Saccades to remembered targets: the effects of smooth pursuit and illusory stimulus motion.

1. Measurements were made in four normal human subjects of the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display that was either stationary or moving horizontally and sinusoidally at +/-9 deg at 0.3 Hz.

Cercospora beticola toxins. Part XVII. The role of the beticolin/Mg2+ complexes in their biological activity. Study of plasma membrane H(+)-ATPase, vacuolar H(+)-PPase, alkaline and acid phosphatases.

Beticolin-1 and beticolin-2, yellow toxins produced by the phytopathogenic fungus Cercospora beticola, inhibit the plasma membrane H(+)-ATPase. Firstly, since beticolins are able to form complexes with Mg2+, the role of the beticolin/Mg2+ complexes in the inhibition of the plasma membrane proton pump has been investigated. Calculations indicate that beticolins could exist under several forms, in the H(+)-ATPase assay mixture, both free or complexed with Mg2+.

Nystagmus.

Acquired nystagmus causes excessive motion of images on the retina, which often reduces visual acuity and produces oscillopsia (illusory motion of the seen world). The pathogenesis of several forms of acquired nystagmus is now better understood and can be related to abnormalities of mechanisms that normally hold gaze steady. Basic research on the pharmacology of the neural pathways responsible for gaze holding has demonstrated an important role for gamma aminobutyric acid and led to new drug treatments for acquired nystagmus and its visual consequences.

Measuring eye movements during locomotion: filtering techniques for obtaining velocity signals from a video-based eye monitor.

Video-based eye-tracking systems are especially suited to studying eye movements during naturally occurring activities such as locomotion, but eye velocity records suffer from broad band noise that is not amenable to conventional filtering methods. We evaluated the effectiveness of combined median and moving-average filters by comparing prefiltered and postfiltered records made synchronously with a video eye-tracker and the magnetic search coil technique, which is relatively noise free. Root-mean-square noise was reduced by half, without distorting the eye velocity signal.

Potassium homeostasis in vacuolate plant cells.

Plant cells contain two major pools of K+, one in the vacuole and one in the cytosol. The behavior of K+ concentrations in these pools is fundamental to understanding the way this nutrient affects plant growth. Triple-barreled microelectrodes have been used to obtain the first fully quantitative measurements of the changes in K+ activity (aK) in the vacuole and cytosol of barley (Hordeum vulgare L.

Bilateral ptosis and upgaze palsy with right hemispheric lesions.

Bilateral ptosis is reported with unilateral hemispheric lesions, suggesting partial lateralization of the control of the levator palpebrae superioris. There is a tight synkinesis between vertical eye and eyelid movements, but a similar, lateralized control of vertical gaze has not been previously described. We report 3 patients with right hemispheric infarctions, in whom bilateral ptosis was accompanied by impaired upward gaze.

Quantitative measurements of eye movements in a patient with Tullio phenomenon.

The Tullio phenomenon consists of vestibular symptoms on exposure to high-intensity acoustic stimuli, reflecting pathological stimulation of semicircular canals or otoliths. We report a patient with posttraumatic Tullio phenomenon to illustrate how precise measurement of eye movements during auditory stimulation, using the magnetic search coil technique, may characterize movements that are not clinically apparent or easily measured by other means. Such measurements in patients with surgically verified lesions may further elucidate the mechanisms responsible for this phenomenon.

Comparison of horizontal, vertical and diagonal smooth pursuit eye movements in normal human subjects.

We compared horizontal and vertical smooth pursuit eye movements in five healthy human subjects. When maintenance of pursuit was tested using predictable waveforms (sinusoidal or triangular target motion), the gain of horizontal pursuit was greater, in all subjects, than that of vertical pursuit; this was also the case for the horizontal and vertical components of diagonal and circular tracking. When initiation of pursuit was tested, four subjects tended to show larger eye accelerations for vertical as opposed to horizontal pursuit; this trend became a consistent finding during diagonal tracking.

The Role of Magnesium, Pyrophosphate, and Their Complexes as Substrates and Activators of the Vacuolar H+-Pumping Inorganic Pyrophosphatase (Studies Using Ligand Protection from Covalent Inhibitors).

Inhibitors preferentially and covalently reactive with cysteine, arginine, histidine, and carboxyl-containing residues were inhibitory to the plant vacuolar H+-transporting inorganic pyrophosphatase (H+-PPase) from Vigna radiata (mung bean) and Beta vulgaris (red beet), but hydrophobic compounds and those reactive with tyrosine and lysine were less effective. Inhibition by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, phenylglyoxal, and N-ethylmaleimide was decreased in the presence of Mg2+ or mixtures of Mg2+ and inorganic pyrophosphate (PPi) but not by PPi alone. None of these ligands affected inhibition by reagents reactive with histidine.

Dysfunction of pontine omnipause neurons causes impaired fixation: macrosaccadic oscillations with a unilateral pontine lesion.

Macrosaccadic oscillations of eyes (MSO) are regarded as a form of saccadic dysmetria secondary to cerebellar dysfunction. They are usually conjugate, horizontal, and symmetric in both directions of gaze. Using magnetic search coils, we studied a patient with MSO that developed five years following head injury and involved synchronously horizontal, vertical, and torsional planes.

A pilot study of gabapentin as treatment for acquired nystagmus.

The effects of the anticonvulsant gabapentin were measured on vision and eve movements in three patients with acquired pendular nystagmus. In two patients, the nystagmus was associated with multiple sclerosis and, in the other, it followed brainstem stroke. A single oral 600 mg dose of gabapentin produced improvement of vision due to changes in ocular oscillations in all three patients.

Dynamic properties of horizontal and vertical eye movements in parkinsonian syndromes.

We studied dynamic properties of horizontal, vertical, and oblique eye movements in 23 patients with the following parkinsonian syndromes: idiopathic parkinsonism (PD), multiple system atrophy (MSA), pure akinesia (PA), progressive supranuclear palsy (PSP), and cortical-basal ganglionic degeneration (CBGD). Compared with age-matched controls, only PSP patients showed slowing of saccades. Patients in all groups showed saccadic hypometria that was most marked vertically.

Eye movements.

Recent discoveries emanating from basic electrophysiological, anatomical, and pharmacological studies have implications for the diagnosis and treatment of clinical disorders of eye movements caused by disease affecting the brainstem and cerebellum. Electrophysiological studies have better defined the role of the superior colliculus in programming of saccades, and the nucleus reticularis tegmenti pontis in saccade-vergence interaction. Pharmacological inactivation studies have demonstrated the important role played by gamma-aminobutyric acid in the normal control of gaze and lead to trials of new agents in the treatments of nystagmus.

Tracking of illusory target motion: differences between gaze and head responses.

We compared ocular and eye-head tracking responses to an illusion of diagonal motion produced when vertical movement of a small visual target was synchronized to horizontal movement of a background display. In response to sinusoidal movement, smooth ocular pursuit followed vertical target motion, with only a small horizontal component. In response to regular stepping movement, all anticipatory saccades were in the direction of the illusion; these erroneous oblique movements were followed by corrective horizontal saccades.

The treatment of superior oblique myokymia utilizing the Harada-Ito procedure.

A woman with superior oblique myokymia (SOM) was cured of her condition by performing a Harada-Ito procedure. This procedure involves transposing the anterior portion of the superior oblique tendon, which is responsible for cyclorotation, nasally to create an effective weakening of the anterior portion of the tendon instead of temporal displacement utilized for superior oblique paresis. We measured the patient's eye movements before and after surgery, using the magnetic search coil technique, and confirmed that (1) the SOM was abolished and (2) vertical eye movements, including saccades, were unaffected.

Two types of foveation strategy in 'latent' nystagmus: fixation, visual acuity and stability.

The authors studied the foveation dynamics of two individuals with latent/manifest latent nystagmus (LMLN) to test the hypothesis that oscillopsia suppression and good visual acuity require periods of accurate target foveation at low slip velocities. Congenital nystagmus (CN) waveforms contain post-saccadic foveation periods; the LMLN waveform does not and yet allows for both oscillopsia suppression and good acuity. During fixation with both eyes open, there were intervals when the eyes were still and correctly aligned; at other times, there was esotropia and nystagmus with slow-phase velocities less than +/- 4 deg/sec and each fast phase pointed the fovea of the fixating eye at the target.

The effects of afferent stimulation on congenital nystagmus foveation periods.

Visual acuity in congenital nystagmus (CN) patients is related primarily to the duration of "foveation periods", during which the image of the target is relatively stationary in the foveal area. Thirteen individuals with CN were studied to test the hypothesis that somatosensory stimulation (vibration or electrical) of either the forehead or the neck damps CN and improves visual acuity. We identified characteristics of the nystagmus waveform that were likely to be important in determining visual acuity and combined these measures into an "acuity function" (NAFP) that correlated well with visual acuity (r2 = 0.

Head perturbations during walking while viewing a head-fixed target.

Background: Inexpensive, head-fixed computer displays are now available that subjects can wear during locomotion.

Hypothesis: Viewing a head-fixed visual display will change the characteristics of rotational head perturbations during natural walking.

Methods: Using a 3-axis angular rate sensor, we measured head rotations during natural or treadmill walking, in 10 normal subjects and 2 patients with deficient vestibular function, as they attempted to view (A) a stationary target at optical infinity; and (B) a target at a distance of 20 cm rigidly attached to the head.

Modulation of high-frequency vestibuloocular reflex during visual tracking in humans.

1. Humans may visually track a moving object either when they are stationary or in motion. To investigate visual-vestibular interaction during both conditions, we compared horizontal smooth pursuit (SP) and active combined eye-head tracking (CEHT) of a target moving sinusoidally at 0.

Evaluation of a video tracking device for measurement of horizontal and vertical eye rotations during locomotion.

We have evaluated a video-based method for measuring binocular horizontal and vertical eye movements of human subjects by comparing it with the magnetic search coil technique. This video tracking system (VTS) uses multiple infrared light sources and small video cameras to simultaneously measure the positions of reflected corneal images and the center of the pupil. The system has a linear range of approximately +/- 40 degrees horizontally and +/- 30 degrees vertically, a sampling rate of 120 Hz (180 Hz with the head fixed), and system noise with standard deviation of < 0.

Investigations of the pathogenesis of acquired pendular nystagmus.

We investigated the pathogenesis of acquired pendular nystagmus (APN) in six patients, three of whom had multiple sclerosis. First, we tested the hypothesis that the oscillations of APN are due to a delay in visual feedback secondary, for example, to demyelination of the optic nerves. We manipulated the latency to onset of visually guided eye movements using an electronic technique that induces sinusoidal oscillations in normal subjects.

Unsatisfactory treatment of acquired nystagmus with retrobulbar injection of botulinum toxin.

Purpose: We quantified the effects of botulinum toxin injected into the retrobulbar space of patients with acquired nystagmus with prominent vertical or torsional components.

Methods: We measured binocular eye rotations in three planes before and after injection of botulinum toxin (10, 12.5, or 25 units) into the retrobulbar space of one eye of each of three patients, ages 28 to 37 years, with acquired pendular nystagmus.

Dynamic properties of the human vestibulo-ocular reflex during head rotations in roll.

We investigated the dynamic properties of the human vestibulo-ocular reflex (VOR) during roll head rotations in three human subjects using the magnetic search coil technique. In the first of two experiments, we quantify the behavior of the ocular motor plant in the torsional plane. The subject's eye was mechanically displaced into intorsion, extorsion or abduction, and the dynamic course of return of the eye to its resting position was measured.