Biomedical subjects

H Collewijn

Publications and source records attributed to H Collewijn.

At least 19 recordsLinked to original sources

PubMed1997

Binocular saccadic eye movements in multiple sclerosis.

We attempted to increase the sensitivity for detection of abnormal binocular saccadic eye movements, particularly of the internuclear ophthalmoplegia (INO) type associated with multiple sclerosis (MS). Saccades of 10 and 20 degrees were binocularly recorded with scleral sensor coils in 10 normal control subjects and 26 patients with definite or probable MS, seven of whom had a clinically manifest INO in one or both directions. In the cases in which this was accompanied by a dissociated nystagmus of the abducting eye, our recordings showed that such secondary saccades were also expressed, in a strongly reduced form, by the adducting eye. The patients with manifest INO showed lower average peak velocities and peak accelerations, especially for adduction of the eye on the affected side, but the distribution of these parameters overlapped with the normal distribution. A much sharper distinction between normals and patients with INOs was found by considering the ratios between peak accelerations and velocities of saccade pairs (abducting eye/adducting eye). These ratios, which eliminate much intra- and inter-individual variability, had a narrow range in normals, and all values for INOs were outside this range. On this basis, the 19 patients without clinically manifest INO were easily separated into subgroups of 14 patients with completely normal interocular ratios and five patients with elevated peak velocity and acceleration ratios, identified as sub-clinical (uni- or bilateral) INOs. Measurements of vertical saccades and of interocular timing differences provided no useful criteria for disturbances of binocular coordination in MS. We conclude that in particular, the acceleration of the adducting eye is strongly reduced in patients with an INO, and that this reduction is best identified by interocular comparison between binocular pairs of saccades.

Adult↗

PubMed1997

Trajectories of the human binocular fixation point during conjugate and non-conjugate gaze-shifts.

This paper describes the spatial trajectories of the binocular fixation point (the intersection point of the two lines of sight) during gaze-shifts within a horizontal plane of regard. Gaze was voluntarily shifted between pairs of real, continuously visible LED targets that were either iso-vergent at 5-25 deg convergence (conjugate version saccades) or differed in vergence angle (by 5-20 deg) as well as in direction (by 5-60 deg; combined version and vergence). Orientations of both eyes were recorded by phase detection in a homogeneous magnetic field with scleral sensor coils. "Conjugate" saccades showed an outward-looping, curved trajectory as a result of transient divergence, typically associated with horizontal saccades. These outward loops were disproportionately larger for far than for near targets, due to the non-linear relation between vergence and distance. Transient divergence increased moderately in magnitude and duration when basic vergence increased from 5 to 25 deg. As a result, transient saccadic disparities increased in angular magnitude as targets got close. Increasing tonic vergence did not, however, slow down conjugate saccades, in contrast to the previously described dynamic slowing effects of vergence on version during gaze-shift involving simultaneous vergence and version changes. Convergent and divergent non-conjugate gaze-shifts each had characteristic trajectories; outward loops were much reduced in convergent and virtually absent in divergent movements. The saccadic component of non-conjugate gaze-shifts was preceded by a pre-saccadic vergence component in the direction of the imminent gaze-shift; its magnitude increased systematically with the increase in vergence demand and with the decrease in version demand. For both pre-saccadic convergence and divergence, this pre-saccadic part of the trajectory tended to follow an iso-direction line through the target of origin; directional change did not start until the saccade began. This suggests that for targets that differ in direction as well as distance, control of the vergence and version components of the gaze-shift can be dissociated to some degree. This seems to argue against models of binocular oculomotor control which assume that each eye responds primarily to its own target, and suggests rather that target vergence and target direction may be processed and responded to separately by ocular vergence and version, with a strong interaction between the two oculomotor activities whenever they occur at the same time.

Adult↗

PubMed1997

Gaze-shift dynamics in two kinds of sequential looking tasks.

Gaze-shift dynamics of unrestrained seated subjects were examined. The subjects participated in two tasks. In the first task, they tapped sequences of 3-D targets located on a table in front of them. In the second task, they only looked at similar sequences of targets. The purpose of the task (tapping vs only looking) affected the dynamics of gaze-shifts. Gaze and eye-in-head peak velocities were higher and gaze-shift durations were shorter during tapping than during looking-only. We conclude that task variables affect gaze-shift dynamics, altering characteristics of the so-called saccadic "main sequence".

Fixation, Ocular↗

PubMed1997

Gain and delay of human vestibulo-ocular reflexes to oscillation and steps of the head by a reactive torque helmet. I. Normal subjects.

Vestibulo-ocular reflexes (VOR) were evaluated with a reactive torque helmet that imposed high-frequency oscillation (2-20 Hz) or step displacements of the head in the horizontal plane. The present paper describes the experimental and analytical techniques and the results for normal subjects, which will serve as a baseline for the evaluation of vestibular pathology. For comparison, manually controlled head steps were also applied, as described in the literature. Eye and head movements were recorded with magnetic search coils. Non-vestibular effects were avoided by the use of high stimulus frequencies and the analysis of short time-windows (< 100 msec) after steps. Helmet-imposed steps caused a virtually uniform head acceleration (average magnitude 770 degrees/sec) in the first 90 msec. This resulted in a linear relation between eye and head velocities; the gain and delay of the VOR could be calculated independently from the slope and offset of this relation. Such estimates appear more reliable than those obtained with conventional techniques. Normal subjects had a VOR gain of about 0.9 and a delay of about 5 msec. The results of sinusoidal head oscillation were in agreement with the results for steps. The responses to manually generated head steps agreed in general with those to helmet-induced steps, but because of the non-uniform acceleration they allowed a less exact analysis of function.

Acceleration↗

PubMed1997

Gain and delay of human vestibulo-ocular reflexes to oscillation and steps of the head by a reactive torque helmet. II. Vestibular-deficient subjects.

Vestibulo-ocular reflexes (VOR) were evaluated with a reactive torque helmet that imposed high-frequency oscillation (2-20 Hz) or step displacements of the head in the horizontal plane. The present paper describes the results in patients with vestibular deficiencies (labyrinthine defective; LD); experimental and analytical techniques and results for normal subjects were described in Part 1 of this paper. The patient groups included: total unilateral LD (related to acoustic neuroma; n = 40); severe (clinically total) bilateral LD (n = 7); bilateral hyporeflexia (n = 14); unilateral hyporeflexia (n = 11); and patients with LD phenomena that had subsided (n = 3). Helmet-induced head steps provided the most specific information. Characteristically, gain was lowered in one direction or both directions after unilateral or bilateral vestibular lesions, respectively; in general, the magnitude of the gain reduction correlated well with the degree of complaints and disability. Surprisingly, delay was systematically prolonged (up to several tens of milliseconds) in all groups of subjects with manifest vestibular pathology. These results suggest that the determination of delay, in addition to gain of the VOR, is feasible and important in the evaluation of vestibular function. The results of head oscillation generally supported the results for steps, but were somewhat less specific. The responses to manually generated head steps roughly agreed with those to helmet-induced steps, but because of the non-uniform acceleration they allowed a less exact analysis of VOR function.

Acceleration↗

PubMed1997

Deviation of the subjective vertical in long-standing unilateral vestibular loss.

We evaluated changes in the subjectively perceived gravitational vertical as an index of imbalance in the function of the right and left otolith organs. In addition to normal subjects (n = 25), we measured patients with a longstanding (mean 4.5 year +/- 3.2 SD; range 0.5-11.5 years) unilateral vestibular loss after surgery for acoustic neuroma (n = 32), patients with partial unilateral vestibular loss (n = 7) and patients with bilateral vestibular hyporeflexia (n = 8). Normal subjects could accurately align a vertical luminous bar to the gravitational vertical in an otherwise completely dark room (mean setting -0.14 degree +/- 1.11 SD). Patients with left-sided (complete; n = 13) or right-sided (complete; n = 19 and partial; n = 7) unilateral vestibular loss made mean angular settings at 2.55 degrees +/- 1.57 (SD) leftward and 2.22 degrees (+/-1.96 SD) rightward, respectively. These means differed highly significantly from the normal mean (p < 0.00001). In the time interval investigated (0.5-11.5 years) the magnitude of the tilt angle showed no correlation with the time elapsed since the operation. The mean setting by patients with clinically bilateral vestibular loss (-1.17 degrees +/- 1.96 SD; n = 8) did not significantly differ from the control group. The systematic tilts of the subjective vertical in patients with a unilateral vestibular impairment were correlated with their imbalance in canal-ocular reflexes, as reflected by drift during head-oscillation at 2 Hz (r2 = 0.44) and asymmetries in VOR-gain for head-steps (r2 = 0.48-0.67). These correlations were largely determined, by the signs of the asymmetries; correlation between the absolute values of the VOR gain asymmetries and subjective vertical angles proved to be virtually absent. We conclude that the setting of the subjective vertical is a very sensitive tool in detecting a left-right imbalance in otolith function, and that small but significant deviations towards the defective side may persist for many years (probably permanently) after unilateral lesions of the labyrinth or the vestibular nerve.

Ear, Inner↗

PubMed1996

Modulation of the human vestibuloocular reflex during saccades: probing by high-frequency oscillation and torque pulses of the head.

1. We probed the gain and phase of the vestibuloocular reflex (VOR) during the execution of voluntary gaze saccades, with continuous oscillation or acceleration pulses, applied through a torque helmet. 2. Small-amplitude (< 1 degree), high-frequency (10-14 Hz) head oscillations in the horizontal or vertical plane were superimposed on ongoing horizontal gaze saccades (40-100 degrees). Torque pulses to the head ("with" or "against" gaze) were superimposed on 40 degrees horizontal saccades. Eye and head movements were precisely measured with sensor coils in magnetic fields. 3. Techniques were developed to separate the oscillatory (horizontal or vertical) component from the gaze shift and obtain VOR gain and phase with Fourier techniques from the relation between eye-in-head and head oscillations. These involved either subtraction of exactly matching saccades with and without oscillation (drawback: low yield) or time shifting of successive trials to synchronize the oscillations (drawback: slight time blurring of saccades). 4. The results of these matching and synchronization methods were essentially identical and consistent. Presaccadic gain values of the horizontal VOR (typically about unity) were reduced by, on average, approximately 20 and 50% during horizontal saccades of 40 and 100 degrees, respectively. These percentages may be truncated because of methodological limitations, but even after taking these into account (on the basis of simulation experiments with 2 different, theoretical profiles of suppression) our results do not support a complete saccadic VOR suppression for any substantial fraction of saccadic duration. Qualitatively similar changes were found when the vertical VOR was probed during 100 degrees horizontal saccades. 5. Concomitantly with the reductions in gain, VOR phase was advanced by approximately 20 degrees during the saccade. 6. In the wake of gaze saccades, VOR gain was consistently elevated (to approximately 1.0) above the presaccadic level (approximately 0.9). We submit that this mechanism ensures stable fixation of the newly acquired target at a time when the head is still moving substantially. 7. Although the responses to head torque pulses showed idiosyncratic asymmetries, analysis of the differences in eye and head movements for pulses with and against consistently showed a sharp fall of VOR gain at saccadic onset, following an approximately exponential course with a time constant of approximately 50 ms. This decay may be assumed to reflect VOR gain for a period of approximately 50 ms, after which secondary gaze control mechanisms become dominant. 8. The time course of the gain decay and phase shift of the VOR suggest that suppression of the "integrative (position) loop" of the VOR circuit was more complete than suppression of the direct, "velocity" pathway.

Female↗

PubMed1995

The function of visual search and memory in sequential looking tasks.

UNLABELLED: Eye and head movements were recorded as unrestrained subjects tapped or only looked at nearby targets. Scanning patterns were the same in both tasks: subjects looked at each target before tapping it; visual search had similar speeds and gaze-shift accuracies. Looking, however, took longer and, unlike tapping, benefitted little from practice. Looking speeded up more than tapping when memory load was reduced: memory was more efficient during tapping. CONCLUSION: eye movements made when only looking are different from those made when tapping. Visual search functions as a separate process, incorporated into both tasks: it can be used to improve performance when memory load is heavy.

Eye Movements↗

PubMed1995

Voluntary binocular gaze-shifts in the plane of regard: dynamics of version and vergence.

We studied the dynamics of voluntary, horizontal, binocular gaze-shifts between pairs of continuously visible, real three-dimensional targets. Subjects were stabilized on a biteboard to allow full control of target angles, which were made to differ only in distance (pure vergence), only in direction (pure version; conjugate saccades) or in both distance and direction (disjunctive saccades). A wide range of changes in vergence (0-25 deg) and version (0-65 deg) was recorded to study the dynamics of disjunctive saccades, described until now for limited ranges, throughout the horizontal oculomotor range within manual working space, and to study the velocity-duration-amplitude relations ("main sequence") of disjunctive vs conjugate saccades. Pure vergence was almost never observed; divergence, especially, was always associated with saccades. Likewise, horizontal saccades were never strictly conjugate, they always contained a transient divergence-convergence sequence. The amplitude and velocity of these transient components varied systematically with saccadic size. In combined version-vergence movements, vergence was, in general, accelerated and shortened as a function of increasing version. This effect was fairly uniform for divergence, which appeared to increase in velocity by about as much as the transient peak divergent velocity of the version saccade. The intrasaccadic fraction of divergence increased from about 50% to close to 100% as a function of increasing version. For convergence, saccades up to about 20 deg were also accelerating; in this case it appeared as if the transient peak convergent velocity of the version saccade was added to the basic convergence velocity. For larger saccades this effect was partly counteracted by the penetration of an initial divergence associated with the saccade. This initial divergence delayed and slowed down convergence. The intrasaccadic fraction of convergence varied between about 40% and 70%. In disjunctive saccades the individual eyes did not follow the main-sequence parameters of conjugate saccades of comparable sizes, except for the eye that moved with the combination "abduction and divergence". For all other combinations of vergence and version, disjunctive saccades had lower peak velocities and longer durations than conjugate saccades. As a consequence, disjunctive version was also slower than conjugate version. Thus, while version accelerates vergence, vergence slows down version: in the generalized case of three-dimensional gaze-shifts, peak velocities and durations are in between those of the limiting cases of pure version and pure vergence. We conclude that, within manual working space, binocular gaze-shifts are effected by the highly integrated action of conjugate and disjunctive mechanisms, both of which are expressed preferentially in fast, saccadic movements.

Adult↗

PubMed1995

Evaluation of the human vestibulo-ocular reflex at high frequencies with a helmet, driven by reactive torque.

A new technique was developed to test the VOR in humans. A tightly but comfortably fitting helmet was provided with an electronically controlled torque motor that rotated a mass around a vertical axis. Acceleration of the motor caused reactive torque of the helmet in the opposite direction which was transmitted to the (freely movable) head. Sinusoidal head oscillations in the frequency range 2-20 Hz (peak-to-peak amplitudes about 10 degrees and 0.1 degrees respectively) were easily achieved, as well as step displacements of the head with accelerations on the order of 1000 degrees/s2. Limitation of the maximum torque and lack of any rigid attachment of the head to a fixed structure made the technique safe and comfortable. Eye and head rotations were recorded, independently of head translations, with eye and head search coils in a homogeneous a.c. magnetic field. In normal subjects, gain was near unity at 2 Hz: above 8 Hz, gain increased progressively toward 1.1-1.3 at 20 Hz. Phase lag increased from a few degrees at 2 Hz to about 45 degrees at 20 Hz. Above 2 Hz, these results were unaffected by visual conditions; lower gains and increased phase lags were found in subjects with bilateral or unilateral vestibular loss. For step displacements, gain (measured in the first 100 ms) was near unity for normals, near zero after bilateral vestibular loss and strongly asymmetrical after unilateral vestibular loss. Thus, the technique seems highly effective in testing vestibular function with minimal contamination by other systems.

Acceleration↗

PubMed1995

Conjugacy of eyelid movements in vertical eye saccades.

PURPOSE: To examine the conjugacy of lid saccades in normal subjects. METHODS: Saccades of both upper eyelids were recorded simultaneously by means of small, lightweight, magnetic search coils, fixed on each lid. Subjects then made vertical eye saccades between fixed targets. The associated eye saccades were recorded simultaneously by means of magnetic search coils. The authors further examined whether the position of the lid coils affected the recordings. RESULTS: Lid saccades were not as conjugate as their associated eye saccades. Nonconjugacy of lid saccades averaged approximately 8% of the target amplitude, irrespective of saccadic direction. By contrast, nonconjugacy of the associated eye saccades averaged approximately 1% of the target amplitude. Coil position significantly (P < 0.05) affected the recordings. CONCLUSIONS: Lid saccades are not as conjugate as their associated eye saccades. Coil position is critical for the recordings of lid saccades.

Adult↗

PubMed1995

Conjugacy of saccades in deep amblyopia.

PURPOSE: To determine the degree of conjugacy of saccades in humans with one deeply amblyopic eye, to assess whether Hering's law requires good binocular visual acuity. METHODS: By means of magnetic search coils, horizontal saccades were recorded accurately in 11 subjects with unilateral, deep amblyopia. The recordings were compared to those made in 11 normal subjects. In addition, three subjects with amblyopia were submitted to artificial anisometropia, which called for nonconjugate adaptation of their saccades. RESULTS: The saccades of most subjects with amblyopia were nonconjugate. These nonconjugacies often were larger in one direction than in the opposite one. The magnitude of the nonconjugacies varied inconsistently with the size of the saccades. In addition, the amblyopic eye often showed conspicuous drift. The saccades adapted nonconjugately to the imposed anisometropia. CONCLUSIONS: In deep amblyopia, the two eyes often make saccades that are unequal in size. The amblyopic eye does not move aimlessly, roughly following the movements of the normal fellow eye. Instead, the saccades of the amblyopic eye appear to reflect a deliberate oculomotor strategy, bringing visual targets to presumed retinal points of preference.

Adaptation, Ocular↗

PubMed1994

Human vestibulo-ocular responses to rapid, helmet-driven head movements.

High-frequency head rotations in the 2-20 Hz range and passive, unpredictable head acceleration impulses were produced by a new technique, utilizing a helmet with a torque motor oscillating a mass. Unrestrained head and eye movements were recorded using magnetic sensor coils in a homogeneous magnetic field. In order to analyze the influence of the visual system on the vestibulo-ocular reflex (VOR), we took measurements under three experimental conditions: (1) with a stationary visual target; (2) in total darkness with the subject imagining the stationary target; and (3) with a head-fixed target. The results in 15 healthy subjects were highly consistent. At 2 Hz, VOR gain was near unity; above 2 Hz, VOR gain started to decrease, but this trend reversed beyond 8 Hz, where the gain increased continuously up to 1.1-1.3 at 20 Hz. Phase lag increased with frequency, from a few deg at 2 Hz to about 45 degrees at 20 Hz. Above 2 Hz, VOR gain was not significantly different for the three experimental conditions. Head acceleration impulses produced a VOR with near-unity gain in both directions. We also tested three subjects with clinically total bilateral loss of labyrinthine functions. These labyrinthine-defective subjects showed, in comparison to the normal subjects, strikingly lower gains and much longer delays in the VOR during sinusoidal and step-like head movements. These results suggest that our new torque-driven helmet technique is effective, safe and convenient, enabling the assessment of the VOR at relatively high frequencies where both visual and mental influences are minimized.

Eye Movements↗

PubMed1994

Instability of ocular torsion during fixation: cyclovergence is more stable than cycloversion.

We investigated spontaneous variation of binocular torsion. Variation was expressed as SD of torsional eye positions measured over periods up to 32 sec. Subjects viewed a single dot target for periods of 32 sec. In half of the trials a large random-dot background pattern was superimposed on the dot. The movements of both eyes were measured with scleral induction coils. Spontaneous torsional movements were largely conjugate: cyclovergence was much more stable than cycloversion. This difference was not due to roll head movements. Stability of cyclovergence was improved by the background pattern. Although overall stability (SD of position) of cycloversion was unaffected by a background, the background induced or enhanced a small-amplitude torsional nystagmus in 3 out of 4 subjects. We hypothesize that the difference in stability of cycloversion vs cyclovergence reflects the greater importance of torsional retinal correspondence, compared to absolute torsional position. In two subjects we found evidence for the existence of cyclophoria, manifested by systematic shifts in cyclovergence caused by the appearance and disappearance of the background.

Adult↗

PubMed1994

Eye torsion associated with disparity-induced vertical vergence in humans.

Recently, Enright described an unexpected association between disparity-induced vertical vergence and cycloversion (conjugate eye torsion) [Enright (1992) Vision Research, 415, 279]. The present experiments were performed to verify these findings and investigate the nature of this association. We presented subjects with a dichoptic image of concentric circles in which a step in vertical disparity of 1 deg was introduced. After 4 sec the disparity was eliminated. Eye movements were measured with scleral coils. We confirmed Enright's findings in that a left-over right vertical vergence was associated with levo-cycloversion (upper poles towards left shoulder) and vice versa. The size of the cycloversion and the vertical vergence were in the same range. In addition we found that part of the cycloversion response was in the form of a torsional nystagmus and that the relative contribution of the left and right eyes was independent of the horizontal gaze angle. These additional findings are in conflict with the hypothesis, offered by Enright, that the association is caused by a bilateral activity of the superior oblique muscles.

Adult↗

PubMed1994

Eye torsion elicited by oscillating gratings: effects of orientation, wavelength and stationary contours.

We studied binocular cyclorotatory (torsional) eye movements in response to gratings that oscillated sinusoidally in a frontal plane. The square-wave gratings viewed by the right and left eye were presented and controlled separately to induce cycloversion and cyclovergence by oscillation in phase and out of phase. Eye movements were recorded with scleral induction coils. Stimulus oscillation frequency ranged from 0.125 to 1 Hz and the wavelength of the gratings ranged from 0.92 to 25.75 deg of visual angle. Cycloversion and cyclovergence gain were, on average, comparable in magnitude and decreased with increasing oscillation frequency. There was no consistent effect of the wavelength on the magnitude of the responses. In general, responses were considerably higher to gratings that were oriented horizontally than to those oriented vertically. This anisotropy was present both in cycloversion and cyclovergence. It was enhanced in a larger sized stimulus and by presenting stationary, orthogonal contours (mimicking a "shear" movement), but it was not consistently influenced by wavelength. Cyclovergence showed a phase lag, which increased with oscillation frequency but which was independent of wavelength. In contrast, cycloversion showed a slight phase lead which was independent of both oscillation frequency and wavelength.

Adult↗

PubMed1993

Unilateral cholinergic stimulation of the rabbit's cerebellar flocculus: asymmetric effects on optokinetic responses.

In previous work, we have demonstrated an acceleration of the buildup of slow-phase velocity of optokinetic nystagmus (OKN) after bilateral floccular injection of the aselective cholinergic agonist carbachol (Tan and Collewijn 1991; Tan et al. 1992a). In the present study we investigated the effects of unilateral floccular injections of carbachol. Such unilateral injections specifically enhanced the buildup of OKN slow-phase velocity in the direction toward the injected flocculus (ipsiversive). During binocular optokinetic stimulation, this enhancement was expressed in the motion of both eyes. Acceleration of the eye contralateral to the injected flocculus increased from 1 to about 2 degrees/s2, while the acceleration of the ipsilateral eye increased from 1 to about 1.5 degrees/s2. In contrast, buildup of contraversive OKN was unchanged. No changes were found in the steady-state OKN and optokinetic afternystagmus (OKAN). Monocular optokinetic stimulation was only effective in the nasal direction, and the effects of unilateral injection of carbachol were disconjugate. Ipsiversive OKN was enhanced only in the contralateral, seeing eye, while the response of the ipsilateral, covered eye was unchanged. We hypothesize that the directionally specific effect of unilateral cholinergic floccular stimulation on OKN is due to enhancement of predominantly the excitatory phase of modulation of the Purkinje cell's simple-spike activity by carbachol, without a marked effect of carbachol on the inhibitory phase of simple-spike modulation.

Acetylcholine↗

PubMed1993

Shortening of vestibular nystagmus in response to velocity steps by microinjection of carbachol in the rabbit's cerebellar flocculus.

It has been proposed that a common velocity-storage mechanism is responsible for the prolongation of vestibular nystagmus beyond the duration of the change in firing frequency of primary vestibular fibers in response to a step in velocity, and for the production of optokinetic afternystagmus (OKAN). In a previous study, bilateral injection of the aselective cholinergic agonist carbachol in the flocculus shortened the duration of buildup of optokinetic nystagmus (OKN) and the duration of OKAN, suggesting floccular involvement in velocity storage (Tan et al. 1992). In extension to that study of OKN, the present study assesses the effects of floccular carbachol on vestibular nystagmus in response to velocity steps. Our results show that injection of carbachol shortens the duration of vestibular nystagmus from about 13 to about 8 s; a finding which supports a common velocity-storage mechanism for optokinetic and vestibular signals. We propose that the indistinguishable effects of carbachol on OKAN and vestibular nystagmus are due to modification of the transmission of an oculomotor corollary signal, which has been identified electrophysiologically in the flocculus.

Animals↗