Cervico-vestibular and visuo-vestibular interaction. Self-motion perception, nystagmus, and gaze shift

Baseline of upper teeth: (a) Control organ for spatial navigation? (b) Weak point for misaligned posture and pain?

Our observations question both the current doctrine of spatial orientation as processed by vestibular, visual and proprioceptive impressions as well as the horizontal alignment of the eye axis. Indeed our observations suggest spatial orientation as a physically based, largely mechanically transmitted interaction between individual and environment. It is controlled by an interface defined by the baseline of upper teeth. It simultaneously constitutes both body and environment acting as an integral part of that environment. Consequently, the baseline of upper teeth is part of the aforementioned environment. Instead of the eye axis during spatial orientation it aligns the true horizontal absolutely. This was tested by fixing a cross to upper teeth. While walking, running and jumping it did not deviate by more than 2° from the external axis. Subsequently, we inclined the baseline of upper teeth by inserting an asymmetric wafer so that it angulated the eye axis. Immediately, head, visual and vestibular axes tilted unstably with misaligned body posture. Only the indicative cross remained stably aligned to the external axes. The person felt "upright", not noticing his posture had changed. He was then instructed to straighten his shoulders and trunk until his posture was objectively nearly upright again. The voluntary correction caused the indicative cross to tilt. The person felt uneven while being more upright. We concluded that the automatic posture works by "synchronizing" the baseline of upper teeth to the external axis and that the synchronized position is supported by the vestibular system. Benefit of an interface is that the body's movements in the environment simultaneously happen within the baseline of upper teeth. Therein the vectors of the body and the environment are calculated to remain in balance. This model introduces the transmission of the vector information to postural muscles by the dura mater, controlled by tension between C0-C2. The information is skewed by bony dislocations between C0-C2 caused by an inclination of the interface. The resulting misalignments of posture are foreseeable and specifically correspond to the type of inclination. They occur in a broad section of the population. Diagnosed as muscular weakness, they may cause therapy resistant common diseases like back and joint pain after 5-10 years. Following our observations, the inclination of the baseline of upper teeth originates from inattentive changes in the length of upper teeth in dental treatment. Multiple treatments optimizing teeth length in long term patients improved the patients' situation.

Two cases of spinal cord extramedullary tumor with positional vertiginous sensation

CONCLUSIONS

We conclude that neck imaging should be carried out for patients with persistent paroxysmal positional vertigo following diagnostic and/or therapeutic maneuvers.

OBJECTIVE

It is sometimes complicated to diagnose patients with vertigo that is transiently induced by head and neck positioning. Neck-vestibular diseases also induce vertiginous sensation with head and neck movement and need to be ruled out for the diagnosis of benign paroxysmal positional vertigo (BPPV).

PATIENTS AND METHODS

Two elderly female patients visited our hospital with complaints of transient vertigo induced by Dix-Hallpike positioning, suggesting posterior canal BPPV. We carried out gadolinium-enhanced neck MRI in both these cases.

RESULTS

The positional nystagmus was not clearly observed or vertiginous sensation did not show any decay during repeated vestibular examination in either case. These cases were finally diagnosed as spinal cord intradural extramedullary tumor (C3-C4) by means of neck MRI.

Sensory-motor and genito-sphincter dysfunctions in multiple sclerosis

Multiple sclerosis is a chronic demyeliniting disease of the central nervous system which is characterized by an extreme multiplicity of clinical features. Multiple sclerosis can have a profound impact on the quality of life of patients. The induced handicap varies from one patient to an other, and depends on the location of the demyeliniting lesions. Among the symptoms, sensory-motor disorders and genito-sphincter dysfunctions are some of the more disabling. Thus, up to 70% of patients suffer from urinary troubles, and 15 years after the onset of the illness, 50% of patients have difficulties for deambulation. A good knowledge of these pathologies is necessary to improve the management of patients suffering from multiple sclerosis.

Ocular torsion before and after 1 hour centrifugation

To assess a possible otolith contribution to effects observed following prolonged exposure to hypergravity, we used video oculography to measure ocular torsion during static and dynamic conditions of lateral body tilt (roll) before and after 1 h of centrifugation with a Gx-load of 3 G. Static tilt (from 0 to 57 degrees to either side) showed a 10% decrease in otolith-induced ocular torsion after centrifugation. This implies a reduced gain of the otolith function. The dynamic condition consisted of sinusoidal body roll (frequency 0.25 Hz, amplitude 45 degrees) about an earth horizontal and about an earth vertical axis (respectively, "with" and "without" otolith stimulation). Before centrifugation the gain of the slow component velocity (SCV) was significantly lower "with" otolith stimulation than "without" otolith stimulation. Apparently, the contribution of the otoliths counteracts the ocular torsion response generated by the semicircular canals. Therefore, the observed increase in SCV gain in the condition "with" otolith stimulation after centrifugation, seems in correspondence with the decreased otolith gain in the static condition.

Characteristics of saccades induced by neck torsions: a re-examination in the normal guinea pig

Torsion of the neck relative to the fixed head results in several reflexes involving the eyes, the neck and the body. One of these reflexes, the cervico-ocular reflex, has been described as having a small gain in the normal animal. However, when the body of a guinea pig is moved relative to the fixed head with a ramp-like velocity profile, saccades are systematically elicited in the direction of body movement. We re-examined the characteristics of this reflex in the normal guinea pig and demonstrated that: (1) it occurs mainly in the range of high velocity body movements; (2) the latency of the saccades is shorter than previously suspected; (3) the saccades are triggered at specific positions relative to the starting and ending positions of rotation, revealing some degree of flexibility in the reflex. We hypothesize that these saccades of nuchal origin are under the control of the same neuronal circuit as visually triggered saccades and quick phases of vestibular nystagmus. Thus, this nuchal reflex may fundamentally subserve orienting behaviour in normal animal.

Transient deviation of closed eye on head torsion. A kind of neck-ocular reflex

Electrooculographically, torsion of the head with closed eyes causes little appearance of VOR, but a transient ocular deviation (TOD) of about 30 degrees and a maximum velocity of not less than 200 degrees/sec. TOD occurs more significantly during torsion of the head alone than during rotation of the whole body, with a two-fold greater degree of deviation, suggesting the importance of the input from the cervical afferent. TOD occurs even in a condition in which torsion of the head is made to try with the head fixed and as a result of this maneuver, a torsional force is put on the neck toward the direction of head torsion, but the head does not rotate (vestibular afferent is inoperative). Thus, it is supposed that TOD occurs as a result of the fact that the lateral gaze center is activated by perception of the directional information of head torsion from the cervical afferent.

Vestibular neurones in the parieto-insular cortex of monkeys (Macaca fascicularis): visual and neck receptor responses

1. One hundred and fifty-two vestibularly activated neurones were recorded in the parieto-insular vestibular cortex (PIVC) of four awake Java monkeys (Macaca fascicularis): sixty-two were tested systematically with visual stimulation and seventy-nine were tested with various somatosensory stimuli. With very few exceptions all vestibular neurones tested responded to visual and somatosensory stimulation, therefore being classified as polymodal vestibular units. 2. A most effective stimulus for all fifty-eight visually activated PIVC units was movement of a large structured visual pattern in an optimal direction. From forty-four units responsive to a horizontally moving optokinetic striped drum, twenty-nine were activated with optokinetic movement in the opposite direction to the activating vestibular stimulus ('synergistic' response), thirteen were activated optokinetically and vestibularly in the same direction ('antagonistic' responses) and two were biphasic. The gain of the optokinetic response to sinusoidal stimulation (average 0.28 (impulses s-1) (deg s-1)-1 at 0.2 Hz, 56 deg amplitude) was in a range similar to that of the vestibular gain at low frequencies. At 1 Hz some units only showed weak optokinetic responses or none at all, but the vestibular response was still strong. 3. With different 'conflicting' or 'enhancing' combinations of optokinetic and vestibular stimulation no generalized type of interaction was observed, but the responses varied from nearly 'algebraic' summation to no discernible changes in the vestibular responses by additional optokinetic stimuli. With all visual-vestibular stimulus combinations the responses to the vestibular stimulus remained dominant. 4. The optokinetic preferred direction was not related to gravitational coordinates since the optokinetic responses were related to the head co-ordinates and remained constant with respect to the head co-ordinates at different angles of steady tilt. 5. Almost all PIVC units were activated by somatosensory stimulation, whereby mainly pressure and/or movement of neck and shoulders (bilateral) and movement of the arm joints elicited vigorous responses. Fewer neurones were activated by lightly touching shoulders/arms or neck, by vibration and/or pressure to the vertebrae, pelvis and legs. 6. A most effective somatosensory stimulus was sinewave rotation of the body with head stationary. The gain of this directionally selective neck receptor response was in the range of vestibular stimulation. Interaction of vestibular and neck receptor stimulation was either of a cancellation or facilitation type.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction between cervico-ocular and vestibulo-ocular reflexes in normal adults

The interaction of the cervico-ocular reflex (COR) and the vestibulo-ocular reflex (VOR) was studied in 20 human Subjects (Ss) during application of synergistic and antagonistic combinations of neck and vestibular stimuli, and during two different psychophysical tasks related to the Ss' self-motion sensation. Slow and quick eye movement responses were analyzed separately. Neck stimulation produced by horizontal rotation of the trunk about the stationary head elicited slow COR eye movements of very low gain; COR direction was anticompensatory, unlike the compensatory one of the VOR. During either a synergistic combination of neck and labyrinthine stimuli (head rotation on stationary trunk) or an antagonistic combination (head-to-trunk rotation counter to head-in-space rotation), the resulting slow eye movements were slightly larger than those during labyrinthine stimulation alone (whole body rotation). This weak neck contribution could be described by a directionally non-specific enhancement of VOR gain and a linear summation of VOR and COR slow phases. These effects were essentially independent of whether the Ss estimated the magnitude of their head turning or trunk turning in space. If Ss were estimating their trunk turning, neck stimulation also evoked quick eye movements, but these were small and hardly affected the VOR quick phases during the combined stimulations. In contrast, if Ss estimated their head turning, neck stimulation evoked large quick phases, which interfered with the quick phases of the VOR; during the synergistic combination of head and neck stimuli. COR quick phases added to those of the VOR, thereby shifting the gaze in the direction of head rotation (reorientation of gaze). With the antagonistic combination they subtracted, so that the VOR slow phase could compensate the head rotation in space (stabilization of gaze). These findings suggest that (1) the slow phase of the COR has no functional significance in intact humans and (2) the quick phase of the COR plays a role for both stabilization and reorientation of gaze depending on the behavioural context.

Compensatory eye movements during head and body rotation in infants

Eye movements were measured in 2- and 4-month-old infants during rotation in the light and in the dark using a specially constructed infant seat that was rotated sinusoidally at 0.1, 0.25 and 0.5 Hz. As in adults, the phase of the vestibulo-ocular reflex (VOR) was nearly compensatory with respect to head position, and the gain values were generally in the range between 0.4 and 1.4. There were two types of phases for the cervico-ocular (COR) responses: compensatory and anticompensatory. The gain of the COR was 4-6 times larger than that reported for adults. In addition, it was both frequency- and age-dependent. These characteristics of the COR may reflect developmental processes in the infant nervous system. The interaction of the two reflexes (VOR + COR) gave responses similar to when the VOR was elicited alone. The subjects' use of a fixation light raised the gain of the VOR and VOR + COR to about 1.67 and 1.44, respectively. These values were higher than most gains reported for adults. However, they were close to what was predicted (1.53) for the experimental conditions wherein fixation was on a target 25 cm in front of the eyes.

Cervico-ocular eye movements in relation to different neck torsion velocities

Rotation of the trunk with a fixed head causes isolated stimulation of cervical afferent input. Eleven patients with marked cervico-ocular reactions (COR) were selected. A neck torsion test (NTT) was performed with the help of a special apparatus. The resulting cervically induced eye movements consisted of two components. In addition to a cervical nystagmus, with its slow, compensatory phase, a deviation of the mean eye position (shift) in an anticompensatory direction, opposite to trunk rotation was observed. The COR in relation to different neck torsion velocities distinctly showed a tuning curve with maximum reactions between 4 degrees/s and 9 degrees/s. Above these values, a strong decrease in COR resulted. The optimal working range vastly differs from that of the vestibulo-ocular reflex (VOR).

Object-motion detection affected by concurrent self-motion perception: psychophysics of a new phenomenon

Thresholds for object-motion detection are significantly raised when concurrent self-motion perception is induced by either vestibular, or visual, or cervico-somatosensory stimulation. Active sinusoidal horizontal head oscillations with compensatory vestibulo-ocular reflex (VOR) and foveal or eccentrical target presentation; 'passive' head movements with fixation suppression of the VOR; pure body oscillations with the head fixed in space (cervical stimulation); optokinetically induced apparent self-motion (circularvection). This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue. It may reflect the disadventageous side effect due to unspecificness of an otherwise beneficial space constancy mechanism, which provides us with the image of a stable world during locomotion.

Bilateral vestibular loss, oscillopsia, and the cervico-ocular reflex

Oscillopsia during head movement occurs in patients with bilateral vestibular loss and may be transient or persistent. To investigate mechanisms underlying recovery we tested the vestibulo-ocular reflex (VOR), visual-vestibular interaction, and the cervico-ocular reflex (COR); we used a pseudorandom oscillatory stimulus with a frequency band width of 0 to 5 Hz in six patients with bilaterally absent caloric responses and in 10 normal controls. Seven control subjects had low-gain COR responses, but these were anticompensatory with respect to the VOR. Three asymptomatic patients with an absent or grossly deficient VOR had increased oculomotor responses at all frequencies when oscillated in light. Compensatory COR responses were detected in these patients but not in patients with persisting oscillopsia. In some patients with bilateral vestibular loss, augmented cervico-ocular and visual reflexes may compensate, at least partially, for an absent VOR.