Journal of Vestibular Research

Hanes, Douglas A. ; McCollum, Gin

doi: N/Apmid: N/A

Cognitive deficits such as poor concentration and short-term memory loss are known by clinicians to occur frequently among patients with vestibular abnormalities. Although direct scientific study of such deficits has been limited, several types of investigations do lend weight to the existence of vestibular-cognitive effects. In this article we review a wide range of studies indicating a vestibular influence on the ability to perform certain cognitive functions. In addition to tests of vestibular patient abilities, these studies include dual-task studies of cognitive and balance functions, studies of vestibular contribution to spatial perception and memory, and works demonstrating a vestibular influence on oculomotor and motor coordination abilities that are involved in the performance of everyday cognitive tasks. A growing literature on the physiology of the vestibular system has demonstrated the existence of projections from the vestibular nuclei to the cerebral cortex. The goals of this review are to both raise awareness of the cognitive effects of vestibular disease and to focus scientific attention on aspects of cognitive-vestibular interactions indicated by a wide range of results in the literature.

Hanes, Douglas A.; McCollum, Gin

doi: 10.3233/ves-2006-16301pmid: N/A

Cognitive deficits such as poor concentration and short-term memory loss are known by clinicians to occur frequently among patients with vestibular abnormalities. Although direct scientific study of such deficits has been limited, several types of investigations do lend weight to the existence of vestibular-cognitive effects. In this article we review a wide range of studies indicating a vestibular influence on the ability to perform certain cognitive functions. In addition to tests of vestibular patient abilities, these studies include dual-task studies of cognitive and balance functions, studies of vestibular contribution to spatial perception and memory, and works demonstrating a vestibular influence on oculomotor and motor coordination abilities that are involved in the performance of everyday cognitive tasks. A growing literature on the physiology of the vestibular system has demonstrated the existence of projections from the vestibular nuclei to the cerebral cortex. The goals of this review are to both raise awareness of the cognitive effects of vestibular disease and to focus scientific attention on aspects of cognitive-vestibular interactions indicated by a wide range of results in the literature.

Prieur, J.-M.; Bourdin, C.; Sarès, F.; Vercher, J.-L.

doi: 10.3233/ves-2006-16302pmid: N/A

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments [2,16] we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).

Prieur, J.-M. ; Bourdin, C. ; Sarès, F. ; Vercher, J.-L.

doi: N/Apmid: N/A

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments (2,16) we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).

Tribukait, Arne; Eiken, Ola

doi: 10.3233/ves-2006-16303pmid: N/A

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.

Tribukait, Arne ; Eiken, Ola

doi: N/Apmid: N/A

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.

Karmali, Faisal; Ramat, Stefano; Shelhamer, Mark

doi: 10.3233/ves-2006-16304pmid: N/A

During the alternating enhanced and reduced "gravity" levels of parabolic flight, subjects noted that a horizontally eccentric point target viewed binocularly in darkness seemed to split into two targets with vertical divergence. The amount of perceived divergence seemed to depend on instantaneous g level. This perceptual observation suggested a vertical misalignment of the eyes (vertical skew), dependent on the magnitude of g level sensed by the otoliths. While performing a different experiment during parabolic flight we recorded binocular eye position and analyzed these data to corroborate the behavioral observations. Records were obtained from seven trials in five subjects, containing eye alignment in both 0 g and 1.8 g. The recordings confirm the presence of vertical skew that changed with g level. "Skew-differential" was quantified for each trial as the difference in vertical skew from 0 g to 1.8 g. Mean skew-differential was 1.37°; the largest was 2.57°. Statistical significance was assessed using the student t-test and the more correct and stringent Generalized Estimating Equations (GEE). The observed skew is equivalent to a mild strabismus, which is known to result in diplopia. The underlying mechanism may be an asymmetry between the otolith organs on either side, which is centrally compensated in 1 g, but is inappropriately compensated in other gravitational fields. If equivalent amounts of vertical skew were to occur during changes in g level during dynamic phases of flight in high-performance aircraft or space shuttle reentry, the impact on visual fixation might be detrimental to piloting performance.

Karmali, Faisal ; Ramat, Stefano ; Shelhamer, Mark

doi: N/Apmid: N/A

During the alternating enhanced and reduced "gravity" levels of parabolic flight, subjects noted that a horizontally eccentric point target viewed binocularly in darkness seemed to split into two targets with vertical divergence. The amount of perceived divergence seemed to depend on instantaneous g level. This perceptual observation suggested a vertical misalignment of the eyes (vertical skew), dependent on the magnitude of g level sensed by the otoliths. While performing a different experiment during parabolic flight we recorded binocular eye position and analyzed these data to corroborate the behavioral observations. Records were obtained from seven trials in five subjects, containing eye alignment in both 0 g and 1.8 g. The recordings confirm the presence of vertical skew that changed with g level. "Skew-differential" was quantified for each trial as the difference in vertical skew from 0 g to 1.8 g. Mean skew-differential was 1.37°; the largest was 2.57°. Statistical significance was assessed using the student t-test and the more correct and stringent Generalized Estimating Equations (GEE). The observed skew is equivalent to a mild strabismus, which is known to result in diplopia. The underlying mechanism may be an asymmetry between the otolith organs on either side, which is centrally compensated in 1 g, but is inappropriately compensated in other gravitational fields. If equivalent amounts of vertical skew were to occur during changes in g level during dynamic phases of flight in high-performance aircraft or space shuttle reentry, the impact on visual fixation might be detrimental to piloting performance.

Magnusson, M.; Andersson, G.; Gomez, S.; Johansson, R.; Mårtensson, A.; Karlberg, M.; Fransson, P.A.

doi: 10.3233/ves-2006-16305pmid: N/A

A previous study showed that vibratory stimulation of neck muscles in humans induced short-latency electromyographic (EMG) activation of lower leg muscles, producing postural reactions at the feet. These findings indicated that cervical proprioception contributes to stabilization of stance through rapidly integrated pathways. However, as vibration may excite both proprioceptive and vestibular afferents, and because of the proximity of neck muscles to the vestibular apparatus, neck muscle vibration could also have activated the vestibular system thereby contributing to the effect observed. To investigate any possible contribution of vestibular stimulation, vibratory stimuli were applied bilaterally and separately to the splenius muscles of the neck and the planum mastoideum overlying the vestibular organs. Ten normal subjects, with eyes closed, were exposed to vibratory stimulation of two different amplitudes and frequencies. Responses were assessed by EMG activity recorded from tibialis anterior and gastrocnemius muscles of both legs and by changes in center of pressure as measured by a force platform. Results indicated that vibration induced reproducible EMG and postural responses in the anteroposterior direction, particularly on cessation of vibration. EMG and postural responses were considerably lower and less consistent with mastoid vibration compared with neck muscles vibration. Previous reports suggest that vibratory stimulation could propagate to the vestibular organs and generate a vestibular-induced postural activation. However, our findings indicate that cervical muscles afferents play a dominant role over vestibular afferents when vibration is directed towards the neck muscles.

Magnusson, M. ; Andersson, G. ; Gomez, S. ; Johansson, R. ; Mårtensson, A. ; Karlberg, M. ; Fransson, P.A.

doi: N/Apmid: N/A

A previous study showed that vibratory stimulation of neck muscles in humans induced short-latency electromyographic (EMG) activation of lower leg muscles, producing postural reactions at the feet. These findings indicated that cervical proprioception contributes to stabilization of stance through rapidly integrated pathways. However, as vibration may excite both proprioceptive and vestibular afferents, and because of the proximity of neck muscles to the vestibular apparatus, neck muscle vibration could also have activated the vestibular system thereby contributing to the effect observed. To investigate any possible contribution of vestibular stimulation, vibratory stimuli were applied bilaterally and separately to the splenius muscles of the neck and the planum mastoideum overlying the vestibular organs. Ten normal subjects, with eyes closed, were exposed to vibratory stimulation of two different amplitudes and frequencies. Responses were assessed by EMG activity recorded from tibialis anterior and gastrocnemius muscles of both legs and by changes in center of pressure as measured by a force platform. Results indicated that vibration induced reproducible EMG and postural responses in the anteroposterior direction, particularly on cessation of vibration. EMG and postural responses were considerably lower and less consistent with mastoid vibration compared with neck muscles vibration. Previous reports suggest that vibratory stimulation could propagate to the vestibular organs and generate a vestibular-induced postural activation. However, our findings indicate that cervical muscles afferents play a dominant role over vestibular afferents when vibration is directed towards the neck muscles.