"Velocity leakage" in the pigeon vestibulo-ocular reflex

The transfer characteristics of the vestibulo-ocular reflex (VOR), and of the semicircular canal primary afferents (SCPAs) that drive it, have been studied in several species. In monkeys and cats, the dominant time constant describing horizontal VOR dynamics (tau hv) is longer than that (tau c) of horizontal SCPAs. This lengthening of the time constant has been attributed to a "velocity storage" mechanism that has been modeled as a positive feedback loop in the VOR pathways. We have studied the transfer characteristics of horizontal and vertical VOR and SCPAs in unanesthetized pigeons. In this species the dominant time constants of both the horizontal and vertical VOR (tau hv and tau vv) are shorter that tau c. This finding indicates that time constants characterizing the lower frequency response of the VOR can be lengthened or shortened depending on the species. We propose that in the pigeon the "velocity leakage" mechanism can be modeled by substituting negative feedback for positive feedback in the model of the VOR pathways. Negative feedback can also account for the further shortening of tau hv and tau vv as VOR gain increases with arousal. Additionally, making the negative feedback loop nonlinear can model the dependency of lower frequency VOR phase on amplitude, and skew in VOR waveforms. Pigeon VOR and SCPA dynamics also differ in their adaptive properties and higher frequency behavior. A predominance of input from highly adaptive SCPAs is proposed to account for the increased adaptation of the vertical VOR as compared with SCPAs overall. A pure time-delay associated with VOR operation can explain the phase lag of the VOR relative to SCPAs at higher frequencies.     

Recent advances in the pharmacology of the vestibulo-ocular reflex system

Recent advances in the pharmacology of the vestibulo-ocular reflex have had a major impact on our understanding of the vestibular system, the sensory system primarily concerned with the stabilization of gaze and posture during head movement. Increasing evidence suggests that afferent transmission from the receptor hair cells in the vestibular labyrinth to the vestibular nerve probably involves glutamate acting on a number of excitatory amino acid receptor subtypes. Furthermore, hair-cell sensitivity appears to be regulated by cholinergic, GABA-mediated and, possibly, peptide-mediated efferent feedback from the CNS. Likewise, it seems clear that an excitatory amino acid, probably glutamate, is the major transmitter used by the vestibular nerve in its synapses with neurones of the brainstem vestibular nucleus. In this review, Paul Smith and Cynthia Darlington discuss the large number of receptor subtypes that have been identified in the vestibular nucleus, including receptors for several peptides that may have a role in co-transmission.     

Optokinetic-vestibular interaction in patients with increased gain of the vestibulo-ocular reflex

We studied optokinetic nystagmus (OKN), optokinetic afternystagmus (OKAN) and visual-vestibular interaction in five patients with markedly elevated vestibulo-ocular reflex (VOR) gain due to cerebellar atrophy. All had impaired smooth pursuit, decreased initial slow phase velocity of OKN, and impaired ability to suppress the VOR with real or imagined targets. OKN slow phase velocity gradually built up over 25-45 s, reaching normal values for low stimulus velocities (< or = 30 deg/s). Initial velocity of OKAN was increased, but the rate of decay of OKAN was normal. These findings can be explained by models that include separate velocity storage and variable gain elements shared by the vestibular and optokinetic systems.     

Gaze stabilization by optokinetic reflex (OKR) and vestibulo-ocular reflex (VOR) during active head rotation in man

Vestibulo-ocular reflex (VOR)-optokinetic reflex (OKR) interaction was studied in normal human subjects during active sine-like head movements in the horizontal plane for a variety of vestibular-optokinetic stimulus combinations (frequency range, 0.05-1.6 Hz). At low to mid frequencies (< 0.2 Hz) the eyes tended to be stabilized on the optokinetic pattern, independently of whether the head, the pattern, or both were rotated. At higher frequencies, the OKR gain was attenuated and, in each of the differing stimulus combinations, the eyes became increasingly stabilized in space. Qualitatively similar results were obtained when, for the same visual-vestibular combinations, the head was passively rotated at 0.05 and 0.8 Hz. The data could be simulated by a model which assumes a linear interaction of vestibular and optokinetic signals. It considers the OKR with its negative feedback loop of primordial importance for image stabilization on the retina and the VOR only as a useful addition which compensates for the limited bandwidth of the OKR during high frequency/velocity head rotations in a stationary visual environment.     

Dual adaptation and adaptive generalization of the human vestibulo-ocular reflex

In two experiments, we examined the possibility that the human vestibulo-ocular reflex (VOR) is subject to dual adaptation (the ability to adapt to a sensory rearrangement more rapidly and/or more completely after repeated experience with it) and adaptive generalization (the ability to adapt more readily to a novel sensory rearrangement as a result of prior dual adaptation training). In Experiment 1, the subjects actively turned the head during alternating exposure to a visual-vestibular rearrangement (target/head gain = 0.5) and the normal situation (target/head gain = 0.0). These conditions produced both adaptation and dual adaptation of the VOR but no evidence of adaptive generalization when tested with a target/head gain of 1.0. Experiment 2, in which exposure to the 0.5 gain entailed externally controlled (i.e., passive) whole body rotation, resulted in VOR adaptation but no dual adaptation. As in Experiment 1, no evidence of adaptive generalization was found.     

Dynamics and kinematics of the angular vestibulo-ocular reflex in monkey: effects of canal plugging

Dynamics and kinematics of the angular vestibulo-ocular reflex in monkey: effects of canal plugging. J. Neurophysiol. 80: 3077-3099, 1998. Horizontal and roll components of the angular vestibulo-ocular reflex (aVOR) were elicited by sinusoidal rotation at frequencies from 0.2 Hz (60 degrees/s) to 4.0 Hz ( approximately 6 degrees/s) in cynomolgus monkeys. Animals had both lateral canals plugged (VC, vertical canals intact), both lateral canals and one pair of the vertical canals plugged (RALP, right anterior and left posterior canals intact; LARP, left anterior and right posterior canal intact), or all six semicircular canal plugged (NC, no canals). In normal animals, horizontal and roll eye velocity was in phase with head velocity and peak horizontal and roll gains were approximately 0.8 and 0.6 in upright and 90 degrees pitch, respectively. NC animals had small aVOR gains at 0.2 Hz, and the temporal phases were shifted approximately 90 degrees toward acceleration. As the frequency increased to 4 Hz, aVOR temporal gains and phases tended to normalize. Findings were similar for the LARP, RALP, and VC animals when they were rotated in the planes of the plugged canals. That is, they tended to normalize at higher frequencies. A model was developed incorporating the geometric organization of the canals and first order canal-endolymph dynamics. Canal plugging was modeled as an alteration in the low frequency 3-db roll-off and corresponding dominant time constant. The shift in the low-frequency 3-dB roll-off was seen in the temporal responses as a phase lead of the aVOR toward acceleration at higher frequencies. The phase shifted toward stimulus velocity as the frequency increased toward 4.0 Hz. By incorporating a dynamic model of the canals into the three-dimensional canal system, the spatial responses were predicted at all frequencies. Animals were also stimulated with steps of velocity in planes parallel to the plugged lateral canals. This induced a response with a short time constant and low peak velocity in each monkey. Gains were normalized for step rotation with respect to time constant as (steady state eye velocity)/(stimulus acceleration x time constant). Using this procedure, the gains were the same in canal plugged as in normal animals and corresponded to gains obtained in the frequency analysis. The study suggests that canal plugging does not block the afferent response to rotation, it merely shifts the dynamic response to higher frequencies.     

Maculo-ocular reflex and visual perception during vertical acceleration

BACKGROUND: We investigated the effect of vertical acceleration upon the otolithic-ocular reflex of 22 healthy people. The study was performed to obtain standard values for subsequent investigations at patients. METHODS: People sitting on a chair were accelerated in the vertical axis with an amplitude of 4 cm and the frequencies of 0.5 Hz, 1 Hz, 1.5 Hz, 2 Hz, 2.5 Hz and 2.7 Hz. The movements of the ocular globe were initially recorded during vertical acceleration with the eyes closed. Then visual acuity was tested during linear acceleration with the eyes open. As parameters of evaluation we used coherence and alteration of the visual acuity. RESULTS: When the frequency was increased while the eyes were closed, coherence increased and the number of people with vertical eye movements increased. Amplitude was observed to increase and a phase shift occurred. A significant value of coherence (> 0.8) was observed at a frequency above 2.5 Hz. During the test of visual acuity, coherence also increased but did not reach quantity we observed initially. A significant loss of visual acuity occurred at a frequency above 2.5 Hz. A phase shift was also observed. The reason for the loss of visual acuity was the increment of amplitude and the phase shift, which had a negative influence on fixation. CONCLUSIONS: In summary, reactions with closed eyes are best tested at frequencies of 2.5 and 2.7 Hz. We recommended frequencies of 1.5 and 2 Hz for testing visual acuity.     

Effects of anxiety arousal and mental stress on the vestibulo-ocular reflex

Although the subjective reports of patients suggest that anxiety may aggravate vertigo and imbalance, there has been little research into how anxiety might directly affect balance system functioning. We conducted two studies to examine the effect of anxiety and arousal on the vestibulo-ocular reflex (VOR). In the first study, pre-lest fear ratings were obtained from 20 normal subjects and 36 anxious subjects immediately prior to rotation and caloric testing. Fear ratings were significantly correlated with the maximum slow-phase velocity (SPV) of nystagmus induced by caloric testing. In the second study, we assessed the VOR response to rotation of 36 normal subjects under 3 task conditions: a) minimal alerting (counting backwards during rotation), b) physical arousal (induced by exertion prior to rotation); c) mental arousal (induced by performance of stressful mental tasks during rotation). Both the physical and mental tasks induced a significant increase in heart rate compared with the alerting condition. The maximum SPV of the nystagmus induced by rotation was significantly greater during performance of the mental task than in the other two conditions. These combined results indicate that anxiety may influence the gain of the VOR.     

Role of the flocculus of the cerebellum in motor learning of the vestibulo-ocular reflex

Inhalation of metal dust or fume can cause granulomatous lung disease that mimics sarcoidosis. Particular metals that possess antigenic properties which promote granuloma formation include aluminum, barium, beryllium, cobalt, copper, gold, rare earths (lanthanides), titanium, and zirconium. The occupational and environmental exposure history holds the key to linking such metals with seemingly idiopathic disease. We propose clinicians use a systematic approach to investigating the occupational and environmental history and immunologic responses of patients with sarcoidosis, in order to discriminate metal-induced granulomatosis from sarcoidosis.     

Afferent signals from the extraocular muscles of the pigeon modify the vestibulo-ocular reflex

Although the extraocular muscles (EOM) contain stretch receptors it is generally thought that the afferent signals which they provide play no role in the control of eye movement. We have previously shown that these afferent signals do modify both the vestibular responses of single units in the oculomotor control system and the electromyographic responses of the EOM during the vestibulo-ocular reflex (VOR). We have now investigated the effect of EOM afferent signals on the VOR itself, by recording the electro-oculogram of one eye while imposing movements on the other eye during the VOR. Moving the eye in a manner which mimics the slow phase of the VOR, we have found that, as the peak velocity of the imposed eye movement increases, the amplitude of eye movement of the other eye decreases. These results confirm that the output of the VOR itself, expressed as movement of the globe, and not merely some of its component parts, is modified by EOM afferent signals.     

Analysis and neural network modeling of the nonlinear correlates of habituation in the vestibulo-ocular reflex

Through the process of habituation, continued exposure to low-frequency (0.01 Hz) rotation in the dark produced suppression of the low-frequency response of the vestibulo-ocular reflex (VOR) in goldfish. The response did not decay gradually, as might be expected from an error-driven learning process, but displayed several nonlinear and nonstationary features. They included asymmetrical response suppression, magnitude-dependent suppression for lower- but not higher-magnitude head rotations, and abrupt-onset suppressions suggestive of a switching mechanism. Microinjection of lidocaine into the vestibulocerebellum of habituated goldfish resulted in a temporary dishabituation. This suggests that the vestibulocerebellum mediates habituation, presumably through Purkinje cell inhibition of vestibular nuclei neurons. The habituated VOR data were simulated with a feed-forward, nonlinear neural network model of the VOR in which only Purkinje cell inhibition of vestibular nuclei neurons was varied. The model suggests that Purkinje cell inhibition may switch in to introduce nonstationarities, and cause asymmetry and magnitude-dependency in the VOR to emerge from the essential nonlinearity of vestibular nuclei neurons.     

Identification of the location of vestibular lesions on the basis of vestibulo-ocular reflex measurements

Quantitative analysis of electro-oculographic recordings of eye movement in response to precise visual and vestibular stimuli makes possible the differentiation of three categories of vestibular syndromes due to pathological changes in three different parts of the visual vestibulo-ocular reflex arc: (1) decreased vestibulo-ocular reflex gain (e.g., decrease in slow component velocity), but normal fast components and visual-vestibular interaction (labyrinth and eighth nerve); (2) normal slow component velocity but abnormal fast components to all stimuli (pontine or medullar reticular formation); and (3) normal slow component velocity to vestibulo-ocular stimulaton but abnormal visual-vestibular interaction as well as normal fast components (visual-motor pathways or cerebellum).     

Passive sustained turning of the head induces asymmetric gain of the vestibulo-ocular reflex in healthy subjects

In order to test the hypothesis of an interaction between neck proprioception and the vestibulo-ocular reflex (VOR), we rotated 16 healthy subjects both facing forward and with their heads passively turned 70 degrees to either side. We found that gain tended to be lower when the subjects were rotated with their heads turned opposite to the direction of rotation compared to when they were rotated in the same direction, but facing forward. Although our findings were not statistically significant, they suggest that there is a measurable interaction between neck proprioception and the VOR in subjects with normal vestibular function. Asymmetric neck muscle proprioceptive signals seem to give rise to asymmetric functioning of the VOR, which, at least in part, could be the pathogenesis of cervical dizziness. If so, this could lead to misinterpretation of vestibular assessments in patients with neck pain who also complain of dizziness.     

Development of intuitive theories of motion: Curvilinear motion in the absence of external forces.

96 4.5–12 yr olds and 20 college students were asked to draw the path a ball would take when exiting a curved tube. As in previous studies, many Ss erroneously predicted curvilinear paths. However, a clear U-shaped curve was evident in the data. Preschoolers and kindergartners performed as well as college students, whereas school-aged Ss were more likely to make erroneous predictions. Results of a 2nd study, with 24 preschoolers (mean age 5 yrs 2 mo), suggest that the youngest children's correct responses could not be attributed to response biases or drawing abilities. This developmental trend suggests that the school-aged children are developing intuitive theories of motion that include erroneous principles. Results are related to the "growth errors" found in other cognitive domains and to the historical development of formal theories of motion. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High acceleration impulsive rotations reveal severe long-term deficits of the horizontal vestibulo-ocular reflex in the guinea pig

While there is agreement that unilateral vestibular deafferentation (UVD) invariably produces an immediate severe horizontal vestibulo-ocular reflex (HVOR) deficit, there is disagreement about whether or not this deficit recovers and, if so, whether it recovers fully or only partly. We suspected that this disagreement might mainly be due to experimental factors, such as the species studied, the means chosen to carry out the UVD, or the nature of the test stimulus used. Our aim was to sort out some of these factors. To do this, we studied the HVOR of alert guinea pigs in response to low and high acceleration sinusoidal and high acceleration impulses after UVD by either labyrinthectomy or by vestibular neurectomy. The HVOR in response to high acceleration impulsive yaw rotations was measured before, and at various times after, either unilateral labyrinthectomy or superior vestibular neurectomy. Following UVD, there was a severe impairment of the HVOR for ipsilesional rotations and a slight impairment for contralesional rotations, after either operation. This asymmetrical HVOR deficit in the guinea pig parallels the deficit observed in humans. Between the first measurement, which was made 1 week after UVD, and the last, which was made 3 months after UVD, there was no change in the HVOR. This lack of recovery was the same after labyrinthectomy as after vestibular neurectomy. The HVOR to low and high acceleration sinusoidal yaw rotations were measured after UVD, and the results were compared with those in response to impulsive rotations. For low acceleration sinusoidal rotations (250 degrees/s2), the gain was symmetrical, although reduced bilaterally. As the peak head acceleration increased, the HVOR became increasingly asymmetric. The HVOR asymmetry for sinusoidal rotations was significantly less than for impulsive rotations that had the same high peak head acceleration (2500 degrees/s2). Our results show that the HVOR deficit after UVD is the same in guinea pigs as in humans; that it is the same after vestibular neurectomy as after labyrinthectomy; that it is lasting and severe in response to high acceleration rotations; and, that it is more obvious in response to impulses than to sinusoids.     

Human horizontal vestibulo-ocular reflex initiation: effects of acceleration, target distance, and unilateral deafferentation

The vestibulo-ocular reflex (VOR) generates compensatory eye movements in response to angular and linear acceleration sensed by semicircular canals and otoliths respectively. Gaze stabilization demands that responses to linear acceleration be adjusted for viewing distance. This study in humans determined the transient dynamics of VOR initiation during angular and linear acceleration, modification of the VOR by viewing distance, and the effect of unilateral deafferentation. Combinations of unpredictable transient angular and linear head rotation were created by whole body yaw rotation about eccentric axes: 10 cm anterior to eyes, centered between eyes, centered between otoliths, and 20 cm posterior to eyes. Subjects viewed a target 500, 30, or 15 cm away that was extinguished immediately before rotation. There were four stimulus intensities up to a maximum peak acceleration of 2,800 degrees/s2. The normal initial VOR response began 7-10 ms after onset of head rotation. Response gain (eye velocity/head velocity) for near as compared with distant targets was increased as early as 1-11 ms after onset of eye movement; this initial effect was independent of linear acceleration. An otolith mediated effect modified VOR gain depending on both linear acceleration and target distance beginning 25-90 ms after onset of head rotation. For rotational axes anterior to the otoliths, VOR gain for the nearest target was initially higher but later became less than that for the far target. There was no gain correction for the physical separation between the eyes and otoliths. With lower acceleration, there was a nonlinear reduction in the early gain increase with close targets although later otolith-mediated effects were not affected. In subjects with unilateral vestibular deafferentation, the initial VOR was quantitatively normal for rotation toward the intact side. When rotating toward the deafferented side, VOR gain remained less than half of normal for at least the initial 55 ms when head acceleration was highest and was not modulated by target distance. After this initial high acceleration period, gain increased to a degree depending on target distance and axis eccentricity. This behavior suggests that the commissural VOR pathways are not modulated by target distance. These results suggest that the VOR is initially driven by short latency ipsilateral target distance dependent and bilateral target-distance independent canal pathways. After 25 ms, otolith inputs contribute to the target distance dependent pathway. The otolith input later grows to eventually dominate the target distance mediated effect. When otolith input is unavailable the target distance mediated canal component persists. Modulation of canal mediated responses by target distance is a nonlinear effect, most evident for high head accelerations.     

Early visual function in bobwhite and Japanese quail embryos as reflected by pupillary reflex.

Investigated function within the visual system of 72 bobwhite and 60 Japanese quail embryos (Colinus virginianus and Coturnix coturnix) by the pupillary light reflex technique. The reflex was first reliably elicited on Day 151/2 (60% of total incubation) in Colinus and on Day 111/2 (72% of total incubation) in Coturnix. Temporal onset of visual function, as reflected by this measure, corresponded closely to that found in Peking duck embryos but was 15-18% earlier than in domestic chicks. In assessing the possible significance of early visual function, it was found that light intensities reaching the Ss in ovo were sufficient to elicit pupillary reflexes by Day 161/2 in Colinus and Day 13 in Coturnix. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dose-dependent effect of betahistine on the vestibulo-ocular reflex: a double-blind, placebo controlled study in patients with paroxysmal vertigo

Behavioral adaptations exhibited by two African fossorial mammals for the reception of vibrational signals are discussed. The Namib Desert golden mole (Eremitalpa granti namibensis) is a functionally blind, nocturnal insectivore in the family Chrysochloridae that surface forages nightly in the Namib desert. Both geophone and microphone recordings in the substrate suggest that the golden mole is able to detect termite colonies and other prey items solely using seismic cues. This animal exhibits a hypertrophied malleus, an adaptation favoring detection of low-frequency signals. In a field study of the Cape mole-rat (Georychus capensis), a subterranean rodent in the family Bathyergidae, both seismic and auditory signals were tested for their propagation characteristics. This solitary animal is entirely fossorial and apparently communicates with its conspecifics by drumming its hind legs on the burrow floor. Auditory signals attenuate rapidly in the substrate, whereas vibratory signals generated in one burrow are easily detectable in neighboring burrows. The sensitivity to substrate vibrations in two orders of burrowing mammals suggests that this sense is likely to be widespread within this taxon and may serve as a neuroethological model for understanding the evolution of vibrational communication. Neuroethological implications of these findings are discussed.     

Dynamics of conditioned reflex reorganization in the human visual system

The dymamics of absolute and relative changes in the brightness thresholds of letters recognition was studied in 21 subjects, under conditions of dark adaptation and molecular observation, before and after pairing of one of the letters with electrocutaneous stimulation of the index finger during one session. Isolated electrocutaneous stimulation was applied on the 10th or 35th day after the session. It has been found that after pairings the relative threshold of recognition of the letter previously paired with electrical stimuli (i.e. the threshold in relation to recognition thresholds for the other letters) becomes for three to three and a half hours significantly lower than the initial one. Then there sharply sets in a phase of threshold elevation. Both in the case of double and multiple tests, this phase persists for not less than 35 days. Following an isolated electrical stimulation, a momentary significant lowering of the threshold sets in only for the letter which was paired with it in the first sessions.