Components Of Eye Movements Research Articles

Smooth pursuit eye movements in schizophrenia and affective disorder.

Smooth pursuit eye movement (SPEM) dysfunction is considered to be a promising candidate for a biological marker for genetic vulnerability to schizophrenia. There are conflicting findings regarding the question of what is exactly dysfunctional in SPEM dysfunction and what component of eye movements is really specific to schizophrenia. The purpose of the current study was to help to clarify the nature of (SPEM) dysfunction and its specificity to schizophrenia. Smooth pursuit eye movements of 43 schizophrenic patients, 34 patients with major depression and 42 normal controls were examined using high resolution infrared oculography. These groups were compared on several indices of oculomotor functioning (gain, different saccadic categories). Schizophrenics had a significantly higher catch-up saccade rate than depressed patients and normals. The percentage of subjects with an abnormally high catch-up saccade rate defined as beyond the mean plus 2 S.D. of the normal control group was significantly higher in schizophrenics (27.9%) than in depressed patients (8.8%) and normal controls (0%). Low gain and higher numbers of intrusive saccades tended to be more prevalent in both patient groups but did not distinguish schizophrenics from depressed patients. Low gain and high rates of intrusive saccades contribute to SPEM dysfunction in major depression. Abnormally high rates of catch-up saccades seem to be the oculomotor component in smooth pursuit, that is specific to schizophrenia.

Opsoclonus and ocular flutter

Ocular flutter is an ocular motor disorder consisting of involuntary back-to-back saccades in the horizontal plane without a saccadic interval. In opsoclonus, these pathological eye movements occur not only in the horizontal but also in the vertical plane. Originally, opsoclonus was described as irregular, conjugate, chaotic and partially continuous rapid eye movements. In this review, the clinical picture, differential diagnosis, etiology, natural course and therapeutic concepts for these eye movement disorders are described. It is stressed that continuous and intermittent forms of opsoclonus can be distinguished and that these differences usually correlate with the severity of the underlying disease. In contrast, the intermittent forms of opsoclonus and ocular flutter are usually only distinguished by the lack of a vertical eye movement component in ocular flutter.

Changes in sleep architecture following chronic mild stress

Chronic exposure to mild unpredictable stress causes subsensitivity to rewards (anhedonia). These effects are reversible by chronic treatment with antidepressant drugs, and have been proposed as an animal model of depression. In the present study, sleep architecture, particularly the rapid eye movement (REM) component, was mapped in rats following exposure to chronic mild stress. The study used a unique large scale automated sleep system to record and analyze the sleep signals from 32 rats simultaneously. The effects of stress on sleep were maximal following 21 days of stress, at which time the stressed animals demonstrated decreases in active waking and deep sleep, and disruptions of REM sleep. The changes in REM sleep included increases in the duration of and transitions into REM sleep over the sleep part of the sleep-wake cycle, and most importantly, a reduced latency to the onset of the first REM period. These sleep abnormalities, and in particular the decrease in REM latency, are consistent with those reported in endogenous depression. The results provide further support for the validity of the chronic mild stress paradigm as an animal model to study the mechanisms underlying endogenous depression.

3D Analysis of Nystagmus in Peripheral Vertigo

Three-dimensional analysis of nystagmus was carried out in patients with peripheral vestibular diseases using a computerized image recognition technique developed by us. In the present study, we analyzed data from patients with Meniere's disease and vestibular neuritis with the central premise of localizing the pathology in the peripheral vestibular organs. In Meniere's disease, the recordings of all subjects showed two components of eye movements, namely the horizontal and torsional components. On the other hand, most of the patients with vestibular neuritis exhibited all three components of spontaneous nystagmus. The horizontal and vertical components of nystagmus in patients with vestibular neuritis were directed towards the contralateral side of the lesion and upwards. Based on these results and with reference to animal experiments that have related the eye movements with each labyrinthine end organ, it can be speculated that in Meniere's disease the pathological changes may involve all semicircular canals, whereas the main site of lesion in vestibular neuritis could be localized to the superior vestibular nerve.

Pathological localization of benign paroxysmal positional vertigo--from three-dimensional analysis of nystagmus

Although it has been speculated that benign paroxysmal positional vertigo (BPPV) derives from the utricle or posterior semicircular canal, the origin of BPPV is still controversial. In this study, we investigated the role of the utricle and semicircular canals (especially the vertical semicircular canal) relative to BPPV by three-dimensional analysis, focusing on the horizontal, vertical, and torsional positions by applying our computerized eye movement analysis system. In 13 subjects who were diagnosed as having BPPV, we carried out the positioning nystagmus tests, and analyzed three components of nystagmus. By using a pendular rotation stimulus, we also measured three components of eye movement elicited from the vertical semicircular canals in 5 normal subjects and 2 subjects from whom acoustic tumors were removed by the translabyrinthine approach. We compared two components (vertical and torsional) of BPPV with those of eye movements elicited from the vertical semicircular canals. In BPPV, the slow phase velocity of the torsional component was greater than that of the vertical component. Conversely, the amplitude of the vertical component from the vertical semicircular canals was greater than that of the torsional component. From these results, by analyzing the vestibuloocular reflex of vertical semicircular canals, it is difficult to support the idea that the pathology of BPPV is located in the posterior semicircular canal alone.

Study of non-visually induced smooth pursuit eye movements and their predictability using pseudorandom target motion

It has been found that the smooth pursuit eye movements (SPEM) are elicited by not only visual stimuli but also non-visual information such as the subject's fingertip movement and a moving sound source. We have already reported the quantitative analysis of SPEM which were induced by somatosensory and acoustic information. In the previous study, we used a sinusoidal waveform that could be highly predictable. Since it is wellknown that predictive control has an important role in the normal SPEM, we expect the predictive control to function in non-visually induced SPEM (NVSPEM). We quantitatively analyzed NVSPEM and normal SPEM evoked by pseudorandom target motion in ten human subjects who had no ocular, oculomotor or vestibular disorders. NVSPEM were induced by the following two non-visual targets: 1, subjects' fingertip motion as a somatosensory target ("Somato"), 2, a small loudspeaker (3-cm diameter.) generating white noise with an intensity of about 60 dB (A) as an acoustic target ("Acoustic"). A servo-controlled swing arm of 50cm was used to drive the subject's fingertip and the acoustic target of the small loudspeaker. The horizontal motion of the swing arm was controlled by a personal computer. The pseudorandom target motion was generated by mixing four sinusoids (0.1, 0.2, 0.4, 0.8 Hz) of which the phases were randomly selected and the peak velocities were equally set at 19 deg/s. The mean peak velocity of the target was 26.2 deg/s and the amplitude was limited within 15 deg. Horizontal eye movements were recorded by DC electro-oculography and on an analogue datatape. The experiment was performed for 30 s in complete darkness so that the subjects' fingertip and loudspeaker as such remain invisible to the subject. Signals from the data recorder were smoothed by a low pass analogue filter of 20Hz, after digitization with a sampling frequency of 200 Hz and precision of 12 bits, and stored on a computer. The slow and quick eye movement components, both of which were present in each class of horizontal eye movement investigated, were identified and separated by a computer. Then we developed a method of automatic quantitative analysis of ocular tracking eye movement. Gain and phase values for the smooth pursuit eye movements were obtained in each condition. In the lower frequency area, the gain elicited by the pseudorandom stimulation was lower than the smooth pursuit gain for sinusoidal (predictable) stimulation in all conditions. In the highest frequency, gain values did not differ significantly among the three. For the sinusoidal stimulation, the phase of the smooth component of "Visual" always had a lag and that of "Somato" and "Acoustic" had a lead in lower frequencies. All conditions had a phase shift, decreasing with increasing frequency. For the pseudorandom stimulation the phase of the SPEM had a lead only in the lowest frequency (0.1 Hz). On the other hand, in the NVSPEM the phases of the three lower frequencies had a lead which had a tendency of a larger phase lead with decreasingly frequency. In the highest frequency (0.8 Hz), we could see a short phase lag. These findings support the idea that SPEM and NVSPEM have a mutual or similar physiologic system and overlap part of the anatomical pathway.

Emotional processing during eye movement desensitization and reprocessing therapy of vietnam veterans with chronic posttraumatic stress disorder

This study examined emotional processing and outcome in 17 Vietnam veterans with chronic posttraumatic stress disorder (PTSD) who underwent eye movement desensitization and reprocessing (EMDR) therapy, with and without the eye movement component, in a crossover design. Results supported the occurrence of partial emotional processing, but there were no differences in its extent in the eye-movement versus eyes-fixed conditions. Therapy produced a modest to moderate overall improvement, mostly on the Impact of Event Scale. There was slightly more improvement in the eyes-fixed than eye-movement condition. There was little association between the extent of emotional processing and therapeutic outcome. In our hands, EMDR was at least as efficacious for combat-related PTSD as imaginal flooding proved to be in a previous study, and was better tolerated by subjects. However, results suggest that eye movements do not play a significant role in processing of traumatic information in EMDR and that factors other than eye movements are responsible for EMDR's therapeutic effect. This is a US government work. There are no restrictions on its use.

Firing properties of preposito-collicular neurones related to horizontal eye movements in the alert cat

The projection from the nucleus prepositus hypoglossi (PH) to the superior colliculus (SC) has been proposed to provide a feedback control of collicular saccadic activities. The present study aimed to identify the functional properties of PH neurones projecting to the SC relative to eye movement parameters. Preposito-collicular neurones were identified in alert cats by antidromic invasion and collision tests following electrical stimulations of the contralateral SC. Their discharges were then correlated with the horizontal component of eye movements. Particular attention was given to the timing of discharges relative to saccade onsets. Most preposito-collicular neurones (12/14) displayed transient activities associated to eye velocity, and onsets preceded the saccade onset by 9.4-19.9 ms. The mean eye velocity sensitivity of these "early" preposito-collicular neurones (1.46 +/- 0.53 spikes/s per degree per second) was quite similar to that calculated from a sample of putative motoneurones or interneurones that have been recorded within abducens nucleus and quantified in the same conditions. The remaining two preposito-collicular neurones exhibited transient activity related to saccades, but this followed the transient putative motoneuronal discharge. These "delayed" neurones also had lower eye velocity sensitivities (0.38 sp/s per degree per second and 0.58 sp/s per degree per second, respectively) compared with early neurones. Both classes of preposito-collicular neurones also displayed a subsequent tonic activity correlated with the eye position. Taken together, these results demonstrate that preposito-collicular neurones code both eye position and eye velocity just like ocular motoneurones, but in a predictive manner. The anticipatory discharge of early neurones makes them likely candidates for the control of peak activities of saccade-related collicular neurones, particularly in the caudal colliculus. Delayed preposito-collicular neurones may also participate in the control of collicular activities, but probably in more rostral SC, where peak activities occur later during eye movements together with smaller motor error coding.

The three-dimensional human vestibulo-ocular reflex: response to long-duration yaw angular accelerations.

We recorded three-dimensional eye movements during angular acceleration steps from 0 to 250 degrees/s at 20 degrees/s2 about an earth-vertical axis. Experiments were performed on 27 normal subjects and on 19 patients who had recovered well from unilateral vestibular deafferentation on the right or left side. In addition to compensatory horizontal eye movements, significant vertical and torsional eye movement components were elicited. These vertical and torsional eye velocity traces led to a shift of the axis of eye velocity away from the axis of head velocity. Horizontal, vertical, and torsional velocity components showed clear differences between normals and patients with unilateral vestibular deafferentation. In normals, the axis of eye velocity tilted backward and slightly away from the axis of head velocity. Patients showed similar, but more pronounced, shifts during rotations toward the intact ear and shifts in the opposite direction for rotations toward the operated ear. Eye velocity traces were analyzed with special consideration given to the orientation of the axis of eye velocity. We speculate that the vertical and torsional velocity components may be due to the effects of Listing's plane, as well as the contributions of the otolith signals.

Electrooculographic and performance indices of fatigue during simulated flight

The investigation evaluated specific components of eye and eyelid movement as predictors of performance decrements resulting from pilot fatigue. Ten partially sleep deprived pilots flew a GAT-1 moving-base flight simulator on a 4.5-h sortie. The scored flight portion consisted of eight legs, each leg made up of two segments, a flight maneuvers task (FMT) and a straight and level flying task (SLT). Error scores were calculated across altitude, airspeed, heading, and vertical velocity. An electrooculogram provided measures of blink rate (BR), blink duration, long closure rate (LCR), blink amplitude (BA), saccade velocity, saccade rate, and peak saccade velocity. Subjective fatigue, workload and sleepiness were estimated using the USAFSAM seven-point forced-choice scales, the Stanford Sleepiness Scale, and the USAFSAM Sleep Survey Form. Error scores increased significantly during the first seven legs of the sortie and decreased slightly for the last leg. Subjective reports of fatigue increased significantly over time and were positively correlated with increased error. For the combined data set and for FMTs alone, BA was the best predictor of changes in error with decreased amplitude corresponding to increased error. BR and LCR were the second and third best predictors, respectively. For SLTs alone, LCR and BA were the first and second best predictors of increased error, respectively. The investigation demonstrated that measurable flying performance decrements do occur due to changes in fatigue and that one can measure physiological correlates of those performance decrements.

Initiation of disjunctive smooth pursuit in monkeys: Evidence that Hering's law of equal innervation is not obeyed by the smooth pursuit system

Monkeys generated disjunctive smooth pursuit eye movements when they tracked visual targets that moved toward or away from them. Eye acceleration was computed during the initial 100 msec of pursuit (the open-loop interval) for various target trajectories. The initial acceleration of either eye was a function of the target's motion with respect to that eye, regardless of whether or not the pursuit was conjugate or disjunctive, or performed with one eye occluded. Eye movements produced by fusional vergence could be separated temporally from eye movements produced by smooth pursuit using step-ramp paradigms. The separation of the two responses demonstrates that the fusional vergence system operates in parallel with the smooth pursuit system, presumably to minimize disparity, but not to generate disjunctive components of smooth pursuit eye movements.

Site of interaction between saccade signals and vestibular signals induced by head rotation in the alert cat: functional properties and afferent organization of burster-driving neurons.

1. Extracellular spikes of burster-driving neurons (BDNs) were recorded within and immediately below the prepositus hypoglossi nucleus in the alert cat. BDNs were characterized by short-latency activation after stimulation of the contralateral vestibular nerve (latency: 1.4-2.7 ms) and the ipsilateral superior colliculus (latency: 1.7-3.5 ms). Convergence of vestibular and collicular inputs was found in all of 85 BDNs tested. Firing of BDNs increased during contralateral horizontal head rotation and decreased during ipsilateral rotation. A burst of spikes was induced in association with contralateral saccades and quick phases of nystagmus. 2. BDNs showed irregular tonic discharges during fixation. There was no significant correlation between the firing rate during fixation and horizontal or vertical eye position in most BDNs. During horizontal sinusoidal head rotation, the change in firing rate was approximately proportional to and in phase with contralateral head velocity. The phase lag of the response relative to head angular velocity was 13.8 +/- 20.1 degrees (mean +/- SD) at 0.5 Hz and 7.2 +/- 13.5 degrees at 0.2 Hz on the average. The gain was 0.88 +/- 0.25 (spikes/s)/(degrees/s) at 0.5 Hz and 1.19 +/- 0.49 (spikes/s)/(degrees/s) at 0.2 Hz. 3. Quantitative analysis of burst activity associated with saccades or quick phases indicated that the ON direction of BDNs was contralateral horizontal. The number of spikes in the burst was linearly related to the amplitude of the contralateral component of rapid eye movements. The slope of regression line was, on the average, 1.14 +/- 0.48 spikes/deg. There was no significant difference between the mean slopes for saccades and quick phases. The number of spikes depended on the difference between initial and final horizontal eye positions and not on the absolute eye position in the orbit. The mean burst firing rate was proportional to the mean velocity of the contralateral component of rapid eye movements. The slope of the regression line was 0.82 +/- 0.34 (spikes/s)/(degrees/s). Significant correlation was also found between intraburst instantaneous firing rate and instantaneous component eye velocity. 4. Objects presented in the contralateral visual field elicited a brief burst of spikes in BDNs independent of any eye movement. Contralateral saccades to the target were preceded by an early response to the visual stimulus and subsequent response associated with eye movement. 5. Excitation of BDNs produced by stimulation of the ipsilateral superior colliculus was facilitated by contralateral horizontal head rotation. Therefore saccadic signals from the superior colliculus to BDNs may be augmented by vestibular signals during head rotation.(ABSTRACT TRUNCATED AT 400 WORDS)

Early and late components of smooth pursuit eye movements in schizophrenic patients vs normal controls

Early and late components of smooth pursuit eye movements in schizophrenic patients vs normal controls

Three-component analysis of benign paroxysmal positional nystagmus.

Three-component analysis of Benign Paroxysmal Positional Nystagmus (BPPN), focusing on the horizontal, vertical, and torsional, using a computerized eye movement analysis system, was carried out in 10 patients. Using a pendular rotation stimulus, we also measured three components of eye movement elicited from the vertical semicircular canals in normal subjects. We compared two components (vertical and torsional) of BPPN with that of eye movements elicited from the vertical semicircular canals. In BPPN, the torsional component of eye movements was larger than that of the vertical component. Conversely, the vertical component from the vertical semicircular canals was larger than that of the torsional component. From these results, by analysing the vestibulo-ocular reflex of the vertical semicircular canals, it is difficult to support the idea that the pathology of the BPPV is localized in the posterior semi-circular canal alone.

Nystagmus in benign paroxysmal positional vertigo: a three-component analysis.

Three-component analysis of nystagmus was carried out in 10 patients with benign paroxysmal positional vertigo (BPPV), focusing on the horizontal, vertical and torsional components, with the aid of a computerized eye movement analysis system. Using a pendular rotation stimulus we also measured three eye components of eye movement evoked from the vertical semicircular canals in 3 normal subject; two components (vertical and torsional) of nystagmus in patients with BPPV were compared with that of eye movements derived from the vertical semicircular canals. The time course of slow phase velocity of three components in BPPV patients was similar. In BPPV, the torsional component of eye movements was larger than that of the vertical component without obvious horizontal eye deviation. On the other hand, the vertical component from vertical semicircular canals was larger than that of the torsional component. From the view point of the vestibulo-ocular reflex, it is difficult to support the idea that the pathology of BPPV is localized only to the posterior semicircular canal.

Three-Component Analysis of Benign Paroxysmal Positional Nystagmus

Although it has been speculated that BPPN is due to an abnormality of the utricle or posterior semicircular canal, the origin of BPPN is still controversial. In order to clarify the origin of BPPN, we carried out a three-component analysis of nystagmus, focusing on horizontal, vertical and torsional motion, using a computerized eye movement analysis system. Applying pendular rotation stimuli, we also measured three components of eye movements evoked from the vertical semicircular canals.The eye movements observed as rotatory nystagmus under Frenzel glasses, which are characteristic of BPPN, in most of the subjects had not only torsional, but also vertical and horizontal components. The vertical component dominant over the horizontal component.We compared two components (vertical and torsional) of BPPN with eye movements evoked from the vertical semicircular canals. In BPPN, the torsional component of the eye movement was larger than that of the vertical component. On the other hand, the vertical component of the eye movement from vertical semicircular canals was larger than that of the torsional component.These results suggest that the pathology of BPPN is not located only in the posterior semicircular canal.

Recording characteristics of the eye mark recorder in measurements of vertical eye movements

Electronystagmography (ENG) has been widely used in physiological studies of eye movements. It is generally known that ENG is at a disadvantage in recording the vertical component of eye movements, and thus there has been a great deal of difficulty in physiological studies of vertical eye movements using ENG. The eye mark recorder is an instrument which has already been used in the study of visual point movement in various situations. We tried to apply the eye mark recorder to the recording of eye movements in normal volunteers, and then compared its recording characteristics with those of ENG. When recording vertical eye movements with the eye mark recorder there is little baseline drift and no confusing waves caused by blinking, which is sometimes misinterpreted as nystagmus. The result is easy calibration of the device and more accurate measurement of the slow-phase velocity of nystagmus than ENG. Recording with the eye mark recorder is atraumatic and allows binocular visual stimulation. There are certain other techniques, such as search coil or video oculography, which allow more accurate recording of vertical eye movements than ENG. The search coil techniques, however, requires the attachment of a measuring contact lens during the examination and video oculography is still in development process, so both of them are difficult to use widely. Thus, we found that the eye mark recorder has a great advantage in recording the slow-phase eye velocity of vertical nystagmus and the vertical component of smooth eye movements in humans. We think that eye mark recorder can serve as a powerful new tool to investigate vertical OKN and OKAN.

Head position dependent adjustment of the three-dimensional human vestibuloocular reflex.

We studied the influence of static head position relative to the rotation axis on the three-dimensional (3-D) vestibuloocular reflex (VOR). By means of a 3-D rotating chair and a 3-D magnetic search-coil system, eye movements were recorded in 6 normal human subjects during sinusoidal rotation about an earth-vertical axis (yaw) with the head positioned at different pitch angles and about an earth-horizontal axis (pitch) with the head positioned at different yaw angles. We confirmed that torsional VOR gain is about 2/3 of horizontal and vertical VOR gain leading to non-collinear axes of eye and head rotation whenever torsional head movement components were present with eye movement axes tilting away from the torsional direction. Despite this non-collinearity of stimulus and eye movement rotation axes there was close to perfect adjustment of the different VOR components depending on the angle between gaze direction and stimulation axis, indicating a vectorial summation of gains obtained for rotations in the major body axes (roll, pitch and yaw). The horizontal and vertical eye movement components followed a cosine function of the angle between the plane of rotation and gaze direction. The torsional component followed a sine function.

Dynamic analysis of ocular torsion in parabolic flight using video-oculography

Dynamic ocular torsion was investigated in a group of healthy subjects during the course of parabolic flight by means of our video-based eye movement recording method—video-oculography. This technique enables a non-invasive dynamic measurement of all three dimensions of eye movement in a harsh experimental environment such as parabolic flight. The test subjects were positioned so that the changing resultant gravito-inertial field in the aircraft was aligned with their interaural ( y) axis, primarily stimulating the utricular organs. The analysis of the torsional component of eye movement during the change of gravity between 1.8-0 and 0–1.8 g demonstrated a static component—well known as the ocular counter roll—and a dynamic component, which leads to a slight overshoot in the torsional response. These static and dynamic component of ocular torsion correlate with previous neurophysiological findings.

Three-dimensional aspects of caloric nystagmus in humans: I. The influence of increased gravitoinertial force.

The influence of increased gravitoinertial force on the horizontal vertical and torsional components of caloric nystagmus response was examined. Video-oculographic (VOG) recordings were made on a group of 10 human subjects so that all three components of eye movement could be evaluated. The caloric nystagmus response at all tested g-levels included nystagmus components around all three rotation axes. Over the tested range of 1.0 g to 3.0 g, the results demonstrate that nystagmus intensity does not increase linearly with effective gravitoinertial force but appears to saturate at levels of 2.0 g and beyond. It is proposed that the vertical and torsional nystagmus components were elicited both by caloric stimulation to the (anterior) vertical canals and direct thermal mediation to the otolithic sensory cells. Vertical LZ-nystagmus response was also observed during centrifuge runs (previous to caloric irrigation) at all g-levels and in all subjects. The caloric-induced vertical nystagmus response was also clearly recognisable. The observation of a reduction and inversion of nystagmus intensity during g-transitions agrees with earlier findings and is attributable to the stimulation to the canals during centrifuge acceleration, respectively deceleration.