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PubMed1976

[Position and bony structures of the vestibular apparatus in the guinea pig].

The study of the inner ear of the guinea pig intended to give an explanation to what extent there are differences discernible in relation to the human labyrinth. Additional histological research should clarify the question, if structural differences exist in the osseous labyrinth capsule of the same animal. It has turned out that in normal headbearing the position of the semicircular canals deviates from the human vestibular apparatus. The semicircular canals are nearly vertical to each other, but in comparison to the human labyrinth they are shifted around the longitudinal axis of the utriculus caudal by ca. 30 degrees. In general the position of the vestibulo-cochlear organ is fixed to a great extent by the inclined course of the petrosal pyramid. This different position of the semicircular canals in man and animal is supposed to be due to the phylogenetic evolution and the adjustment to upright walk. Size and extension of the single semicircular canals are very different within the same animal. These differences in size indicate causalities of form and function. The relations in the build of the osseous labyrinth are extremely complicated. Compared to the other corporal regions the static parts of the petrosal pyramid are exceptional massive and of remarkable hard consistency. In the inner capsule of the ear there are three different bone strata to be seen. The characteristic lamel structure is most solid nearest to the semicircular canals. The fetal characteristics in the maturing process of the petrosal bone were traced a long while in the postnatal life. The typical building of the labyrinthal bone structures contributes to the mechanical stability of the capsule.

Animals↗
PubMed1983

Organization of eighth nerve afferent projections from individual endorgans of the inner ear in the teleost, Astronotus ocellatus.

Eighth nerve fibers from the saccule, utricle, lagena, and the anterior, horizontal, and posterior semicircular canals of a cichlid fish were traced to the octavolateralis region of the brainstem using HRP and degeneration methods. The anterior, magnocellular, descending, and posterior nuclei of the octavus column receive inputs from all endorgans, whereas the tangential nucleus receives projections only from the utricle and semicircular canals. The most rostral projections only from the utricle and semicircular canals. The most rostral projection from each endorgan is found in the eminentia granularis of the vestibulolateral lobe of the cerebellum. Sparse terminals are found in the medial reticular formation from the utricle adn semicircular canals, and utricular and saccular remain terminate in the vicinity of the lateral dendrite of the Mauthner cell. Utricular and semicircular canal projections consistently overlap centrally as do saccular and lagenar inputs. Afferent fibers from all endorgans end within relatively distinct regions throughout the octavus column of nuclei. Saccular and lagenar inputs lie dorsal to the semicircular canal terminations. Utricular endings are complex, however, in that they overlap dorsally with saccular and lagenar terminals and ventrally with the semicircular canal inputs. Cerebellar inputs are found only in the eminentia granularis of the vestibulolateral lobe, and the densest terminals are from the utricle and the semicircular canals; the sparsest are from the saccule. Previous studies in fish have indicated that generally the utricle and semicircular canals are concerned with he maintenance of static and dynamic equilibrium whereas the saccule and lagena are concerned with auditory reception. There is recent evidence, however, for multiple functions within individual endorgans. Our anatomical findings suggest that in Astronotus each otolithic endorgan carries more than one modality; that the semicircular canals are concerned solely with an equilibrium function; and that acoustic information is processed dorsally and vestibular information ventrally along the octavus column of nuclei. No single nucleus appears to be solely auditory in function and only the tangential nucleus, situated ventrally in the octavus column, appears to be solely vestibular.

Afferent Pathways↗
PubMed2001

Semicircular canal-otolith organ interaction during off-vertical axis rotation in humans.

The aim of this study was to examine the interaction of signals from the semicircular canals and the otolith organs during off-vertical axis rotation (OVAR). We recorded horizontal eye position using electro-oculography in 22 young normal human subjects and stimulated the vestibulo-ocular reflex with both constant velocity trapezoids and sinusoidal yaw rotations, using both earth-vertical axis rotation (EVAR) and OVAR. We found that per-rotatory long vestibulo-ocular reflex (VOR) time constants during velocity trapezoids were shorter for OVAR than for EVAR, suggesting a reduction in the efficacy of the velocity storage system during OVAR. However, when we tested with very-low-frequency sinusoids (0.01 Hz and below), the phase lead of the VOR re head velocity was smaller during OVAR than EVAR, suggesting a longer time constant and enhanced efficacy of velocity storage during OVAR. These rotational responses can be explained by two competing influences of signals from the otolith organs, one that diminishes the effectiveness of velocity storage and another that contributes to an estimate of head velocity.

Acceleration↗
PubMed2003

Paroxysmal positional vertigo: short- and long-term clinical and methodological analyses of 794 patients.

Between 1995 and 2001, eight Italian clinical centres used the same diagnostic and therapeutic protocol in order to assess the clinical progress of paroxysmal positional vertigo and the benefits of an appropriate follow-up in prevention of relapse. The study population comprises 794 patients affected by paroxysmal positional vertigo. The study protocol comprised diagnostic staging including a complete otoneurological test, an anamnestic questionnaire aimed at identifying any possible risk factor, a blood test in basal conditions and monitoring of blood pressure. If necessary, more specific instrumental tests have been carried out. Appropriate rehabilitative manoeuvres were performed from 1 to 3 times within the same session. The patient was checked 3-5 days later: in the presence of a positive result, the treatment was repeated; if negative, patients were seen at clinical follow-up 7, 30, 180 and 365 days after recovery. Wherever possible, patients have been contacted 2 years after the first treatment and asked to answer a questionnaire and to attend for a clinical check-up. The incidence of paroxysmal positional vertigo appeared to be higher in females and in patients aged 50-70 years, being low in patients under 30. In 88.8% of cases posterior semicircular canals showed a significant involvement; in 6.8% of cases, only involvement of lateral semicircular canals; monolateral (2.7%) and bilateral (1.7%) multicanalar forms were rare. Paroxysmal positional vertigo forms involving posterior semicircular canals have been treated with Semont (simplified by Toupet), Epley, Parnes Price-Jones manoeuvres; those, involving lateral semicircular canals with Vannucchi-Vicini forced position and "barbecue" or Gufoni manoeuvre. Whilst all these manoeuvres were equally effective, longer recovery times have been observed in paroxysmal positional vertigo forms involving lateral semicircular canals when the Vannucchi-Vicini forced position was ineffective. Any relapses have been evaluated at least 15 days after a negative clinical pattern. Possible involvement of other semicircular canals (recurrence) some time after the first onset has been considered separately. Follow-up at 6 months showed recurrence in 12.4% of cases, while being chronic in 1.5% of cases. Only 9.3% of cases showed recurrence at 6 months, no statistically significant difference being observed between vertical (8.9%) and lateral canal (9.6%), forms. Relapses occurred in 3.1% of cases, in one third of which at least two risk factors were detected.

Aged↗
PubMed2003

The bony labyrinth of Neanderthals.

This paper presents a comprehensive comparative analysis of the Neanderthal bony labyrinth, a structure located inside the petrous temporal bone. Fifteen Neanderthal specimens are compared with a Holocene human sample, as well as with a small number of European Middle Pleistocene hominins, and early anatomically modern and European Upper Palaeolithic humans. Compared with Holocene humans the bony labyrinth of Neanderthals can be characterized by an anterior semicircular canal arc which is smaller in absolute and relative size, is relatively narrow, and shows more torsion. The posterior semicircular canal arc is smaller in absolute and relative size as well, it is more circular in shape, and is positioned more inferiorly relative to the lateral canal plane. The lateral semicircular canal arc is absolutely and relatively larger. Finally, the Neanderthal ampullar line is more vertically inclined relative to the planar orientation of the lateral canal. The European Upper Palaeolithic and early modern humans are most similar, although not fully identical to Holocene humans in labyrinthine morphology. The European Middle Pleistocene hominins show the typical semicircular canal morphology of Neanderthals, with the exception of the arc shape and inferiorly position of the posterior canal and the strongly inclined ampullar line. The marked difference between the labyrinths of Neanderthals and modern humans can be used to assess the phylogenetic affinities of fragmentary temporal bone fossils. However, this application is limited by a degree of overlap between the morphologies. The typical shape of the Neanderthal labyrinth appears to mirror aspects of the surrounding petrous pyramid, and both may follow from the phylogenetic impact of Neanderthal brain morphology moulding the shape of the posterior cranial fossa. The functionally important arc sizes of the Neanderthal semicircular canals may reflect a pattern of head movements different from that of modern humans, possibly related to aspects of locomotor behaviour and the kinematic properties of their head and neck.

Adult↗
PubMed2000

Convergence pattern of uncrossed excitatory and inhibitory semicircular canal-specific inputs onto second-order vestibular neurons of frogs. Organization of vestibular side loops.

Second-order vestibular neurons of frogs receive converging monosynaptic excitatory and disynaptic excitatory and inhibitory inputs following electrical pulse stimulation of an individual semicircular canal nerve on the ipsilateral side. Here we revealed, in the in vitro frog brain, disynaptic inhibitory postsynaptic potentials (IPSPs) by bath application of antagonists specific for glycine or gamma-aminobutyric acid-A (GABA(A)) receptors. Differences in the response parameters between disynaptic IPSPs and excitatory postsynaptic potentials (EPSPs) suggested that disynaptic IPSPs originated from a more homogeneous subpopulation of thicker vestibular nerve afferent fibers than mono- or disynaptic EPSPs. To investigate a possible size-related organization of these canal-specific, parallel pathways, we combined long-lasting anodal currents of variable intensities with strong cathodal test pulses, to block pulse-evoked responses reversibly in a graded manner according to the size-related sensitivity of vestibular nerve afferent fibers. The anodal current intensity required to block a particular response component was about 15 times lower than the strength of the cathodal test pulse that activated this response component. These large threshold differences were exploited for a selective anodal suppression of the responses from thick vestibular nerve afferent fibers. In fact, response components known to originate exclusively from thick-caliber afferent fibers such as the electrically transmitted monosynaptic EPSP component exhibited the lowest thresholds for cathodal test pulses and were the first to disappear in the presence of small anodal polarization steps. Thresholds for the activation/inactivation of responses and current intensities required for response saturation/blockade were used to assess the fiber spectrum that evoked the different response components. Mono- and disynaptic EPSPs appeared to originate from a broad spectrum of thick and thin vestibular nerve afferent fibers. The spectrum of afferent fibers that activated disynaptic IPSPs on the other hand was more homogeneous and consisted of thick and intermediate fibers. Such a canal-specific and fiber type-related organization of converging inputs of second-order vestibular neurons via feedforward projections was shown for the first time by this study in frogs, but might also prevail in mammals. Similar differences in these feedforward pathways have been proposed earlier in a vestibular side-loop model. Our results are consistent with the basic assumptions of this model and relate to the processing and tuning of dynamic vestibular signals.

Animals↗
PubMed1991

[Heat radiation--an essential factor of heat transport in caloric vestibular tests? Current experimental findings].

According to the accepted theory, in vestibular testing the caloric stimulus is transported from the auditory canal to the lateral semicircular canal by heat conduction via the bone. Some findings, however, are not consistent with this concept, e.g. the short latency of the vestibular response, and the fact that removing of the osseous bridge does not stop the transport of heat to the semicircular canal. Physically there are three modes of heat transport: conduction, convection, and radiation. So far, only the first two have been discussed with regard to vestibular calorization, however, they fail to explain the findings mentioned above. We carried out experiments on 10 cadaveric temporal bone specimens in order to evaluate the possible effect of heat radiation. With experimental conditions strictly regulated (specimens kept in climate box, 37 degrees C, saturated humidity, standardized irrigation of the auditory canal with 50 ml of water of 50 degrees C in 15 sec., temperature measured by thermistors at selected points of the specimen), the deviation in repeated experiments was within 0.1 degree C. In normal temporal bones a spreading of heat along the osseous structures was found in accordance with heat conduction via the bone. Then the bony bridge between posterior frame of the tympanic membrane and the lateral canal was removed along with the tegmen tympani, leaving the auditory canal and labyrinth connected only by a small anterior-inferior strut. The rise of temperature in the lateral canal, however, was not delayed and reduced, as expected, but faster and greater than in the original situation. If, now, a reflecting shield was inserted in the cleft between tympanic membrane and labyrinth the heat transfer was dramatically reduced. A similar effect could be achieved in the intact middle ear by a shield or by filling the cavity with gel. Convection as means of heat transport could be excluded. The experiments show that heat transport in the vestibular calorization is a complex process, which besides heat conduction involves radiation as an essential factor. This explains a number of experimental and clinical findings that, so far, had been unclear.

Bone Conduction↗
PubMed1999

Magnetic resonance cisternography using the fast spin echo method for the evaluation of vestibular schwannoma.

Neuroimaging of vestibular schwannoma was performed with the fat-suppression spoiled gradient recalled acquisition in the steady state (SPGR) method and magnetic resonance (MR) cisternography, which is a fast spin echo method using a long echo train length, for the preoperative evaluation of the lateral extension of the tumor in the internal auditory canal, and the anatomical identification of the posterior semicircular canal and the nerves in the canal distal to the tumor. The SPGR method overestimated the lateral extension in eight cases, probably because of enhancement of the nerves adjacent to the tumor in the canal. The posterior semicircular canal could not be clearly identified, and the cranial nerves in the canal were shown only as a nerve bundle. In contrast, MR cisternography showed clear images of the lateral extension of the tumor and the facial and cochlear nerves adjacent to the tumor in the internal auditory canal. The anatomical location of the posterior semicircular canal was also clearly shown. These preoperative findings are very useful to plan the extent to which the internal auditory canal can be opened, and for intraoperative identification of the nerves in the canal. MR cisternography is less invasive since no contrast material or radiation is required, as with thin-slice high-resolution computed tomography (CT). MR cisternography should replace high-resolution CT for the preoperative neuroradiological evaluation of vestibular schwannoma.

Adult↗
PubMed1981

A comparison of the horizontal and vertical vestibulo-ocular reflexes of the rabbit.

1. The gain and phase of the horizontal (H.v.o.r.) and vertical (V.v.o.r.) vestibulo-ocular reflexes were measured in rabbits. The V.v.o.r. was evoked by sinusoidal rolls about the longitudinal axis of the rabbit. This axis was maintained at different orientations with respect to the earth horizontal axis: V.v.o.r. 0 degrees , prone; V.v.o.r. 90 degrees , ;nose-up'; V.v.o.r. 180 degrees , supine; V.v.o.r. 0 degrees L, left side down.2. In contrast to the H.v.o.r., the V.v.o.r. 0 degrees had a higher gain (eye velocity/head velocity) and a smaller phase lead (eye position + 180 degrees with respect to head position) at low frequencies of sinusoidal vestibular stimulation (+/- 10 deg, 0.005-0.05 Hz). At higher frequencies (0.05-0.8 Hz), the H.v.o.r. and V.v.o.r. 0 degrees were equivalent in both gain and phase.3. The low-frequency gain of the V.v.o.r. was smallest in the ;nose-up' orientation. The V.v.o.r. 90 degrees was equivalent in both gain and phase to the H.v.o.r. over the entire range of frequencies tested (0.005-0.8 Hz). Threshold angular accelerations for the H.v.o.r. and V.v.o.r. 90 degrees were below 0.04 deg/sec(2).4. The compensatory eye movements of the H.v.o.r. were frequently interrupted by anticompensatory re-setting eye movements. These anticompensatory re-setting eye movements were present in the V.v.o.r. 90 degrees , but not in the V.v.o.r. 0 degrees .5. An estimate gain and phase of the otolithic component of the V.v.o.r. 0 degrees was derived by subtraction of the V.v.o.r. 90 degrees (semicircular canal signal) from the V.v.o.r. 0 degrees (semicircular canal signal+otolith signal). This procedure was based on the assumption that the signals from the otolith organs and vertical semicircular canals combine linearly.6. The V.v.o.r. 180 degrees provided an interesting test of the assumption of linear combination of otolithic and semicircular canal signals by reversing the phase of the modulated otolithic signal. The data indicated that the V.v.o.r. 180 degrees is non-linear.

Animals↗
PubMed1995

Vestibular and visual climbing fiber signals evoked in the uvula-nodulus of the rabbit cerebellum by natural stimulation.

1. The cerebellar uvula-nodulus receives vestibular projections from primary and secondary vestibular afferents as well as vestibularly related climbing fibers. It also receives visually related information from climbing fiber pathways. In this experiment we investigated how this information is mapped onto the uvula-nodulus. We studied the specificity, dynamics, and topographic distribution of climbing fiber responses (CFRs), simple spike responses, and mossy fiber terminal responses evoked by vestibular and optokinetic stimulation in rabbits anesthetized with alpha-chloralose. 2. Vestibularly evoked CFRs were found in the ventral uvula and nodulus. These responses were evoked during static roll tilt of the rabbit about a longitudinal axis and by sinusoidal oscillation about the longitudinal axis. Purely static responses were attributed to stimulation of the utricular otolith by the linear acceleration of gravity. CFRs that lacked a static component were attributed to activation of the semicircular canals. 3. Using a "null technique" we showed that the canal-sensitive CFRs were caused by stimulation of the anterior or posterior semicircular canals. Of the CFRs classified as canal related, 96% could be attributed to stimulation of the vertical semicircular canals. 4. Increases in CFRs were correlated with decreases in simple spike responses in half the Purkinje cells from which we recorded. These climbing-fiber-induced pauses in simple spikes occurred during spontaneous climbing fiber discharge as well as during climbing fiber discharge evoked by vestibular stimulation. The duration of this pause was inversely proportional to the spontaneous level of simple spikes before the occurrence of a CFR. In the other half of the recorded population of Purkinje cells, vestibularly driven CFRs did not alter the simple spike responses. 5. Vestibularly and visually mediated CFRs were topographically represented on the surface of the uvula-nodulus. CFRs driven by ipsilateral otolithic inputs were distributed over the entire mediolateral surface of the uvula-nodulus. CFRs driven by the ipsilateral posterior semicircular canal were distributed in a sagittal strip approximately 1.5 mm wide, extending laterally from the midline of the nodulus. CFRs driven exclusively by horizontal, posterior-->anterior optokinetic stimulation of the ipsilateral eye were distributed in a sagittal strip approximately 0.5 mm wide located 0.5-1.0 mm from the midline and restricted to the ventral nodulus. CFRs driven by the ipsilateral anterior semicircular canal were found in a sagittal strip approximately 1.0 mm wide extending 1.0-2.0 mm from the midline. 6. The sagittal, topographically arrayed climbing fiber strips effectively map a mediolateral gradient of possible postural responses based on vestibular and optokinetic information.

Adaptation, Physiological↗
PubMed2004

[Selective stimulation of the equilibrium organ using monochromatic near infrared].

BACKGROUND: The aim of this study was, to establish, if a selective thermal warm-stimulation using monochromatic near infrared radiation (NIR) in healthy persons, patients with chronic otitis media (chronic mucosal inflammation) and after radical surgery of one ear shows quantitative or qualitative changes of the nystagmus reaction. PATIENTS AND METHODS: Healthy persons (n = 3), patients with a large central defect of the tympanic membrane (n = 5) and after radical ear surgery (n = 6) were examined. In healthy persons a stimulation with monochromatic NIR (lambda = 980 nm) of several areals of the external auditory canal was performed. In patients with large defects of the tympanic membrane the promontorium was stimulated. In patients with a radical cave of the ear a selective NIR-stimulation of the region of the vertical and the anterior semicircular canal was performed. The horizontal semicircular canal was visible as a landmark. Registration of the nystagmus was performed by means of videonystagmography. RESULTS: In healthy persons the mean slow phase velocity of the nystagmus depended on the stimulated region. But there was no qualitative change of three dimensional eye movement. Stimulation of the promontorium showed a strong directional horizontal nystagmus. In patients with a radical cave the stimulation of the regions of the three semicircular canals showed a qualitative difference in three dimensional eye movement. NIR-stimulation showed in all cases a nystagmus into the stimulated ear. CONCLUSIONS: The method of monochromatic near infrared stimulation can be used for selective stimulation of several regions of the external auditory canal, the promontorium and the regions of the semicircular canals in a radical cave of the ear as well as to prove the warm reaction of the equilibrium organ. A specific nystagmus after stimulation of the semicircular canal-region in a radical cave of the ear could be an indication for a normal semicircular canal function.

Adult↗
PubMed1988

[Effect of the stimulus medium--water or air--in thermal evaluation of the vestibular apparatus].

The influence of the stimulus medium in thermal vestibular tests has been investigated by many authors, comparing nystagmus reactions after air and water irrigations. We first measured temperature changes in the ear canal and in the horizontal semicircular canal after both kinds of stimuli, using human temporal bone preparations, which were placed in a water bath of 37 degrees C. Irrigations were done with air of 45 and 27 degrees C with a flow of 5 l/min during 45 s and with 100 ml water of 44 and 30 degrees C during 30 s. The maximum temperature changes in the ear canal are almost equal after both kinds of irrigation (see Figs. 2 and 3). The change of temperature, however, lasts longer after water irrigation. The time constants are 20 and 57 s for the decay after warm and cold water irrigation and 9 and 20 s after air irrigation, respectively. The maximum temperature change in the lateral part of the horizontal semicircular canal is 0.4 and -0.3 degree after warm and cold irrigation with water. The corresponding values after irrigation with air are 0.1 and -0.15 degree. In addition, we investigated the effect of irrigating temporal bone preparations with perforated tympanic membranes (Fig. 4). After irrigation with air of 45 degrees C, the temperature in the horizontal semicircular canal decreased due to evaporation of humidity in the tympanic cavity. The equipment of choice for the irrigation of such ears is a stimulator reported by Scherer, where water flows through a silicon bubble which coats the ear canal.(ABSTRACT TRUNCATED AT 250 WORDS)

Air↗
PubMed2000

Three-dimensional spatial characteristics of caloric nystagmus.

We investigated the three-dimensional spatial characteristics of caloric nystagmus during excitation and inhibition of the lateral semicircular canal in five normal human subjects. Each subject was repositioned in 45 degrees steps at 1-min intervals such that the right lateral semicircular canal plane was reoriented in pitch, from 135 degrees backwards from the upright position to 135 degrees forwards, while the right ear was continuously stimulated with air at 44 degrees C. In orientations in which caloric stimulus resulted in excitation of the right lateral semicircular canal, the eye velocity axis was orthogonal to the average orientation of the right lateral semicircular canal plane. However, in orientations in which caloric stimulus resulted in inhibition of the right lateral semicircular canal, the eye velocity axis was orthogonal to the average orientation of the left and not the right lateral semicircular canal plane. These findings suggest that velocity and direction of caloric nystagmus depend not only on the absolute magnitude of vestibular activity on the stimulated side but also on the differences in activity between the left and right vestibular nuclei, most probably mediated centrally via brainstem commissural pathways.

Adult↗
PubMed1997

Canal-specific excitation and inhibition of frog second-order vestibular neurons.

Second-order vestibular neurons (secondary VNs) were identified in the in vitro frog brain by their monosynaptic excitation following electrical stimulation of the ipsilateral VIIIth nerve. Ipsilateral disynaptic inhibitory postsynaptic potentials were revealed by bath application of the glycine antagonist strychnine or of the gamma-aminobutyric acid-A (GABA(A)) antagonist bicuculline. Ipsilateral disynaptic excitatory postsynaptic potentials (EPSPs) were analyzed as well. The functional organization of convergent monosynaptic and disynaptic excitatory and inhibitory inputs onto secondary VNs was studied by separate electrical stimulation of individual semicircular canal nerves on the ipsilateral side. Most secondary VNs (88%) received a monosynaptic EPSP exclusively from one of the three semicircular canal nerves; fewer secondary VNs (10%) were monosynaptically excited from two semicircular canal nerves; and even fewer secondary VNs (2%) were monosynaptically excited from each of the three semicircular canal nerves. Disynaptic EPSPs were present in the majority of secondary VNs (68%) and originated from the same (homonymous) semicircular canal nerve that activated a monosynaptic EPSP in a given neuron (22%), from one or both of the other two (heteronymous) canal nerves (18%), or from all three canal nerves (28%). Homonymous activation of disynaptic EPSPs prevailed (74%) among those secondary VNs that exhibited disynaptic EPSPs. Disynaptic inhibitory postsynaptic potentials (IPSPs) were mediated in 90% of the tested secondary VNs by glycine, in 76% by GABA, and in 62% by GABA as well as by glycine. These IPSPs were activated almost exclusively from the same semicircular canal nerve that evoked the monosynaptic EPSP in a given secondary VN. Our results demonstrate a canal-specific, modular organization of vestibular nerve afferent fiber inputs onto secondary VNs that consists of a monosynaptic excitation from one semicircular canal nerve followed by disynaptic excitatory and inhibitory inputs originating from the homonymous canal nerve. Excitatory and inhibitory second-order (secondary) vestibular interneurons are envisaged to form side loops that mediate spatially similar but dynamically different signals to secondary vestibular projection neurons. These feedforward side loops are suited to adjust the dynamic response properties of secondary vestibular projection neurons by facilitating or disfacilitating phasic and tonic input components.

Animals↗
PubMed2006

Posterior canal dehiscence syndrome caused by an apex cholesteatoma.

OBJECTIVE: To compare audio-vestibular findings caused by a dehiscence of the posterior semicircular canal with those found in the superior canal dehiscence syndrome. STUDY DESIGN: Case report. SETTING: University hospital, tertiary referral center. PATIENT: The 44-year-old woman suffered from a gradual hearing loss with pulse-synchronous tinnitus as well as sound and pressure-induced vertigo. INTERVENTION: Audio-vestibular testing and high-resolution computed tomography. MAIN OUTCOME MEASURE: The superior canal dehiscence syndrome is caused by failure of normal postnatal bone development in the middle cranial fossa leading to absence of bone at the most superior part of the superior semicircular canal. The typical features for this syndrome are sound- and pressure-induced vertigo with torsional eye movements, pulse synchronous tinnitus and apparent conductive hearing loss in spite of normal middle-ear function. We present a patient with very similar symptoms and findings who, instead, had a posterior semicircular canal dehiscence caused by an apex cholesteatoma. CONCLUSION: Patients with semicircular canal dehiscence have common auditory-vestibular features regardless of which of the two vertical semicircular canals is affected. The only obvious difference between the two is the vertical component of the sound and pressure-induced eye movements (which beats in opposite directions).

Adult↗
PubMed1988

Spatial coordination of compensatory eye movements in vertebrates: form and function.

The semicircular canals of the labyrinth of vertebrates provide one way of motion detection in three-dimensional space. The fully developed form of the vertebrate labyrinth consists of six semicircular canals, three on each side of the head, whose spatial arrangement (vertical canals are placed diagonally in the head, horizontal canals are oriented earth horizontally) follows three interconnected principles: 1) bilateral symmetry, 2) push-pull operational mode, and 3) mutual orthogonality. Other sensory and motor systems related to vestibular reflexes, such as the extraocular muscles or the "optokinetic" coordinate axes encoded in the activity of the visually driven cells of the accessory optic system, share the same geometrical framework. This framework is also reflected in the anatomical networks mediating compensatory eye movements, linking each of the semicircular canals to a particular set of extraocular muscles (so-called principal vestibuloocular reflex connections to yoke muscles). These classical vestibulo-oculomotor relationships have been verified at many levels of the vertebrate hierarchy, including lateral- and frontal-eyed animals. The particular spatial orientation of the semicircular canals requires further comment and phylogenetic evaluation. The spatial arrangement of the vertical canals is already present in fossil ostracoderms, and is also exemplified in lampreys, the modern forms of once abundant agnathan species that populated the Silurian and Devonian oceans. The lampreys and ostracoderms lack horizontal canals, which appear later in all descendent vertebrates. The fully developed vertebrate labyrinth with its six semicircular canals displays distinct differences that are obvious when comparing distant taxa (e.g. elasmobranchs versus other vertebrates). Whereas the common crus of the semicircular canals in teleosts through mammals is formed between the anterior and the posterior semicircular canal, it occurs between the anterior and the horizontal canal in elasmobranchs. However, despite this morphological difference, these two vertebrate labyrinth prototypes constitute a functionally identical solution. A similar analysis holds for certain invertebrate species (crab, octopus, squid), which display an even wider variety in the physical expressions of movement detection systems when compared to vertebrates. Although the physical expressions of motion detection systems differ in the animal kingdom, the functional solutions (providing the best signal-to-noise ratio) with adherence to bilateral symmetry, push-pull operational mode, and mutual orthogonality are identical.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Congenital anomalies of the inner ear.

This study investigated congenital anomalies occurring in the inner ear, with particular attention to their features, localizations, and frequencies. Seventy-seven human temporal bones obtained from 53 individuals, aged one day to 39 years, each of whom had anomalies of the external ear, middle ear, and/or inner ear, were used for this study. The temporal bones had been removed at autopsy, fixed, dehydrated, embedded in celloidin, and sectioned horizontally or vertically at 20 microns. Every tenth horizontal section or every 20th vertical section was stained with hematoxylin and eosin, mounted, and studied under a light microscope. There were 206 inner ear anomalies (117 in the vestibular system, 79 in the cochlea, 10 in the internal auditory meatus) in the 51 bones studied. Fifty-four different features of anomalies were present at 33 different locations in the inner ear. The most frequent anomalies observed were shortened cochlea (23 bones), enlarged vestibule (17 bones), wide cochlear aqueduct (16 bones), absence of lateral semicircular canal (14 bones), and large osseous lateral semicircular canal (10 bones). The most common site of inner ear anomalies was thus the lateral semicircular canal, which was involved in 46 of the 206 anomalies observed; the anomalies in this organ were variable in type. The implications of inner ear anomalies are discussed as they relate to fetal development, inner ear dysfunction, and clinical interpretation of polytomographic studies.

Abnormalities, Multiple↗
PubMed1988

A clinical sign of canal paresis.

Unilateral loss of horizontal semicircular canal function, termed canal paresis, is an important finding in dizzy patients. To our knowledge, apart from head-shaking nystagmus, no clinical sign of canal paresis has yet been described and the term derives from the characteristic finding on caloric tests: little or no nystagmus evoked by either hot or cold irrigation of the affected ear. We describe a simple and reliable clinical sign of total unilateral loss of horizontal semicircular canal function: one large or several small oppositely directed, compensatory, refixation saccades elicited by rapid horizontal head rotation toward the lesioned side. Using magnetic search coils to measure head and eye movement, we have validated this sign in 12 patients who had undergone unilateral vestibular neurectomy.

Eye Movements↗