Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEMICIRCULAR CANALS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55Linked to original sources
PubMed2002

The Dlx5 homeobox gene is essential for vestibular morphogenesis in the mouse embryo through a BMP4-mediated pathway.

In the mouse embryo, Dlx5 is expressed in the otic placode and vesicle, and later in the semicircular canals of the inner ear. In mice homozygous for a null Dlx5/LacZ allele, a severe dysmorphogenesis of the vestibular region is observed, characterized by the absence of semicircular canals and the shortening of the endolymphatic duct. Minor defects are observed in the cochlea, although Dlx5 is not expressed in this region. Cristae formation is severely impaired; however, sensory epithelial cells, recognized by calretinin immunostaining, are present in the vestibular epithelium of Dlx5(-/-) mice. The maculae of utricle and saccule are present but cells appear sparse and misplaced. The abnormal morphogenesis of the semicircular canals is accompanied by an altered distribution of proliferating and apoptotic cells. In the Dlx5(-/-) embryos, no changes in expression of Nkx5.1(Hmx3), Pax2, and Lfng have been seen, while expression of bone morphogenetic protein-4 (Bmp4) was drastically reduced. Notably, BMP4 has been shown to play a fundamental role in vestibular morphogenesis of the chick embryo. We propose that development of the semicircular canals and the vestibular inner ear requires the independent control of several homeobox genes, which appear to exert their function via tight regulation of BPM4 expression and the regional organization of cell differentiation, proliferation, and apoptosis.

Alleles↗
PubMed1999

Canal and otolith afferent activity underlying eye velocity responses to pitching while rotating.

Pitching the head while rotating (PWR) combines periodic activation of the semicircular canals and the otoliths to generate pitch and roll eye deviations and continuous horizontal nystagmus. Monkeys were tested after individual pairs of semicircular canals were plugged and single units were recorded in the vestibular nerve while the animals were sinusoidally pitched 20-40 deg about a spatial horizontal axis with 5- and 16-s periods and simultaneously rotated about a spatial vertical axis at 30-120 deg/s. As previously shown, the steady-state horizontal response disappeared after plugging the vertical semicircular canals, but was maintained when the lateral canals were plugged. When the left anterior and right posterior canal (LARP) pair was left intact, the steady-state response depended on the axis about which the pitching took place. When the axis was normal to the LARP plane, there was no steady-state response. When the pitching axis was perpendicular to the LARP normal, the response was maximal. Firing rates of otolith units were approximately in phase with pitch position, and the addition of rotation about a vertical axis did not change the response. Lateral canal units did not have a steady-state modulation during pitch or constant velocity rotation. During PWR, they oscillated at twice the pitch frequency. This corresponded to the frequency at which the canal was maximally activated as it aligned with the plane of rotation. The amplitude of modulation increased proportionally to rotational velocity, but the phase remained the same. These characteristics were unchanged during roll while rotating (RWR), which induces little continuous nystagmus. Anterior and posterior canal units were maximally excited near pitch-velocity maxima and minima, respectively, during pure pitching. During PWR, however, the phases of both components simultaneously shifted toward each other and toward being in phase with otolith units. The peak excitation tended toward a forward-pitch position when the rotation was to the ipsilateral side, and toward a backward pitch position when the rotation was to the contralateral side. With 120-deg/s rotation during a 16-s pitch period, the phase difference between anterior and posterior canal units was as small as 17 deg. These data support the postulate that the correlation between vertical canal and otolith units is the critical factor in generating continuous unidirectional horizontal nystagmus during PWR.

Animals↗
PubMed1988

Correlation of high-resolution computed tomography and gross anatomic sections of the temporal bone: II. Vestibular apparatus.

High-resolution computed tomography (CT) of isolated temporal bones was performed in the transaxial, coronal, and sagittal planes at 1.5-mm intervals. The temporal bones were then sectioned at 2.0-mm intervals in planes parallel to the CT scans. The structures making up the vestibular apparatus were identified, and the planes in which each is best visualized were selected for the illustrations. The vestibule, oval window, tympanic cavity, and tympanic portion of the facial nerve are best seen in the transaxial and coronal planes; the arch of the superior semicircular canal in the transaxial plane and its limbs in the coronal plane; the arch of the posterior semicircular canal in the coronal and sagittal planes and its limbs in the transaxial plane; and the common crus in the sagittal plane. The horseshoe-shaped lateral semicircular canal is displayed in the transaxial plane, and the relationship of its lateral limb to the tympanic segment of the facial nerve is best demonstrated in the sagittal plane. The ampullae of all three canals can be appreciated equally well in all three planes.

Humans↗
PubMed2006

Bone conducted vibration selectively activates irregular primary otolithic vestibular neurons in the guinea pig.

The main objective of this study was to determine whether bone-conducted vibration (BCV) is equally effective in activating both semicircular canal and otolith afferents in the guinea pig or whether there is preferential activation of one of these classes of vestibular afferents. To answer this question a large number (346) of single primary vestibular neurons were recorded extracellularly in anesthetized guinea pigs and were identified by their location in the vestibular nerve and classed as regular or irregular on the basis of the variability of their spontaneous discharge. If a neuron responded to angular acceleration it was classed as a semicircular canal neuron, if it responded to maintained roll or pitch tilts it was classified as an otolith neuron. Each neuron was then tested by BCV stimuli-either clicks, continuous pure tones (200-1,500 Hz) or short tone bursts (500 Hz lasting 7 ms)-delivered by a B-71 clinical bone-conduction oscillator cemented to the guinea pig's skull. All stimulus intensities were referred to that animal's own auditory brainstem response (ABR) threshold to BCV clicks, and the maximum intensity used was within the animal's physiological range and was usually around 70 dB above BCV threshold. In addition two sensitive single axis linear accelerometers cemented to the skull gave absolute values of the stimulus acceleration in the rostro-caudal direction. The criterion for a neuron being classed as activated was an audible, stimulus-locked increase in firing rate (a 10% change was easily detectable) in response to the BCV stimulus. At the stimulus levels used in this study, semicircular canal neurons, both regular and irregular, were insensitive to BCV stimuli and very few responded: only nine of 189 semicircular canal neurons tested (4.7%) showed a detectable increase in firing in response to BCV stimuli up to the maximum 2 V peak-to-peak level we delivered to the B-71 oscillator (which produced a peak-to-peak skull acceleration of around 6-8 g and was usually around 60-70 dB above the animal's own ABR threshold for BCV clicks). Regular otolithic afferents likewise had a poor response; only 14 of 99 tested (14.1%) showed any increase in firing rate up to the maximum BCV stimulus level. However, most irregular otolithic afferents (82.8%) showed a clear increase in firing rate in response to BCV stimuli: of the 58 irregular otolith neurons tested, 48 were activated, with some being activated at very low intensities (only about 10 dB above the animal's ABR threshold to BCV clicks). Most of the activated otolith afferents were in the superior division of the vestibular nerve and were probably utricular afferents. That was confirmed by evidence using juxtacellular injection of neurobiotin near BCV activated neurons to trace their site of origin to the utricular macula. We conclude there is a very clear preference for irregular otolith afferents to be activated selectively by BCV stimuli at low stimulus levels and that BCV stimuli activate some utricular irregular afferent neurons. The BCV generates compressional and shear waves, which travel through the skull and constitute head accelerations, which are sufficient to stimulate the most sensitive otolithic receptor cells.

Acoustic Stimulation↗
PubMed2006

[Landmark of facial nerve in middle ear surgery].

OBJECTIVE: To re-evaluate landmarks for facial nerve in middle ear surgery through temporal bone dissection and facial nerve surgery. METHODS: Some relative landmarks were found through 44 facial nerves dissection in cadaver and 106 cases of facial nerve decompression surgery. RESULTS: (1) Landmarks for vertical segment of the facial nerve: the vertical line in combined point between posterior and middle 1/3 horizontal semicircular canal clews the posterior edge of facial nerve; the prolong line of superior radian of incus short process clues to the anterior edge of the facial nerve, the facial nerve and horizontal semicircular canal are almost in the same plane. (2) Landmarks for horizontal segment of the facial nerve: the facial nerve tracks forward inferior to short process of incus and anterior to horizontal semicircular canal carina in 30 angel. The facial nerve, locating posterior and superior to cochleariform process and parallel with it, forms the step of middle-superior tympanic cavity and tracks forward to geniculate ganglion. (3) location of geniculate ganglion: The same distance prolong line of stapes head to cochleariform process clues to geniculate ganglion. (4) Location of the chorda tympani nerve: chorda tympani nerve, leaving tympanic sulcus at 3 clock of bone canaline left ear and at 9 clock of bone canaline right ear, tracks forward along tympani sulcus and then cross between long process of incus and manubrium. It lies in the border of pars tensa and pars flaccid and is about 5 - 8 mm from the stylomastoid foramen to where the chorda tympani nerve leaves the facial nerve. There is no difference of facial nerve structure in temporal bone dissection and in surgery. CONCLUSIONS: The fixed landmarks of middle ear are the frame of reference of facial nerve, in which horizontal semicircular canal is most invariable; and the safety of surgery will be improved by the reference of the facial nerve.

Ear, Middle↗
PubMed2002

Vibration-induced shift of the subjective visual horizontal: a sign of unilateral vestibular deficit.

BACKGROUND: Vibration to the head or neck excites vestibular and neck muscle spindle afferents. Can such vibrations improve the sensitivity of the subjective visual horizontal (SVH) test to chronic unilateral deficit of the vestibular system? DESIGN: Controlled experimental study. SETTING: Tertiary referral center. PATIENTS AND CONTROLS: Thirteen healthy subjects and 23 patients with chronic unilateral vestibular deficits after vestibular neurectomy or neurolabyrinthitis. Results of head-impulse test showed unilateral loss of function of all 3 semicircular canals in 14 patients and loss of anterior and lateral semicircular canals in 9 patients. INTERVENTION: Unilateral vibration (92 Hz; 0.6-mm amplitude) applied to sternocleidomastoid muscle (SCM) or mastoid bone. MAIN OUTCOME MEASURE: Results of SVH test (in degrees). RESULTS: Without vibration, 13 of 23 patients and all healthy subjects had SVH of less than 3 degrees (sensitivity, 43%; specificity, 100%). During vibration to the ipsilesional SCM, SVH increased to greater than 3 degrees in 21 of 23 patients but in only 1 of 13 healthy subjects (sensitivity, 91%; specificity, 92%). The patient group had significantly greater SVH shifts to the ipsilesional side than did healthy subjects in response to SCM and mastoid bone vibration on either side. The SVH shift during vibration to the ipsilesional SCM was significantly greater than that during vibration to the contralesional muscle (P<.001) or to the mastoid bone on either side (P<.05). The vibration-induced SVH shift was significantly greater in those patients with loss of 3 semicircular canals than in those with loss of 2 (P<.01). CONCLUSIONS: The sensitivity of the SVH test to chronic unilateral vestibular deficits can be improved by applying vibration to the SCM. The magnitude of vibratory SVH shift is related to the extent of unilateral deficit of the otolithic organs, vertical canals, or both.

Adult↗
PubMed1993

Interpretation of the combined galvanic test. Findings from cases with vestibular neuronitis.

The combined galvanic test (CGT) was developed in our department for simultaneous recording of galvanic eye movement test (GEMT) and galvanic body sway test (GBST). Twelve cases of vestibular neuronitis were studied first with the caloric test, and then with the CGT. The findings of the caloric test corresponded to those of the GEMT, but did not always correspond to those of the GBST. Thus we suggest that the GBST reflects an abnormality in a system different from that reflected by the caloric test and GEMT. It is likely that the caloric response mainly originates from the semicircular canal system. Thus the GEMT may reflect an abnormality in the semicircular canal system, while the GBST reflects an abnormality in the otolithic system. The CGT may thus be a feasible method of differentiating the disorders of the semicircular canal system from those of the otolithic system in the vestibular nervous system.

Adult↗
PubMed2001

Directional sensitivity of anterior, posterior, and horizontal canal vestibulo-ocular neurons in the cat.

Neurons subserving the vestibulo-ocular reflex transform the directionality and timing of input from semicircular canals into commands that are appropriate to rotate the eyes in a compensatory fashion. In order to assess the degree to which this transformation is evident in vestibular nucleus neurons of alert cats, we recorded the extracellular discharge properties of 138 second-order vestibular neurons in the superior and medial vestibular nucleus, including 64 neurons identified as second-order vestibulo-ocular neurons by antidromic responses to oculomotor nucleus stimulation and short-latency orthodromic responses to labyrinth stimulation (1.3 ms or less). Neuronal response gains and phases were recorded during 0.5-Hz sinusoidal oscillations about many different horizontal axes and during vertical axis rotations to define neuronal response directionality more precisely than in past studies. Neurons with spatial responses similar to anterior semicircular canal afferents were found to have more diverse maximal activation direction vectors than neurons with responses resembling those of posterior or horizontal canal afferents. The mean angle from neuron response vector to the axis of the nearest canal or canal pair was 19 degrees for anterior canal second-order neurons (n=28) and 20 degrees for anterior canal second-order vestibulo-ocular neurons (n=18), compared with 11 degrees for posterior canal second-order neurons (n=43) and 11 degrees for posterior canal second-order vestibulo-ocular neurons (n=25). Only two second-order vestibulo-ocular neurons (3%) showed a marked dependence of response phase on rotation direction, which is indicative of convergent inputs that differ in both dynamics and directionality. This suggests that spatiotemporal convergence is uncommon in the three-neuron vestibulo-ocular reflex arc of the cat. Neuron vectors included many that were closely aligned with canal axes and several that were better aligned with oblique or superior rectus extraocular muscle excitation axis vectors. Only single examples of second-order vestibulo-ocular neuron vectors were approximately aligned with the pitch and roll coordinate axes. We conclude that second-order vestibulo-ocular neurons do not exclusively represent either the semicircular canal sensory coordinate frame or the extraocular muscle excitation motor coordinate frame, and instead are mostly distributed on a continuum between the input and output coordinate frames, with anterior canal neurons having the widest distribution of directionality.

Action Potentials↗
PubMed2001

Canal-otolith interaction in the fastigial nucleus of the alert monkey.

To determine the contribution of the otoliths as well as the horizontal and vertical semicircular canals to the response of "vestibular only" neurons in the rostral fastigial nucleus of the alert monkey, we applied natural sinusoidal vestibular stimuli (0.6 Hz; +/-15 deg) around different axes. During the experiment the monkey sat erect in a primate chair with the head immobile. Semicircular canal responses were investigated during tilted yaw stimulation around an earth vertical axis. The tilt angle was varied by 30 deg and included the optimal plane for horizontal canal stimulation (15 deg nose down from the stereotactic plane). The otoliths and mainly the vertical canals made contributions during stimulation around an earth-fixed horizontal axis (vertical stimulation). Head orientation was also slowly altered (2-3 deg/s) over a range of 180 deg under both stimulus conditions (tilted yaw and vertical stimulation). Neuronal data for each paradigm were fitted by a least squares best-sine function. Computation of the hypothetical contributions made by all three pairs of semicircular canals and the otoliths to these responses showed that 74% of the 46 neurons investigated received an otolith input; in most instances it was combined with a canal input. Neurons most often received input from the horizontal and vertical canals as well as the otoliths. Only a minority of neurons received a purely otolith (13%), vertical canal (13%), or horizontal canal (4%) input. Conventional criteria (head position-related activity, spatiotemporal convergence, STC) failed to detect an otolith contribution in several such instances. Thus, canal-otolith convergence is the general rule at this central stage of vestibular information processing in the fastigial nucleus. The large variety of response types allows these neurons to participate in multiple tasks of vestibulospinal movement control.

Animals↗
PubMed1995

[Study on vomiting and the vestibulo-autonomic reflex].

When vestibular organs are abnormally stimulated, autonomic reactions such as nausea, vomiting, palpitation, etc., occur, indicating the existence of fiber connections from the vestibular organs to the autonomic centers. The relationship between the "vomiting center" in the medulla oblongata as described by Borison and Wang and the vestibular nucleus remains obscure. To investigate the central mechanism of vomiting caused by vestibular stimulation, the intragastric pressure, gastric peristalsis and respiration during electric stimulation of the medullary vomiting center and the semicircular canal nerve were recorded in 12 adult cats. Evoked potential was also recorded while electrically stimulating the semicircular canal nerve. When the peripheral labyrinth was stimulated, a conflicting result was founded, namely, that the pressure in the stomach increased or decreased. Retching or vomiting-like behavior was observed in several sites when the dorsolateral portion of the reticular formation of the medulla was stimulated. It was found that neural structures in the dorsolateral portion of the reticular formation of the medulla were associated with the semicircular canal nerve, but retching or vomiting-like behavior was not always observed during stimulation there.

Animals↗
PubMed2005

Quantitative study of the vestibular sensory epithelium in cochleosaccular dysplasia.

BACKGROUND: Cochleosaccular dysplasia is the most common pathologic finding seen in children with profound congenital sensorineural hearing loss. There has been no quantitative study on the peripheral vestibular system in cochleosaccular dysplasia. OBJECTIVE: To investigate quantitatively the extent of pathologic changes of the vestibular sensory epithelium in cochleosaccular dysplasia. SUBJECTS AND METHODS: Thirteen temporal bones with congenital deafness from 10 individuals were selected for this study from the temporal bone collection of University of Minnesota that showed suitable pathologic findings for the histopathologic criteria of cochleosaccular dysplasia. Age-matched normal control temporal bones were also selected. The vestibular hair cells including types I and II hair cells were counted separately in the saccular macula, utricular macula, and three cristae of the semicircular canals using Nomarski microscopy. RESULTS: The hair cell densities of types I and II hair cells in the macula of the saccule in cochleosaccular dysplasia were significantly decreased compared with the data of normal subjects. Both types I and II hair cells in the utricular macula and the cristae of the three semicircular canals in cochleosaccular dysplasia were well preserved, and no significant difference was observed between findings of cochleosaccular dysplasia and normal controls in the utricle and the three semicircular canals. CONCLUSIONS: In cases with cochleosaccular dysplasia, the neurosensorial hair cells of the saccule were affected; however, the osseous labyrinth, the membranous utricle, and the semicircular canals were normal. Further studies should be performed to establish the pathogenesis of cochleosaccular dysplasia in humans.

Adolescent↗
PubMed1978

[On the reaction of the sense cells in the cristae ampullares to experimental loads in guinea pigs (author's transl)].

The different experimental tests brought the explanation about the ampullae sensory epithelium. It was shown that the transmission of impulses by the peripheral sensory cells can lead to swelling as well as to shrinkage of their nuclei. The spicific stimulus for the semicircular canals is the angular acceleration as well as lateral pendular movement. We managed, however, to proove by single semicircular canal, also by linear acceleration a certain transmission of stimuli. The higher the movement frequency, the larger is the volume variations of the sensory nuclei. The cells of the upper and the lateral semicircular canals response to a lateral right-left-deviations with a considerable increase of their nuclear volume. Excluse of a left rotation the sensory cells of all ampullae of the right side react with an increase of their nuclear volume. On the contrary those of the left side react with a decrease of their nuclear volume. Only the upper ampulla respond to a forwards-backwards-movement, also to a vertical dropmovement with a slight swelling of their sensory nuclei. All ampullae of both petrous bones reactet to alternating right-left rotation with a shrinkage of their nuclei. Further more we succeded in recording certain structure and form variation in the claimed sensory cells. More experiments on the cells give rise to nuclear pyknosis. The cytoplasme of the cell body participates also in the process of recharging and decharging of the action potential.

Acceleration↗
PubMed1999

Paroxysmal positional vertigo syndrome.

INTRODUCTION: This study was initiated to investigate the differential diagnosis of patients with benign paroxysmal positional vertigo (BPPV) of different canals' origin. METHODS: The eye movements of 292 patients were evaluated with the use of Frenzel glasses and infrared video cameras after positional tests. Epley's canal repositioning procedure (CRP) was conducted, with appropriate modifications for individual cases, on every patient. RESULTS: Two different types of positional nystagmus were observed corresponding to the presence of otoliths in the lumen of each of the semicircular canals and on the cupola of the horizontal semicircular canal. The posterior canal was involved in 250 patients unilaterally and 23 patients bilaterally. The anterior canal variety was observed in four patients. In the horizontal canal, nine were of the cupulolithiasis and six of the canalithiasis variety. In seven patients. the affected canal converted to a different location. The canal repositioning procedure eliminated vertigo and abnormal eye movements in 88% of the unilateral posterior canal variety. The success rate of the procedure in the other varieties was 50%. CONCLUSION: Positional vertigo can have characteristics corresponding to the presence of otolith particles in each of the semicircular canals. The treatment requires different strategies to move the otoliths, depending on their location in the vestibule.

Aged↗
PubMed1991

Cyclic AMP modulates sensory-neural communication at the vestibular end organ.

Adenosine 3':5'-cyclic phosphate (cAMP) is a second messenger that plays an important role in mediating neuronal interactions in many systems. A possible role for cAMP in sensorineural communication at the vestibular end organ was studied. The putative roles for cAMP action investigated here were: the ability of cAMP to act as the second messenger for the efferent transmitter, acetylcholine, and the possible involvement of cAMP in modulating spontaneous or mechanically-evoked afferent nerve firing. Levels of cAMP were increased pharmacologically with forskolin, 3-isobutyl-1-methyl xanthine (IBMX) and dibutyryl cAMP. Changes in multiunit afferent nerve firing measured from the ampullar nerve of the semicircular canal, and the transepithelial potential measured across the neuroepithelium of the semicircular canal were recorded. At selected doses, all drugs produced a similar increase in spontaneous multiunit afferent nerve firing with a concomitant decrease in the transepithelial potential. Mechanically-evoked hair cell activity and the response to exogenously applied acetylcholine were unaffected by these drugs. We are suggesting that the excitatory aspects of the acetylcholine response are not mediated via a cAMP-dependent mechanism. However, cAMP does play an important role in modulating spontaneous afferent nerve firing in the semicircular canal. The finding that spontaneous afferent nerve firing can be biochemically modulated without altering mechanically-induced afferent firing is novel and deserves further investigation.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Mechanical properties of membranous labyrinths measured with a microtension tester.

Mechanical properties of the semicircular canals of guinea pigs, frogs and water fishes, and of human membranous labyrinths were tested. Tensile strength of the semicircular canals of guinea pig, frog and water fish was greater in the order of guinea pig, frog and fish. In the human membranous labyrinth, the saccular membrane was the weakest, followed by Reissner's membrane, the utricular membrane and the semicircular canal. These values were converted from tensile strength to breakage pressure. The breakage pressure of the saccular membrane was 64.0 mmHg.

Animals↗
PubMed1993

Current view of the mechanism of benign paroxysmal positioning vertigo: cupulolithiasis or canalolithiasis?

Theoretical evidence is presented that all the typical features of BPPV (benign paroxysmal positioning vertigo) cannot be explained by cupulolithiasis in that otoconial debris become settled on the cupula of the posterior semicircular canal. A free floating clot of inorganic particles (heavier than endolymph) in the ampullofugal branch of the posterior semicircular canal is more likely to cause the syndrome. The clot always gravitates to the most dependent part of the canal as soon as the patient's head is moved in a way that alters the angle between the canal's plane and the gravity vector. As compared to a plunger (depending on the direction it moves) the clot produces push or pull forces on the cupula, thereby eliciting the BPPV attack. This clot-induced endolymph flow mechanism is compatible with all features of BPPV such as latency, limited duration, fatigability, change in direction of the induced nystagmus, and the efficacy of physical therapy in both posterior and horizontal semicircular canal BPPV. The floating clot is only activated by changes in position of the head relative to the gravitational vector (positioning vertigo) but not by prolonged static positions of the head (positional vertigo), which fits clinical experience. Therefore, canalolithiasis rather than cupulolithiasis provides a better definition of the underlying mechanism in BPPV.

Endolymph↗
PubMed1991

Computed tomographic findings around the vestibular aqueduct in Menière's disease.

High resolution transverse axial CT encompassing the lateral semicircular canal was used to study the visualization of the vestibular aqueduct and to measure the minimum distance between the posterior semicircular canal and the posterior petrous surface (P-P distance) in Meniere's disease and chronic otitis media. The results indicate that the development of the bone between the posterior semicircular canal and the posterior petrous surface, which usually contains the endolymphatic sac, is significantly poorer in affected ears than in nonaffected ears in unilateral Meniere's disease, and much poorer than in chronic otitis media.

Female↗
PubMed2003

The response of vestibulo-ocular reflex pathways to electrical stimulation after canal plugging.

The vestibulo-ocular reflex (VOR) allows clear vision during head movements by generating compensatory eye movements. Its response to horizontal rotation is reduced after one horizontal semicircular canal is plugged, but recovers partially over time. The majority of VOR interneurons contribute to the shortest VOR pathway, the so-called three-neuron arc, which includes only two synapses in the brainstem. After a semicircular canal is plugged, transmission of signals by the three-neuron arc originating from the undamaged side may be altered during recovery. We measured the oculomotor response to single current pulses delivered to the vestibular labyrinth of alert cats between 9 h and 1 month after plugging the contralateral horizontal canal. The same response was also measured after motor learning induced by continuously-worn telescopes (optically induced motor learning). Optically induced learning did not change the peak velocity of the evoked eye movement (PEEV) significantly but, after a canal plug, the PEEV increased significantly, reaching a maximum during the first few post-plug days and then decreasing. VOR gain also showed transient changes during recovery. Because the PEEV occurred early in the eye movement evoked by a current pulse, we think the observed increase in PEEV represented changes in transmission by the three-neuron arc. Sham surgery did not result in significant changes in the response to electrical stimulation or in VOR gain. Our data suggest that different pathways and processes may underlie optically induced motor learning and recovery from plugging of the semicircular canals.

Animals↗