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PubMed1979

Cortical activation pattern during saccadic eye movements in humans: localization by focal cerebral blood flow increases.

Regional cerebral blood flow (rCBF) was measured in human subjects during saccadic eye movements by a 254-channel dynamic gamma camera. Focal rCBF increases were repeatedly observed in an area within the middle precentral and premotor regions which corresponds to the frontal eye field in humans. Our findings suggest that this region is localized between the "face" and "hand" areas in the precentral gyrus and extends anteriorly out of the primary motor strip into the adjacent premotor zone. In addition, saccades were associated with focal blood flow increases in regions corresponding to the frontal supplementary motor area and to the posterior temporooccipital visual association cortex. Similar changes in patterns of rCBF occurred during contralateral and ipsilateral horizontal saccades and also during vertical saccades, and did not differ between the right and left hemispheres. Focal rCBF increases were observed in the frontal eye field during several additional test procedures including ocular fixation and visual perception of a nonmoving target, auditory stimulation with closed eyes, and reading. It is presumed that these focal flow increases reflect increased localized neuronal activity and metabolic rate and therefore permit visualization of the cortical activation pattern associated with saccadic eye movements in humans.

Cerebral Cortex↗
PubMed1999

Effect of infantile strabismus on visuomotor development in the squirrel monkey (Saimiri sciureus): optokinetic nystagmus, motion VEP and spatial sweep VEP.

PURPOSE: To determine whether squirrel monkeys made artificially strabismic in infancy had ocular fixation abnormalities, directional asymmetries of horizontal optokinetic nystagmus (OKN) and asymmetries of motion visually evoked potentials (MVEPs) similar to those of humans with infantile strabismus. METHODS: Esotropia was produced in a newborn squirrel monkey by surgical tenotomy of both lateral rectus muscles. The alignment and eye rotations of the monkey were examined longitudinally and VEP testing was performed at the age of one year. Visual acuity was measured using spatial frequency sweep VEPs (SSVEP) in response to grating stimulation. OKN was tested under conditions of monocular viewing using full-visual-field, vertically oriented, moving stripes. MVEPs in response to horizontal motion were recorded with the animal sedated to reduce the possibility of eye movement artifact. RESULTS: The artificially strabismic squirrel monkey displayed a constant, committant esotropic strabismus accompanied by latent nystagmus. Monocular SSVEP acuity was subnormal in one eye, consistent with mild monocular strabismic amblyopia. The monkey demonstrated asymmetric OKN favoring nasally-directed stimulus motion when viewing with either eye. Monocular MVEPs were also characterized by a horizontal asymmetry with a directional bias inverted 180 degrees between the right and the left eyes. The eye movements and MVEP asymmetries were similar to those observed in strabismic macaque monkeys and humans with early-onset strabismus. Neither the OKN asymmetry nor the MVEP asymmetry was evident in a normal squirrel or normal macaque monkey. CONCLUSION: The artificially strabismic squirrel monkey is an appropriate eye movement and VEP model for the study of neural mechanisms in human infantile strabismus.

Animals↗
PubMed1977

Visuomotor ataxia.

Visuomotor ataxia is a disorder of movement performed under visual control. It can occur in the absence of disturbance of ocular fixation and in the absence of spatial agnosia. This disorder may extend over the whole visual field or it may be localized to one visual half-field, right or left. It may involve both hands or one hand only, so that visuomotor ataxia may be divided into: (1) Unilateral visuomotor ataxia, localized to a single field. In this case it may affect both hands or a single hand. It is direct when the hand is ataxic in the ipsilateral visual field and it is crossed when the hand is ataxic in the contralateral visual field; (2) Bilateral visuomotor ataxia, involving the whole visual field. Each hand may be ataxic only in the contralateral visual field, that is, bilateral crossed visuomotor ataxia; or in the ipsilateral field when it is called bilateral direct visuomotor ataxia. The observed clinical variations which are described here imply the existence of both direct and crossed visuomotor connections, the latter probably crossing the corpus callosum in the splenium.

Adult↗
PubMed1992

The development of fixing and focusing behaviour in normal human infants as observed with the Otago photoscreener.

The Otago photoscreener is an optical instrument which gives a very sensitive indication of the accuracy with which a subject's eyes are fixing and focusing. Early experience suggested that this instrument could be used effectively to screen for the presence of amblyogenic factors in pre-verbal infants. This communication describes the development of ocular fixation and focusing in 137 normal infants who were followed at regular intervals during the first year of life. Accurate fixation and focusing was found in 13% of three-month-old infants, in 68% of six-month-old infants and in 76% of one year olds. The levels of 'focusing' visual acuity obtained from the photoscreen data are considerably better than the levels of cortical acuity measured by the standard behavioral and electrophysiological methods. This suggests that human infants fix and focus accurately for a considerable period before they are able to perceive all the details obtained in their retinal images.

Amblyopia↗
PubMed1985

The influence of physostigmine on visual-vestibular interaction in hereditary ataxias.

Visual suppression of caloric nystagmus was studied in five patients with hereditary ataxia before and after administration of physostigmine. All patients had an initial abnormal ocular fixation index that improved after physostigmine was given. The data indicate that there is a partly reversible disturbance of visual-vestibular interaction in patients with hereditary ataxia, caused by an impairment of a central cholinergic mechanism.

Adult↗
PubMed1977

Square-wave jerks: a disorder of microsaccades?

A patient with presenile dementia had instability of ocular fixation caused by small rapid horizontal eye movements (square-wave jerks). High resolution recordings of these eye movements were characteristic of microsaccades, which ordinarily occur during fixation, in all respects except amplitude. In addition, the patient showed complete absence of normal microsaccades. We suggest that microsaccades have become altered in our patient to form a clinical disorder of fixation.

Caloric Tests↗
PubMed2000

Neural mechanisms of visual feature grouping.

The present work relates compositions of visual scenes to signals in visual cortex and to cortical circuit models in order to understand neural mechanisms of perceptual feature grouping. It starts from the hypothesis that synchronization and decoupling of cortical gamma-activities (35-90 Hz) define the relations among visual objects. Here we concentrate on synchronization related to two basic visual situations, (1.) static retinal stimulation during ocular fixation, and (2.) transient stimulation during sudden luminance modulations or shifts in object position. For testing the synchronization hypothesis we investigated signal correlations of multiple micro-electrode recordings in visual cortex areas V1 and V2 of behaving monkeys. Static retinal stimuli induce gamma-activities that are loosely phase-coupled among neighboring neural populations of an object's cortical representation. This can explain why synchronization, measured by spectral coherence, is restricted to few millimeters cortex. Such patches of gamma-synchronization become de-coupled across the representation of an object's contour, and thereby can code figure-ground segregation. Transient stimuli evoke synchronized volleys of stimulus-locked activities that are typically non-rhythmic and include low frequency components in addition to those in the gamma-range. It is argued why stimulus-induced and stimulus-locked phase-coupled activations are both appropriate for supporting perceptual feature grouping. Clues for basic neural mechanisms participating in feature grouping are provided by our biologically motivated simulations of synchronization in cortical structures. (1.) Local populations generate gamma-oscillations via feedback inhibition during states of static retinal stimulation. (2.) Bidirectional facilitatory connections serve for phase-coupling among neighboring neural populations. (3.) Spike transmission delays, increasing with cortical distance, can explain the restriction of gamma-coherence to patches of few millimeters cortex. (4.) The size of synchronization patches in one visual area (e.g., V1) can define the size of classical receptive fields at the consecutive level of visual processing (V2) if Hebbian learning is operative. This may explain the increase in receptive field size at consecutive levels of visual processing. In conclusion, our results and those of others are supportive for the hypothesis that phase-coupled gamma-signals can code feature grouping and object continuity. However, convincing experimental proofs showing directly the dependence of perceptual grouping on cortical phase-coupling are still lacking.

Animals↗
PubMed1972

Orienting response hypernormality in frontal cats.

Results obtained in collaboration with B. Dreher are summarized. Ocular fixation was the indicator of the orienting response, and pupillary dilatation and ECoG arousal to olfactory stimuli were the indicators of the arousal response. To make precise recording possible, animals with pretrigeminal brain stem transection were used. After ablation of the anterior sigmoid gyrus or proreal gyrus the fixation response was enhanced and its resistance to habituation was strongly increased. On the other hand, the pupillary dilatation and ECoG arousal to olfactory stimuli and the background pupillary diameter and ECoG activity were unaffected. The hypernormality of the orienting response can be partially responsible for the disinhibition of the locomotor responses in go-no go differentiation and for the impairment of locomotor delayed responses in frontal carnivores.

Animals↗
PubMed2006

Information processing during face recognition: the effects of familiarity, inversion, and morphing on scanning fixations.

Where we make ocular fixations when viewing an object likely reflects interactions between 'external' object properties and internal 'top-down' factors, as our perceptual system tests hypotheses and attempts to make decisions about our environment. These scanning fixation patterns can tell us how and where the visual system gathers information critical to specific tasks. We determined the effects of the internal factors of expertise, experience, and ambiguity on scanning during a face-recognition task, in eight subjects. To assess the effects of expertise, we compared upright with inverted faces, since it is hypothesized that inverted faces do not access an orientation-dependent face-expert processor. To assess the effects of experience, we compared famous with novel faces, as famous faces would have stronger internal representations than anonymous ones. Ambiguity in matching seen and remembered faces was manipulated with morphed faces. We measured three classes of variables: (i) total scanning time and fixations; (ii) the spatial distribution of scanning; and (iii) the sequence of scanning, using first-order Markov matrices for local scan structure and string editing for global scan structure. We found that, with inverted faces, subjects redistributed fixations to the mouth and lower face, and their local and global scan structure became more random. With novel or morphed faces, they scanned the eyes and upper face more. Local scan structure was not affected by familiarity, but global scan structure was least random (most stereotyped) for novel upright faces. We conclude that expertise (upright faces) leads to less lower-face scanning and more predictable global patterns of information gathering. Experience (famous faces) leads to less upper-face scanning and more idiosyncratic global scan structures, suggesting a superseding influence of facial memories. With morphed faces, subjects return to the upper face to resolve ambiguity, implying a greater importance of this region in face recognition.

Adult↗
PubMed1988

Cerebral metabolism and patterned visual stimulation: a positron emission tomographic study of the human visual cortex.

We studied the impact of visual stimulation upon cerebral metabolism in normal young men using FDG-PET. Results obtained from subjects receiving patterned visual stimulation while performing an ocular fixation task were compared with results from ocular fixation alone. Visual stimulation in the macular region of either hemifield produced significant increases in metabolism of the contralateral posterior striate cortex. Visual stimulation induced highly significant asymmetries in metabolism of the prefrontal and inferior parietal cortices. Metabolic activation in extrastriate areas tended to be right-sided. These findings support the classic notion of retinotopic organization within the primary visual sensory cortex. They also indicate that the patterns of cerebral metabolism are not equivalent between the two cerebral hemispheres. This latter finding suggests that in humans the right cerebral hemisphere may be specialized for visual processing.

Adolescent↗
PubMedDate not supplied

Computer analysis of fixation-suppression of caloric nystagmus.

Effects of the ocular fixation upon caloric nystagmus were quantitatively analyzed and compared between normal subjects and patients by using a PDP 11/40 computer. The slow-phase velocity was the best parameter to separate normal from abnormal visual fixation. An analysis of caloric nystagmus with failure of fixation-suppression (FFS) made it possible to classify patterns of FFS into three types. The combination of FFS with impairment of the optokinetic responses provides a useful diagnostic tool with respect to lesions located between the brain stem and the cerebellum.

Adult↗
PubMed1999

Short-latency visual stabilization mechanisms that help to compensate for translational disturbances of gaze.

Recent studies in primates have revealed short-latency visual tracking mechanisms that help to stabilize the eyes during translational disturbances of the observer, and so operate as backups to otolith-mediated vestibulo-ocular reflexes. One such mechanism generates version eye movements to help stabilize gaze when the moving observer looks off to one side, utilizing binocular disparity to help single out the images in the plane of fixation (ocular following). Two others generate vergence eye movements to help maintain binocular alignment on objects that lie ahead: one responds to the radial patterns of optic flow (radial-flow vergence) and the other to the changes in binocular parallax (disparity vergence). Accumulating evidence suggests that, despite their short latency, all are mediated by the medial superior temporal area of cortex.

Adaptation, Physiological↗
PubMed1993

[Comparison of sevoflurane and halothane in pediatric anesthesia].

In the present study we compared sevoflurane (group S) and halothane (group F) as used in pediatric endotracheal anesthesia. The subjects consisted of 100 pediatric patients, each 50 in group S and F, most of whom underwent otorhinolaryngological surgery. Anesthesia was induced with nitrous oxide-oxygen-sevoflurane (GOS) (S 3-5%) or nitrous oxide-oxygen-halothane (GOF) (F 1.5-2.5%), and maintained with GOS (S 2-3%) or GOF (F 1.0-1.5%). In comparing the groups with respect to anesthetic induction, group S required 2.1 min for the loss of consciousness, 6.1 min for ocular fixation and 9.7 min for completion of intubation, while in group F the time intervals for the above items were 2.4, 4.9 and 10.2 min, respectively. No significant differences were found between the two groups except in the loss of consciousness and ocular fixation. Comparison of the groups during maintenance of anesthesia revealed no significant differences, although pulse rate and diastolic blood pressure increased in both groups. When the groups were compared for awakening from anesthesia, group S required 10.1 min for awakening and 11.9 min for extubation, while in group F the time was 13.0 min and 15.4 min, respectively. These values were significantly different. The present study demonstrated that sevoflurane anesthesia is rapid in both induction and awakening as compared with halothane anesthesia, and that GOS inhalation anesthesia with single use of sevoflurane can be usefully applied to pediatric endotracheal anesthesia.

Anesthesia, Inhalation↗
PubMedDate not supplied

Visual suppression of caloric nystagmus in normal individuals.

The effects of opening of the eyes and of ocular fixation upon caloric nystagmus were investigated during the period of maximum intensity of caloric nystagmus in a series of 32 normal individuals. The percentage reduction in slow-phase velocity induced depended upon the test conditions, but, on the other hand, did not depend upon the temperature of the water applied as caloric stimulus. This latter fact favors the theory of visual suppression of the caloric test. Another striking finding was that a clear correlation definitely existed between the percentage reduction of suppression in slow-phase velocity and that in the multiplication product of amplitude by nystagmus frequency (P.A.F.) during the period of eye opening and ocular fixation. The percentage of suppression in slow-phase velocity is interchangeable with that in P.A.F., which broadens the practical scope of the routine test.

Adolescent↗
PubMed1977

ENG analysis of 150 cases of posterior fossa disease.

Analysis of the ENG records of 150 patients with well substantiated neurologic disease involving the structure of the posterior fossa revealed a high incidence of diminished optic fixation inhibition (DOFI) of caloric induced nystagmus. DOFI is defined as less than 50 percent decrease of speed of the slow phase when eyes are open and fixated. The whole group was subdivided into seven subgroups according to type and location of disease and the incidence of DOFI was found to vary significantly in the different subgroups. The highest incidence was found in the group of cerebellar mass lesions and in the group of degenerative diseases, most of which had cerebellar involvement. A review of the literature reveals work done by others showing that suppression of vestibular reflexes induced by high speed turning and also habituation of caloric induced nystagmus is dependent on optic fixation inhibition (opto-vestibular reflex.). It has been shown that the flocculonodular lobe of the cerebellum has an inhibitory effect on the effects of vestibular activity by both destructive and stimulating techniques. Afferent and efferent pathways between the cerebellum and primary vestibular reflex arcs have been extensively described. It has been shown that cerebellar nodulectomy severely interferes with acquisition of habituation and retention of previously acquired habituation. Since habituation and suprression of vestibular nystamus depend on optic fixation inhibition and equally on the cerebellum, it is reasonable to infer that the opto-vesitubular inhibitory reflex is mediated by the crebellum. The clinical data of the 150 cases were analyzed for correlation of DOFI and other cerebellar signs. This analysis gives a high incidence of correlation: 66 percent of the cases having DOFI also had other cerebellar signs, whereas only 19 percent of cases that did not have DOFI had other cerebellar signs. These data lend further support to the inference that the cerebellum is involved in mediation of the opto-vestibular inhibitory reflex. Under most circumstances visual perception of the environment during movement depends on an inter-reaction between the vestibulo-oculomotor and the opto-vestibular reflexes. Eye movements during head movements are entirely different with eyes closed than with eyes open and fixating. In fact, it can be shown that ocular fixation is far more efficient during head movements than it is during movement of an object with head stationary. It is probable that fixation in the former case is the result of vestibulo-oculomotor slow phase activity modified by the opto-vestibular inhibitory reflex and elimination of the fast phase. A defect in the latter should result in a sense of spatial insecurity during movement by virtue of altered visual perception. The opto-vestibular inhibitory reflex is a central descending reflex probably mediated through the cerebellum. It is easy to test during and ENG. It is essential to normal visual perception during head movement...

Brain Diseases↗