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PubMed1977

Influence of the saccule, lagena and vertical posterior canal on the ipsilateral horizontal and vertical anterior semicircular canals in Rana esculenta: role of receptor-receptor fibres.

The influence of the efferent vestibular system being eliminated, the spontaneous activity of single afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By stimulating electrically the nerves of the vertical posterior canal, lagena or saccule as well as by sectioning these nerves and then using statistical methods, it is shown that the receptor-receptor fibres arising from the above mentioned receptors have generally an inhibitory influence on the afferent activity from the horizontal and vertical anterior canals.

Animals↗

PubMed2004

Superior semicircular canal dehiscence syndrome. Case report.

The authors present the case of a man who had superior semicircular canal dehiscence syndrome in addition to chronic otitis media. This case is atypical because the patient coincidentally had middle ear and mastoid disease, which previously had been treated surgically. The prior ear surgery delayed the diagnosis of superior semicircular canal dehiscence syndrome and increased the complexity of the repair of the superior semicircular canal dehiscence. Superior semicircular canal dehiscence syndrome is a recently recognized syndrome resulting in acute or chronic vestibular symptoms. The diagnosis is made using history, vestibular examination, and computerized tomography studies. Neurosurgeons should be aware that patients with superior semicircular canal dehiscence syndrome who experience disabling chronic or acute vestibular symptoms can be treated using a joint neurosurgical-otological procedure through the middle cranial fossa.

Acute Disease↗

PubMed2006

Auditory function in patients with surgically treated superior semicircular canal dehiscence.

OBJECTIVE: To characterize preoperative and postoperative audiologic findings in patients with superior semicircular canal dehiscence syndrome. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Patients with documented superior semicircular canal dehiscence syndrome (according to history, vestibular testing, and high-resolution computed tomography imaging) who underwent surgical repair of their dehiscence. INTERVENTION: Middle fossa craniotomy for superior semicircular canal plugging and/or resurfacing. MAIN OUTCOME MEASURES: Audiologic testing both before and after surgery with pure-tone threshold measurements of air and bone conduction. RESULTS: Twenty-nine subjects underwent surgical repair of superior semicircular canal dehiscence. Overall, there were no statistically significant differences by paired t test in hearing before or after surgery, in either air-conduction or bone-conduction thresholds, for 19 patients that had no previous surgical history. At least partial closure of air-bone gap was achieved in five patients. One patient with previous stapes surgery had significantly worse hearing both before and after canal repair compared with those without previous surgery. Two patients who had undergone previous middle fossa surgery with incomplete resolution of symptoms developed sensorineural hearing loss after revision surgery. Previous middle-ear exploration and tympanostomy tube placement did not seem to affect audiologic outcomes. Surgical hearing results did not differ according to method of canal repair (plugging versus resurfacing). CONCLUSION: Primary middle fossa repair of superior semicircular canal dehiscence is not associated with sensorineural hearing loss and, in some cases, can lead to normalization of conductive hearing loss. Revision middle fossa repair or previous stapes surgery may be associated with postoperative sensorineural hearing loss.

Adult↗

PubMed1995

Treatment of labyrinthine fistula with interruption of the semicircular canals.

Evaluation of postoperative hearing acuity and equilibrium was performed in eight patients with labyrinthine fistula caused by cholesteatoma, in which at least one of the semicircular canals (five cases, lateral; one case, superior; one case, posterior; and one case, both lateral and superior) was interrupted during eradication of the matrix and granulations from the semicircular canals. The interrupted semicircular canals were obliterated firmly with autologous materials such as fascia, perichondrium, bone chips, and cartilage. The observation period ranged from 9 months to 3.3 years. Postoperative hearing was unaltered or improved in seven patients, and decreased by 12 dB in one patient. Postoperative disequilibrium lasting more than 2 weeks was experienced in two patients and disappeared at the second and fifth postoperative months, respectively. Relief from fistula symptoms was complete after surgery, indicating adequacy of this procedure in one-stage open-method tympanoplasty. The present study indicates that manipulation of the semicircular canal with awareness can be conducted without damaging the cochlear function, and that the treatment of labyrinthine fistulas should be performed very carefully but not so conservatively as to lead to future problems. In some cases of deep fistulas of the semicircular canals, interruption and/or obliteration of the semicircular canals can be the most proper procedure.

Adult↗

PubMed1996

Otolith-semicircular canal interaction during postrotatory nystagmus in humans.

The otolith-semicircular canal interaction during postrotatory nystagmus was studied in ten normal human subjects by applying fast, short-lasting, passive head and body tilts (15, 30, 45, or 90 degrees in the roll or pitch plane) 2 s after sudden stop from a constant-velocity rotation (100 degrees/s) about the earth-vertical axis in yaw. Eye movements were measured with three-dimensional magnetic search coils. Following the head tilt, activity in the semicircular canal primary afferents continues to reflect the postrotatory angular velocity vector in head-centered coordinates, whereas otolith primary afferents signal a different orientation of the head relative to gravity. Despite the change in head orientation relative to gravity, postrotatory eye velocity decayed closely along the axis of semicircular canal stimulation (horizontal in head coordinates) for large head tilts (90 degrees) and also for small head tilts (15-45 degrees) for reorientations in the pitch plane. Only for small head tilts (15-45 degrees) in the roll plane was there a reorientation of the eye rotation axis toward the gravitational vector. This reorientation was approximately compensatory for 15 degrees head tilts. For 30 degrees and 45 degrees head tilts the eye rotation axis tilted toward the gravitational vector by about the same amount as for 15 degrees head tilts. These results suggest that, with the exception of small head tilts in the roll plane, there was no compelling data showing a relationship between the eye rotation axis and head tilt and that postrotatory nystagmus is largely organized in head-centered rather than gravity-centered coordinates in humans. This indicates a rudimentary, nonlinear, and direction-specific interaction of semicircular canal and otolith signals in the central vestibular system in humans.

Adult↗

PubMed2003

Molecular genetic advances in semicircular canal abnormalities and sensorineural hearing loss: a report of 16 cases.

OBJECTIVES: The study goals were (1) to determine if the degree and pattern of semicircular canal dysmorphology and the presence or absence of a cochlea in patients with congenital sensorineural hearing loss predict audiologic outcome, severity, or the frequencies involved and (2) to review the recent advances in molecular genetics of the semicircular canals and correlate this information with audiologic and anatomic patterns seen in our series of patients. DESIGN AND SETTING: We conducted a retrospective study at a tertiary care center with a large otologic and cochlear implant service. PATIENTS AND METHODS: The study population consisted of 16 patients with congenital sensorineural hearing loss in 28 congenitally malformed inner ears consisting of semicircular canal dysplasia or aplasia, with or without cochlear malformation. History, physical examination, computed tomography scans, and serial audiograms were reviewed. Factors analyzed included other phenotypic dysmorphology characteristic of syndromes, audiometric configuration, severity and type of hearing loss, and the presence of associated inner ear anomalies other than the vestibular system. An extensive review of the literature regarding molecular genetic factors in semicircular canal anomalies, with or without cochlear abnormalities, was performed. RESULTS: Sixteen patients (31 ears) were identified with profound sensorineural hearing loss and semicircular canal abnormalities. Only 3 patients had known syndromes, although 4 patients had other congenital anomalies. Most radiographic detectable abnormalities were bilateral. Audiograms of the patients demonstrated pure tone averages between 90 and 100 dB in the affected ears with few exceptions. No correlation was found between type and severity of malformation of either the cochlea or semicircular canals with the severity of hearing loss. There was no stepwise progression of hearing loss increasing malformation severity. Seven of the 16 patients received cochlear implants. Of these 7, 3 patients had cochlear hypoplasia and 1 patient had a common cavity deformity. Audiologic follow-up on all 7 patients revealed improvement in both speech assessment threshold and pure tone average. Presence or absence of the cochlea was not a factor in outcome after cochlear implantation. CONCLUSION: We have assembled the largest series of patients with semicircular canal dysmorphology, with or without various cochlear abnormalities. Our study failed to correlate the type and severity of semicircular canal malformation with any specific audiologic outcome. The variation in hearing loss severity and pattern even in patients with similar bony radiographic findings must be explained by other non-radiologically detectable defects, likely abnormalities in membranous labyrinthine development. New molecular genetic discoveries have linked specific genes to the development of certain inner ear structures in mice studies. The independent development of the individual semicircular canals in relation to the cochlea and vestibule and the variability in hearing loss suggest a more complex embryologic process than merely an arrest in development as previously thought. As genetic studies are extended into humans, we will likely be able to stratify these patients by molecular defect and severity of hearing loss.

Adolescent↗

PubMed1986

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.

Action Potentials↗

PubMed1997

Transection and occlusion of lateral semicircular canal in guinea pigs.

Audiologic and histopathologic examinations were made after occlusion of the lateral semicircular canal in eight guinea pigs. The lateral semicircular canal was drilled out, and then the canal lumens were plugged with muscle pieces. After a serial recording of auditory brain stem responses for 2 months, histologic specimens of the temporal bones were prepared in the lateral semicircular canal plane. One animal developed profound hearing loss due to suppurative labyrinthitis. The other seven animals showed no significant threshold elevation during this period. Histopathologic examination revealed that the bone defect on the lateral canal was replaced with newly formed bone; the perilymphatic and endolymphatic spaces maintained their compartmentalization; and the membranous endolymphatic canal healed to form complete blind ducts. These findings suggest that proper management of the injured semicircular canal is important for maintenance of postoperative hearing.

Animals↗

PubMed1980

Vertical semicircular canal inputs to cat extraocular motoneurons.

Synaptic potentials were recorded in identified extraocular motoneurons in anesthetized cats, following stimulation of ampullary nerves of the anterior and posterior semicircular canals. Superior rectus motoneurons received disynaptic EPSPs and IPSPs following stimulation of the two ampullary nerves of the anterior and posterior semicircular canals, respectively. In the inferior rectus motoneurons, the effects of anterior and posterior semicircular canal stimulation were a mirror image of those on superior rectus motoneurons. Inferior oblique motoneurons developed disynaptic EPSPs and IPSPs following stimulation of the ampullary nerves of the contralateral anterior and ipsilateral posterior semicircular canals, respectively. In addition, some inferior oblique motoneurons displayed disynaptic IPSPs following stimulation of the contralateral ampullary nerve of the posterior semicircular canal. In the superior oblique (trochlear) motoneurons, disynaptic EPSPs and IPSPs were recorded after stimulation of the contralateral posterior and ipsilateral anterior semicircular canals, respectively. There was no significant connection between the ampullary nerves of the vertical semicircular canals and motoneurons innervating lateral and medial rectus muscles.

Animals↗

PubMed2000

Low-frequency otolith and semicircular canal interactions after canal inactivation.

During sustained constant velocity and low-frequency off-vertical axis rotations (OVAR), otolith signals contribute significantly to slow-phase eye velocity. The adaptive plasticity of these responses was investigated here after semicircular canal plugging. Inactivation of semicircular canals results in a highly compromised and deficient vestibulo-ocular reflex (VOR). Based on the VOR enhancement hypothesis, one could expect an adaptive increase of otolith-borne angular velocity signals due to combined otolith/canal inputs after inactivation of the semicircular canals. Contrary to expectations, however, the steady-state slow-phase velocity during constant velocity OVAR decreased in amplitude over time. A similar progressive decrease in VOR gain was also observed during low-frequency off-vertical axis oscillations. This response deterioration was present in animals with either lateral or vertical semicircular canals inactivated and was limited to the plane(s) of the plugged canals. The results are consistent with the idea that the low-frequency otolith signals do not simply enhance VOR responses. Rather, the nervous system appears to correlate vestibular sensory information from the otoliths and the semicircular canals to generate an integral response to head motion.

Animals↗

PubMed2004

Hair-cell versus afferent adaptation in the semicircular canals.

The time course and extent of adaptation in semicircular canal hair cells was compared to adaptation in primary afferent neurons for physiological stimuli in vivo to study the origins of the neural code transmitted to the brain. The oyster toadfish, Opsanus tau, was used as the experimental model. Afferent firing-rate adaptation followed a double-exponential time course in response to step cupula displacements. The dominant adaptation time constant varied considerably among afferent fibers and spanned six orders of magnitude for the population ( approximately 1 ms to >1,000 s). For sinusoidal stimuli (0.1-20 Hz), the rapidly adapting afferents exhibited a 90 degrees phase lead and frequency-dependent gain, whereas slowly adapting afferents exhibited a flat gain and no phase lead. Hair-cell voltage and current modulations were similar to the slowly adapting afferents and exhibited a relatively flat gain with very little phase lead over the physiological bandwidth and dynamic range tested. Semicircular canal microphonics also showed responses consistent with the slowly adapting subset of afferents and with hair cells. The relatively broad diversity of afferent adaptation time constants and frequency-dependent discharge modulations relative to hair-cell voltage implicate a subsequent site of adaptation that plays a major role in further shaping the temporal characteristics of semicircular canal afferent neural signals.

Adaptation, Physiological↗

PubMed1998

Three-dimensional eye movement analysis during caloric stimulation used to test vertical semicircular canal function.

HYPOTHESIS AND BACKGROUND: Quantitative caloric testing is considered to be one of the most sensitive parameters in the diagnosis of peripheral vestibular disorders. In the past, because of limitations in the methods, the evaluation of the caloric response was restricted to mainly lateral semicircular canal functions. In this study, the authors tried to extend caloric testing to the function of all semicircular canals by using three-dimensional (3-D) analysis techniques. METHODS: The authors studied in seven normal subjects 3-D eye movement responses to air caloric of the right ear with the subjects positioned in standard caloric position (lateral semicircular canal vertical) or such that one of the three semicircular canals of the right side was horizontal. Movement of the left eye was measured in 3-D with a dual-magnetic search coil. During stimulation, 10 seconds of maximum response were selected and desaccaded to yield the slow-phase velocity profile. From this profile, the average magnitude and direction of the eye rotation axis (velocity vector) were calculated in head coordinates. RESULTS: In all subjects, in standard caloric position, warm caloric produced eye velocity vectors that clustered closely along the direction expected from an excitation of the right lateral semicircular canal. When the subjects were positioned with one of the vertical semicircular canals horizontal, the orientation of the velocity vectors shifted toward a direction expected from the combined excitation of the lateral and the other vertical semicircular canal and vice versa. CONCLUSIONS: The 3-D eye movement recordings during caloric stimulation in different head positions allow the evaluation of the function of all semicircular canals.

Adult↗

PubMed1988

The influence of temporary blockage of semicircular canals on the loss and recovery of vestibuloocular reflexes.

The efficacy of the technique of semicircular canal plugging in selectively blocking the function of individual semicircular canals was evaluated in rabbits. The horizontal and vertical vestibuloocular reflexes (HVOR, VVOR) and the horizontal optokinetic reflex (HOKR) were measured before the horizontal or anterior semicircular canals (HSCs, ASCs) were plugged bilaterally with small spindles of silver wire. These reflexes were also measured after the plugs were removed. The gain of the HVOR was reduced to less than 0.05 at all frequencies tested after plugs were inserted into the HSCs. The gain of the HOKR was not influenced by the plugging operation. These data were interpreted to mean that the plugs blocked the normal fluid dynamics of the HSCs, but did not alter the spontaneous activity of HSC afferents. The gain of the VVOR was not reduced by plugs of the HSCs. The gain of the VVOR was reduced by plugs of the ASCs. The residual VVOR was attributed to stimulation of the utricular otoliths at lower frequencies and stimulation of the posterior semicircular canals at higher frequencies. The gain of the HVOR was reduced 10-40% by plugs of the ASCs. These data, in conjunction with the presence of a small residual gain of the HVOR following bilateral plugs of the HSCs, suggest that the ASCs contribute to the HVOR. The gains of the HVOR and VVOR recovered to within 88% of the preplug values once the plugs of the HSCs or ASCs were removed. However, the protracted time course of this recovery, 10-15 d, indicated that the plugging operation, although reversible, does cause some temporary damage to the peripheral labyrinth.

Animals↗

PubMedDate not supplied

[The structure and function of the semicircular canals].

This review discusses present-day concepts concerning the structure and function of semicircular canals of the vestibular apparatus. It is indicated that the data available today about the function of semicircular canals suggest that they should be considered as a system with distributed parameters and that particular attention should be given not only to canal-canal interaction but also to canal-otolith interaction. A special section is allowed for the discussion of an agreement between mathematical description of the behavior of semicircular canals and experimental data. This work is of theoretical and practical importance and can help clarify the potential role of semicircular canals in the development of space motion sickness.

Humans↗

PubMed2006

Operative management of a posterior semicircular canal dehiscence.

OBJECTIVE: The objective of this study was to describe the operative management of posterior canal dehiscence. METHODS: A transmastoid approach to and plugging of the posterior canal was performed for posterior semicircular canal dehiscence (PSCD). RESULTS: Postoperatively, the patient exhibited improvement in conductive hearing loss and vestibular symptoms. CONCLUSIONS: PSCD can cause symptoms identical to that of superior semicircular canal dehiscence. Successful PSCD plugging can be performed without visualization of the actual area of dehiscence.

Adult↗

PubMed1989

Responses of pigeon horizontal semicircular canal afferent fibers. I. Step, trapezoid, and low-frequency sinusoid mechanical and rotational stimulation.

1. The horizontal semicircular canals of anesthetized (barbiturate/ketamine) pigeons were stimulated by rotational and by mechanical stimulation. 2. The mechanical stimulation consisted of making a small (less than 1 mm) fistula in the lateral part of the bony horizontal semicircular canal and, after inserting a probe coupled to a piezoelectric micropusher through the fistula, providing controlled indentation of the exposed membranous horizontal semicircular duct. 3. Extracellular action potentials from single horizontal semicircular canal primary afferent (HCA) fibers were recorded during sinusoidal rotational and during step, ramp, and sinusoidal mechanical stimulation. 4. The mean spontaneous discharge rate of 160 horizontal canal afferents was 86 +/- 4 (SE) spikes/s. This rate was not significantly different from that reported previously for pigeon HCA fibers recorded with the horizontal canal intact (i.e., no fistula introduced). 5. Sinusoidal mechanical indentation of the horizontal semicircular duct produced clearly entrained action potentials on 36 HCA fibers for a range of peak displacements from +/- 0.5 to +/- 30 microns. Action potentials were never modulated on afferents (n greater than 100) identified as innervating the anterior and posterior semicircular canals or the otolith organs during mechanical stimulation of the horizontal semicircular canal, even for displacements as large as 30 microns. 6. Intensity functions relating peak firing frequency (spikes per second) and peak probe displacement (micrometers) for 1.0-Hz sinusoidal mechanical stimulation were linear over the range 1.0-5.0 microns. The most sensitive units (6/36, 17%) showed response saturation as the stimulus magnitude was extended to 7 microns and beyond. 7. In 15 of 36 units, both mechanical and rotational sinusoidal stimulation (1.0 Hz) were applied to the same unit. The duct indentation magnitudes were 1.0, 2.5, 5.0, and 7.0 microns and the rotational velocities were 5, 10, and 20 deg/s. The constant of proportionality found to equate the peak response produced by rotational to that elicited by mechanical stimulation was 7.0 deg.sec-1/1.0 microns. 8. Bode plots and best-fit transfer functions of the frequency response (0.05-10.0 Hz) of 14 HCAs exposed to both mechanical and rotational stimulation were nearly identical. 9. Parameters for best-fit transfer functions, responses to step, and trapezoidal duct displacements were in excellent agreement with previous rotational studies carried out using the pigeon. 10. Although the mechanisms by which focal identation of the horizontal membranous duct produce responses have not yet been determined, primary afferent responses using this method of stimulation are directly comparable with rotatory stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

Impulsive testing of individual semicircular canal function.

In order to test the human angular vestibulo-ocular reflex in the dynamic range of normal head movements, we measured 3-dimensional compensatory eye-movement responses to low-amplitude (10-12 degrees), high-acceleration (3000-4000 degrees/s/s), passive, manually delivered head rotations (head "impulses") in the three planes of the semicircular canals in normal subjects, in subjects who had recovered from surgical unilateral vestibular deafferentation, and in patients after acute unilateral peripheral vestibulopathy, that is, from vestibular "neuritis." We found that canal-plane head impulses away from an intact semicircular canal, that is, toward a lesioned semicircular canal, invariably produce a vestibulo-ocular reflex with permanently low gain, typically less that 0.4 if the lesion is complete. These results are a necessary consequence of primary semicircular canal afferents being driven into inhibitory saturation by rapid angular accelerations. With practice, clinicians can learn to recognize the telltale compensatory saccades that patients with unilateral loss of semicircular canal function will make if asked to look at an earth-fixed target during head impulses in any one of the three semicircular canal planes.

Head Movements↗

PubMedDate not supplied

The EMG development of the longissimus and multifidus muscles after plugging the horizontal semicircular canals.

The effects of plugging both horizontal semicircular canals at the 5th postnatal day (P5) on the development of the EMG of two back muscles (the M. longissimus lateralis and the M. multifidus) were studied in rats between P5 and P46. The EMG was related to locomotion, grooming, and rearing of these rats. Special attention was paid to locomotor behavior. After this vestibular deprivation, the development of a consistent temporal relation between burst activity in the EMG of both Mm. longissimii laterales and the swing phase of one hind paw was retarded by about 3 days. The development of coupling of maximal activity in the M. longissimus lateralis to the swing phase of one of the hind paws was even more retarded. No differences were observed between normal and vestibularly deprived rats during the development of activity in the Mm. multifidi. Our results indicate that information from the horizontal semicircular canals is essential for dynamic postural development and probably, therefore, for motor development in general. Furthermore, lack of such information has effects on the fine tuning of back muscle activity during locomotion at least until P40.

Animals↗