Vestibular-evoked electromyographic responses in soleus: a comparison between click and galvanic stimulation

The aim of this study was to demonstrate, if possible, vestibulospinal reflex responses in soleus using a stimulus known to be capable of exciting vestibular afferents, namely 100-dB (NHL) clicks. We were able to show short-latency electromyographic (EMG) responses after clicks in five of eight normal subjects, and then we compared these responses with those after transmastoid galvanic stimulation (12 normal subjects). Stimulation of the side towards which the head was rotated (i.e. the side facing backwards) with either clicks or the cathode (anode applied to the opposite side) gave an initial excitatory response in soleus, while click or cathodal stimulation of the opposite side (i.e. the side facing forwards) gave an initial inhibitory response. Onset latencies and modulation with changes in postural task were identical for both click- and galvanic-evoked responses. In addition, there was a significant correlation between the amplitudes of the responses in soleus after click and galvanic stimulation (R2=0.72). These similarities suggest that the earliest reflex responses in soleus after clicks and galvanic stimulation may be mediated by a common central pathway. In contrast, there was no correlation between the amplitudes of responses evoked by 100-dB clicks in soleus and those evoked by the same stimulus in the sternocleidomastoid. We conclude that vestibular activation by clicks can evoke reflex responses in lower-limb muscles and these responses have similar characteristics to the earliest responses evoked by galvanic vestibular stimulation.     

The adequate stimulus for avian short latency vestibular responses to linear translation

Transient linear acceleration stimuli have been shown to elicit eighth nerve vestibular compound action potentials in birds and mammals. The present study was undertaken to better define the nature of the adequate stimulus for neurons generating the response in the chicken (Gallus domesticus). In particular, the study evaluated the question of whether the neurons studied are most sensitive to the maximum level of linear acceleration achieved or to the rate of change in acceleration (da/dt, or jerk). To do this, vestibular response thresholds were measured as a function of stimulus onset slope. Traditional computer signal averaging was used to record responses to pulsed linear acceleration stimuli. Stimulus onset slope was systematically varied. Acceleration thresholds decreased with increasing stimulus onset slope (decreasing stimulus rise time). When stimuli were expressed in units of jerk (g/ms), thresholds were virtually constant for all stimulus rise times. Moreover, stimuli having identical jerk magnitudes but widely varying peak acceleration levels produced virtually identical responses. Vestibular response thresholds, latencies and amplitudes appear to be determined strictly by stimulus jerk magnitudes. Stimulus attributes such as peak acceleration or rise time alone do not provide sufficient information to predict response parameter quantities. Indeed, the major response parameters were shown to be virtually independent of peak acceleration levels or rise time when these stimulus features were isolated and considered separately. It is concluded that the neurons generating short latency vestibular evoked potentials do so as "jerk encoders" in the chicken. Primary afferents classified as "irregular", and which traditionally fall into the broad category of "dynamic" or "phasic" neurons, would seem to be the most likely candidates for the neural generators of short latency vestibular compound action potentials.     

Disruption of the Saccharomyces cerevisiae YAP3 gene reduces the proteolytic degradation of secreted recombinant human albumin

In real-life situations, such as during locomotion, or while driving a vehicle, it is necessary to maintain visual fixation and tracking in the presence of the visual flow of the surroundings, which represents a potentially adequate stimulus for the elicitation of optokinetic nystagmus. The present study is concerned with the influence of vestibular disorders, whether pathological or experimentally induced, on those cortically controlled fixation mechanisms, predominantly in the smooth pursuit system, which are involved in suppressing optokinetic information. The study examines the possibility of obtaining an objective measure to assist in counselling patients with unilateral vestibular loss on their vehicle driving ability. To this end, the influence of optokinetic and vestibular stimulation on the execution of smooth pursuit target tracking was measured by recording eye movements during a combination of standard pursuit tasks (0.25, 0.5 and 1 Hz sinusoidal) against standard optokinetic striped backgrounds (0, 30 and 60 degrees/sec). The influence of vestibular imbalance, induced in healthy subjects (n = 35) by unilateral caloric irrigation, and caused by unilateral vestibular loss (in five patients), was also examined under these conditions. During induced vestibular imbalance in normal subjects, and to a greater extent in the tested patients, significant deficits in smooth pursuit gain and increases in saccade frequency were observed during target pursuit against an optokinetic background. Moreover, the findings indicate that the most sensitive parameter for the influence of vestibular optokinetic stimuli on smooth pursuit is frequency of saccades, rather than the gain factor. The tests described here are appropriate for clinical and medico-legal assessment of the influence of vestibular disorder on vehicle driving.     

Uncrossed disynaptic inhibition of second-order vestibular neurons and its interaction with monosynaptic excitation from vestibular nerve afferent fibers in the frog

1. Eighth nerve evoked responses in central vestibular neurons (n = 146) were studied in the isolated brain stem of frogs. Ninety percent of these neurons responded with a monosynaptic excitatory postsynaptic potential (EPSP) after electrical stimulation of the ipsilateral VIIIth nerve. In 5% of these neurons, the EPSP was truncated by a disynaptic inhibitory postsynaptic potential (IPSP), and in 5% of these neurons a pure disynaptic IPSP was evoked. 2. Disynaptic IPSPs superimposed upon apparently pure EPSPs were revealed by bath application of the glycine receptor antagonist strychnine (0.5-5 microM) or of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline (0.5-2 microM). The evoked EPSP increased in most central vestibular neurons (strychnine: 15 out of 16 neurons; bicuculline 26 out of 29 neurons). At higher stimulus intensities, the evoked spike discharge increased from 2 to 3 spikes before up to 8-10 spikes per electrical pulse during the application of blocking agents. The unmasked disynaptic inhibitory component increased with stimulus intensity to a different extent in different neurons. 3. Lesion studies demonstrated that these inhibitory components were generated ipsilaterally with respect to the recording side. The disynaptic strychnine-sensitive inhibition was mediated by neurons located either in the ventral vestibular nuclear complex (VNC) or in the adjacent reticular formation. The spatial distribution of the disynaptic inhibition was investigated by simultaneous recordings of VIIIth nerve-evoked field potentials at different rostrocaudal locations of the VNC. A significant strychnine-sensitive component was detected in the middle and caudal parts but not in the rostral part of the VNC. A bicuculline-sensitive component was detected in the rostral and in the caudal parts but not in the middle part of the VNC. In view of a similar rostrocaudal distribution of glycineor GABA-immunoreactive neurons in the VNC of frogs, our results suggest that part of the disynaptic inhibition is mediated by local interneurons with a spatially restricted projection area. 4. The monosynaptic EPSP of second-order vestibular neurons was mediated in part by N-methyl-D-aspartate (NMDA) and in part by non-NMDA receptors. The relative contribution of the NMDA receptor-mediated component of the EPSP decreased with stronger stimuli. This negative correlation could have resulted from a preferential activation of NMDA receptors via thick vestibular nerve afferent fibers. Alternatively, the activation of NMDA receptors became disfacilitated at higher stimulus intensities due to the recruitment of disynaptic inhibitory inputs. Comparison of data obtained in the presence and in the absence of these glycine and GABAA receptor blockers indicates a preferential activation of NMDA receptors via larger-diameter vestibular nerve afferent fibers. 5. The kinetics of NMDA receptors (delay, rise time) activated by afferent nerve inputs were relatively fast. These fast kinetics were independent of superimposed IPSPs. The association of these receptors with large-diameter vestibular nerve afferent fibers suggests that fast NMDA receptor kinetics might be matched to the more phasic response dynamics of the large diameter vestibular afferent neurons to natural head accelerations.     

A ''neural'' response with 3-ms latency evoked by loud sound in profoundly deaf patients

A large negative deflection with a latency of 3 ms was observed in the auditory brainstem response (ABR) waveforms of some patients with peripheral profound deafness. This deflection was termed the N3 potential. In this paper, we review patients with the N3 potential and discuss the characteristics of abnormal ABR waveforms. The origin of the N3 potential was also discussed, especially with respect to vestibular evoked potentials. In most of the patients, audiograms showed no response to the maximum output of an audiometer in the high-frequency range and a residual response in the low-frequency range. The N3 potentials were noted at intensities of 80 dB nHL or greater. As the stimulus intensity increased, the amplitude of the potential increased and the latency decreased. A high repetition rate (83.3/s) of the click stimulus influenced the latency and amplitude of the N3 potential. The potential was replicated on retest within less than a month, and had a consistent latency and amplitude over the scalp. The results indicate that the N3 potential is not an electrical artifact but a physiological neural response evoked by a loud sound. The N3 potential is most likely not an auditory evoked response from cochlear or a response from a semicircular canal, because it has a 3-ms latency, a sharp waveform, and is unassociated with vertigo. The results suggest that the N3 potential may be a saccular acoustic response.     

Characterization of vestibular potentials evoked by linear acceleration pulses in the chinchilla

The objective of this study was to improve vestibular evoked potentials as a qualitative parameter for vestibular function in small laboratory animals. Linear upward acceleration pulses (up to 8 g within 1 ms) were applied to the head of anesthetized chinchillas. Electrophysiologic responses recorded by a chronically implanted electrode within the facial nerve canal consisted of an initial negative potential, labeled N1, within the first millisecond following the onset of acceleration. This potential was followed by a series of positive and negative potentials found to be highly labile to acoustic masking. The initial negative potential was only minimally sensitive to acoustic masking and persisted following surgical cochlear ablation, but completely disappeared following administration of potassium chloride into the inner ear. Recorded from the contralateral ear, N1 was unaffected by these procedures. Amplitudes of N1 decreased with attenuating stimulus intensity (1.45 microV/dB), whereby N1 latencies slightly increased (-0.015 ms/dB). These data, when coupled with the ability to completely abolish N1 with potassium intoxication while the contralateral ear remained intact, indicate that this potential represents electrophysiologic activity resulting from activation of the ipsilateral vestibular labyrinth.     

Use of multivariate analysis in medical chemistry]

If the repeated presentation of a single (standard) auditory stimulus is randomly interspersed with a second acoustically different (deviant) stimulus, the cortical activity evoked by the deviant stimulus can contain a negative component known as the mismatch negativity (MMN). The MMN is derived by subtracting the averaged response evoked by the standard stimulus from that evoked by the deviant stimulus. When the magnitude of the response is small or the signal-to-noise ratio is poor, it is difficult to judge the presence or absence of the MMN simply by visual inspection, and statistical detection techniques become necessary. A method of analysis is proposed to quantify the magnitude and statistically evaluate the presence of the MMN based on time-integrated evoked responses. This paper demonstrates the use of this integrated mismatch negativity (MMNi) analysis to detect the MMN evoked by stimulus contrasts near the perceptual threshold of two subjects. The MMNi, by virtue of being equivalent to a low-pass filtered response, presents an almost noise-free estimate of MMN magnitude. A single measure of the integrated evoked response at a fixed time point is used in a distribution-free statistic that compares the magnitude of the averaged response evoked by the deviant stimulus with a magnitude distribution derived from 200 subaveraged responses to the standard stimulus (with the number of sweeps per average equal to that of the deviant stimulus). This allows a calculation of the exact probability for the null hypothesis that the negative magnitude of the response evoked by the deviant stimulus is drawn from the magnitude distribution of responses evoked by the standard stimulus. Rejection of this hypothesis provides objective evidence of the presence of the MMN.     

Functional outcome of vestibular rehabilitation in patients with abnormal sensory-organization testing

A goal of vestibular rehabilitation is to improve the functional status of patients with balance disorders. Despite the focus of vestibular rehabilitation on function, few objective data describe the outcome of vestibular rehabilitation in terms of balance function. In this prospective observational study, we tested a well-defined patient cohort (n = 67) with abnormal pretreatment sensory-organization testing who were undergoing vestibular rehabilitation. Patient outcomes were determined by using objective and subjective measures of function before and after rehabilitation. Overall, 60% of patients showed objective improvement of balance function; 25% of patients improved to normal. Analysis of success and failure of vestibular rehabilitation is important as an aid to appropriate patient counseling and efficient use of rehabilitation resources.     

COAE thresholds: 1. Effects of equal-amplitude versus subtraction methods

Although research has demonstrated that click-evoked otoacoustic emissions (COAEs) elicited by high-level stimuli are useful for identifying hearing loss, the ability of COAEs to predict behavioral thresholds has not been adequately tested. Results of studies comparing COAE thresholds and behavioral thresholds have been equivocal, perhaps due to the need for a more rigorous approach to COAE threshold estimation. The present study was designed to address several methodological concerns in COAE threshold testing, particularly the effects of two methods of stimulus presentation on COAE testing and threshold calculation. In an attempt to make COAE threshold estimation consistent across participants, COAE threshold calculations were based on mean noise floor levels across participants. COAE and noise floor levels were measured in 15 participants using both equal-amplitude clicks and a subtraction method. Broadband COAEs were analyzed into 1/3 octave bands, so that input/output functions could be examined and COAE thresholds could be calculated for each 1/3 octave band. Comparison of the two stimulus methods indicated several differences. Mean noise floor levels for the equal-amplitude method were approximately 6 dB lower than those measured for the subtraction method across frequency. In many cases COAEs evoked using the equal-amplitude method were higher in amplitude than those evoked using the subtraction method. COAE thresholds measured using the equal-amplitude click stimuli were significantly lower than those measured using the subtraction method. The significantly higher thresholds obtained using the subtraction method may be attributed in part to the reduction of COAE amplitude by the subtraction procedure, and not merely to the higher noise level. Slopes of the input/output functions were not significantly different between the two stimulus methods. These results suggest that the equal-amplitude method is preferable for COAE threshold testing because lower noise floor and larger amplitude COAEs may be obtained in the same test time.     

Activity and excitability to electrical current of cortical auditory receptive neurons of awake cats as affected by stimulus association

1. Unit activity and excitability were studied at the midlateral and suprasylvian cortex of naive, blink-conditioned and "randomization" cats. The latter received the same CS and US as did the conditioned animals, but in random temporal order and with random intertrial intervals with mean comparable to that used for conditioning. The randomization group failed to develop a blink CR. 2. With conditioning, spontaneous and evoked unit discharges were increased above levels found in naive animals. Correspondingly, levels of extracellularly injected current required to elicit a spike discharge were lower in conditioned than in naive animals. In addition, in the conditioned animals, the degree of enhancement of evoked activity and excitability was found to be greatest in the units that responded to the CS, as opposed to units that responded to another auditory stimulus of equal intensity but of no special behavioral significance vis-a-vis the conditioned reflex. 3...     

Reduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates. II. Comparison of fixed amplitude with amplitude modulated stimuli

We have previously shown that acute electrical stimulation of the auditory nerve using charge-balanced biphasic current pulses presented continuously can lead to a prolonged decrement in auditory nerve excitability (Tykocinski et al., Hear. Res. 88 (1995), 124-142). This work also demonstrated a reduction in electrically evoked auditory brainstem response (EABR) amplitude decrement when using an otherwise equivalent pulse train with a 50% duty cycle. In the present study we have extended this work in order to compare the effects of electrical stimulation using both fixed amplitude electrical pulse trains and amplitude modulated (AM) pulse trains that more accurately model the dynamic stimulus paradigms used in cochlear implants. EABRs were recorded from guinea pigs following acute stimulation using AM trains of charge-balanced biphasic current pulses. The extent of stimulus-induced reductions in the EABR were compared with our previous results using either fixed amplitude continuous, or 50% duty cycle pulse trains operating at 0.34 microC/phase (2 mA, 170 micros/phase) at 400 or 1000 pulses/s (Tykocinski et al., Hear. Res. 88 (1995) 124-142). The AM pulse train, operating at the same rates, was based on a 1-s sequence of the most extensively activated electrode of a Nucleus Mini-22 cochlear implant using the SPEAK speech processing strategy exposed to 4-talker babble, and delivered the same total charge as the fixed amplitude 50% duty cycle pulse train. Two hours of continuous stimulation induced a significant, rate-dependent reduction in auditory nerve excitability, and showed only a slight post-stimulus recovery for monitoring periods of up to 6 hours. Following 2 or 4 h of stimulation using an otherwise equivalent pulse train with a 50% duty cycle or the AM pulse train, significantly less reduction in the EABR was observed, and recovery to pre-stimulus levels was generally rapid and complete. These differences in the extent of the recovery between the continuous waveform and both the 50% duty cycle and AM waveforms were statistically significant for both 400 and 1000 pulses/s stimuli. Consistent with our previous results, the stimulus changes observed using AM pulse trains were rate dependent, with higher rate stimuli evoking more extensive stimulus-induced changes. The present findings show that while stimulus-induced reductions in neural excitability are dependent on the extent of stimulus-induced neuronal activity, the use of an AM stimulus paradigm further reduces post-stimulus neural fatigue.     

Reversible malabsorption of folic acid in the elderly with nutritional folate deficiency

The question of the point of impact of the electric current in the galvanic vestibular test is not solved. An important feature is that, after destruction of both the vestibular end organs, a galvanic nystagmus can still be provoked. The effect of a direct current on the spontaneous nystagmus following partial or total destruction of the vestibular end organs was investigated. The frequency of the spontaneous nystagmus diminishes when the electric stimulus causes an eye movement in the same direction as the fast phase of the nystagmus, the frequency increases when the polarity of the electric stimulation is reversed. Simultaneous application of torsion-swing and electric stimulation causes a summation of the separate effects. Our findings confirm the conculsions drawn by Ledoux (4, 5) from his findings in frogs.     

Melatonin. Physiology, pathophysiology and possible therapeutic approaches

Patients presenting with the major brain arteries (MBA) pathologies were examined by a novel diagnostic tool relying on prolonged latent evoked potentials in response to rotating stimulation (EPR), which allowed an objective quantitative assessment to be performed of central vestibular dysfunction. This approach in the form of a computer programme permitted the testing of patients presenting with MBA pathologies during the preclinical stage of the condition, prior to carrying out such complicated surgical studies as angiography. The EPS method is simple, cost-effective, and convenient in screening examinations, enabling the brain vascular pathology to be detected during the stage of early functional disorders.     

fMRI study of face perception and memory using random stimulus sequences

A new functional magnetic resonance imaging (fMRI) method was used to investigate the functional neuroanatomy of face perception and memory. Whole-brain fMRI data were acquired while four types of stimuli were presented sequentially in an unpredictable pseudorandom order at a rate of 0.5 Hz. Stimulus types were a single repeated memorized target face, unrepeated novel faces, nonsense scrambled faces, and a blank screen. Random stimulus sequences were designed to generate a functional response to each stimulus type that was uncorrelated with responses to other stimuli. This allowed fMRI responses to each stimulus type to be examined separately using multiple regression. Signal increases were found for all stimuli in ventral posterior cortex. Responses to intact faces extended to more anterior locations of occipitotemporal cortex than did responses to scrambled faces, consistent with previous studies of face perception. Responses evoked by novel faces were in regions of ventral occipitotemporal cortex medial to regions in which significant responses were evoked by the target face. The repeated target face stimulus also evoked activity in widely distributed regions of frontal and parietal cortex. These results demonstrate that cortical hemodynamic responses to interleaved novel and repeated stimuli can be distinguished and measured using fMRI with appropriate stimulus sequences and data analysis methods. This method can now be used to examine the neural systems involved in cognitive tasks that were previously impossible to study using positron emission tomography or fMRI.     

Variations in learning reflect individual differences in sensory function and synaptic integration

With the invertebrate Hermissenda as subjects, variability in acquisition of a learned association between light and rotation was correlated with the magnitude of the unconditioned responses elicited by these stimuli. Moreover, learning was facilitated by increasing stimulus intensity. In the isolated nervous system, pairings of light and mechanical stimulation of the animal's vestibular hair cells resulted in an increase in the excitability of B photoreceptors (an in vitro index of learning) that was strongly correlated with the strength of the synaptic interaction between the hair cells and the photoreceptors and weakly correlated with the magnitude of the light response in the photoreceptors. Because these in vitro results are not attributable to motor or motivational variables, they suggest that the efficacy of synaptic integration between sensory systems and sensory transduction is the primary determinant of the variability in learning.     

Intravenous gentamicin therapy in bilateral Menière disease

BACKGROUND: The treatment of severe forms of bilateral Menière's disease remains an especially challenging task. Similar problems also occur in debilitating Menière's disease in the only hearing ear. The intramuscular titration therapy with streptomycin has been the means of choice since 1984 to minimize the risk of total hearing loss in cases of severe bilateral disease. METHOD: Since 1989 we have treated six out of 21 cases of bilateral Menière's disease by intravenous application of 2 x 120 mg gentamicin in Ringer's solution for several days. Additionally we reported on two cases in 1988. Only minor amounts of gentamicin were applied to sedate the function of both vestibular organs while avoiding damage to the cochlea. RESULTS: In two cases hearing approved approximately about 10 dB, in two cases hearing remained stable, and in two cases hearing worsened about 10 dB. Five of six patients showed minor excitability in caloric tests on both sides, they did not complain of vertigo attacks one to five years after therapy. CONCLUSION: Given that only very small amounts of gentamicin are applied to sedate the function of the vestibular organ while causing almost no damage to the cochlea, this method seems to be an excellent means for treatment of bilateral Menière's disease. Patients do not experience severe problems with equilibrium afterwards, and the treatment can be repeated as often as necessary.     

Spinal mechanisms underlying persistent pain and referred hyperalgesia in rats with an experimental ureteric stone

Spinal neurons processing information from the ureter have been characterized in rats 1-4 days after the implantation of an experimental ureteric stone and compared with those of normal rats. The effects of a conditioning noxious stimulation of the ureter in the presence of the hyperalgesia evoked by the calculosis also were examined. Extracellular recordings were performed at the T12-L1 segments of the spinal cord. In rats with calculosis, more neurons expressed a ureter input (53 vs. 42% in normal rats); such cells being more likely to show background activity, at a higher rate than normals (6.6 +/- 1.2 vs. 3.2 +/- 0.9 spikes/s; mean +/- SE) and increasing with the continuing presence of the stone. The threshold pressure for a ureteric response was higher than in normal rats (79 +/- 5 vs. 54 +/- 4 mmHg) but the neurons failed to encode increasing intensities of stimulation. Thirty-five percent of the neurons with exclusively innocuous somatic receptive fields had a ureter input in rats with calculosis, whereas none were seen in normal rats. A noxious ureteric distention applied to neurons with ureter input evoked a complex mixture of increases and decreases in somatic receptive field size and/or somatic input properties markedly different from the generalized increases in excitability seen when such a stimulus was applied to normal animals. We conclude that the presence of a ureteric stone evokes excitability changes of spinal neurons (enhanced background activity, greater number of ureter-driven cells, decreased threshold of convergent somatic receptive fields), which likely account for the referred hyperalgesia seen in rats with calculosis. However, further noxious visceral input occurring in the presence of persistent hyperalgesia produces selective changes that cannot be explained by a generalized excitability increase and suggest that the mechanisms underlying maintenance of hyperalgesia include alteration of both central inhibitory and excitatory systems.     

Perceptual load alters visual excitability.

Increasing perceptual load reduces the processing of visual stimuli outside the focus of attention, but the mechanism underlying these effects remains unclear. Here we tested an account attributing the effects of perceptual load to modulations of visual cortex excitability. In contrast to stimulus competition accounts, which propose that load should affect simultaneous, but not sequential, stimulus presentations, the visual excitability account makes the novel prediction that load should affect detection sensitivity for both simultaneous and sequential presentations. Participants fixated a stimulus stream, responding to targets defined by either a color (low load) or color and orientation conjunctions (high load). Additionally, detection sensitivity was measured for a peripheral critical stimulus (CS) presented occasionally. Increasing load at fixation reduced sensitivity to the peripheral CSs; this effect was similar regardless of whether CSs were presented simultaneously with central stimuli or during the (otherwise empty) interval between them. Controls ruled out explanations of the results in terms of strategic task prioritization. These findings support a cortical excitability account for perceptual load, challenging stimulus competition accounts. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Experimental study of vestibular neurectomy

The authors describe an experimental study carried out on baboons. After unilateral vestibular neurectomy, the behaviour disorders on the one hand, and on the other, modifications and temporal development of reflex muotatic excitability of the spine using Hoffmann's reflex method are analyzed. As far as behaviour is concerned, a four-day period of motor restriction following the operation causes more marked residual disorders in comparison with controls. From the neurophysiological point of view, neurectomy results in seriously disordered spinal reflexes characterized by ipsilateral hypo-excitability developing in there stages: a tw-day initial critical phase during which the disorders are at their worst, a four-day recuperative stage with partial regression of the disorders, finally a chronic compensation stage in which spinal excitability returns to normal after several months.     

Eye movements evoked by proprioceptive stimulation along the body axis in humans

Proprioceptive input arising from torsional body movements elicits small reflexive eye movements. The functional relevance of these eye movements is still unknown so far. We evaluated their slow components as a function of stimulus frequency and velocity. The horizontal eye movements of seven adult subjects were recorded using an infrared device, while horizontal rotations were applied at three segmental levels of the body [i.e., between head and shoulders (neck stimulus), shoulders and pelvis (trunk stimulus), and pelvis and feet (leg stimulus)]. The following results were obtained: (1) Sinusoidal leg stimulation evoked an eye response with the slow component in the direction of the movement of the feet, while the response to trunk and neck stimulation was oriented in the opposite direction (i.e., in that of the head). (2) In contrast, the gain behavior of all three responses was similar, with very low gain at mid- to high frequencies (tested up to 0.4 Hz) but increasing gain at low frequencies (down to 0.0125 Hz). We show that this gain behavior is mainly due to a gain nonlinearity for low angular velocities. (3) The responses were compatible with linear summation when an interaction series was tested in which the leg stimulus was combined with a vestibular stimulus. (4) There was good correspondence of the median gain curves when eye responses were compared with psychophysical responses (perceived body rotation in space; additionally recorded in the interaction series). However, correlation of gain values on a single-trial basis was poor. (5) During transient neck stimulation (smoothed position ramp), the neck response noticeably consisted of two components -- an initial head-directed eye shift (phasic component) followed by a shift in the opposite direction (compensatory tonic component). Both leg and neck responses can be described by one simple, dynamic model. In the model the proprioceptive input is fed into the gaze network via two pathways which differ in their dynamics and directional sign. The model simulates either leg or neck responses by selecting an appropriate weight for the gain of one of the pathways (phasic component). The interaction results can also be simulated when a vestibular path is added. This model has similarities to one we recently proposed for human self-motion perception and postural control. A major difference, though, is that the proprioceptive input to the gaze-stabilizing network is weak (restricted to low velocities), unlike that used for perception and postural control. We hold that the former undergoes involution during ontogenesis, as subjects depend on the functionally more appropriate vestibulo-ocular reflex. Yet, the weak proprioceptive eye responses that remain may have some functional relevance. Their tonic component tends to stabilize the eyes by slowly shifting them toward the primary head position relative to the body support. This applies solely to the earth-horizontal plane in which the vestibular signal has no static sensitivity.