Contribution of the Vestibular Apparatus to Postural Control when Rising from a Chair

Objective—The everyday act of rising from a chair is known to require the combined angular control of a number of the body's joints, especially those within the pitch plane. Precisely how this control is exerted, however, remains controversial. The aim of this study was to obtain a better understanding of the contribution made by the vestibular apparatus to postural control of the body and head when an individual rises from a chair.

Material and Methods—A total of 24 healthy controls and 38 patients with varying degrees of vestibular dysfunction were examined. Electromagnetic motion sensors were used to analyze the angular control of the head and body as subjects rose from a chair with their eyes open or closed.

Results—We found that unilateral vestibular dysfunction caused fixation of the head with respect to the body, resulting in a loss of spatial stability of the head which was not compensated for by visual input. Visual input did appear to compensate for bilateral vestibular loss, enabling patients with bilateral vestibular apparatus impairment or central disorders to fix the position of their head in space.

Conclusion—The act of rising from a chair is normally controlled by vestibular and proprioceptive input; the head is aligned according to the gravitational reference so as to obtain stable visual information. In patients with unilateral vestibular hypofunction, posture is still controlled by these two inputs, although the ability to align the head is diminished. In patients with bilateral vestibular hypofunction or a central disorder, head alignment is maintained using visual input, although it may not be the sole or predominant stabilizing force.     

Contribution of the vestibular apparatus to postural control when rising from a chair

OBJECTIVE: The everyday act of rising from a chair is known to require the combined angular control of a number of the body's joints, especially those within the pitch plane. Precisely how this control is exerted, however, remains controversial. The aim of this study was to obtain a better understanding of the contribution made by the vestibular apparatus to postural control of the body and head when an individual rises from a chair. MATERIAL AND METHODS: A total of 24 healthy controls and 38 patients with varying degrees of vestibular dysfunction were examined. Electromagnetic motion sensors were used to analyze the angular control of the head and body as subjects rose from a chair with their eyes open or closed. RESULTS: We found that unilateral vestibular dysfunction caused fixation of the head with respect to the body, resulting in a loss of spatial stability of the head which was not compensated for by visual input. Visual input did appear to compensate for bilateral vestibular loss, enabling patients with bilateral vestibular apparatus impairment or central disorders to fix the position of their head in space. CONCLUSION: The act of rising from a chair is normally controlled by vestibular and proprioceptive input; the head is aligned according to the gravitational reference so as to obtain stable visual information. In patients with unilateral vestibular hypofunction, posture is still controlled by these two inputs, although the ability to align the head is diminished. In patients with bilateral vestibular hypofunction or a central disorder, head alignment is maintained using visual input, although it may not be the sole or predominant stabilizing force.     

Correlations between posturographic findings and symptoms in subjects with fractures of the condylar head of the mandible

Our study examined the posture of 15 patients who had sustained a simple unilateral or bilateral fracture of the condylar head of the mandible as a result of sports or traffic accidents. Following preliminary testing of vestibular function, the patients underwent balance testing: Romberg test with eyes closed (EC), Romberg EC and bite test (ECBT), EC and head retroflexed (ECR). The study parameters were: surface (S) of the statokinesigram, stomatognathic influence index related to S (SSI), and postural oscillations on the frontal plane (X). In keeping with the literature, we felt that the following pattern in static balance suggested a posture destabilised by the stomatognathic system: SSI values of less than 60, reduction of S in the transition from EC to ECR, pathological increase of postural oscillations on the X plane. The study was completed by obtaining a list of new symptoms reported by the patients (altered bite, fullness, tinnitus, pain, loss of balance). The most significant patterns were observed in patients with vestibular dysfunctions and neck pain. It seems that a fracture of the condylar head can affect postural behaviour, although proprioceptive changes alone are not enough to cause true loss of balance and there must be concomitant vestibular dysfunction. The stabilometric pattern is not conditioned by the extent of the trauma or the related treatment. In terms of proprioceptive elements, the presence of muscle pain seems to point to cervical muscle tension as the main culprit in the onset of posttraumatic instability.     

Somatosensory shift of postural control in dizzy patients

Conclusions: Postural control is dependent on the visual system in normal conditions. Shift from visual to somatosensory dependence in dizzy patients suggests that utilizing the stable visual references is recommended for the rehabilitation of dizzy patients. Objectives: To investigate which of the visual or somatosensory system is mainly used for substitution of the impaired spatial orientation in dizzy patients. Methods: We recruited 189 consecutive patients with or without dizziness and vestibular dysfunction. Dizzy patients were divided into three groups: acute, episodic, and chronic dizziness. Vestibular function was assessed by caloric test, traditional head impulse test, and head shaking nystagmus. Visual or somatosensory dependence of spatial orientation was assessed by posturography on a solid surface or on foam in eyes open or closed condition. The foam ratio (posturography with/without foam) when eyes were closed was indicative of somatosensory dependence of postural control, whereas the Romberg ratio on foam showed visual dependence. (Romberg ratio on foam)/(foam ratio with eyes closed) was calculated and used as an index of the visual/somatosensory dependence of postural control. Results: The visual/somatosensory ratio of postural control was significantly lower in dizzy patients as well as patients with vestibular dysfunction, however, no differences were found between acute, episodic, and chronic dizziness.     

Short-term Adaptation in the Peripheral Auditory System is Related to the AMPA Receptor

A pattern of sound-induced paroxysms of the eye and head and other spinal motor neuron synkinesis (Tullio's phenomenon) in human subjects always implies either a pathological contiguity of the tympano-ossicular chain and membranous labyrinth or a dehiscence of the bone overlying the superior semicircular canal. However, it has become clear in the last decade that sound-evoked vestibular stimulation is not only a sign of disease but also a physiological phenomenon. The examination of such physiologically sound-induced vestibular (saccular) responses contributes today to the clinical testing of the vestibular organ, mainly in the form of vestibular-evoked myogenic potentials. In this study it was observed that, in a group of 20 normal subjects, a 500 Hz tonal stimulus of high intensity (105 dB HL=118.5 dB SPL), applied monoaurally, elicited postural responses. Each subject was studied under 4 different conditions: (i) head facing forwards, eyes open; (ii) head facing forwards, eyes closed; (iii) head rotated &;#44 90° to the right, eyes closed; and (iv) head rotated 90° to the left, eyes closed. Body sway, measured using a force platform, was recorded in all subjects, with eyes either open or closed. Postural responses, which were also elicited with a 250 Hz tonal stimulus, were not observed with a tone of 2000 Hz, with legs slightly flexed or with binaural stimulation. The postural sway (head facing forwards, eyes open or closed) was in a lateral direction towards the stimulated ear: with the stimulus applied to the right ear the subject had postural sway towards the right, with the stimulus applied to the left ear towards the left. When the head was rotated &;#44 90° sideways and the stimulus was given facing forwards (i.e. head rotated contralaterally to stimulated ear) the postural sway was in a forward direction; when the head was rotated &;#44 90° sideways and the stimulus was given facing backwards (i.e. head rotated ipsilaterally to stimulated ear) the postural sway was in a backward direction. The mean values (mm) of body sway obtained with the head facing forwards and the eyes closed were higher than those with the eyes open (21.7 and 22.8 vs 15.7 and 14.7 for the right and left ears, respectively); higher mean values were obtained with the head turned to the side contralateral to the ear stimulated and the eyes closed (29.3 and 24.8 for the right and left ears, respectively). Under this condition the body sway was mainly in a forward direction. The sound-evoked vestibulopostural reflex seems to be a useful test for exploring the saccular function and, as a click-evoked vestibulocollic reflex, can be considered a physiological Tullio phenomenon.     

Sound-evoked postural responses in normal subjects

A pattern of sound-induced paroxysms of the eye and head and other spinal motor neuron synkinesis (Tullio's phenomenon) in human subjects always implies either a pathological contiguity of the tympano-ossicular chain and membranous labyrinth or a dehiscence of the bone overlying the superior semicircular canal. However, it has become clear in the last decade that sound-evoked vestibular stimulation is not only a sign of disease but also a physiological phenomenon, The examination of such physiologically sound-induced vestibular (saccular) responses contributes today to the clinical testing of the vestibular organ, mainly in the form of vestibular-evoked myogenic potentials. In this study it was observed that, in a group of 20 normal subjects, a 500 Hz tonal stimulus of high intensity (105 dB HL = 118.5 dB SPL), applied monoaurally, elicited postural responses. Each subject was studied under 4 different conditions: (i) head facing forwards, eyes open; (ii) head facing forwards, eyes closed; (iii) head rotated approximately 90 degrees to the right, eyes closed: and (iv) head rotated approximately 90 degrees to the left, eyes closed. Body sway, measured using a force platform, was recorded in all subjects, with eyes either open or closed. Postural responses, which were also elicited with a 250 Hz tonal stimulus, were not observed with a tone of 2000 Hz, with legs slightly flexed or with binaural stimulation. The postural sway (head facing forwards, eyes open or closed) was in a lateral direction towards the stimulated ear: with the stimulus applied to the right ear the subject had postural sway towards the right, with the stimulus applied to the left ear towards the left. When the head was rotated approximately 90 degrees sideways and the stimulus was given facing forwards (i.e. head rotated contralaterally to stimulated ear) the postural sway was in a forward direction; when the head was rotated approximately 90 degrees sideways and the stimulus was given facing backwards (i.e. head rotated ipsilaterally to stimulated ear) the postural sway was in a backward direction. The mean values (mm) of body sway obtained with the head facing forwards and the eyes closed were higher than those with the eyes open (21.7 and 22.8 vs 15.7 and 14.7 for the right and left ears, respectively); higher mean values were obtained with the head turned to the side contralateral to the ear stimulated and the eyes closed (29.3 and 24.8 for the right and left ears, respectively). Under this condition the body sway was mainly in a forward direction. The sound-evoked vestibulopostural reflex seems to be a useful test for exploring the saccular function and, as a click-evoked vestibulocollic reflex, can be considered a physiological Tullio phenomenon.     

A quantitative analysis of postural control in elderly patients with vestibular disorders using visual stimulation by virtual reality

IntroductionPostural instability is one the most common disabling features in vestibular disorders.ObjectiveThis study aimed to analyze the limit of stability and the influence of manipulation of visual, somatosensorial and visual–vestibular information on postural control in older adults with vestibular disorder, with and without a history of falls.MethodsCross-sectional study. Participants – 76 elderly patients with vestibular disorder (G1, without falls; G2, with falls) and 41 healthy elderly subjects (control group; CG). Using posturography, analyzed were limit of stability area, body center of pressure, and velocity of oscillation in the standing position in 10 conditions, including open/closed eyes, unstable surface with eyes closed, saccadic and optokinetic stimuli, and visual–vestibular interaction.ResultsLimit of stability area in CG was better compared with G1-2, and center of pressure values were worse in G1 than in CG. Center of pressure area in all conditions and velocity of oscillation in the following conditions: open/closed eyes, optokinetic stimulation, and visual–vestibular interaction showed worse values in G2 than in CG. Center of pressure area in the following conditions: open/closed eyes, saccadic and optokinetic stimuli, visual–vestibular interaction, and unstable surface with eyes closed showed worse values in G2 than in G1.ConclusionOlder adults with vestibular disorder presented reduced limit of stability and increased postural sway in the following conditions: conflict between visual and somatosensory information and visual–vestibular interaction. Deterioration in postural control was significantly associated with history of falls.     

First trial response to sudden support surface displacement: The effect of vestibular compensation

Conclusion: The effect of visual condition is more intense in the first trial response in normal subjects and patients and in last trial response only in patients. The first trial effect is more evident in compensated patients in the eyes open condition with any type of perturbation, and in non-compensated patients with the angular displacements in either visual condition. Objective: The study of body reaction to FTR can help to understand the complex mechanisms involved in the postural response and to develop new therapies to improve stability and prevent falls in unilateral vestibular deficit (UVD). This work describes the adaptation effect and the visual influence on the postural response to repetitive balance perturbation stimulus in normal subjects, compensated, and uncompensated UVD patients. Methods: The magnitude of displacement has been measured when the support surface is linearly or angularly displaced. The differences between results in the first and late trial, and the differences between the eyes open and eyes closed situation have been compared. Results: Compensated patients recover the adaptation ability to unexpected changes on the support surface through visual preference mechanism. Not compensated patients present hypermetric postural response with greater instability in the eyes open and eyes closed situations.     

Influence of visually induced self-motion on postural stability

Conclusion Our results indicate that the illusion of self-motion is a significant factor leading to spatial disorientation.

Objective Under normal circumstances, self-motion is perceived in response to motion of the head and body. However, under certain conditions, such as virtual reality environments, visually induced self-motion can be perceived even though the subject is not actually moving, a phenomenon known as “vection”. The aim of this study was to examine the possible influence of illusory self-rotation (circular vection) on postural adjustments.

Material and methods The subjects were 10 young females with no history of ocular or vestibular disease. Video-motion analysis was applied to measure postural movements during vertical optokinetic stimulation.

Results For most subjects, movement of the visual surroundings induced head and body displacements in the same direction as that of the visual stimulus, regardless of the onset of self-motion perception. However, there was a significant increase in postural instability after the subjects began to perceive false self-motion in the opposite direction to that of the visual stimulus.     

Visual influence on postural control,with and without visual motion feedback

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly (p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.     

Visual Influence on Postural Control,With and Without Visual Motion Feedback

Body sway was investigated in 20 healthy subjects to determine whether visual input must contain motion feedback information from the surroundings in order to influence postural control. Posturography was used to record body sway under the following visual conditions: eyes open with or without a restricted visual field; eyes open in ganzfield white light; eyes open in darkness with a head-fixed visual target; eyes open in darkness; and eyes closed in darkness. Stance was perturbed by means of a pseudorandomly applied vibratory stimulation to the calf muscles. Least sway was found with eyes open in an unrestricted visual field but increased in a restricted visual field. Greatest sway was found without visual motion feedback, i.e. under the following conditions: eyes closed; eyes open in darkness; eyes open in ganzfield white light; and with a head-mounted fixation point. Sway was significantly ( p < 0.05) greater with eyes open in darkness compared with eyes closed during the initial 50 s with perturbations. After 150 s, sway was almost identical under the four test conditions without visual motion feedback. Standing with eyes open in darkness was initially a disadvantage compared with having the eyes closed. The postural control system may be programmed to expect visual feedback information when the eyes are open, which may delay changes in postural strategy.     

New posture equilibrometer for the diagnosis of vestibular disease

Summary The vestibulospinal level of vestibular function is commonly neglected in the evaluation of vertiginous patients. We have now developed a new posture equilibrometer. A transducer is placed on the head of the subject being tested. With this meter we can record body swaying, X (left-right) and Y (fore-aft) components of angular displacement, angular velocity, and angular acceleration. A detailed analysis of the data can be made by having patients keep their eyes either open or closed during the Romberg test. The head is turned left or right in this test, while the eyes are opened and closed in the Mann test. The posture equilibrometer has enabled us to evaluate more precisely vestibulospinal function and sensory interactions. Offprint request to: N. C. Zhong     

Vestibular and stabilometric findings in whiplash injury and minor head trauma

Vertigo and postural instability following whiplash and/or minor head injuries is very frequent. According to some authors, post-whiplash vertigo cannot be caused by real injury to vestibular structures; other authors maintain that vestibular damage is possible even in the case of isolated whiplash, with vascular or post-traumatic involvement. Furthermore, many of the balance disorders reported after trauma can be justified by post-traumatic modification to the cervical proprioceptive input, with consequent damage to the vestibular spinal reflex. The aim of this study was to evaluate the vestibular condition and postural status in a group of patients (Group A, n = 90) affected with balance disorders following whiplash, and in a second group (Group B, n = 20) with balance disorders after minor head injury associated with whiplash. Both groups were submitted to videonystagmography (VNG) and stabilometric investigation (open eyes - O E, closed eyes - CE, closed eyes with head retroflexed - CER) within 15 days of their injuries and repeated within 10 days after conclusion of cervical physiotherapy treatment. The VNG tests revealed vestibulopathy in 19% of cases in Group A (11% peripheral, 5% central, 3% in an undefined site) and in 60% of subjects in Group B (50% peripheral, 10% central). At the follow-up examination, all cases of non-compensated labyrinth deficit showed signs of compensation, while there were two cases (2%) in Group A and one case (5%) in Group B of PPV. As far as the altered posturographic recordings are concerned, while there was no specific pattern in the two groups, they were clearly pathologic, especially during CER. Both in OE and in CE there was an increase in the surface values and in those pertaining to shifting of the gravity centre on the sagittal plane, which was even more evident during CER. In Group A, the pre-post-physiotherapy comparison of CER results showed that there was a statistically significant improvement in the majority of the parameters after treatment. Moreover, in Group B there was frequent lateral shifting of the centre of gravity that was probably linked with the high percentage of labyrinth deficits. The comparison between the first and second stabilometric examinations was statistically significant only in those parameters referring to gravity centre shifting on the frontal plane, which was probably due to the progressive improvement in the associated vestibulopathy rather than to the physiotherapy treatment performed for the cervical damage. Hence, our study confirms that only in a minority of cases can whiplash cause central or peripheral vestibulopathy, and that this is more probable after minor head injury associated with whiplash. In addition, our data confirm that static stabilometry is fundamental for assessing postural deficits following a cervical proprioceptive disorder. In these cases, in fact, analysis of the different parameters and the indices referring to cervical interference not only permits evaluation of altered postural performance, but also detects and quantifies destabilisation activity within the cervical proprioceptive component.     

Effect of head orientation on human postural stability following unilateral vestibular ablation.

Effective interpretation of vestibular inputs to postural control requires that orientation of head on body is known. Postural stability might deteriorate when vestibular information and neck information are not properly coupled, as might occur with vestibular pathology. Postural sway was assessed in unilateral vestibulopathic patients before and acutely, 1, 4, and 18+ months after unilateral vestibular ablation (UVA) as well as in normal subjects. Postural equilibrium with eyes closed was quantified as scaled pk-pk sway during 20 s trials in which the support surface was modulated proportionally with sway. Subjects were tested with the head upright and facing forward, turned 45 degrees right, and 45 degrees left. Equilibrium was uninfluenced by head orientation in normal subjects. In contrast, patients after UVA showed both a general reduction in stability and a right/left head orientation-dependent asymmetry. These abnormalities adaptively recovered with time. It is concluded that vestibular inputs to postural control are interpreted within a sensory-motor context of head-on-body orientation.     

Head and body sway in response to vertical visual stimulation

Conclusions. Postural responses differed according to the stimulus direction, i.e. vertical visual stimulation induced head rather than trunk displacements. Accordingly, it could be that center of foot pressure (COP) responses tended to underestimate the postural sway during visual stimulation. Objectives. To investigate head and body sway in response to vertical visual surround motion, and to examine the correlation between the displacements of head and body segments derived from video-motion analysis and COP measurements. Material and methods. Postural sway was assessed in 10 young female subjects by video-motion analysis of four different head and body segments, and by use of force-plate posturography. Head and body sway in the pitch plane was induced by rotating a random pattern of dots about the subject's inter-aural axis at a constant acceleration of 1°/s² or a constant velocity of 60°/s in darkness. Results. Generally, head displacement was greater than that of other body parts during vertical optokinetic stimulation (OKS). In most subjects, maximum head displacements were induced in the same direction as the visual motion. Downward OKS induced a forward head and body sway. The COP trajectory correlated well with the displacements of each head and body segment during downward OKS. In contrast, postural responses to upward OKS were complicated in terms of their time course. The correlation coefficient between each head and body segment and the COP varied among individuals for upward OKS.     

Nonsequential vector analysis of body sway in Menière's disease]

Body sway test which examines the vestibulo-spinal reflex is sensitive for evaluating vestibular dysfunction in patients with vertigo, dizziness or unsteadiness. Body sway is usually evaluated by measuring the length and area of traces on the force platform. However, it is not necessarily possible to evaluate abnormal body sway with these indicators because there is a discrepancy between sway length and area. In the present study, 8 directional vectro-posturography was developed and applied to the patients with Meniere's disease. Averaging of measurements at moving 3 points was used to eliminate high frequency noise over 4.92Hz. The subjects consisted of 66 patients with unilateral Meniere's disease and 31 normal controls. Eight directional vectrogram allowed measurement of shift area and directionality, simultaneously. The patient's group showed statistically significant body sway in the right forward and left backward direction with eyes open, in all the directions with eyes closed, when compared with the control's group. The effect of vision on postural stability was studied by obtaining 8 directional Romberg's quotients. The patients with Meniere's disease had significantly in forward-backward, and left-forward and right-backward direction when compared with controls. However, laterality of the affected side was not detected from the vectrogram. The effect of endolymphatic sac operation on postural stability was evaluated in the patients of unilateral Meniere's disease who showed progressive hearing loss and resisted conservative medication therapy. The results showed unstable body sway in the condition with eyes closed until at least 4 months after the operation. The patients with Meniere's disease presented pathological body sway, even during symptom free periods, when examined with 8 directional vector posturography. Power spectral analysis of body sway indicated that most energy was distributed at frequencies lower than 0.5Hz. Nevertheless, directional preponderance of body sway was characterized by higher frequency components. The findings infers that postural stability at the frequency range over 0.5Hz, may be governed by the input of vestibular organs.     

Effect of head extension on equilibrium in normal subjects

A dynamic posturography system was used to test the effect of 55 degrees head extension on postural sway in 20 normal subjects. There was a highly significant increase in sway with head extension under two conditions; in both, the support surface moves proportionally to body sway angle (sway-referenced feedback). The largest increase in sway occurred when the eyes were closed and the support surface was sway-referenced. This latter condition removes vision, reduces the effectiveness of ankle proprioception, and forces the subject to depend mostly on vestibular information for equilibrium. We suggest that head extension increases sway because the utricular otoliths are put into a disadvantageous position. This may be another example of the role of utricular input in the control of balance.     

Eye movements during torso rotations in labyrinthine-defective subjects

The aim of this study was to examine whether the chronic loss of vestibular function modifies perceptual and oculomotor responses during torso rotations in darkness. Subjects (4 patients with complete vestibular loss and 7 healthy volunteers) were seated on a rotating chair. Stimuli consisted of sinusoidal chair rotations (+/-30 degrees, 0.1 Hz and 0.011 Hz). We used 2 conditions: space stationary head (neck stimulation) and space stationary head and shoulders (torso stimulation). Horizontal eye deviations and slow component of eye movements were analysed. The results showed that eye movements and perception of head motion in space during neck stimulation were similar to those during torso stimulation both in normal and labyrinthine-defective (LD) subjects. During low-frequency chair rotations (0.011 Hz) all subjects perceived illusory head or head and shoulder rotation in space (as if the lower part of the body was stationary relative to the room) and shifted their gaze in the direction of illusory head rotation. In these conditions there was no significant difference in eye movements between normal and LD subjects. During higher frequency chair rotations (0.1 Hz), LD subjects had significantly larger eye deviations as well as increases in the gain of the slow component of eye movements relative to normals. In these conditions patients mostly perceived illusory head or head and shoulder rotation in space while normal subjects mainly perceived the head as stationary in space. The results indicate that 1) neck and torso rotations can evoke similar ocular responses in LD subjects, 2) the chronic loss of vestibular function modifies the representation of axial body segment motion relative to space.     

The Role of Neck Dissection in the Treatment of Supraglottic Laryngeal Cancer

Objectives - Vestibular compensation, the recovery that follows unilateral vestibular deafferentation (UVD), is a model for central nervous system plasticity. Recovery from the static symptoms of UVD may involve temperature-dependent processes that modulate the immediate effects of UVD and/or the capability of the central nervous system to undergo adaptive plasticity. In this study we investigated changes in oculomotor and postural vestibular symptoms resulting from low body temperature during UVD. Material and methods - To study the effect of low temperatures at the time of UVD on vestibular compensation, we compared the rate of compensation and peak values for postural [roll head tilt (RHT) and yaw head tilt (YHT)] and oculomotor [spontaneous nystagmus (SN)] symptoms in three groups of guinea pigs. Animals in Group 1 (n=6) were maintained at 38°C throughout unilateral labyrinthectomy (UL). Animals in Group 2 (n=6) were not temperature-controlled and animals in Group 3 (n=4) were cooled with ice to 25°C throughout UL. Results - Cooled animals showed significantly higher rates of SN upon recovery from anaesthesia and took a significantly longer time to compensate. Cooled animals were also slower to compensate for postural symptoms (RHT and YHT), with 2 animals showing no compensation for RHT 52 h after UL. Conclusion - Hypothermia (25°C) during UVD surgery exacerbates postural and oculomotor symptoms following UL and significantly slows recovery.     

Direction of Galvanically-induced Vestibulo-postural Responses during Active and Passive Neck Torsion

The direction of a postural response induced by galvanic vestibular stimulation depends on the head and trunk position. The relative importance of afferent information (proprioception) and efferent motor command/corollary discharge is unknown. We studied the direction of body sway evoked by galvanic vestibular stimulation in 9 healthy subjects during active and passive head positioning at 0° frontal position, 35° to the left, and 75° to the right, using a custom-built collar. At 0° and 75° there were no significant differences in sway direction between active and passive head positioning. The galvanic stimulation invoked sway toward the anode, mainly in the inter-aural direction. The sway direction differed significantly between active and passive positioning at 35° to the side (p&lt;0.05). When the head was actively kept in this position, the body sway was mainly in an inter-aural direction. The sway shifted to a naso-occipital direction when the head was passively positioned at 35°. Our results indicate that the afferent proprioceptive information has the largest influence on the direction of the galvanically-induced postural response, although some dependence on efferent motor commands and non-linear cervical proprioception cannot be ruled out entirely.