Smooth-pursuit Movements Research Articles

Clinical experiences with a new apparatus for bedside use in the eye tracking test

When a human subject follows a moving object with his eyes, two different types of movement are noted : smooth pursuit movements and rapid, jerky changes of position known as saccades. Smooth pursuit movements enable the fovea to be maintained on a continuously moving object, whereas saccades serve to bring the fovea promptly on to an eccentric point in the visual field.Eye tracking test (ETT) for investigation of smooth pursuit movements is nowadays one of routine tests in neurotological or neuro-ophthalmological clinics and various apparatuses have been used. However, as patients have to sit in front of them during the test, most serious patients in the neuro-surgical ward cannot be examined before surgery. For this reason one of the authors (Y. Chiba) designed a new handy apparatus for ETT at the bedside, and Mr. Shyosuke Matsuoka (Director of Mochizuki Electric Co. Ltd.) developed it as shown in Figures 1 and 2.The apparatus has 64 light targets using L.E.D. As the light targets line up straight and a red light is turned on and off, one by one, the red target seems to move smoothly and continuosly on a line back and forth due to residual light.The procured records are as accurate as those obtained with apparatus in neurotological clinics, and clinical experiences demonstrated several merits : 1) As it is small and portable, it can be easily used either at the bedside or in an outpatient clinic.2) It can be used at the bedside even in patients who cannot be easily transported because of severe increased intracranial pressure or marked vertigo.3) Even infants can follow a red target with interest, because the target moves back and forth automatically.4) Vertical smooth pursuit movements can also be easily examined by turning the apparatus 90°.5) Patients can also be examined while in a sitting position when the grip part of the apparatus is connected with the attached stand.6) The price is reasonable.

Abnormal Ocular Motility with Brainstem and Cerebellar Disorders

The disorders of ocular motility seen in association with brainstem or cerebellar disorders may point to rather specific anatomical or pathological correlations. Pontine gaze palsy reflects involvement of the pontine paramedian reticular formation. Internuclear ophthalmoplegia signifies a lesion in the medial longitudinal fasciculus. Skew deviation may result from a lesion anywhere in the posterior fossa. Ocular bobbing typically results from a pontine lesion. The Sylvian aqueduct syndrome is characteristic of involvement in the upper midbrain-pretectal region, usually a pinealoma. Cerebellar lesions may be manifested by gaze paresis, skew deviation, disturbances of saccadic or smooth pursuit movements, ocular myoclonus, or several characteristic forms of nystagmus. Familiarity with these disorders may be of great help to the physician dealing with a patient with a possible posterior fossa lesion.

Cerebellar role in smooth pursuit movement.

It is generally believed that pursuit eye movements are unaffected by cerebellar cortical atrophy or cerebellectomy. The present study was performed on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial injury or cerebellar tumors. Eye movements were measured by DC electro-oculography. A clear disparity of the slow phase of the optokinetic nystagmus was observed. When eye movements were contralateral to the ablated side the slow phase of optokinetic nystagmus was statistically slower than drum or visual field velocity. It is suggested that the cerebellum network is involved in the mechanisms of the smooth pursuit movement.

Parietal lobe mechanisms for directed visual attention

1. Experiments were made on the cortex of the inferior parietal lobule in 10 hemispheres of six alert, behaving monkeys. The electrical signs of the impulse discharges of single cortical cells were recorded as the monkeys executed tasks requiring them to fixate stationary visual targets, track those which moved slowly, and to make saccadic movements to foveate those which suddenly jumped from one locus to another within the field of view. A total of 907 neurons of area 7 were identified in terms of their physiological properties, particularly the correlation of their activity with the oculomotor components of these behavioral acts of directed visual attention; 480 of these were located by cytoarchitectural layer. Most identifiable cells of area 7 are visuomotor neurons, in a special and conditional sense. Their discharge frequencies increase before and during those steady fixations and movements of the eyes which secure and maintain foveation of objects, but only if the visual targets engaged are linked by a strong motivational drive; in our experiments, one between thirst and the light whose dimming the animal has learned to detect for liquid reward. We have identified and studied three major classes of neurons in area 7. 2. The visual fixation neurons (57%) accelerate discharge synchronously with fixation of a visual object the animal desires. The incremented discharge continues until reward, but then declines abruptly even when there is no immediate shift of the line of gaze. Fixation neurons are relatively inactive during those casual fixations by which the animal insepcts the surrounding environment. Mist fixation neurons subtend gaze fields limited to one quadrant or half of the total gaze field. The sum of the gaze fields of the fixation neurons in one hemisphere is weighted moderately toward the contralateral side. Fixation cells also discharge during slow pursuit movements in any direction so long as the movement stays within the gaze field of the neuron under study. About 40% of fixation cells are suppressed before and during saccadic movements of the eyes to a new target within the gaze field of the fixation cell. Those suppressed are located preferentially in layer V of the cortex. Suppression is maximal for saccades directed contralaterally to the hemisphere under study. 3. Visual tracking neurons are active during oculomotor pursuit of slowly moving visual objects, not during steady fixations. They show a marked directional but no laterality relation, and are suppressed before and during a visually evoked saccade superimposed on the smooth pursuit movement. The rate of discharge is a flat function of tracking speed so that these cells do not appear to emit signals which specify the speed of smooth pursuit movements. 4. The saccade neurons are active before and during visually evoked saccadic movements of the eyes but not before spontaneous saccades, no matter whether made in light or near darkness. The discharge of saccade neurons leads the eye movement by as much as 150 ms (mean, 73 ms)...

Concerning the Mathematical Description of the Oculomotor System Based on Neurophysiological Experiments in the Alert Monkey

Summary Single unit data from the Oculomotor nucler in alert monkeys were analyzed for periods of spontaneous eye movements and conditioned smooth pursuit movements. The presented results lead to the conclusion that the nypothesis for a mathematical description of the “final common pathway” by means of a single linear first order differential equation(Robinsun, 1970) can be replaced now by pairs of differential equations for each functional state of the system(e.g. fixation or tracking movements) for the following reasons: 1 During fixation there exist two linear characteristics for the impulse rate(IR) versus eye position because of the static hysteresis(Eckmiller, 1974), which describes the IR-difference between positions reached in the agonist phase(IR-increase) and those reached in the antagonist phase(IR-decrease). 2 Changes from fixation to visual tracking movements lead to changes in the impulse rate level at a given eye position (Eckmiller, 1975). Therefore a mathematical description must take these changes into account. 3 During visual tracking movements there exist different slopes in the characteristics for IR versus eye velocity in the agonist phase compared to the antagonist phase (Eckmiller, Mackeben, 1976). A model is presented which explains the measured characteristics for IR versus eye position and velocity for these oculomotor motoneurons in terms of a supra-nuclear and a nuclear superposition of eye position and velocity signals. This model makes use of recent findings by Keller(1974).

Ocular motor dysfunction in total and hemicerebellectomized monkeys.

Studies of ocular motor function in monkeys undergoing either total or hemicerebellectomies has revealed the following abnormalities which can be attributed to cerebellar dysfunction: 1. Loss of smooth pursuit movements 2. Gaze-fixation nystagmus 3. Loss of inhibitory input on the vestibular apparatus reflected in a decreased latency and prolonged response to caloric stimuli. It is intimated that the role of the hemicerebellum deals with ipsilateral tone and its effect on eye movements.

Function Organization of primate oculomotor system revealed by cerebellectomy.

Unilateral cerebellar lobectomy was carried out in young and mature macaques. There is no significant abnormality in saccadic eye movement or in the vestibulo-ocular reflex. There is a constant drift of the eyes in the contralateral direction, and the abilities to maintain eccentric gaze and to make smooth pursuit movements are jointly affected. The syndrome is transient in young monkeys, and even bilateral cerebellar lobectomy carried out serially leaves some ability to hold eccentric gaze and pursue smoothly. The findings permit the conclusion that the primate oculomotor organization depends on the active maintainence of straight ahead gaze. Saccades move the eyes in a coordinated way, and are also associated with correlated innervation to hold the gaze in the new position. Since cerebellar interventions which cause centripetal drift also always produce defects in pursuit movements, the abilities to maintain eccentric gaze and to pursue smoothly must have a common origin.

The discharge characteristics of single units in the oculomotor and abducens nuclei of the unanesthetized monkey.

1. Extracellular single unit records were obtained in the brainstem oculomotor complex of alert monkeys. 2. Maintained eye position, smooth pursuit and saccadic eye movement appear to be brought about by the same population of neurons. 3. Increasing deviation in eye position for fixation and for smooth pursuit movement is accomplished in two ways: (a) increase and decrease in firing rate and (b) change in the number of neurons discharging concurrently. 4. Saccadic eye movement is brought about by a rapid burst of firing in these same units. Saccade size is determined by the duration of the burst; the speed of the saccade appears to be influenced both by discharge frequency and the size of the neuronal pool discharging in synchrony. 5. A small population of units discharges specifically in association with vergence operations, increasing their firing rate to convergence and decreasing it to divergence.

Single unit activity in the frontal eye fields of unanesthetized monkeys during eye and head movement.

Single unit activity in the frontal eye field was investigated in unanesthetized monkeys during eye and head movement. Two types of cells (I and II) were found. Type I fired during voluntary saccadic movement occuring in a given direction and also during the fast phase of optokinetic and vestibular nystagmus. Cells of this type were silent during smooth pursuit movement and the slow phase of nystagmus. It was found that the firing pattern of Type I cells was maintained irrespective of head movement.

Oculomotor pursuit of vertical sinusoidal targets.

THERE are two principal types of gross eye movements, saccadic (flickering movements) and smooth (continuous compensatory or pursuit movements). Of the two, smooth movements have by far the lower velocity limit. An increasingly popular technique for investigation of the smooth system's performance has been to elicit pursuit of targets moving in sinusoidal motion for a range of test frequencies. One outstanding investigation1 using this method puts the smooth pursuit system's saturation point at some 20°–30°/s (that is appropriate up to only 1.0–1.5 Hz for a peak to peak target amplitude of 8.8°). This contrasts, incidentally, with the saccadic system's known ability2 to exceed 700°/s of appropriate velocity (during flicks between two fixation points).

An analysis of rapid eye movements of sleep in the monkey

Eye movements and the parietal EEG were measured in two Macaca mulatta monkeys during natural sleep. Most of the eye movements during the REM period occurred at velocities less than 50 deg/sec which corresponds to the velocity range of smooth pursuit movements in the awake monkey. Saccades or rapid fixation changes also occur during REM sleep but take up only 0.5% of the total episode time. In addition, the eye often turns at velocities intermediate to the normal saccadic and smooth pursuit velocities, exhibiting a type of movement which is not observed in the awake animal. During one-third of the REM episode the eye undergoes loop-shaped trajectories composed of movements of different velocities and there is a constancy of the velocity histograms among REM episodes. Neither of these phenomena were observed in the awake monkey suggesting that the interpretation that all eye movements during REM sleep are related to dream content should be made with caution.

Saccadic and smooth pursuit eye movements in the monkey.

1. Voluntary eye movements were measured in the chronic, unanaesthetized monkey. A training technique is described which conditions the animals to follow a large variety of target trajectories.2. The eye movements of the monkey are not qualitatively different from those of man. In response to random target motions the monkey also employs a combination of saccadic and smooth pursuit movements.3. Monkeys execute their saccades more rapidly than humans.4. Monkeys are capable of attaining smooth pursuit velocities which are twice as fast as those of man.5. Most of the critical experiments showing the separate nature of the saccadic and smooth pursuit modes in man have been performed on monkeys with similar results.6. Therefore, if one remains aware of the quantitative differences between the two primates, results of neurophysiological studies of the occulomotor system of the monkey can be expected to have considerable relevance when extrapolated to man.

IMPAIRED OCULAR PURSUIT MOVEMENTS.

Testing for the presence or absence of nystagmus is a routine part of every clinical, neurological examination. When this is done by moving the examiner's finger s-l-o-w-l-y across the visual field of the patient, one can also observe at the same time whether the patient's eyes follow the moving finger in a smooth manner or not. Occasionally it will be noted that the normally smooth pursuit movement is replaced by a saccadic motion. The eyes follow the moving finger in a series of short steps. They tend to overshoot the target, remain fixed for a brief period, and then advance ahead of the moving finger. The phenomenon differs from nystagmus inasmuch as it lacks the slow and fast component, is not present when the patient's gaze is held steady, and is not related to dysfunction of the vestibular-cerebellar system. The patient is usually subjectively unaware of the impaired performance and