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  • 1. Brantberg, K.
    et al.
    Fransson, P A
    Bergenius, J.
    Tribukait, Arne
    Karolinska Hospital.
    Tilt suppression, OKAN, and head-shaking nystagmus at long-term follow-up after unilateral vestibular neurectomy1996Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 6, nr 4, s. 235-241Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The functional status of the velocity storage mechanism was studied in patients at long-term follow-up (2 to 4 years) after unilateral vestibular neurectomy. The time constant of the vestibulo-ocular reflex (VORtc), the effect of head tilt on postrotatory nystagmus, optokinetic after-nystagmus (OKAN), and nystagmus after rapid head shaking were studied in 10 patients. In agreement with previous findings, VORtc was found to be short and most patients manifested OKAN, suggesting that unilateral peripheral vestibular loss is associated with a complete loss of storage within the the VOR but only a partial loss of velocity storage for visual input. However, at postrotatory head tilt the VOR time constant was further shortened, supposedly due to discharge of functioning velocity storage. Moreover, most patients manifested nystagmus after head shaking. These findings on tilt suppression and head-shaking nystagmus suggest that velocity storage within the VOR may function even in patients with complete unilateral vestibular lesions.

  • 2. Brantberg, Krister
    et al.
    Tribukait, Arne
    Karolinska Hospital.
    Vestibular evoked myogenic potentials in response to laterally directed skull taps2002Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 12, nr 1, s. 35-45Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that midline forehead skull tap stimulation evokes similar VEMP. In the present study, the influence of skull tap direction on VEMP was studied in 13 normal subjects and in five patients with unilateral vestibular loss. Gentle skull taps were delivered manually above each ear on the side of the skull. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Among the normals, laterally directed skull taps evoked "coordinated contraction-relaxation responses", i.e. skull taps on one side evoked a negative-positive "inverted" VEMP on that side and a positive-negative "normal" VEMP on the other side. Among patients with unilateral vestibular function loss, skull taps above the lesioned ear evoked similar coordinated contraction-relaxation responses. However, skull taps above the healthy ear did not evoke that type of response. These findings suggest that laterally directed skull taps activate mainly the contralateral labyrinth.

  • 3. Brantberg, Krister
    et al.
    Tribukait, Arne
    Karolinska Hospital.
    Fransson, Per-Anders
    Vestibular evoked myogenic potentials in response to skull taps for patients with vestibular neuritis2003Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 13, nr 2-3, s. 121-130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that skull tap stimulation evokes similar VEMP. In the present study, the differences between the click-induced and the skull-tap induced VEMP were studied in 18 patients at onset of vestibular neuritis. Gentle skull taps were delivered manually above each ear on the side of the skull and on the forehead midline. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Abnormal skull tap VEMP were found in the majority of the patients (10/18, 56%). However, only 4/18 (22%) showed asymmetry in the click-induced VEMP. The high percentage of abnormal skull tap VEMP might suggest that this response is not only dependent on the inferior division of the vestibular nerve, because the inferior division of this nerve is usually spared in vestibular neuritis. Moreover, the patients with abnormal skull tap VEMP differed from those with normal VEMP in their settings of the subjective visual horizontal with static head tilt in the roll plane. This might suggest that skull tap VEMP are (also) related to utricular function.

  • 4.
    Tribukait, Arne
    Karolinska Hospital.
    Semicircular canal and saccular influence on the subjective visual horizontal during gondola centrifugation1999Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 9, nr 5, s. 347-357Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements of the subjective visual horizontal (SVH) were performed in 11 healthy test persons during an increase of the resultant gravitoinertial force vector in a large swing-out gondola centrifuge. Three levels of hypergravity (1.5 g, 2.0 g, 2.5 g) were used, each with a duration of 4 minutes and with 1-2 minute pauses at 1.0 g in between. The direction of the resultant gravitoinertial force vector was always parallel with the head and body length axis. Hence, there was no roll stimulus to the otolith organs. The swing-out of the gondola during acceleration, however, is sensed by the vertical semicircular canals as a change in roll head position, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge there was a tilt of the SVH relative to the resultant gravitoinertial horizontal. This tilt gradually decayed during the 4-minute period of recordings. For a subgroup of seven test subjects who had completely normal ENG-recordings in 1 g environment, the initial offset of SVH and the time constants for exponential decay were determined for each g level; initial offsets: 9.9 degrees (1.5 g), 7.7 degrees (2.0 g), 6.1 degrees (2.5 g); time constants: 89s (1.5 g), 74s (2.0 g), 37s (2.5 g). The offset of SVH is interpreted as being the result of mainly the stimulus to the vertical semicircular canals during acceleration of the centrifuge. The slow decay, however, does not correspond to the dynamics of the semicircular canal system, and is suggested to reflect some kind of central position storage mechanism. A smaller offset and more rapid decay for the higher g loads may be explained by an increasing dominance of graviceptive input, presumably from the saccules. In conclusion, these results might suggest the role of the vertical semicircular canals as well as the sacculus in the formation of SVH. They may also have relevance with regard to the spatial disorientation problem in aviators.

  • 5.
    Tribukait, Arne
    Karolinska Hospital.
    Subjective visual horizontal in the upright posture and asymmetry in roll-tilt perception: independent measures of vestibular function2006Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 16, nr 1-2, s. 35-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The subjective visual horizontal (SVH) was measured in the upright position and at 10, 20, and 30 degrees of head and body tilt to the right and left. Normal subjects (n=25) were tested on two separate occasions with an interval of 1-14 days. Test variables considered were the SVH in the upright position, the perception of tilt to the right and left, calculated on the basis of the SVH in the upright and tilted positions, and the asymmetry in tilt perception. There was no correlation between the perception of tilt to the right and to the left r=0.10). Neither was there any correlation between the SVH in the upright position, representing a resting asymmetry, and the asymmetry in tilt perception, i.e. the response asymmetry (r=0.17). However, for each variable, there was a high correspondence between data obtained at test and retest (r ranged from 0.68 to 0.89, p<0.001), suggesting that the independence between variables is not due to noise. Findings are discussed taking into consideration the possible roles of otoliths and semicircular canals in the formation of the SVH. In an attempt to explain the independence between the two measures of asymmetry it is hypothesized that while the otoliths must be essential for the perception of static lateral tilt, the SVH in the upright position to a considerable degree reflects semicircular canal function.

  • 6.
    Tribukait, Arne
    et al.
    Swedish Defence Research Agency.
    Eiken, Ola
    Swedish Defence Research Agency.
    Changes in the perceived head transversal plane and the subjective visual horizontal induced by Coriolis stimulation during gondola centrifugation2006Inngår i: Journal of Vestibular Research-Equilibrium & Orientation, ISSN 0957-4271, E-ISSN 1878-6464, Vol. 16, nr 3, s. 105-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For studying the influence of the vertical semicircular canals on spatial orientation in roll, the subjective visual horizontal (SVH) and the subjective transversal plane of the head (STP) were measured in a situation where the vertical canals sense a roll-velocity stimulus while the otolith organs persistently signal that the head is upright in roll. During gondola centrifugation (resultant gravitoinertial force vector 2.5 G, gondola inclination 66 degrees) subjects were exposed to controlled rotational head movements (angular speed 27 degrees/s, magnitude 40 degrees) about the yaw (body z-) axis, produced by means of a motor-driven helmet. This causes a roll-plane Coriolis stimulus to the canals, while the otoliths persistently sense upright head position in roll. The subjects reported intense sensations of rotation and tilt in the roll plane. This was reflected in tilts of both the SVH and STP. The initial tilt of the SVH was 13.0 +/- 9.7 degrees (mean +/- S.D., n=10). The STP was changed in the opposite direction. The initial tilt was 23.8 +/- 12.2 degrees (mean +/- S.D., n=5). The changes in the SVH and STP were not of equal magnitude. A few subjects who had almost no deviations in the SVH showed pronounced tilts of the STP. The time constant for exponential decay of the tilts of the SVH and STP was on average approximately 1 minute. These findings indicate that a difference in activity of the vertical canals in the right versus left ear may cause substantial tilts of the SVH even if there is no asymmetry in the activity of the otolith system. Further, the canal stimulus may induce a tilt of the fundamental egocentric frame of reference.

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