Biomedical subjects
Publications and source records attributed to S Ron.
A new robust method for the approximation of physiological signals is proposed. The noise must satisfy only one condition: that the probabilities for positive and negative values are equal. Our results illustrate that the proposed method provides a more accurate approximation of signals than either the least square error or the least absolute deviation method in cases that include unknown noise density.
Saccadic characteristics were examined in 15 patients with unilateral hemispheric stroke. Eye movements were measured by a standard electro-oculogram technique. In patients with cortical infarcts, mean gain values were lower than in the control subjects for eye movements directed away from the infarct (contralateral), but higher for eye movements towards the infarct (ipsilateral) (p < 0.025). We suggest that impairment of efferent neural signals from the affected hemisphere of stroke patients may decrease excitation of the contralateral neural circuits and inhibition of the ipsilateral neural circuits of the brainstem saccade generator.
An inexpensive circuit to compensate for DC offset is presented. The circuit may be connected in a straightforward manner to any currently existing DC isolation amplifier and causes no deterioration in the performance of the system. The offset voltage is measured at discrete time intervals and then subtracted from the input signal. A switch is provided to bypass the offset compensation when the latter is not required.
Prolonged work with visual display units (VDUs) may result in a wide range of subjective complaints of visual fatigue and somatic disorders. Accepted tests for measuring the physiological correlates of eye discomfort are lacking. In this study, we tested accommodation and convergence, which are most often linked experimentally with VDU work. The tests were carried out on 16 VDU and 13 control workers aged 24 to 43 years, before work at the beginning of the week (first examination) and again four days later at the end of the work day (second examination). The results in VDU workers showed that both accommodation and convergence range significantly decreased. In addition, those workers with powerful accommodative or convergence ranges at the initial examination had a higher decrease. We suggest that accommodation and convergence measurements can be used to evaluate visual fatigue objectively in VDU workers.
Patients with hemispheric lesions frequently suffer from equilibrium impairment that may be prolonged and may interfere with rehabilitation. In an effort to clarify whether this phenomenon is related to vestibular dysfunction, we examined the relationship of the horizontal vestibulo-ocular reflex (VOR) with stability in 15 patients with unilateral hemispheric stroke. The study included electro-oculographic recording of the VOR while the patients were rotated in a vestibular chair. Stability was scored in accordance with the patients' ability to maintain equilibrium in six graded positions. The findings demonstrated relationship between VOR gain (eye/head displacement) and equilibrium. It is suggested that the "loss of balance" after stroke may be related to an impairment of the corticovestibular modulation of the vestibular function.
1. Eye-head co-ordination in the horizontal plane was studied in four human subjects using two successive flashes in the same direction, either increasing in eccentricity (IE), or decreasing in eccentricity (DE). 2. Results showed that for both conditions, head movements preceded eye movements and were typically longer or followed by a slow gaze movement. This slow movement was due to a vestibulo-ocular reflex gain of less than one. Gaze accuracy was achieved by small head movement adjustments. 3. Gaze movement to an IE stimulus had a staircase pattern, and to a DE stimulus, a pulse-step pattern or one gaze saccade to the final flash eccentricity. 4. In some cases, however, in response to a DE stimulus, the eye and head movements were directed to different displacements (dissociation); i.e. the head movement started towards the first flash eccentricity with a concomitant eye saccade to the second flash eccentricity. When this occurred, gaze movement did not resemble a pulse-step pattern. 5. It is suggested that non-visually orienting gaze is driven mainly by head movement. Eye and head movements can be either tightly coupled or dissociated, depending on the stimulus pattern.
This study examined vestibular function following hemispheric ischemic strokes, by testing the suppression of the vestibulo-ocular reflex (VOR). Fifteen patients with cortical or subcortical infarcts several months after a unilateral hemispheric stroke were compared with control subjects. The results indicated impairment of VOR suppression in patients with cortical infarcts. It is suggested that cortical infarcts may induce a mild and symmetrical impairment of vestibular activity which may be responsible for mild and transient imbalance in patients who undergo stroke.
Anisodamine, an analog of atropine, was isolated first in China. Patch-clamp technique was used to study the inhibitory effect of anisodamine (Ani) on acetylcholine receptor on the membrane of muscle innervated by neuron. Neural tube in embryo of Xenopus laevis were cultured. By whole-cell clamp and outside-out patch, we found that the inhibitory effect of Ani was obvious on both miniature end-plate currents (MEPC) and single channel. This effect was reversible and the minimal concentration for complete inhibition was 60 mumol.L-1, vs 1 and 0.5 mmol.L-1 for atropine and scopolamine, respectively. Our results indicate that Ani blocks both M-ACh and N-ACh receptors.
It is well established that visual display unit (VDU) operators complain of visual fatigue and visual stress during after-work hours. The present study was divided into two parts. In the first part, standard eye examinations were performed on a group of VDU workers (n = 32) and a control group (n = 15); those subjects who were found to have correct vision (n = 16 and 13, respectively) participated in the second part. The eye examinations revealed that on the average, the VDU workers suffered more than twice as many visual impairments as the controls. In those with correct vision, the near point of accommodation was measured at the beginning of the workday at the start of the week, and at the end of the workday, four days later. In the VDU group, the decrease in accommodation was uniformally distributed between zero and 1.0 diopter, whereas among the non-VDU workers, 77% of the decrease was between zero and 0.25 diopter. The dynamic range of accommodation in the VDU workers on the second examination was smaller than on the first. We conclude that some of the visual stress and visual fatigue that developed at work hindered visual activities after work.
Cortical areas were explored with regard to saccade control: the lateral intraparietal (LIP) area is involved in the spatial aspects of sensorimotor processing; the supplementary motor area in goal-directed gaze control; and from lesion studies; the posterior parietal cortex in triggering visually guided saccades. Different studies have suggested that the spatial-to-temporal transformation takes place in the superior colliculus (SC) and the cerebellum. When the vestibulo-ocular reflex (VOR) produces inadequate eye movements, other supplementary mechanisms (e.g. non-visual, saccade) may play a role in correcting gaze. A classification of central vestibular disorders of the brainstem and VOR has been proposed, as manifested in any one of the three major planes of action (yaw, pitch and role).
Tight coupling between eye and head movements has been observed in response to a single visual target offset. On this basis, when the visual stimulus consists of two successive steps in the same (horizontal) direction, either increasing in eccentricity (staircase) or decreasing in eccentricity (pulse-step) gaze should be due to concomitant eye and head angular displacement. That is, the eyes and head should aim at each target displacement so that their combined movement matches target offset. We have tested this hypothesis in five healthy subjects. The measured variables were head and gaze offset, the interval between two consecutive saccades from onset to onset (I) and the response delay between onset of the second step and onset of the first gaze saccade (D). With both staircase and pulse-step stimuli, the eye saccade preceded the head movement, and the gaze response either had the stimulus profile pattern or consisted of one gaze saccade to the final target offset. In response to staircase stimuli, I decreased concomitantly with an increase in D; with pulse-step stimuli, as D increased, I decreased slightly in three subjects and decreased markedly in two subjects. Dissociation between the eye and head movements could clearly be demonstrated with pulse-step stimuli: the first gaze saccade to the target pulse displacement was accompanied by a head movement to the target step offset. We also observed cases in which the gaze saccade to the target step displacement was made simultaneously with the head movement to the target pulse offset. Our study extends previous observations in head fixed condition and illustrates that in the majority of cases, when the head is free and a visual pulse step stimulus is presented, both the saccadic and head systems have the ability to modify or cancel the initial neural command to move to the first target displacement. When this modification takes place in only one system, eye and head movements are dissociated.
Two experiments have been designed to test whether the saccadic system takes target motion into consideration in computing saccade amplitude. In one experiment, while the subject fixated straight ahead, either a horizontal ramp-step-ramp or a horizontal step-ramp target moved from left to right. After the step, the subject had to make a saccade and follow the target. In the second set of experiments, the target, after an initial step, moved extrafoveally from up to down at fixed velocity; a tone, signaling the subject to make a saccade to the target and follow it, was delivered either after a variable delay (previewed condition) or simultaneously with the initial target step (non-previewed condition). In both experiments, eye position at saccade end was statistically different from target position 100 msec before saccade onset only when the target slow motion was presented before the step (i.e. in horizontal ramp-step-ramp and in previewed H-step V-ramp paradigms), suggesting that target motion could be used by the saccadic system to extrapolate the future target position, only if the subject is given enough time to observe the target ramp motion before the step.
Previous studies indicate that in response to a step-ramp visual target movement, the saccade amplitude approximates target displacement 100 ms before saccade onset. This study examines whether the saccadic system takes target motion into consideration when computing saccadic amplitude, if target movement is seen by the subject before he is requested to make a saccade. In the first experiment, while the subject fixated at the target (laser dot) and maintained fixation, the target jumped to the left and moved to the right at a fixed velocity. At some predetermined site, the target jumped a step to the right and continued to move in that direction. After the target step, the subject had to make a saccade and follow target motion. In the second experiment, while the subject fixated at the target and maintained fixation, the target jumped to the right and up and moved down at a fixed velocity. At some predetermined site, an auditory signal was given, and the subject had to make a saccade and follow target motion. Results in both experiments showed that the eye position was statistically different from the target displacement at 100 ms before saccade onset, indicating that the saccadic system uses target velocity in computing saccade amplitude.
Cats were tested for their ability to follow a dot target which periodically jumps horizontally from side to side. They can learn to perform saccadic tracking of various stimulus frequencies, and often they produce saccades predicting the target displacements. The preferred stimulus frequency for response to synchronize was in the 0.5-Hz range. Cats tend to undershoot the target. They also tend to adopt a strategy of locking predominantly to one direction of displacement, but they can be trained to reverse this preferred side or to lock to both sides. Saccades to the preferred side are more accurate, and longer and slower in comparison to saccades to the other side, thus demonstrating a velocity-accuracy trade-off phenomenon in the cat responses. Saccadic characteristics as expressed by the main sequence are apparently a stable property independent of the stimulus frequency.
Tapping responses were recorded in a group of patients who sustained lesions from cerebrovascular accidents and from an age-matched group of healthy subjects. In each experiment the stimuli were an auditory signal, a flash, or a light touch on the arm, delivered either at random intervals or at fixed time intervals of 1, 2, 3, or 4 s. The tapping response was done with each hand separately (first experiment) or with each hand alternately (second experiment). Healthy subjects, 'predicted' the stimuli (response time less than 150 ms), when the 'preferred' fixed time interval was used. One group of patients (n = 3), did not predict the stimuli at the preferred fixed intervals when tapping was done with the hand related to the involved hemisphere. The second group of patients (n = 3) did not predict the stimuli when tapping was done with either hand.
A mathematical model of eye tracking of periodic square wave target motion has previously been proposed. In this work the model was further studied with regard to saccadic response time to symmetrical square wave target motion in 6 patients with unilateral parietal lesions following cerebrovascular accidents. Three types of saccadic response time were noted. In patients with type I, saccades contralateral to the damaged hemisphere had similar characteristics to those found in ipsilateral direction, but with longer response time. In those with type II, the saccadic response time was about the same on movement in either direction for repetitive target cycle durations of 1.2 or 2.0 s. In patients with type III, the target motion could not be predicted, in either direction.
Although benign tumorous lesions of the liver are rare, they can be found particularly among women in the preclimacteric age group. Usually, the clinical findings are non-characteristic. Differentiation from other space-occupying growths can be difficult due to the variable appearance of focal nodular hyperplasia. The selective angiogram is typical in some cases and no further radiological procedures are required. Nevertheless, histological examinations should be performed for complete clarification.
The symptomatology of congenital fibrosis of extraocular muscles, markedly restricted eye movements, blepharoptosis and chin elevation were found in 10 individuals and three generations of one family. The mode of inheritance is compatible with a variable expressive dominant trait. Our experience with the surgical management of the condition using more aggressive procedures than currently employed is described.