear acceleration in the fore-aft direction at the moment of treadmill start-up. Linear head position (i.e., ability to stabilize the head) was measured during and following the stimulus. A mechanical system prevented head rotation. Two series of 60 trials were performed before TR (control 1 and control 2 series) and one after TR. Before TR, subjects drifted rearward at an average drift velocity ± S.D. = 3.1 ± 0.9 cm / s . This drift was reasonably stable over time within and between the two control series. After TR, head holding ability was further impaired, with subjects having more difficulty to stabilize their head after treadmill start-up. In the first 10 trials after the arrest of TR, the average drift velocity was significantly larger than before TR (6.1 ± 1.5 cm / sec , p < 0.01 ). Recovery to control values followed a roughly exponential time course, with 67% impairs the ability to sense and/or respond to fore-aft linear accelerations of the head following treadmill start-up in the absence of vision. Show more

Keywords: torso rotation, linear acceleration, locomotion, head displacement, human

DOI: 10.3233/VES-2000-10105

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 41-49, 2000

Authors: Das, Vallabh E. | Yaniglos, Stacy | Leigh, R. John

Article Type: Research Article

Abstract: The goal of this study was to investigate the influence of light, without retinal slip information, on the ability to generate eye movements to compensate for head rotations. Subjects were rotated sinusoidally at 1.0, 2.0 or 3.0 Hz at a peak velocity of 30 deg/sec while they: 1) performed mental arithmetic in darkness; 2) attempted to view the remembered location of a stationary target in darkness; 3) attempted to view the remembered location of the stationary target through translucent contact lenses that allowed the passage of light but did not provide any target information (ganzfeld stimulus); 4) directly viewed the …illuminated stationary target. The gain of compensatory eye movements was least while subjects viewed through the translucent contact lenses (median = 0.76), intermediate while subjects either performed mental arithmetic in darkness (median = 0.84) or attempted to view the remembered location of the target in darkness (median = 0.84), and greatest if they actually viewed the target (median = 0.95). Our findings suggest that factors other than light alone account for the increased gain of compensatory eye movements that occurs when subjects view rather than imagine a stationary target. Show more

Keywords: VOR, visual-vestibular, ganzfeld, oculomotor, human

DOI: 10.3233/VES-2000-10106

Citation: Journal of Vestibular Research, vol. 10, no. 1, pp. 51-55, 2000