Lateral Ampullary Nerve Research Articles

Restoring the High-Frequency Dynamic Visual Acuity with a Vestibular Implant Prototype in Humans

Introduction: The vestibular implant could become a clinically useful device in the near future. This study investigated the feasibility of restoring the high-frequency dynamic visual acuity (DVA) with a vestibular implant, using the functional Head Impulse Test (fHIT). Methods: A 72-year-old female, with bilateral vestibulopathy and fitted with a modified cochlear implant incorporating three vestibular electrodes (MED-EL, Innsbruck, Austria), was available for this study. Electrical stimulation was delivered with the electrode close to the lateral ampullary nerve in the left ear. The high-frequency DVA in the horizontal plane was tested with the fHIT. After training, the patient underwent six trials of fHIT, each with a different setting of the vestibular implant: (1) System OFF before stimulation; (2) System ON, baseline stimulation; (3) System ON, reversed stimulation; (4) System ON, positive stimulation; (5) System OFF, without delay after stimulation offset; and (6) System OFF, 25 min delay after stimulation offset. The percentage of correct fHIT scores for right and left head impulses were compared between trials. Results: Vestibular implant stimulation improved the high-frequency DVA compared to no stimulation. This improvement was significant for “System ON, baseline stimulation” (p = 0.02) and “System ON, positive stimulation” (p < 0.001). fHIT scores changed from 19 to 44% (no stimulation) to maximum 75–94% (System ON, positive stimulation). Conclusion: The vestibular implant seems capable of improving the high-frequency DVA. This functional benefit of the vestibular implant illustrates again the feasibility of this device for clinical use in the near future.

Ethical, anatomical and physiological issues in developing vestibular implants for human use1

Effort towards the development of a vestibular implant for human use are being made. This paper will summarize the first important steps conducted in Geneva towards this ambitious goal. Basically, we have faced three major issues. First, an ethical issue. While it was clear that such development would require the collaboration of human volunteers, it was also clear that stimulation of the vestibular system may produce periods of significant incomfort. We know today how to minimize (and potentially eliminate) this type of incomfort. The second issue was anatomical. The anatomical topology of the vestibular system is complex, and of potentially dangerous access (i.e. facial nerve damage). We choose not to place the electrodes inside the ampullae but close the vestibular nerve branches, to avoid any opening of the inner ear and limit the risk of hearing loss. Work on cadaver heads, confirmed by acute stimulations trials on patients undergoing ear surgery under local anesthesia, demonstrated that it is possible to stimulate selectively both the posterior and lateral ampullary nerves, and elicit the expected vertical and horizontal nystagmic responses. The third issue was physiological. One of the goal of a vestibular implant will be to produce smooth eye movements to stabilize gaze direction when the head is moving. Indeed, after restoring a baseline or "rest" activity in the vestibular pathways with steady-state electrical stimulation, we demonstrated that modulation of this stimulation is producing smooth eye movements. In conclusion, humans can adapt to electrical stimulation of the vestibular system without too much discomfort. Surgical access to the posterior and lateral ampullary nerves have been developed and, electrical stimulation of the vestibular system can be used to artificially elicit smooth eye movements of different speeds and directions, once the system is in adapted state. Therefore, the major prerequisites to develop a prototype vestibular implant for human use are fulfilled.

Fusion as an Evolutionary Principle of the Vertebrate Labyrinth

This study was undertaken to demonstrate changes in the innervation of vestibular and auditory sense organs with the evolutionary ascent of the vertebrate labyrinth. Dissected labyrinths and their nerve supply prepared by the Sudan black B technique of Rasmussen were examined and photographed with a Canon A100 camera interfaced with a Zeiss operating microscope. In lizards and alligators, the utricular sense organ is represented by 2 small maculae, each with a separate nerve branching off the ampullary nerves to the anterior and lateral canal cristae. These 2 maculae fuse into a bilobed macula with ascent in frogs and pigeons, eventually becoming a single large macula with its nerve supply from the superior vestibular division in guinea pigs, cats, lions, monkeys, and humans. Along with these changes, there is a fusion of the lateral and anterior canal ampullary nerves and of the bifurcating branches of the vertical canal ampullary nerves. The saccular macula is single, but receives a dual innervation from the superior division (anterior ramus) and the inferior division (posterior ramus) of the eighth nerve in alligators, pigeons, guinea pigs, cats, lions, monkeys, and humans. The main innervation is usually from the inferior division; however, saccular innervation is from the inferior division in lizards and from the superior division in frogs. The auditory sense organ is represented by a curved tube with a low-frequency receptor (lagena) at its distal end in lizards, alligators, and pigeons. In mammals, in which there is a coiled cochlea with a variable number of turns, low frequencies are recorded at the apical turn. This configuration may represent fusion of the lagena into the apical end of the auditory sense organ. Fusion of sense organs and of their nerve supply appears to be an evolutionary principle in the vertebrate labyrinth.

Central Projections from Singular Parts of the Vestibular Labyrinth in the Guinea Pig

Primary afferent projections from singular parts of the vestibular labyrinth were studied in the guinea pig. The posterior ampullary nerve, the common trunk of the anterior and lateral ampullary nerves, as well as fibers innervating the macula sacculi or the macula utriculi were traced with crystals of horseradish peroxidase (HRP) lyophilisate. Posterior, as well as anterior and lateral ampullary fibers were found to project extensively to the superior vestibular nucleus, but also reached the other main vestibular nuclei. Saccular fibers projected mainly to the lateral parts of the lateral vestibular nucleus and to the adjoining descending and superior vestibular nuclei as well as to group y. Modest projections could be followed to the medial vestibular nucleus. Furthermore, a distinct saccular projection to the cochlear nuclei was evident. Utricular projections reached the four main vestibular nuclei with a denser accumulation of fibers within ventral parts of the lateral, descending and superior vestibular nuclei.

Horseradish peroxidase labeling of the central pathways in the medulla of the ampullary nerves in the chicken, Gallus gallus

The purpose of the present study was to place horseradish peroxidase on the distal processes of the three ampullary nerves in 6-8-week-old chickens so that we could identify the ganglion cells associated with each nerve and trace the specific central pathways taken by each nerve in the brainstem. We are especially interested in the pathways of the colossal vestibular fibers, which may play a role in a fast reflex pathway as suggested by their large caliber and electrotonic mode of transmission in the tangential vestibular nucleus. The cells of origin of each ampullary nerve occupy discrete portions of the vestibular ganglion. Those vestibular ganglion cells giving rise to the posterior ampullary nerve (PAN) occupy the posterior portion of Scarpa's ganglion; the ganglion cells producing the anterior (AAN) and lateral (LAN) ampullary nerves occupy the anterior ganglion, within the dorsal and ventral portions, respectively. Centrally the vestibular fibers occupy discrete portions of the tangential vestibular nucleus before bifurcating into ascending and descending tracts. The tangential nucleus receives afferents from the colossal fibers, which form spoon endings, and also from the fine vestibular fibers, which form small terminals. The ascending fibers of the posterior ampullary nerve are associated with the nucleus piriformis; the ascending fibers of the anterior and lateral ampullary nerves occupy discrete cell groups of the vestibulo-cerebellar nucleus. All three ampullary nerves have descending branches that course through the retrotangential nucleus into the descending vestibular nucleus (DVN). Within the descending vestibular nucleus, the descending fibers of the posterior ampullary nerve run dorsally and centrally, whereas fibers of the anterior ampullary nerve course ventromedially, and the lateral ampullary nerve fibers take a ventrolateral course until all three fiber bundles converge in the posterior tip of the descending vestibular nucleus. The ascending and descending fibers of each ampullary nerve form collaterals that pass to the ventrolateral and dorsomedial parts of the medial vestibular nucleus. These collaterals are derived exclusively from the fine and medium diameter vestibular fibers. Some of these ascending fibers form a distinctive tract that courses posteriorly within medial regions of the dorsomedial part of the medial vestibular nucleus. The colossal vestibular fibers, which are found within all three ampullary nerves, conform to the ampullary pathways as described, excluding the innervation of the medial vestibular nucleus.

An experimental study on the isolated lateral semicircular canal of the bull frog.

We used isolated lateral semicircular canals from the bull frog, Rana catesbeiana. The cupula was removed from the crista and a glass micropipette was used to depress the sensory cilia on the crista toward the utricular side. Five points on the crista were selected for stimulation. Decremental time constants of the lateral ampullary nerve action potentials were measured. The longest time constant was obtained from stimulation to the wide portion of the crista. The time constant progressively decreased as the narrow side of the crista was approached. These results indicate that the lateral semicircular canal crista is equivalent to the halved posterior semicircular canal crista in terms of both morphology and physiology.

カエル外側半規管に関する実験的研究

The lateral semicircular canals of bull frogs were isolated and the cupula was removed from the crista and the sensory cilia on the crista were depressed toward the utricular side by a glass micropipette. Five points on the crista were selected for stimulation. Decremental time constants of the lateral ampullary nerve action potentials were measured. The longest time constant was obtained from stimulation of the wide portion of the crista. The time constant progressively decreased as the narrow side of the crista was approached. These results indicate that the lateral semicircular canal crista is equivalent to the halved posterior semicircular canal crista in terms of both morphology and physiology.

Sensitivity of the vestibular system to acoustic stimuli.

Cochlea-deprived pigeons were placed on a rotating platform and stimulated with sound after fenestration of the lateral canal. The whole nerve action potentials evoked by the sound stimulus were suppressed by the rotatory stimulus. The time course of this suppression makes the lateral crista the most acceptable site of generation of the action potential. In another type of experiment, single unit responses were recorded from the lateral ampullary nerve during stimulation with sound. Phase-lock of the response to the stimulus was best for frequencies fom 0.5 to 1 kHz.

Effect of different vestibular lesions upon body equilibrium function in squirrel monkeys.

By utilizing the squirrel monkey rail test, postoperative compensation status after unilateral saccular macula destruction, unilateral utricular nerve section and unilateral lateral ampullary nerve section, were studied in a quantitative fashion and the results were statistically compared. First, it was confirmed that the preoperative random assignments of subjects were evenly distributed among different experimental categories and therefore inter-categoric statistical comparisons of postoperative status were valid. Minimal effect after the unilateral saccular macula ablation toward the maintenance of body equilibrium was reconfirmed. The utricular input is probably the most important for the maintenance of body equilibrium function, inasmuch as slightly less equilibrium disturbance was found after unilateral lateral ampullary nerve cut even though the difference was not significant.

Effects of lateral ampullary nerve section in squirrel monkeys.

Bodily dysequilibrium after lateral ampullary nerve section (unilateral) and the mode of systemic compensation were quantitatively investigated in subhuman primates. Although initially, rail thresholds were seriously altered, the rail threshold decline (average) on the eighth postoperative day was insignificant at the 0.05 level when compared to the preoperative rail threshold value. The performance profile required a longer time to regain postoperative status. The present experiment confirmed the importance of the lateral semicircular canal crista for the maintenance of bodily equilibrium (locomotive) function.

A contribution to the mechanism of vestibular nystagmus. The role of afferent impulses.

Lateral ampullary nerve and lateral ampulla were electrically stimulated with a single shock and repetitive shocks in anesthetized and unanesthetized cats with potentials in the vestibular and oculomotor nuclei were observed. The following results were obtained.1. Evoked potentials recorded in the vestibular and oculomotor nuclei in response to the repetitive shocks differed remarkably from the potentials produced by a single shock. A characteristic negative wave, termed an M wave, was evoked concomitant with the slow phase of nystagmus only by repetitive shocks. With the administration of muscle relaxant the nystagmus and the M waves disappeared at the same time.2. The possibility of afferent connections from the sensory endings in the extraocular muscles to the midbrain and the brain stem, was seriously considered.3. It was reasonably interpreted that the accumulation of M waves in the central nervous system was an important factor, which also was coordinated through the neural regulation of the CNS to ...

Influence of lateral rectus muscle contractions on the abducens nerve discharge evoked by vestibular nerve stimulation

The potential evoked in the abducens nerve by stimulating with single shocks the contralateral lateral ampullary nerve consisted of two negative waves having different characteristics in terms of latency, refractory period, and drug reaction. The first negative wave had a short latency and refractory period and, probably, represented the sum of discharges from the three neuron bisynaptic arcs which provide a direct route from the semicircular canals to the extraocular muscles. The second wave presumably represented the multisynaptic indirect route. Direct stimulation of the lateral rectus muscle caused a facilitative effect upon the second wave of the abducens nerve potential, evoked by lateral ampullary nerve stimulation, within 12 to 35 msec after the stimulation. The facilitative effect was abolished by sectioning the trigeminal nerve.

Pathological and functional changes following hemisection of the lateral ampullary nerve.

An attempt was made to section the canalicular branch of the lateral ampullary nerve in the cat. In successful cases the section was associated with degeneration of both sensory and marginal epithelium and the stroma. The animals showed signs of an acute vestibular disorder consisting of disequilibrium, spontaneous nystagmus toward the unoperated ear, type III positional nystagmus, perverted nystagmus in response to caloric irrigation on the operated side, and a directional preponderance toward the unoperated ear during optokinetic, caloric and rotatory tests. Section of superior and/or lateral ampullary nerves to a certain extent mimicked the clinical signs of a labyrinthectomy. The clinical implications of the vestibular disorder associated with damage localized to the crista ampullaris is discussed.

Crossed vestibular connections in the frog.

The crossed vestibular root to the area statica and reticular formation was investigated in frogs by the electrophysiological method. The area statica formed by the nucleus magnocellularis and ventral nucleus presented spontaneous activity, which increased in frequency and amplitude with both clockwise and counter-clockwise rotatory stimulation. In addition, the nucleus magnocellularis responded to acoustic stimuli. Labyrinthectomy carried out in several ways demonstrated that signals arising in one semicircular canal were transmitted to the area statica of both sides. An extensive area of the reticular formation of both sides exhibited spontaneous activity, which also increased in frequency and amplitude with both clockwise and counter-clockwise rotatory stimulation. The results showed that the signals from one lateral semicircular canal are transmitted to the reticular formation of both sides. The lateral ampullary nerve at rest exhibited spontaneous activity, which increased in frequency and amplitude ...