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At least 19 recordsLinked to original sources
PubMed1992

Saccadic eye movements in Parkinson's disease: II. Remembered saccades--towards a unified hypothesis?

Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched normal controls in a series of saccadic paradigms in order to test various hypotheses relating to the origin of the Parkinsonian saccadic defect. The paradigms comprised a reflex saccade paradigm, a standard remembered saccade paradigm, a remembered saccade paradigm with delayed centre-offset, and a remembered saccade paradigm with a second target flash immediately prior to saccade execution. Finally, subjects executed both reflex and remembered saccades in a standard remembered paradigm (the "two-saccade" paradigm). As has been reported previously, Parkinsonian subjects demonstrated hypometria on all remembered saccade paradigms, particularly the "two-saccade" paradigm. There was, however, no significant difference between the first three remembered saccade paradigms. These studies serve to refute a simple attentional capture hypothesis, and a hypothesis that suggests that the abnormality of remembered saccades is due to concurrent reflex saccade suppression. On the basis of the results, further hypotheses are advanced in an attempt to explain all published work on Parkinsonian saccades.

Aged↗
PubMed1992

Saccadic eye movements in Parkinson's disease: I. Delayed saccades.

The saccadic eye movements of nine patients with Parkinson's disease were compared to those of nine age-matched controls in two paradigms generating volitional saccades. In both paradigms, subjects had to make delayed saccades to peripheral LED targets: a peripheral target appeared 700 msec before a buzzer sounded, the buzzer being the signal to make a saccade to the target. In the first paradigm ("centre-off"), the fixation target was extinguished simultaneously with buzzer onset. In the second ("centre-remain") it was not extinguished until 1000 msec later. The results showed that for outward saccades in both paradigms, there was no difference between Parkinsonian patients and controls, but saccadic latencies were significantly shorter in the "centre-remain" paradigm. The initial outward saccades were indistinguishable from the normal, reflex saccades of the same subjects. However, saccades returning to the centre (a type of remembered target saccade) were hypometric and showed multistepping. Both effects were more pronounced in patients with Parkinson's disease. The significance of these findings in terms of current hypotheses about the nature of the Parkinsonian saccadic deficit is discussed.

Aged↗
PubMed1992

Burst discharges of fastigial neurons in macaque monkeys are driven by vision- and memory-guided saccades but not by spontaneous saccades.

Discharges from 61 saccadic burst neurons in the fastigial oculomotor region were recorded for two trained macaque monkeys during vision-guided or memory-guided saccades or spontaneous saccades in the dark. Although these neurons exhibited vigorous, burst discharges during both vision-guided and memory-guided saccades, only weak bursts were observed during spontaneous saccades in the dark. Especially in 10 of the 61 neurons, saccadic burst discharge was almost completely absent during spontaneous saccades in the dark. These findings suggest that the cerebellum plays an important role in the control of vision-guided saccades as well as memory-guided saccades, but not of spontaneous saccades in the dark.

Animals↗
PubMed1992

Saccades to targets in three-dimensional space: dependence of saccadic latency on target location.

The latency of saccadic movements to targets appearing at various positions in three-dimensional visual space was measured in four experiments. The first experiment confirmed that latencies of saccades to visual targets are greater in the lower visual field and showed that the increase is not influenced by the vertical starting position of the eye in the orbit, nor by a time gap between the fixation offset and the target onset. A hypothesis that this visual field difference was caused by a link between downward saccades and convergence movements was tested by recording saccade latencies when the targets were in a different depth plane from that of the original fixation. We did not find any direct support for the vergence involvement hypothesis, although the lower/upper visual field effect was shown to decrease consistently in monocular viewing. It was also shown that saccades to targets positioned in a different depth plane have longer latencies. In a final experiment, the visual field effect was shown to depend on the egocentric rather than the gravitational vertical.

Adult↗
PubMed1992

Dependence of presaccadic cortical potentials on the type of saccadic eye movement.

Premovement cortical potentials were studied with 4 types of saccadic eye movement: (a) visually triggered saccades of normal reaction time (RT; regular saccades); (b) visually triggered saccades of extremely short RT (express saccades); (c) saccades towards predicted target locations (anticipatory saccades); (d) saccades back towards predicted location of fixation point (refixation saccades). With all 4 saccade types a "presaccadic negativity" with the maximum at the vertex (Cz) was observed. A bilaterally symmetrical component contained in this potential (being smallest with almost unconsciously performed refixation saccades and smaller in trained than in naive subjects) appeared to be related mainly to the subjects' volitional effort. In addition, anticipatory and refixation saccades were preceded by an early, widespread contralateral negativity, which we relate to cortical activities that prepare, in general terms, action within or towards the hemifield containing the saccade goal. During the 60 msec before anticipatory saccades, a negativity occurred over the contralateral central lead, which may reflect neural activation in the frontal eye field (FEF) and premotor cortex. In contrast, regular saccades were preceded 30 msec before onset by a negativity over the contralateral parietal cortex, which probably reflects an activation of parietal visuo-motor neurons. No lateralization of the cortical potentials was observed before express saccades, which suggests that these saccades are generated in a reflex-like way mainly by subcortical mechanisms.

Adult↗
PubMed1992

Saccade-vergence interactions in humans.

1. We recorded eye movements in four normal human subjects during refixations between targets calling for various combinations of saccades and vergence. We confirmed and extended prior observations of 1) transient changes in horizontal ocular alignment during both pure horizontal saccades (relative divergence followed by relative convergence) and pure vertical saccades (usually divergence for upward and convergence for downward saccades); 2) occasional, high-frequency (20-25 Hz), conjugate oscillations along the axis orthogonal to the main saccade; and 3) the speeding up of horizontal vergence by both horizontal and vertical saccades. 2. To interpret these findings, we developed a hypothesis for the generation of vergence to step changes in target depth, both with and without associated saccades. The essential features of this hypothesis are 1) the transient changes in horizontal ocular alignment during pure horizontal saccades reflect asymmetries in the mechanical properties of the lateral and medial rectus muscles causing adduction to lag abduction; 2) pure vergence movements in response to step changes in target depth are generated by a neural network that uses a desired change in vergence position as its input command and instantaneous vergence motor error (the difference between the desired change and the actual change in vergence) to drive vergence premoter neurons; and 3) the facilitation of horizontal vergence by saccades arises from nonlinear interactions in central premotor circuits. 3. The hypothetical network for generating pure vergence to step changes in target depth is analogous in structure to the local feedback model for the generation of saccades and has the same conceptual appeal. With the assumption of a single nonlinearity describing the relationship between a vergence motor error signal and the output of the neurons that generate promoter vergence velocity commands, this model generates pure vergence movements with peak velocity-amplitude relationships and trajectories that closely match those of experimental data. 4. Several types of models are proposed for the central, nonlinear interaction that occurs when saccades and vergence are combined. Common to all models is the idea that omnidirectional pause neurons (OPN), which are thought to gate activity for saccade burst neurons, also gate activity for saccade-related vergence. In one model we hypothesize the existence of a separate class of saccade-related vergence burst neurons, which generate premotor horizontal vergence commands but only during saccades. In a second model we hypothesize separate right eye and left eye saccadic burst neurons that receive not only conjugate, but also equal but oppositely directed vergence error signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Enduring dysmetria and impaired gain adaptivity of saccadic eye movements in Wallenberg's lateral medullary syndrome.

Saccadic eye movements and the adaptive control of their amplitudes were examined in patients with Wallenberg's lateral medullary syndrome. Half of the patients had permanent saccadic dysmetria. Their primary saccades had asymmetric amplitudes: those made in response to an ipsilateral target step (i.e. to the lesion side) tended to be hypermetric and saccades made in response to a contralateral target step were strongly hypometric. Multiple correction saccades were needed for target fixation. The adjustment of the amplitude of artificially induced hypermetric saccades, called gain adaptivity, was examined experimentally by using double target steps. The first target step elicited the primary saccade which triggered a further target displacement. This second, intra-saccadic target displacement was opposite to the first target step and caused the primary saccade to overshoot the final target position. In this way a post-saccadic target position error was generated which had to be corrected for foveal fixation. With repetition of this stimulus sequence the saccadic control system of normal subjects made an adjustment in amplitude of the main saccade such that the overshooting gradually diminished. After a few hundred trials primary saccades became orthometric with respect to the final target position; in respect to the first target step they were, however, strongly hypometric. The experimental data show that patients with Wallenberg's syndrome had a reduced capability to readjust saccadic amplitude. This observation together with the enduring saccadic dysmetria suggest that adaptive gain control of saccades is impaired in patients with lesions restricted to the dorsolateral medulla. It is speculated that these lesions most likely disrupt olivo-cerebellar pathways which are believed to be of paramount importance in visuo-motor adaptation of the cerebellum.

Adaptation, Physiological↗
PubMed1992

Saccadic dysmetria in a patient with a right frontoparietal lesion. The importance of corollary discharge for accurate spatial behaviour.

Double-step experiments have demonstrated that retinotopic coding is inadequate to explain the spatial performance of the saccadic system. In such experiments a subject is asked to make two successive saccades to fixate two sequentially flashed targets each of which disappears before the first saccade. Despite the dissonance thus created between the retinal location of the second target and the saccade necessary to acquire it, normal humans and monkeys perform the task perfectly well. Single unit recording in monkeys indicates that neurons in the superior colliculus, frontal eye fields and in parietal cortex generate a spatially accurate signal during the performance of double-step saccades, which is thought to be obtained by combining a retinotopic signal with a signal corollary to the previous saccadic eye movement. We studied saccadic eye movements in a patient with a right fronto-parietal lesion using single- and double-step tasks. Single saccades into the left (contralesional) hemifield had longer latency and were hypometric relative to those into the right (ipsilesional) hemifield. Varying the initial orbital position had no effect on the latency and accuracy of saccades to left and right retinal stimuli. When the patient was asked to do a double-step task with targets flashed first into the right field and then into the left field, she performed well. When she was asked to do the same task with a target flashed first into the left field and then into the right field she made the first saccade correctly but never acquired the second target, even though this required her to make a saccade in the normal direction to a stimulus that appeared in the normal field. Such a deficit therefore cannot be one of retinotopic or spatial coding, nor can it be one of generating a certain direction of saccade. We suggest that the deficit is a failure of corollary discharge, the inability to register the amplitude and direction of a saccade into the contralesional field, and use that information to update the representation of the location of the next saccade target.

Aged↗
PubMed1992

Dynamics and efficacy of saccade-facilitated vergence eye movements in monkeys.

1. Four macaque monkeys were trained to fixate visual targets. Eye movements were recorded binocularly using the search coil technique. Saccades, vergence movements, and combinations of the two were elicited by training the monkeys to alternate the gaze between real visual targets that differed in viewing distance and eccentricity with respect to the monkeys' heads. 2. When they shifted the gaze between targets that were at different viewing distances, the monkeys made vergence eye movements. For targets placed along the midsagittal plane, the monkeys often made binocularly symmetric vergence movements. The peak speed of symmetric divergence movements increased linearly with vergence amplitude by 5.7 deg/s per degree of vergence. The peak speed of symmetric convergence movements increased linearly with vergence amplitude by 7.9 deg/s per degree of vergence. 3. For gaze shifts between targets placed eccentrically with respect to the midsagittal plane and at different viewing distances, the monkeys made saccades in combination with vergence eye movements. When a saccade occurred during a vergence movement, peak vergence eye speed increased abruptly and reached a peak that was proportional to the speed of the saccade. For four monkeys, peak divergence speed ranged from 242 to 315 deg/s and peak convergence speed ranged from 257 to 340 deg/s for 16-deg vergence and 20-deg saccadic eye movements. 4. For gaze shifts between far targets at the same viewing distance but different eccentricities, saccadic eye movements were transiently disjunctive even though there was no vergence requirement. Initially, the eyes diverged and then converged to restore fixation to the correct depth plane. Divergence was followed by convergence regardless of the direction of the saccade. 5. The presence of transient saccade-related disjunctive eye movements suggested that the abrupt increase in peak vergence speed during combined saccadic and vergence eye movements was produced by the linear addition of a vergence eye movement and the saccade-related transients. Consistent with this hypothesis, the rate of change in peak vergence speed during various-sized saccades between far targets (no vergence required) was similar to the rate of change in peak vergence speed during combined saccadic and vergence movements. However, the peak vergence speeds during the combined movements were higher than predicted by the linear addition hypothesis, suggesting the presence of an additional mechanism. 6. The saccade-related increase in peak vergence speed during combined saccades and vergences led to a significant decrease in the amount of time required to complete vergence movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Burst discharges of mossy fibers in the oculomotor vermis of macaque monkeys during saccadic eye movements.

Mossy fiber activity was recorded from the oculomotor vermis (lobules VIc and VII) during visually guided saccades. Saccade-related activities of 99 mossy fiber units were observed in two alert macaque monkeys. Ninety-six units were characterized by high-frequency bursts of firing in response to visually guided saccades (burst unit). These units were silent during all periods of fixation in any gaze position. Three units showed eye position-related tonic discharges with saccadic bursts. The lead time of saccadic bursts ranged from 2.6 to 80.5 ms (mean 27.9 ms, SD 16.6 ms). About 75% of the burst units exhibited a long lead burst characterized by a slow buildup, while the remaining units showed short lead bursts with a sharp onset. About 80% of the units showed burst in association with contralaterally directed saccades. The remaining units exhibited bursts in association with ipsilateral saccades. Preferred directions in this population covered the entire field including the vertical and the oblique. About 68% of long lead burst units exhibited the movement field which consists of a whole sector of the entire oculomotor range (directional type). About 32% of long lead burst units showed the movement field which is a closed area within the oculomotor range (vectorial type). On the other hand, peak frequency of short lead burst units increased in proportion to saccade amplitude. The end of the burst in all units always preceded the completion of saccade. The end of burst was time-locked to the completion of saccade, so that the lead time from the end of burst to the end of saccade was consistent among these units and, was constant regardless of saccadic amplitude. The duration between the peak and the offset of burst was correlated with the amplitude of saccade (0.63 < or = r < or = 0.83). Long lead burst of mossy fibers was almost comparable to burst activity in the nucleus reticularis tegmenti pontis (NRTP), while short lead burst of mossy fibers closely resembles activity of excitatory burst neurons in the paramedian pontine reticular formation (PPRF). These findings suggest that the cerebellum receives command signal from the superior colliculus via the NRTP and feedback signal from the PPRF.

Animals↗
PubMed1979

The role of the flocculus of the monkey in saccadic eye movements.

1. Purkinje cell discharges were recorded from the flocculus of monkeys either spontaneously making saccadic eye movements (saccades) or trained to fixate a small visual target presented on a tangent screen. In the trained monkeys, saccades of known magnitude and direction were induced by changing the position of the fixation target. 2. Among 513 Purkinje cells, 343 units (66.9%) paused during saccades in all directions (286 units) or in particular directions (57 units). In most units, there were intimate temporal relationships between the beginnings of pauses and saccades, and between the ends of pasuses and saccades. 3. The pause in activity preceded saccades by an average of 9.6 msec, with a maximum lead time of 30 msec. In a fraction of the units (7.6%), the pause started after the onset of saccades. 4. There were 104 units (20.3%) which showed bursts during saccades in all directions (eighty-two units) or in particular directions (twenty-two units). 5. In sixty-six units (12.8%) a burst was associated with saccades in one direction and a pause in the opposite direction. 6. The burst in the burst and burst-pause units preceded saccades by an average of 3.8 msec. There was no significant difference in the lead times between these two groups of units. 7. There was a linear relationship between the duration of the pause in Purkinje cell activity and that of the accompanying saccade. A linear relationship was also seen between the pause duration and the magnitude of saccade.

Action Potentials↗
PubMed1992

The conjugacy of human saccadic eye movements.

Binocular measurements of instantaneous velocity vectors in normal human subjects during saccades showed: (1) considerable trial to trial variation in peak velocity, saccade duration, and saccade curvature despite saccade accuracy; (2) variations in one eye were mirrored by similar variations in the other eye, with a high positive correlation. The high correlation between the peak velocities suggest that saccades in the two eyes are driven by a common saccade generator. Assuming that a local feedback loop guides saccades, the high correlation between saccade durations and between saccade curvatures suggests that both eyes are guided by common feedback. If so, monocular adaptation must occur downstream from the saccade generator.

Humans↗
PubMed1992

A quantitative analysis of saccades and smooth pursuit during visual pursuit tracking. A comparison of schizophrenics with normals and substance abusing controls.

The eye movements of schizophrenic patients are characterized by decreased smooth pursuit gain and an increased frequency of saccades. However, the nature of these saccades and their function during smooth pursuit has not been clearly defined. To address this issue we examined the eye movements of 22 schizophrenic patients, 20 substance abusing patients (primarily alcohol; some with concomitant cocaine and/or cannabis abuse), and 17 normal controls during a visual pursuit task using infra-red oculography. A computerized pattern recognition algorithm divided pursuit eye movements into two basic components: smooth pursuit and saccadic eye movements. The algorithm also determined eye position error and velocity error before and after each saccade. Schizophrenic patients had lower smooth pursuit gain (p less than 0.02) and made more saccades during smooth pursuit (p less than 0.02) than either comparison group. When saccades were assigned to subcategories based on direction and position error, only the frequency of 'catch-up' saccades differentiated schizophrenic patients from the comparison groups (p less than 0.05). Smooth pursuit gain was negatively correlated with saccadic frequency among all three subject groups. Eye velocity preceding saccades was significantly lower among the schizophrenic patients, but pre or post saccadic position error did not differ among the three groups. Discrete analysis of the fine structure of visual pursuit tracking may lead to a better understanding of eye movement abnormalities in schizophrenia.

Adult↗