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PubMed2002

Neurophysiological markers of vulnerability to schizophrenia: sensitivity and specificity of specific quantitative eye movement measures.

Eye-tracking deficits in schizophrenic patients and relatives have generated interest in using eye movements to mark schizophrenia liability. Efforts to develop specific quantitative measures have provided insight into the nature of the deficit and suggested what underlying neurophysiological mechanisms are involved. This study used receiver operating characteristic curve analyses to evaluate and compare the sensitivity, specificity, and overall accuracy of predicting disease liability using single and combined specific and global quantitative measures. Results indicate that measures of predictive pursuit and leading saccades significantly increased predictive accuracy compared with traditional global measures. Combining specific measures provided greater predictive accuracy compared with single measures. Implications for the use of specific eye movement measures to define schizophrenia-related phenotypes in genetic studies are discussed.

Adult↗
PubMed2005

Hemodynamic response to emotional memory recall with eye movement.

Previous studies on rapid eye movement sleep have demonstrated the effect of eye movement on emotional memory. However, the brain mechanism involved in the influence of the eye movement on the emotional recall remains unclear. We investigated the prefrontal response during an emotional memory recall with and without eye movement. Ten healthy volunteers were recruited. The changes in concentration of oxygenated hemoglobin ([oxy-Hb]) in the prefrontal cortex were examined using near-infrared spectroscopy (NIRS) during a task that involved emotional recall with and without eye movement. Six participants demonstrated a significant increase in [oxy-Hb] during emotional recall, and the level of increase was reduced through repeated emotional recall with eye movement. The results suggest that eye movement is associated with a reduction in the hemodynamic response to emotional memory recall.

Adult↗
PubMed1995

[Quantitative analysis of smooth pursuit eye movement].

Abnormalities of smooth pursuit eye movement (SPEM) have been estimated, mainly using the wave form on an electro-oculogram, in a qualitative way. Many methods for quantitative analysis of SPEM have been designed, though most are still uncommon in present clinical use. Using a personal computer, we developed a method of automatic quantitative analysis of ocular tracking eye movement recorded by electro-oculography (EOG). The design concept of this method is based on the observation that eye movement during ocular tracking consists of two different kinds of eye movements, one is SPEM and the other is saccade. The combination of SPEM and saccade (composite eye movement: CEM) commonly appears during ocular tracking. These two kinds of eye movement are essentially different not only in behavior but also about involved neural pathway in the central nervous system. From this point of view, we believe that the two kinds of eye movements involved in ocular tracking should be evaluated separately. The analysis method is outlined as follows. A horizontal sinusoidally moving visual target was employed to elicit ocular tracking eye movements. The test frequencies were set at 0.1, 0.2, 0.4 and 0.8Hz, and the amplitude of target motion was 15 deg at each frequency. The 20 seconds of eye movement data measured by EOG were fed into the computer through a digital-analog converter for further analysis. Using our original saccade detection algorithm, based on the physiological behavior of saccades, the saccadic components were detected and removed from the eye movement wave. The remaining parts, fragments of SPEM, were connected by means of interpolating defective parts. The reconstructed wave was a slow cumulative eye position curve (SCEP). Sinusoidal target motion, CEM and SCEP were processed by the FFT (Fast Fourier Transformation) method. Bode plots were applied to summarize the gain and phase of responses to SCEP and the target motion wave. These processes enable us to estimate abnormalities of SPEM such as low gain, abnormal phase shift and large trends in tested duration. We conclude that the method described here is useful for quantitative estimation of SPEM in clinical neuro-otological examinations.

Adult↗
PubMed2001

Chameleons have independent eye movements but synchronise both eyes during saccadic prey tracking.

The movements of both eyes and the head were recorded with search coils in unrestrained, freely moving chameleons. As a main result I found that the generation of saccades in the left and the right eye was either independent from each other or was highly correlated according to the behavioural situation. When no prey item was fixated, disconjugate saccades were observed which was in accordance with earlier observations in chameleons. During prey tracking the chameleons switched to a different oculomotor behaviour and pursued the moving prey with synchronous saccades. At higher target velocities, the tracking movement of the head was also saccadic and was synchronised with the two eyes. Binocular coupling affected only the timing of the saccades but not the metrics: the amplitudes of the synchronous saccades were usually different in the two eyes. These observations suggest the existence of two independent premotor neuronal circuits for left and right eye saccadic motor control in the chameleon. Binocular coupling in prey-tracking chameleons is probably achieved by neuronal coupling of these premotor circuits during eye-head coordination. The ability to switch between synchronous and uncoupled saccadic eye movements has not been described for any other vertebrate. This unique ability of the chameleon may help to understand the organisation of the oculomotor system of other vertebrates since evidence for separate left eye and right eye saccade generation and position control has recently also been reported in primates.

Animals↗
PubMed2004

The time course of visual information accrual guiding eye movement decisions.

Saccadic eye movements are the result of neural decisions about where to move the eyes. These decisions are based on visual information accumulated before the saccade; however, during an approximately 100-ms interval immediately before the initiation of an eye movement, new visual information cannot influence the decision. Does the brain simply ignore information presented during this brief interval or is the information used for the subsequent saccade? Our study examines how and when the brain integrates visual information through time to drive saccades during visual search. We introduce a new technique, saccade-contingent reverse correlation, that measures the time course of visual information accrual driving the first and second saccades. Observers searched for a contrast-defined target among distractors. Independent contrast noise was added to the target and distractors every 25 ms. Only noise presented in the time interval in which the brain accumulates information will influence the saccadic decisions. Therefore, we can retrieve the time course of saccadic information accrual by averaging the time course of the noise, aligned to saccade initiation, across all trials with saccades to distractors. Results show that before the first saccade, visual information is being accumulated simultaneously for the first and second saccades. Furthermore, information presented immediately before the first saccade is not used in making the first saccadic decision but instead is stored and used by the neural processes driving the second saccade.

Humans↗
PubMed1992

The use of video in assessing and illustrating abnormal eye movements in young children.

Eye movement studies can be useful in neuro-ophthalmological investigations of infants and young children. In our laboratory we use a combination of an electro-oculogram and video to record eye movements. A composite video image is created consisting of an image of the electro-oculographic eye movement trace superimposed on an image of the patient's eyes and face. This permits the qualitative clinical appearance of the case to be illustrated simultaneously with the quantitative eye movement trace.

Electrooculography↗
PubMed1996

Central mesencephalic reticular formation (cMRF) neurons discharging before and during eye movements.

1. One hundred twenty neurons were recorded in the central mesencephalic reticular formation (cMRF) of four rhesus monkeys, trained to make visually guided and targeted saccadic eye movements. Eye movements were recorded with the head fixed, using electrooculography (EOG) or subconjunctival scleral search coils. Seventy-six percent (92/120) of cells discharged before and during contraversive visually guided or targeted rapid eye movements, and 76% of these (70/92) responded during contraversive spontaneous saccades in the dark. cMRF neurons had large contraversive movement fields and either a high (> 10 spikes/s) or low background level of spontaneous activity in the dark. The optimal movement vectors (i.e., saccades with greatest response) were predominantly horizontal, although many had a vertical component. Cells with optimal movement vectors within +/- 25 degrees of pure vertical were more rostral in the MRF and were excluded from the analysis. 2. A subgroup of cMRF neurons (31 of 92) that discharged before and during visually guided saccades were examined for visual sensitivity. Slightly less than one-half of these cells (42%, 13/31) were visuomotor units, i.e., they responded to visual targets in the absence of eye movement. The other 58% (n = 18) did not discharge during the visual probe trial; they were movement-related cells. 3. Microstimulation (threshold 40-60 microA at 333 Hz) at the sites of many of these cMRF neurons produced contraversive saccadic eye movements at short latency (< 40 ms). The amplitude and direction of the elicited saccades were similar to the optimal movement vector determined from single-unit recording. This suggested that cMRF cells recorded at the same locus of electrical microstimulation participated in the network responsible for the production and control of rapid eye movements. 4. The 92 saccade-related neurons were divided into two groups on the basis of their background discharge rate. Firing rates for both low background (28%, n = 26) and high background (72%, n = 66) cells increased approximately 30 ms before contraversive saccades and reached a peak discharge just before saccade onset. The low background neurons had either no activity or generated a few spikes just before the end of ipsiversive saccades. The steady rate of discharge (> 10 spikes/s) of high background neurons was inhibited from approximately 20 ms before ipsiversive saccades until just before saccade end. 5. Cells were also subdivided on the basis of how their discharge rates fell at the end of saccades. Clipped cells (38%, n = 35) had activity that fell sharply with saccade offset. Partially clipped cells (62%, n = 57) had persistent firing in the 100 ms following the saccade that was > 20% higher than the firing during the 100 ms before the saccade. 6. Latencies between the 90% point on the rising edge of the peak discharge and the start of the saccade were < or = 5.3 ms for eye movement-related cells in two monkeys. Longer latencies (11-19 ms) were found when measured between the 10% point on the rising edge of the peak discharge and saccade onset. These latencies were equal to or shorter than those obtained for eye movement-related burst neurons in the intermediate and deep layers of the superior colliculus analyzed similarly. Delays between the peak discharge and peak eye velocity were 13.6-15.1 ms for the same group of cMRF eye movement-related cells. These were significantly shorter than the delays measured for eye movement neurons in the superior colliculus (SC) of one of the monkeys. These findings suggest that the buildup discharge of cMRF neurons occurs early enough before saccades to contribute to saccade triggering. The peak discharge, however, occurs with or after the burst in the SC, suggesting that this portion of the discharge serves a function other than saccade triggering. 7. The number of spikes in bursts associated with eye movement was correlated with saccade parameters.

Animals↗
PubMed2003

Haptic texture affects the kinematics of pointing movements, but not of eye movements.

Discrepant findings on the degree of eye-hand coupling suggest its dependence on the task. One task characteristic modulating this coupling may be the relevance of certain target attributes for each motor system. We tested this assumption by comparing eye and hand movements towards targets of different haptic texture, a target attribute which is behaviourally relevant only to the hand, not the eye. Pointing to a slippery target (fur) resulted in longer hand movement time than to a rougher target (sandpaper). This effect was due to an increased ratio of time spent in deceleration. In contrast, eye movement time was invariant across different haptic target textures. Thus, information about target texture is used differently by eye and hand.

Adult↗
PubMed2003

Direction of saccadic and smooth eye movements induced by electrical stimulation of the human frontal eye field: effect of orbital position.

The present study reports on the direction of saccadic and smooth eye movements, which were induced electrically from the human dorsolateral frontal cortex including the human frontal eye field (FEF). The eye position prior to stimulation was varied in order to examine its effect on induced eye movement direction. The five patients of the study underwent invasive presurgical evaluation for pharmacoresistant epilepsy. The present data show that the direction of electrically induced eye movements was always contralateral and either horizontal or oblique upward if the eye started from the primary position. The elicited direction was changed if the eyes started from an eccentric position. The frequency of oblique eye movements was increased and oblique downward responses were induced, which were not observed if the eye started from the primary position. This was found for saccades and, especially, for smooth eye movements. Head movements, which were almost exclusively induced with saccades, did not depend on initial orbital position. Four conclusions can be drawn. Firstly, saccades and smooth eye movements induced from the human dorsolateral cortex including the human FEF have the same directional bias. Secondly, the frequent upward responses and the absence of downward responses induced from the primary position suggests either a more numerous or a more superficial representation of neurons that code for the former direction. Thirdly, at some sites the direction of saccades and smooth eye movements varies depending on the initial orbital position. Since these directional changes were observed without changes in eye-head coordination, our data suggest that stimulation of the FEF might evoke goal-directed saccades or interferes with a resettable saccade integrator. Fourthly, human studies that investigate eye movements induced from the lateral frontal cortex need to control eye position prior to stimulation.

Adolescent↗
PubMed2006

Non-rapid eye movement sleep with low muscle tone as a marker of rapid eye movement sleep regulation.

BACKGROUND: It was recently reported that epochs of non-REM sleep (NREMS) with low muscle tone represent a partial correlate of REM sleep (REMS). To further investigate this phenomenon, episodes of restricted night-time sleep (23:00-03.00 h) and subsequent morning sleep (10:00-13:00 h) were analysed. RESULTS: Epochs of NREMS with low muscle tone (NLMT) were identified. Their frequency was higher in morning sleep than in night sleep. At night, the latency to the first occurrence of NLMT showed a bimodal distribution with modes at sleep onset and close to REMS onset. In morning sleep, the distribution was unimodal with the mode at sleep onset. An episode of NLMT at sleep onset occurred in 35.5% of the night sleep episodes and in 60.9% of the morning sleep episodes without sleep onset REMS (SOREMS). Also SOREMS occurred predominantly in morning sleep. REMS episodes were longer and NREMS episodes shorter in morning sleep than in night sleep, whereas cycle duration did not differ. Simulating the time course of slow-wave activity revealed a close correspondence between empirical and computed values for night sleep, and some discrepancies for morning sleep. CONCLUSION: The results provide further evidence that NREMS with low muscle tone is a marker of REMS regulation. NLMT at sleep onset may represent an early manifestation of REMS.

Adult↗
PubMed1984

Characteristics of smooth eye movements with stabilized targets.

Eye movements of two subjects were recorded with a Double Purkinje Image Tracker while they pursued horizontal triangle or ramp stimuli (1, 2, 4 or 8 degrees/sec, p--p 8 degrees). Subjects then attempted to imitate their smooth pursuit eye movement patterns with an electronically-stabilized target or with an afterimage. Next, they attempted to reset the velocity of the stimulus to their memory of the velocity they had previously pursued. The smooth pursuit eye movements of both subjects were very similar. Their attempts to imitate this pattern of eye movements with a stabilized target were only partially successful and subject to large, qualitative individual differences. These differences did not arise from faulty memories of the nature of the pursuit stimuli. Similar results were obtained on the vertical meridian, with a lighted background, and with the stabilized target in eccentric retinal positions. We conclude that stabilization techniques are of dubious value in elucidating properties of the human smooth pursuit subsystem.

Afterimage↗
PubMed1991

Visual motion commands for pursuit eye movements in the cerebellum.

Eye movements that follow a target (pursuit eye movements) facilitate high acuity visual perception of moving targets by transforming visual motion inputs into motor commands that match eye motion to target motion. The performance of pursuit eye movements requires the cerebellar flocculus, which processes both visual motion and oculomotor signals. Electrophysiological recordings from floccular Purkinje cells have allowed the identification of their firing patterns during generation of the image velocity and image acceleration signals used for pursuit. Analysis with a method based on a behavioral model converted the time-varying spike trains of floccular Purkinje cells into a description of the firing rate contributed by three visual motion signals and one oculomotor input. The flocculus encodes all the signals needed to guide pursuit.

Animals↗
PubMed1991

Effects of lithium treatment on eye movements.

Smooth pursuit eye movements (SPEMs) of 11 bipolar manic patients were impaired during lithium treatment, which, however, improved their clinical condition. SPEM impairment was evident in a general qualitative degradation of eye tracking integrity, in a tendency for gain to be lowered, and in an increase in the number of saccadic events. Individual differences in the nature and magnitude of effects of lithium on eye movements were noteworthy.

Adult↗
PubMed2001

Cancellation of self-induced retinal image motion during smooth pursuit eye movements.

When our eyes are tracking a target that is moving in front of a structured background, global motion of equal speed is induced in the opposite direction. This effect has been termed reafference, which, astonishingly, does not significantly affect the execution of such pursuit eye movements. Employing brief and unexpected injections of full-field motion during ongoing human smooth pursuit, we demonstrate that the sensitivity for full-field motion is reduced strongly in the direction opposite to the eye movement, i.e. the direction of reafferent background motion. Our experiments further characterize this asymmetry in visual motion processing and provide a preliminary explanation for the accuracy of the pursuit system despite self-induced motion.

Adult↗
PubMed1983

The effect of increasing age on the latency for saccadic eye movements.

The latency for saccadic eye movements to a visual stimulus was studied in 59 adults whose ages ranged from 20.7 to 79.5 years. All were free of neurologic disease and drug use. Horizontal eye movements were recorded by electrooculography and the latency from the onset of a peripheral visual stimulus to the onset of a saccadic refixation eye movement was determined. A linear regression analysis revealed a correlation between increasing age and increasing latency for saccadic refixation eye movements. The direct relationship between increasing age and increasing latency for saccadic eye movements is a factor that should be taken into account in eye-movement studies as well as other methodologies such as tachistoscopic studies in which saccadic eye movements play a role in study design.

Adult↗
PubMed1993

The biology and function of rapid eye movement sleep.

Rapid eye movement sleep, a stage of sleep that appears to be present in all marsupial and terrestrial placental mammals, was first identified in 1953. Although the brainstem mechanisms responsible for its generation have been clarified, the function of rapid eye movement sleep remains elusive. Recent findings suggest a role in memory processing.

Animals↗
PubMed1998

Premotor commands encode monocular eye movements.

Binocular coordination of eye movements is essential for stereopsis (depth perception) and to prevent double vision. More than a century ago, Hering and Helmholtz debated the neural basis of binocular coordination. Helmholtz believed that each eye is controlled independently and that binocular coordination is learned. Hering believed that both eyes are innervated by common command signals that yoke the eye movements (Hering's law of equal innervation). Here we provide evidence that Hering's law is unlikely to be correct. We show that premotor neurons in the paramedian pontine reticular formation that were thought to encode conjugate velocity commands for saccades (rapid eye movements) actually encode monocular commands for either right or left eye saccades. However, 66% of the abducens motor neurons, which innervate the ipsilateral lateral rectus muscle, fire as a result of movements of either eye. The distribution of sensitivity to ipsilateral and contralateral eye movements across the abducens motor neuron pool may provide a basis for learning binocular coordination in infancy and adapting it throughout life.

Abducens Nerve↗
PubMed2000

Gender differences and reproducibility in exploratory eye movements of normal subjects.

Exploratory eye movements were recorded using an eye-mark recorder in 48 normal subjects (24 male and 24 female). Gender differences were examined regarding four eye movement parameters such as the mean gazing time, the total number of gazing points, and the mean eye scanning length and the total eye scanning length. The mean gazing time of women was significantly longer than that of men, and the total number of gazing points of women was significantly less than that of men. The mean eye-scanning length of men and women did not differ. The total eye scanning length of men was significantly longer than that of women. Reproducibility between sessions of the four eye movement parameters above was expressed as Pearson correlation coefficients (r) in 24 healthy adults before and after a month interval, yielding respective coefficients of 0.65, 0.42, 0.56 and 0.61. These results suggested that differences in exploratory eye movements between men and women may reflect differences in the characteristics of visual information processing and also confirmed the reproducibility of exploratory eye movement parameters.

Adult↗