Vestibulospinal Reflexes Research Articles

Impaired vestibular–proprioceptive interaction in cerebellar patients

Background: Vestibulo-spinal reflexes depend on adequate interaction between vestibular and proproceptive signals. Animal experiments indicate that the cerebellum is involved in this fundamental task. Cerebellar disease often leads to deficits in motor control, e.g. stance and gait ataxia. This study examines if vestibular-proprioceptive interaction might be one clinically relevant component of motor disturbance in cerebellar disease. Methods: Patients with cerebellar disorders of different etiology and normal controls were subjected to sinusoidal galvanic vestibular stimulation (0.16Hz) while standing on a force platform that measured reflectory body sway. Head-on-trunk position in the horizontal plane was altered systematically between +-60 degrees, controlled by a mechanical restraining device. Results: Normal controls exhibited a systematic dependence of their dominant sway direction on head-on-trunk position, as previously shown, keeping sway direction approximately aligned with their interaural line. In contrast, this systematic dependence was absent or attenuated in many cerebellar patients. Conclusion: In accord with results from animal experiments, the present data indicate that processing of vestibular and proprioceptive signals can be impaired in cerebellar patients. This impairment of vestibularproprioceptive interaction may be an important aspect of deficient motor control, particularly of gait and stance ataxia, in cerebellar disease.

Aspekty otoneurologiczne wczesnych postaci stwardnienia rozsianego (SM)

Sclerosis multiplex (SM) is characterized by multifocality of neurological changes and polyphasic course. The disease is caused by indefinite factors in the circumstances of genetically determined immune disorders. The aim of study. An attempt was made to identify otoneurological symptoms accompanying the early stage of sclerosis multiplex (SM). Material and research methods. 103 patients (diagnosed with uncharacteristic otoneurological symptoms, in further clinical observation defined as SM prodromes) were retrospectively examined. The following factors were taken into consideration: character and intensity of dizziness, results of static and dynamic tests, electronystagmography (ENG), caloric test, eye tracking and optokinetic nystagmus. Conclusion. Disorders of: vestibulospinal reflexes, eye tracking, optokinesis, time and regularity of caloric nystagmus occur in the very early stages of SM.

Responses of Reticulospinal Neurons in the Lamprey to Lateral Turns

When swimming, the lamprey maintains a definite orientation of its body in the vertical planes, in relation to the gravity vector, as the result of postural vestibular reflexes. Do the vestibular-driven mechanisms also play a role in the control of the direction of swimming in the horizontal (yaw) plane, in which the gravity cannot be used as a reference direction? In the present study, we addressed this question by recording responses to lateral turns in reticulospinal (RS) neurons mediating vestibulospinal reflexes. In intact lampreys, the activity of axons of RS neurons was recorded in the spinal cord by implanted electrodes. Vestibular stimulation was performed by periodical turns of the animal in the yaw plane (60 degrees peak to peak). It was found that the majority of responding RS neurons were activated by the contralateral turn. By removing one labyrinth, we found that yaw responses in RS neurons were driven mainly by input from the contralateral labyrinth. We suggest that these neurons, when activated by the contralateral turn, will elicit the ipsilateral turn and thus will compensate for perturbations of the rectilinear swimming caused by external factors. It is also known that unilateral eye illumination elicits a contralateral turn in the yaw plane (negative phototaxis). We found that a portion of RS neurons were activated by the contralateral eye illumination. By eliciting an ipsilateral turn, these neurons could mediate the negative phototaxis.

The vestibulo-ocular and the vestibulospinal reflexes: noradrenergic influences on the plastic changes which affect the cerebellar cortex during vestibular adaptation.

The vestibulo-ocular and the vestibulospinal reflexes: noradrenergic influences on the plastic changes which affect the cerebellar cortex during vestibular adaptation.

Responses of Purkinje-cells of the cerebellar anterior vermis to stimulation of vestibular and somatosensory receptors

In decerebrate cats, sinusoidal rotation of the forepaw around the wrist modifies the activity of the ipsilateral forelimb extensor triceps brachii (TB) and leads to plastic changes of adaptive nature in the gain of vestibulospinal (VS) reflexes (VSRs). Both effects are depressed by functional inactivation of the cerebellar anterior vermis, which also decreases the gain of VSRs. In order to better understand the mechanisms of these phenomena, the simple spike activity of Purkinje (P-) cells was recorded from the vermal cortex of the cerebellar anterior lobe during individual and/or combined stimulation of somatosensory wrist, neck and vestibular receptors. About one third of the recorded units were affected by sinusoidal rotation of the ipsilateral forepaw around the wrist axis (0.16 Hz, ±10°). Most of these neurons (∼60%) increased their activity during ventral flexion of the wrist and decreased it during the oppositely directed movement, with an average phase lag of −141° with respect to the position of maximal dorsiflexion. The remaining cells (∼40%) were excited during dorsiflexion of the wrist, with an average phase lead of 59° with respect to the extreme dorsal flexion. Both populations showed comparable response gains, with an average value of 0.42±0.52, S.D., imp/s/deg. About half of the recorded units were also tested during sinusoidal roll tilt of the animal around the longitudinal axis (0.16 Hz, ±10°), leading to stimulation of labyrinthine receptors. When both stimuli were applied simultaneously, the responses to combined stimulation usually corresponded to the sum of individual responses. While the phase distribution of somatosensory responses was clearly bimodal, vestibular responses showed phase angle values uniformly scattered between ±180° and 0°, so that, during combined stimulation, each neuron could be maximally activated by coupling the two stimuli with a particular phase relation. Finally, a proportion of the recorded neurons was also tested during sinusoidal rotation of the body around its longitudinal axis, with the head fixed in space, leading to stimulation of neck receptors. The proportion of neurons affected by individual stimulation of vestibular or neck receptors (81% and 72%, respectively) was larger than that of wrist-driven neurons. Convergence of signals from vestibular, somatosensory wrist and neck receptors was found in 18% of the neurons analyzed. In conclusion, the results of this study show that somatosensory signals from the forelimb: i) modulate the activity of a sizeable proportion of neurons located within the cerebellar anterior vermis and ii) interact widely with labyrinthine and neck signals at this level. Moreover, iii) this corticocerebellar region is largely dominated by vestibular and neck signals that may be utilized to build up a neuronal representation of the position of body in space. These findings suggest that: 1) the modulation of TB activity induced by rotation of the ipsilateral wrist may at least partially depend upon the simultaneous changes in P-cell activity and 2) the interaction of vestibular and somatosensory wrist signals at P-cell level may represent the substrate of the plastic changes that affect the VSR when animal tilt and wrist rotation are driven together. A preliminary report of these data has been presented [ Bruschini L, Manzoni D, Pompeiano O (2000) Responses of cerebellar Purkinje cells to forepaw rotation in decerebrate cat. Pflügers Arch 440:R31].

Organization of dye‐coupled cerebellar granule cells labeled from afferent vestibular and dorsal root fibers in the frogRana esculenta

Application of neurobiotin to the nerves of individual labyrinthine organs and dorsal root fibers of limb-innervating segments of the frog resulted in labeling of granule cells in the cerebellum showing a significant overlap with a partial segregation in the related areas of termination. In different parts of the cerebellum, various combinations of different canal and otolith organ-related granule cells have been discerned. The difference in the extension of territories of vertical canals vs. horizontal canals may reflect their different involvement in the vestibuloocular and vestibulospinal reflex. Dye-coupled cells related to the lagenar and saccular neurons were localized in more rostral parts of the cerebellum, whereas cells of the utricle were represented only in its caudal half. This separation is supportive of the dual function of the lagena and the saccule. The territories of granule cells related to the cervical and lumbar segments of the spinal cord were almost completely separated along the rostrocaudal axis of cerebellum, whereas their territories were almost entirely overlapping in the mediolateral and ventrodorsal directions. The partial overlap of labyrinthine organ-related and dorsal root fiber-related granule cells are suggestive of a convergence of sensory modalities involved in the sense of balance. We propose that the afferent input of vestibular and proprioceptive fibers mediated by gap junctions to the cerebellar granule cells subserve one of the possible morphological correlates of a very rapid modification of the motor activity in the vestibulocerebellospinal neuronal circuit.

Impaired vestibular-proprioceptive interaction in cerebellar patients

Background: Vestibulo-spinal reflexes depend on adequate interaction between vestibular and proproceptive signals. Animal experiments indicate that the cerebellum is involved in this fundamental task. Cerebellar disease often leads to deficits in motor control, e.g. stance and gait ataxia. This study examines if vestibular-proprioceptive interaction might be one clinically relevant component of motor disturbance in cerebellar disease. Methods: Patients with cerebellar disorders of different etiology and normal controls were subjected to sinusoidal galvanic vestibular stimulation (0.16Hz) while standing on a force platform that measured reflectory body sway. Head-on-trunk position in the horizontal plane was altered systematically between +-60 degrees, controlled by a mechanical restraining device. Results: Normal controls exhibited a systematic dependence of their dominant sway direction on head-on-trunk position, as previously shown, keeping sway direction approximately aligned with their interaural line. In contrast, this systematic dependence was absent or attenuated in many cerebellar patients. Conclusion: In accord with results from animal experiments, the present data indicate that processing of vestibular and proprioceptive signals can be impaired in cerebellar patients. This impairment of vestibularproprioceptive interaction may be an important aspect of deficient motor control, particularly of gait and stance ataxia, in cerebellar disease.

Vestibular rehabilitation and 6-month follow-up using objective and subjective measures

Conclusions. Vestibular rehabilitation improves quality of life by reducing the degree of handicap, improving the ability to perform everyday tasks and providing long-term rehabilitation stability (at 6 months). Recovery of the vestibulo-ocular reflex and the vestibulo-spinal reflex efficiency was proven by the objective results obtained in this study. Vestibular rehabilitation improves both subjective and objective parameters, although no significant correlation between these two indices was found. Objective. To determine the outcome of subjective and objective parameters and long-term rehabilitation stability after vestibular rehabilitation in 43 patients with vestibular disorders. Material and methods. The subjective tests used were the Medical Outcomes Study 36-item Short Form, the Dizziness Handicap Inventory and the Activity-specific Balance Confidence scale. The objective tests used were video-oculoscopy, dynamic visual acuity, the Equitest and the Dynamic Gait Index. All indices were evaluated before and after rehabilitation and at follow-up. Results. All patients showed an improvement in quality of life and a reduction in handicap due to dizziness. Improvement in objective test results was also seen. These results were stable at follow-up. A correlation was found between different subjective measures, but there was no correlation between subjective and objective measures.

Adaptive modification of the cat℉s vestibulospinal reflex during sustained and combined roll tilt of the whole animal and forepaw rotation: Cerebellar mechanisms

In decerebrate cats, the electromyogram (EMG) activity of the forelimb extensor triceps brachii (TB) increases during side-down roll tilt of the whole animal (vestibulospinal reflex, VSR) at about 0.15 Hz. (±10°), while decreases during side up tilt. On the other hand, the TB activity increases during dorsal flexion of the ipsilateral forepaw (0.15 Hz, ±5°–10°), but decreases during ventral flexion. In six experiments, these stimuli were synergistically associated (side-down tilt coincided with dorsal flexion of the forepaw), so that the EMG modulation of the TB activity was greater than that induced by the individual stimuli. During a 3-h period of this sustained stimulation, the amplitude of the pure VSR progressively increased to reach the maximum value at the end of the third hour and persisted unmodified during the post-adaptation period (1 h). In three experiments, animal tilt and forepaw rotation were antagonistically associated (side-down tilt coincided with ventral flexion of the forepaw). In these instances the VSR gain remained on the average stable, but, at the end of the 3-h period of combined stimulation, a proportion of TB responses to animal tilt showed a phase reversal. In a digitigrade animal like the cat, a dorsal flexion of the wrist is associated with a decrease in limb length and would occur when the extensor tone is not appropriate to support body weight; we propose, therefore, that somatosensory volleys elicited by wrist rotation modify the gain of VSR so as to maintain postural stability. Inactivation, on the side of muscle recording, of the corticocerebellar region which projects to the lateral vestibular nucleus of Deiters, by local microinjection of the GABA-A agonist muscimol (0.5 μl at 16 μg/μl), decreased the already adapted gain of VSR. In conclusion, the results of this study suggest that somatosensory reafferent inputs to the cerebellar vermis are used to plastically modify the gain of VSR, when external forces produce changes in the final posture of the foot during animal tilt.

The Vestibular System

Overview Development of the vestibular system The molecular biological approach to studies of the vestibular system Biomechanics of the semicircular canals and otolith organs Cellular properties of the vestibular sensory periphery Morphophysiology of the vestibular sensory periphery The vestibular nuclei The angular and linear vestibulo-ocular reflexes, the perception of linear motion, and velocity storage The vestibulo-colic and vestibulo-spinal reflexes The vestibular cerebellum Motor learning in the vestibular system The vestibular control of the autonomic system Clinical applications of vestibular basic research.

The value of dynamic posturography (Equitest) in preparing an expert's report

Expert appraisals of vestibular disorders and their effects on daily life are essentially based on an evaluation of the patient's subjectively described symptoms. The aim of the present study was to ascertain the extent to which dynamic posturography is able to assist in the preparation of expert's reports. 60 patients underwent a survey of their balance impairment. Both a nystagmus analysis, with its objective criteria, and dynamic posturography were carried out. The investigation into reduction of fitness for work (MdE) made reference to the criteria specified in the table by STOLL. The data obtained were subjected to both correlation and variance analysis. Although the results of this analysis revealed no direct statistical dependency, they indicated a tendency for the composite values to be correlated with the nystagmus scores and/or the MdE values (when the nystagmus score and/or the MdE increases, the composite value decreases). The Equitest is, according to the available data, not able to replace the currently valid MdE scores. Nevertheless, it represents a means of providing objective data about the vestibulo-spinal reflex. The test also reveals any tendencies towards simulation and aggravation. In the context of a specific nystagmus analysis, the Equitest offers an additional means of providing an objective background to back up the more subjective assessment of MdE.

Cognitive functioning in Lyme borrellosis

Lyme borreliosis is a tick-borne disease, transmitted by Ixodes ticks, most frequently diagnosed in the USA and in many European countries. Its etiologic agent is a spirochete Borrelia burgdorferi sensu lato. One of the forms of Lyme borreliosis is neuroborreliosis. This disease attacking the central and peripheral nervous systems causes many diagnostic and therapeutic difficulties. It is the most prevalent form of B. burgdorferi infection in Europe, less frequently observed in the United States. Neurological disorders accompanying B. burgdorferi infections are caused by direct influence of the Borrelia and their products on nervous cells.Lesions of the central and peripheral nervous systems associated with neuroborreliosis that may affect the function of the vestibular organ have incited the authors to carry out research assessing the function of the labyrinth in a group of infected patients and to compare the results with a control group of healthy subjects.The research covered 32 patients with the infection, aged 21–64 (x = 42,3 years) including 13 (40%) women and 19 (60%) men hospitalized due to Lyme borreliosis.The following factors were taken into consideration: character and intensity of dizziness, results of static and dynamic tests, electronystagmography (ENG), caloric test, hearing test.In 56% of subjects with neuroborreliosis, vertigo and balance disorders were observed (in over 25% regular, and in 22% – very intense). Spontaneous nystagmus was found in 16% of subjects, directional in 25%. The caloric tests showed, statistically more frequent than in the control group, disorders in the regularity of nystagmus, directional preponderance and canal paresis.Disorders of: vestibulospinal reflexes, time and regularity of caloric nystagmus occur in the neuroborreliosis.

Evidence for reflex and perceptual vestibular contributions to postural control.

Vestibular signals are known to have an important role in stance under specific conditions. Potentially these effects could be modulated by vestibular reflexes or by voluntary responses to perceived vestibular signals. Our preliminary aim was to confirm that vestibulospinal reflexes change in parallel with sway under different postural conditions, and then to determine whether any relationship was present between these reflexes and body sway within fixed postural conditions. Sixteen subjects (eight male, eight female) were tested in conditions assessing the effects of vision (eyes open or closed), support surface (firm or compliant), external support (with or without) and stance width (feet apart or together). Sway (centre of pressure) in the anteroposterior (AP) and mediolateral planes was measured using a force platform. A subgroup of 11 subjects (five male, six female) underwent testing to measure short (SL) and medium latency (ML) reflexes from soleus. Bipolar, transmastoid galvanic stimulation (1 mA, 200 ms) was administered while subjects stood in the most unstable of our conditions (eyes closed, compliant surface and feet together). In the final part, to assess possible perceptual contributions to body sway, short duration AP sway levels were measured and expressed in angular terms (sway in mrad, velocity in mrad s(-1)) in the 11 subjects for both our baseline (eyes open, firm surface and feet apart) and most unstable conditions. Average sway levels increased more than seven-fold between conditions and had significant, positive correlations with reported changes in mean vestibulospinal reflexes under similar conditions (overall r = 0.75, P < 0.001). However, the SL reflex for the subgroup of 11 subjects had a significant negative correlation (r = -0.71; P = 0.014) with the degree of AP sway in the condition with maximum reliance on vestibular inputs (eyes closed, compliant surface, and feet together). Under baseline conditions, 5/125 (4%) of the short-term AP sway displacements were above the threshold previously reported for the detection of imposed sway. In the unstable condition, when sway was increased, 43/138 (31%) of the short-term AP sway movements were above the threshold for perception of imposed body sway based on vestibular signals. Our results confirm that vestibulospinal reflexes appear to be acutely facilitated as body sway increases. For the most unstable condition, when non-vestibular information was absent or attenuated, subjects with larger SL reflexes had less AP sway, suggesting that the SL reflex acted to attenuate sway. Under the same condition, short duration sway levels increased such that 31% were above the previously published threshold for detection using vestibular afferents. We conclude that both vestibular reflexes and perceptual signals appear to have a specific role in the maintenance of upright stance, under conditions in which other sources of postural information are attenuated or absent.

An evaluation of postural stability and the effects of middle-ear drainage on vestibulo-spinal reflexes of children with chronic otitis media with effusion

Objective: Many authors agree that chronic otitis media with effusion (OME) are the main causes of vertigo and balance disturbances in children.The aim of this work was the stabilometric evaluation of postural stability and the influence of middle ear drainage on vestibulo-spinal reflexes in children with OME. Methods: Fifteen children with OME (5–14 years old, 13 males and two females) were selected for bilateral drainage of the middle ear after conservative treatment proved ineffective. The control group consisted of 15 healthy children of an analogous age range. Static and quasi-dynamic posturography was performed to evaluate balance. The tests were performed three times: 1 day before drainage, 1 day after drainage and 4 weeks after drainage. Parameters including the field of the developed area and the average velocity of body deflection were analysed. Results: There was statistically significant elevation of stabilogram parameters in almost all the tests in children with OME as compared to the control group. The changes in the stabilogram parameters were analysed with reference to the timing of the evaluation. Significant improvement was noted after the fluid was removed from the ear, although recovery was not complete after 4 weeks. Conclusions: The presence of fluid in the middle ear impairs the functioning of the balance system in children. Postural stability and the quantity of vestibulo-spinal reflexes seem to depend on the functional condition of the middle ear. Prolonged cases of OME could potentially handicap a child’s motor development.

Galvanic evoked vestibulospinal and vestibulocollic reflexes in stroke

Objective: Following stroke, the startle reflex, mediated via the reticulospinal tract, is often facilitated. Vestibulospinal reflexes are another bulbospinal reflex, abnormalities of which may contribute to impaired body posture and stance following stroke. We recorded galvanic evoked vestibulospinal and vestibulocollic reflexes to assess whether these showed similar changes to those for startle following stroke affecting the pons and above. Methods: Twenty-four stroke subjects (aged 40–82) were studied in the vestibulospinal part of the study, 21 stroke subjects (aged 40–81 years) were studied in the vestibulocollic part, including 18 studied in both. Transmastoid galvanic (DC) current was used to stimulate the vestibular nerve. Vestibulocollic responses were recorded from the sternocleidomastoid muscles and vestibulospinal responses from over soleus in standing subjects. Results: Vestibulocollic reflex amplitudes and latencies showed no significant differences between the two sides. Similarly short latency (SL) and medium latency (ML) vestibulospinal reflexes did not differ significantly in frequency, latency or amplitude between the affected and unaffected legs. Conclusions: Vestibular reflexes are not facilitated by stroke at or above the pontine level. The exaggeration of startle by stroke may be specific to this reflex.

Trunk position influences vestibular responses of fastigial nucleus neurons in the alert monkey.

Vestibulospinal reflexes play an important role for body stabilization during locomotion and for postural control. For an appropriate distribution of vestibular signals to spinal motoneurons, the orientation of the body relative to the head needs to be taken into account. For different trunk positions, identical vestibular stimuli must activate different sets of muscles to ensure body stabilization. Because the cerebellar vermis and the underlying fastigial nucleus (FN) might be involved in this task, vestibular neurons in the rostral FN of alert rhesus monkeys were recorded during sinusoidal vestibular stimulation (0.1-1.0 Hz) in the roll and pitch planes at different trunk-re-head positions (center and +/-45 degrees ). From the sensitivity and phase values measured in these planes, the response properties in the intermediate planes and the stimulus orientation eliciting the optimal response [response vector orientation (RVO)] were calculated. In most neurons, the RVOs rotated systematically with respect to the head, when trunk-re-head position was altered, so that they tended to maintain their orientation with respect to the trunk. Sensitivity and phase at the RVO were not affected. This pattern was the same for neurons in the right and left FN and independent of stimulus frequency. The average sensitivity of this partially compensatory RVO shift in response to trunk-re-head displacements, evaluated by linear regression analyses, was 0.59 degrees / degrees (n = 73 neurons). These data show that FN neurons may encode vestibular information in a coordinate system that is closer to a trunk-centered than to a head-centered reference frame. They indicate an important role of this nucleus in motor programs related to posture and gait control.

Characterizing and treating dizziness after mild head trauma.

The objectives of this study were to characterize patterns of dizziness seen after mild head trauma and to examine the diagnosis and treatment of this disorder. Prospective patient registry. Tertiary referral center. Fifty-eight cases of active duty and retired military personnel who sustained mild head trauma and had resultant dizziness. Vestibular evaluation, characterization by group, and treatment. Outcome measures include characterization of diagnosis types, patient distribution by diagnosis type, and patient outcome. Individuals suffering from dizziness after mild head injury were divided into three diagnostic groups. Forty-one percent of the individuals suffered from posttraumatic vestibular migraines, 28% of the individuals had posttraumatic positional vertigo, and 19% of the individuals were classified as posttraumatic spatial disorientation. The remaining 12% of the patients could not be characterized. The positional group had objective physical examination findings, which cleared with treatment in all cases. The migraine group of patients and the disorientation group of patients had distinct abnormalities of the vestibulo-ocular reflex (VOR) and the vestibulo-spinal reflex (VSR). Eighty-four percent of the migraine group demonstrated an improvement of these test results as compared with 27% of the disorientation group. Mean time to return to work was less than 1 week for the positional group, 3.8 weeks for the migraine group, and greater than 3 months for the disorientation group. Using our patient registry of individuals suffering from dizziness after mild head trauma, we were able to characterize the majority of these cases into one of three more specific diagnostic groups. We present diagnostic criteria, suggested treatment guidelines, and our prognostic data.

Fos and FRA protein expression in rat precerebellar structures during the Neurolab Space Mission

Changes in gene expression were examined in precerebellar structures during and after space flight. These structures included the inferior olive (IO), the source of climbing fibers, and the lateral reticular nucleus (LRt) and basilar pontine nuclei (PN), sources of mossy fibers. We examined two immediate early gene products with two different time courses of expression: Fos, which persists only for a few (6–8) h after activation and FRA expression, which lasts for longer periods of time, i.e. hours and/or days after activation. Gravity effects on Fos and FRA gene expression were evident in vestibular and visual areas of the IO, including the dorsomedial cell column, the beta subnucleus and the dorsal cap of Kooy of the medial nucleus (which projects to the flocculonodular lobe, i.e. to the vestibular area of the IO involved in the olivary control of the vestibulo-ocular reflex (VOR)). Gene expression also affected the subnuclei A, B, and C and the caudal part of the medial IO. These olivary regions do not receive vestibular afferents, but rather spinal afferents, and are particularly involved in the olivary control of the vestibulospinal reflex (VSR). Changes in Fos expression were also observed in the LRt and the PN. We suggest that sensory substitution, in which signals produced by a subject’s own activity replace activity normally provided by macular stimulation, contributes to the recovery of microgravity-related postural and motor deficits. While no consistent increases in FRA expression occurred in vestibular IO regions 24 h after launch, consistent increases in FRA expression occurred 24 h after landing. We hypothesize that this asymmetrical pattern of gene expression resulted from (i) tonic microgravity experienced after launch counteracting the effects of increased phasic gravitational forces experienced during launch, and (ii) the tonic gravitational field experienced after landing potentiating the effects of increased phasic gravitational forces experienced during landing. The specificity of these results is demonstrated by an absence of direct gravity-related changes in Fos expression in other precerebellar structures such as the external cuneate nucleus, group X, and the dorsal column nuclei that transmit exteroceptive and proprioceptive signals to thalamic nuclei and somatosensory areas of the cerebral cortex. The gravity-related Fos and FRA expression changes in the IO and the LRt seen here are of interest in view of the important role their projections play in adaptive gain changes of the VOR and VSR during sustained visuo-vestibular and neck-vestibular stimulation.

Vestibular testing abnormalities in individuals with motion sickness.

The goal of this study was to compare the results of vestibular testing in individuals with motion sickness to a group of control subjects. Studying motion sickness is difficult, because no animal model has been developed and symptoms rarely occur outside motion environments. Tests that can be performed in normal laboratory settings, which help to identify individuals with motion sickness, may be valuable in characterizing this disorder. Twenty active duty military individuals with well-documented motion sickness were tested. The test battery included sinusoidal rotational chair testing to calculate vestibulo-ocular reflex function, step-velocity testing to calculate vestibular time constants, and posturography testing to assess vestibulo-spinal reflex status. The results of this test battery were compared with a set of age- and sex-matched controls without motion sickness. Vestibular test abnormalities were demonstrated in individuals with motion sickness. Vestibulo-spinal reflex function on posturography was normal in the control group but abnormal in 70% of the individuals with motion sickness. In addition, 5% of the control group demonstrated a minimal shortening of the absolute time constant, whereas 60% of the individuals with motion sickness had abnormal absolute time constants. A significant percentage of individuals with motion sickness demonstrate abnormalities in their time constant or vestibulo-spinal reflex function. These abnormalities can be detected using standard, land-based vestibular tests. These preliminary results have implications in understanding the etiology of motion sickness and may provide outcome measures to be used in treating motion sickness.

The Vestibulospinal Reflex in Humans: Effects on Paraspinal Muscle Activity

Objective --To elucidate the electromyographic (EMG) patterns elicited in the superficial paraspinal muscles (sacrospinalis, ileocostalis lomborum, longissimus dorsi and splenium cervicis). Material and Methods --In normal subjects adapted to the dark and standing on a force platform, EMG patterns were elicited in the superficial paraspinal muscles by means of unilateral cold caloric stimulation of the labyrinth. Results --Almost concomitantly with the occurrence of postural derangement of the subject's trunk and head, the EMG patterns of the paraspinal muscles on both sides showed significant and consistent changes. In particular, the paraspinal muscles ipsilateral to the stimulated side showed a significant reduction in activity, while the homologous muscles of the contralateral side markedly increased their activity, with a consistent delay in comparison to the contralateral muscles. Moreover, the EMG changes occurred in a hierarchic fashion in the caudal-rostral direction. In fact, the more powerful and longer-lasting effects were consistently observed in the more caudal muscles, i.e. the sacrospinalis and ileocostalis, while the effects on the longissimus dorsi and splenium cervicis muscles were weak and inconsistent. Conclusion --These results suggest a possible use for the EMG patterns resulting from unilateral cold caloric stimulation for clinical evaluation of the vestibulospinal reflex.