Cholinergic control in the floccular cerebellum of the rabbit.
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Acetylcholine↗
Biomedical subjects
J van der Steen
Publications and source records attributed to J van der Steen.
[Multiple sclerosis in family practice].
OBJECTIVE: To study the family physician's role in the diagnosis and treatment of multiple sclerosis (MS) patients. DESIGN: Descriptive. SETTING: Nederlands Instituut voor Onderzoek van de Gezondheidszorg, Utrecht, The Netherlands. METHOD: In the Dutch National survey of morbidity and intervention in general practice, data were collected by 161 general practices throughout the Netherlands (161 family physicians) regarding contacts with patients during three months. These data were examined for contacts which resulted in the diagnosis of MS and for comorbidity. RESULTS: MS patients (n = 118) had 4.3 encounters per 3 months with their family physician and (or) the practice assistant. In 5 patients MS was diagnosed for the first time. Apart from neurological complaints characteristic of MS the family physician was consulted most frequently for sleeping disorders, urinary tract infections and urine incontinence. One-third of patients depended on social security and 26% had a paid job. CONCLUSION: The family physician was consulted relatively frequently by MS patients. Apart from sleeping disorders remarkably few psychic complaints were noted.
Adult↗
Acetylcholine enhances optokinetic modulation of floccular Purkinje cells.
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Acetylcholine↗
Unequal amplitude saccades produced by aniseikonic patterns: effects of viewing distance.
This study describes differences in horizontal and vertical disconjugate saccades under far and close viewing conditions of two dichoptically presented aniseikonic random checkerboard patterns. At far viewing, disconjugacy of horizontal saccades requiring divergence was accomplished intrasaccadically after several minutes; for convergence the intrasaccadic disconjugacy was limited. Size differences partially persisted in open-loop trials. At close viewing intrasaccadic divergent changes in conjugacy were instantaneous, but motor storage during open-loop was absent. It is concluded that disconjugate saccades to targets at far distance lead to an adaptation process, whereas at close viewing distance horizontal disparity is a visual compensation process used directly to scale the relative amplitudes of both eyes, not leading to adaptation. The time-course of disconjugate vertical saccades was much slower, with mostly postsaccadic vergence. Nearby viewing enhanced the disconjugacy of vertical saccades.
Adaptation, Physiological↗
Unequal saccades produced by aniseikonic patterns: a model approach.
This study addresses a possible mechanism for fast disconjugate adaptation of binocular horizontal saccades. Disconjugacy of binocular saccades was elicited by two dichoptically presented, identical but aniseikonic, random checkerboard patterns. Adaptation was achieved with the patterns at far distance (144 cm). In this condition, which requires a relatively small (8%) size difference of the saccades, a short learning period was mandatory for the binocular saccades to become disconjugate. The saccadic modifications were superimposed on an idiosyncratic pattern of intra-saccadic yoking. A model of saccadic signal generation is described, that has been used to separate the contributions on saccadic disconjugacy provided by modification of visual inputs processing, which alters the motor-system inputs, and by modification of the control system: the adaptation. We identified three major components of the saccadic command (two phasic and one tonic) that contribute and in a specific way to the saccadic yoking and disconjugacy. The model analysis proposes that separate control mechanisms exist operating on these phasic and tonic signals. We show that the saccadic system can generate the vergence component shown by our aniseikonic saccades. We discuss a distributed-parallel implementation of the saccadic system able to provide both the conjugate and disconjugate components of control.
Adaptation, Physiological↗
Three-dimensional organization of optokinetic responses in the rabbit.
1. Three-dimensional rotations of both eyes were measured in alert rabbits during optokinetic stimulation about axes lying in the horizontal plane or about an earth-vertical axis, with either one or both eyes viewing the stimulus. Optokinetic stimulus speed was 2 degrees /s, either continuous or alternating in polarity (triangular stimulus). In addition to the gains of the responses, the orientations of the response axes relative to the stimulus axes were determined. 2. In comparison to the response to constant-speed optokinetic stimulation about the vertical axis, the response to constant-speed optokinetic stimulation about horizontal axes was characterized by the lack of a speed buildup. In many cases, slow phase tracking was good as long as the eye was within the central oculomotor range but deteriorated when eye deviation became more eccentric and fast phases failed to be generated. These features suggest that the optokinetic reflex about horizontal axes functions as a position-control system, rather than as a velocity-control system. 3. Binocular optokinetic stimulation at constant speed (2 degrees/s) about the roll axis (0 degrees azimuth horizontal axis) elicited disconjugate responses. Although the gain of the response was not significantly different in the two eyes (0.38 for downward and 0.44 for upward stimulation), the response axes of the two eyes differed by as much as 51 degrees. 4. Monocular, horizontal axis optokinetic stimulation at constant speed elicited responses that were grossly dissociated between the two eyes. The magnitude of the responses was anisotropic in that it varied with the azimuthal orientation of the stimulus axis; the maximum gain for each eye (0.41 for the seeing and 0.33 for the covered eye) was at 135 degrees azimuth for each eye. The axis orientation and direction (sense of rotation) of the optokinetic stimulus eliciting the maximal response for each eye coincided with the optic flow normally associated with the maximal excitation of the corresponding ipsilateral anterior canal. 5. Binocular, triangular optokinetic stimulation with small excursions (+/- 10 degrees), which avoided the saturation problems of constant-speed stimulation, elicited adequate responses without systematic directional asymmetries. Gain was approximately 0.9 for all stimulus axis orientations in the horizontal plane. 6. During monocular stimulation with triangular stimuli, the response of the seeing eye showed a gain of approximately 0.5 for all orientations of the stimulus axis. In contrast, the covered eye showed anisotropic responses, with a maximum gain of approximately 0.5 during stimulation of the seeing eye about its 45 degree axis.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Foveation dynamics in congenital nystagmus. I: Fixation.
Congenital nystagmus (CN) has been described as a 'fixation' nystagmus implying an inability to fixate a target. However, each cycle of CN contains a target-foveation period during which the eye velocity is at, or near, zero. Prolongation of foveation time, reduction of retinal image velocity and cycle-to-cycle foveation repeatability all contribute to increased visual acuity. We developed several methods to accurately measure the dynamics of foveation in CN; their use is illustrated on an individual with typical idiopathic CN and no afferent defects. During eight 5-second intervals of fixation on a stationary target, the horizontal standard deviation (SD) of the mean foveation position (FPOS) was 12.82 minarc and the SD of foveation velocity was 118.36 minarc/sec. The SD of the means of total eye position and of the non-foveating peak of the CN were 43.17 and 25.32 minarc respectively. The mean foveation-time interval (eye velocity less than or equal to 4 degrees/sec) was 57.27 msec. The SD FPOS for the best 1-second interval (4 successive CN cycles), in a typical 5-second record, was 0.71 minarc. Histograms revealed peaks of eye position at 0 +/- 10 minarc and of eye velocity at 0 +/- 240 minarc/sec. The small vertical component of the CN (16 minarc peak-to-peak) had a SD of 6.56 minarc. A nystagmus foveation function related to visual acuity was derived that was more sensitive than CN intensity. The increased visual acuity resulting from the use of convergence or base-out prisms was due to increased foveation time. Although it might appear that CN is a defect of fixation, this individual with CN had strong fixation reflexes in the sense that he was able to accurately (within 1 minarc) achieve (interbeat) and maintain (intrabeat) target foveation for appreciable periods of time. Our data support the hypothesis that individuals with idiopathic CN do not have a primary disturbance of fixation.
Fixation, Ocular↗
Foveation dynamics in congenital nystagmus. II: Smooth pursuit.
It has been shown that, during 5 seconds of fixation, an individual with congenital nystagmus (CN) can repeatedly (beat-to-beat) foveate (SD = 12.87 minarc) and maintain low retinal slip velocities (SD = 118.36 minarc/sec). Smooth pursuit data from several CN subjects showed that eye velocities during these foveation intervals approximated target velocity. Despite some claims that CN is caused by absent or "reversed" smooth pursuit, those with CN hardly ever experience oscillopsia or exhibit any accompanying symptoms of such deficits in pursuit; they are able to master sports requiring tracking of rapidly moving small objects (e.g. racquetball or handball). We developed and describe several new methods to accurately assess the function of smooth pursuit in an individual with typical idiopathic CN. We investigated the dynamics of CN foveation periods during smooth pursuit to test the hypothesis that eye velocities would match target velocities during these periods. Unity or near-unity instantaneous (beat-to-beat) pursuit gains of both experimenter-moved and subject-moved targets at peak velocities ranging from only a few deg/sec up to 210 degrees/sec were measured. The dynamic neutral zone was found to shift oppositely to target direction by amounts proportional to the increase in target speed. Our methods proved that eye velocity is made to match target velocity during the foveation intervals and support the conclusion that smooth pursuit in individuals with CN is functioning normally in the presence of the CN oscillation. In addition, we hypothesize that the same fixation mechanism that prevents oscillopsia during fixation of stationary targets, also does so during pursuit.
Fovea Centralis↗
Foveation dynamics in congenital nystagmus. III: Vestibulo-ocular reflex.
It has been shown that, during fixation of a stationary target with a fixed head, an individual with congenital nystagmus (CN) can repeatedly (beat-to-beat) foveate (within 13 minarc) and maintain low retinal slip velocities (less than 4 degrees/sec). With the head in motion, vestibuloocular reflex (VOR) data showed eye velocities during these foveation periods that approximation head velocity. Despite some claims that the VOR of CN subjects was deficient or absent, individuals with CN hardly ever complain of oscillopsia or exhibit any of the symptoms that would accompany such deficits in the VOR, whether during simple walking and running or while skiing down a mogul field. We developed and describe several different and unrelated methods to accurately assess the function of the VOR in an individual with typical idiopathic CN. We investigated the dynamics of CN foveation periods during head rotation to test the hypothesis that eye velocities would match head velocities during these periods. At about 1 Hz, horizontal VOR instantaneous (beat-to-beat) gains were 0.96 in the light and 0.94 in the dark while imaging a stationary target. Vertical VOR gains were 1.00 and 0.99 for these two conditions at the same frequency; the CN was horizontal. Also, during the VOR there is a CN neutral-zone shift comparable to that found during smooth pursuit. Our methods demonstrated that gaze velocity was held constant during foveation periods and we conclude that the VOR in this subject is functioning normally in the presence of the CN oscillation. Based on our findings in this and previous studies, we hypothesize that CN may be due to a peripheral instability.
Fovea Centralis↗
Visually induced cycloversion and cyclovergence.
Binocular cyclorotatory (torsional) eye movements in response to visual patterns, which oscillated sinusoidally in the frontal plane, were recorded with scleral induction coils in human subjects. Conjugate cycloversion and disjunctive cyclovergence were directly compared by in-phase and out-of-phase oscillation of the same pattern. Stimulus motion had a frequency of 0.2 Hz and amplitudes of 2-8 deg. Both response types had a similar and low gain (about 0.2 averaged over all subjects). Cycloversion showed no time lag, while cyclovergence lagged by about 600 msec. Non-fusible patterns were effective in eliciting cycloversion, but not cyclovergence. Apart from this, the nature of the pattern (randomly distributed dots, regular rows of dots, horizontal or vertical grating, Julesz stereogram or images with a pictorial significance) had only the slightest effect on the magnitude of the responses.
Adult↗
Injections of beta-noradrenergic substances in the flocculus of rabbits affect adaptation of the VOR gain.
Noradrenaline (NA) has been implicated as a neuromodulator in plasticity, presumably facilitating adaptive processes. Recent experiments by others have suggested a modulatory role of NA in adaptive changes in the vestibulo-ocular reflex (VOR). These experiments showed that general depletion of brain NA resulted in a decreased ability to produce adaptive changes in the VOR gain. In order to identify the specific brain region responsible for these effects, as well as the nature of the adrenoceptors involved, we injected beta-adrenergic substances bilaterally into the flocculus of rabbits. The flocculus is known to receive noradrenergic afferents and, moreover, ablation of the flocculus interferes strongly with the normal adaptive changes in the VOR gain. We injected the beta-agonist isoproterenol and the beta-antagonist sotalol, and compared the adaptive capacity of the rabbits after these injections to that in a situation without injection. The rabbit was oscillated in a direction opposite to the direction of motion of the platform on which the rabbit was mounted, a condition which normally results in an increase in the VOR gain, measured either in light or in darkness. Injection of the beta-agonist did not greatly affect the adaptation of the VOR measured in the light. In darkness, the increase in gain after the injection of isoproterenol was larger than in the non-injection experiments in 9 out of 10 rabbits. The beta-antagonist sotalol reduced the adaptation of the VOR gain significantly in the light, as well as in darkness. In a control condition without pressure for adaptation (only intermittent testing of the VOR gain over a period of 2.5 h), the gain of the VOR either remained unaffected or was only slightly affected by similar injections of beta-adrenergic agents in individual rabbits. For the group as a whole, these effects were insignificant. We conclude from these results that noradrenergic systems facilitate the adaptation of the VOR gain to retinal slip in rabbits, without affecting the VOR gain directly. At least part of this influence is exerted through beta-receptors located in the cerebellar flocculus.
Adaptation, Physiological↗
Visual and oculomotor function in optic chiasma-sectioned rabbits.
Anatomical and physiological findings indicate that the crossed optic fibres of the rabbit have a crucial role in binocular vision. In order to directly examine the visual functions of the uncrossed fibre system, a technique of sectioning the optic chiasma midsagitally was developed. Both normal and chiasma-sectioned rabbits were tested on a variety of visual discrimination tasks as well as such oculomotor control functions as the optokinetic and vestibulo-ocular reflexes. Following transection of all contralateral retinal projections, rabbits were found to retain the same visual capacity for detection of intensity and orientation differences as before the operation. There was, however, a complete loss of optokinetic reflexes and a 50% reduction of the vestibulo-ocular reflex both in the light and in the dark.
Animals↗
Radiation protection during treatment of children with 131I-meta-iodobenzylguanidine.
This paper describes the radiation protection procedures that were used in caring for three children treated with therapeutic amounts of 131I-meta-iodobenzylguanidine. Since it was not possible to leave a child alone in a shielded room for several days, the presence of one parent was requested during the treatment. The dose equivalent to the parent was kept to an acceptable level of approximately 1 mSv. This dose equivalent was almost completely due to external radiation since blocking of the parent's thyroid led to a negligible dose equivalent from internal contamination.
3-Iodobenzylguanidine↗
Effects of unilateral frontal eye-field lesions on eye-head coordination in monkey.
We studied the effects of unilateral frontal eye-field (FEF) lesions on eye-head coordination in monkeys that were trained to perform a visual search task. Eye and head movements were recorded with the scleral search coil technique using phase angle detection in a homogeneous electromagnetic field. In the visual search task all three animals showed a neglect for stimuli presented in the field contralateral to the lesion. In two animals the neglect disappeared within 2-3 wk. One animal had a lasting deficit. We found that FEF lesions that are restricted to area 8 cause only temporary deficits in eye and head movements. Up to a week after the lesion the animals had a strong preference to direct gaze and head to the side ipsilateral to the lesion. Animals tracked objects in contralateral space with combined eye and head movements, but failed to do this with the eyes alone. It was found that within a few days after the lesion, eye and head movements in the direction of the target were initiated, but they were inadequate and had long latencies. Within 1 wk latencies had regained preoperative values. Parallel with the recovery on the behavioral task, head movements became more prominent than before the lesion. Four weeks after the lesion, peak velocity of the head movement had increased by a factor of two, whereas the duration showed a twofold decrease compared with head movements before the lesion. No effects were seen on the duration and peak velocity of gaze. After the recovery on the behavioral task had stabilized, a relative neglect in the hemifield contralateral to the lesion could still be demonstrated by simultaneously presenting two stimuli in the left and right visual hemifields. The neglect is not due to a sensory deficit, but to a disorder of programming. The recovery from unilateral neglect after a FEF lesion is the result of a different orienting behavior, in which head movements become more important. It is concluded that the FEF plays an important role in the organization and coordination of eye and head movements and that lesions of this area result in subtle but permanent changes in eye-head coordination.
Animals↗
Human eye movements associated with blinks and prolonged eyelid closure.
Eye movements associated with eyelid closure were recorded in human subjects with search coils, embedded in self-adhering scleral annuli, in a magnetic field. In contrast to classical notions, voluntary as well as reflex blinks were consistently accompanied by transient downward and nasalward movements of both eyes with amplitudes 1-5 degrees. These eye movements had a shorter duration than the upper lid movements, and the shapes of the spatial trajectories of eye and lid movements were not similar. The trajectory of the eye movements was only modestly affected by gaze eccentricities up to 15 degrees; there was a tendency for the downward component to be enhanced by looking upward, and vice versa. Restraining of the lids of one eye in the open or closed position did not significantly alter the eye movements during (attempted) blinks. Velocity-amplitude-duration relations of the down- and upward components were similar for the same eye before and after closure and for the closed eye and the contralateral unrestrained eye. The velocity-amplitude-duration characteristics of saccades were also unaffected by prolonged closure of the lids of one eye. Prolonged, voluntary closure of the lids was followed by a slow, tonic ocular deviation, which was consistently upward in half of the subjects and consistently downward in the other half. Additional horizontal components were highly variable even within subjects. In one subject the downward deviation was converted into upward deviation when lid closure was mechanically impeded. We conclude that elevation of the eye ball (Bell's phenomenon) does not occur during short blinks and only in about half of the subjects during voluntary unrestrained prolonged lid closure. Our evidence does not support the possibility that the transient eye movements during blinks are caused primarily by a mechanical interaction between the lids and the eye (or the scleral annulus). More likely, they are a secondary effect of an active cocontraction of extraocular muscles that primarily results in retraction of the eye.
Adult↗
Vision in the presence of known natural retinal image motion.
Previously we reported that failures of compensatory eye movements led to appreciable binocular retinal image motion during head rotation. Subjectively, the visual world appeared clear, fused, and stable under these conditions. The present experiments examined these impressions psychophysically. The spatial modulation transfer function of subjects with known retinal image motion was measured during head rotation. We found that contrast sensitivity was reduced for gratings over 6 cycles/degree and was increased for lower spatial frequencies. Our results, when compared with Kelly's [J. Opt. Soc. Am. 69, 1340-1349 (1979)] measurements made with artificially moving stabilized gratings, show that natural retinal image motion is less harmful to contrast sensitivity at high spatial frequencies and more beneficial at low spatial frequencies. Furthermore, we had previously found that natural retinal image motion was different in each eye during head movement but no diplopia was noticed. We confirmed this subjective impression by measuring forced-choice stereoacuity thresholds concurrent with binocular head and eye recordings. Stereoacuity was not disturbed by large fixation disparities or high vergence velocities. Recordings also were made while a fused Julesz stereogram was viewed during attempts to break fusion with violent head movements. Fusion could not be broken. Stereograms turned on during violent head movement fused rapidly. We conclude that vision is better with natural retinal image motion than expected from experiments done with stabilized heads.
Head↗
Voluntary selection of the target for smooth eye movement in the presence of superimposed, full-field stationary and moving stimuli.
Prior work has shown that smooth eye movements in the presence of both stationary and moving stimuli are determined, at least in part, by the voluntary selection of either the stationary or the moving stimulus as the target for smooth eye movements. The effectiveness of voluntary selection in eliminating the influence of the stimuli not selected (i.e. backgrounds) on smooth eye movement is not known because prior studies used targets and backgrounds with different physical characteristics. Thus, effects of voluntary selection were confounded with the relative strength of target and background as stimuli for smooth eye movements. We measured eye movements (resolution 1') of two highly-experienced eye movement subjects with a target and background with the same physical characteristics: two, identical, full-field, superimposed patterns of randomly-positioned dots (1 dot/deg2 or 8 dots/deg2). One field was stationary and the other moved at 70.2 minarc/sec. The effect of the moving background on smooth eye movements when the stationary field was the target, and the effect of the stationary background on smooth eye movements when the moving field was the target was negligible (0-4% for one subject; 0-2% for the other). The influence of the background on smooth eye movements was affected by a six-fold reduction in the intensity of either the target or background, but effects of such intensity changes were small and different for each subject. Taken together, these results show that the effectiveness of voluntary selection in eliminating the influence of background stimuli on smooth eye movements can be virtually complete. Any observed influence of the background--however small--can be attributed to voluntary factors (e.g. subjects' failure to apply sufficient effort or attention) rather than to the operation of an involuntary mechanism that automatically integrates velocity information from target and background. The attention and effort required to ensure that voluntary selection is perfect may impair the accuracy of psychophysical judgments made about the background.
Attention↗
A comparison of oculomotor pursuit of a target in circular real, beta or sigma motion.
Pursuit of a point target in real or apparent motion upon a dark, diffusely lighted or structured background was recorded with a scleral coil technique. Smooth and saccadic components were separated and analyzed with computer techniques. Sigma-pursuit was superior to pursuit of beta- or real motion: smooth pursuit gain was higher, saccadic rate was lower and the detrimental effect of a structured background was smaller. Due to directional errors, smooth pursuit velocity often exceeded target velocity when this was smaller than about 10 degrees/sec. However, the smooth component in the correct direction of the target motion had a gain less than or equal to 1.0 and decreasing at higher target velocities for all pursuit modes, inclusive sigma-pursuit.
Eye Movements↗