Eye movements during motor imagery and execution reveal different visuomotor control strategies in manual interception.

Previous research has investigated the degree of congruency in gaze metrics between action execution (AE) and motor imagery (MI) for similar manual tasks. Although eye movement dynamics seem to be limited to relatively simple actions toward static objects, there is little evidence of how gaze parameters change during imagery as a function of more dynamic spatial and temporal task demands. This study examined the similarities and differences in eye movements during AE and MI for an interception task. Twenty-four students were asked to either mentally simulate or physically intercept a moving target on a computer display. Smooth pursuit, saccades, and response time were compared between the two conditions. The results show that MI was characterized by higher smooth pursuit gain and duration while no meaningful differences were found in the other parameters. The findings indicate that eye movements during imagery are not simply a duplicate of what happens during actual performance. Instead, eye movements appear to vary as a function of the interaction between visuomotor control strategies and task demands.

Eye tracker outcomes in a randomized trial of 40 sessions of hyperbaric oxygen or sham in participants with persistent post concussive symptoms.

PURPOSE: Eye movements may offer a sensitive method to measure response to intervention in mild traumatic brain injury (mTBI). METHODS: The Brain Injury and Mechanisms of Action of Hyperbaric Oxygen for Persistent Post-Concussive Symptoms after Mild Traumatic Brain Injury Study (BIMA) randomized 71 participants to 40 sessions of hyperbaric oxygen or sham. A companion normative study (Normal) enrolled 75 participants. An eye tracking system measured left and right eye movements for saccadic and smooth pursuit. At baseline two smooth pursuit tasks, circular and horizontal ramp, and four saccadic tasks, horizontal and vertical step, reading, and memory guided-on tasks differentiated BIMA from Normal participants. The change from baseline in these tasks were measured and compared between interventions and against Normal participants at 13 weeks and six-month follow-up using the two-sample t-test. The Holm-Bonferroni procedure was used to adjust for multiple testing. RESULTS: Change from baseline in eyetracker measures for participants assigned to the hyperbaric oxygen arm did not significantly differ from those assigned to the sham arm at post-randomization time points 13 weeks and six months. Consistent shifts of BIMA participant values toward Normal values at 13 weeks and six months were observed for overall fixation duration, forward saccadic duration, and number of lines read for the reading task, number of misses on the memory guided-on task, and absolute intersaccadic interval velocity and absolute saccadic amplitude on the circular task. The distributions between Normal and BIMA participants were no longer statistically significantly different at 13 weeks and six months post enrollment for these measures. CONCLUSION: The baseline differences between BIMA and Normal suggest potential vulnerability of the smooth pursuit system and the saccadic system. During the six-month follow-up period, improvement toward Normal was seen on some measures in both the hyperbaric oxygen and sham intervention arms without difference between intervention groups. IDS: clinicaltrials.gov Identifiers NCT01611194 and NCT01925963.

The mindful eye: Smooth pursuit and saccadic eye movements in meditators and non-meditators.

BACKGROUND: This study examined the effects of cultivated (i.e. developed through training) and dispositional (trait) mindfulness on smooth pursuit (SPEM) and antisaccade (AS) tasks known to engage the fronto-parietal network implicated in attentional and motion detection processes, and the fronto-striatal network implicated in cognitive control, respectively. METHODS: Sixty healthy men (19-59years), of whom 30 were experienced mindfulness practitioners and 30 meditation-naïve, underwent infrared oculographic assessment of SPEM and AS performance. Trait mindfulness was assessed using the self-report Five Facet Mindfulness Questionnaire (FFMQ). RESULTS: Meditators, relative to meditation-naïve individuals, made significantly fewer catch-up and anticipatory saccades during the SPEM task, and had significantly lower intra-individual variability in gain and spatial error during the AS task. No SPEM or AS measure correlated significantly with FFMQ scores in meditation-naïve individuals. CONCLUSIONS: Cultivated, but not dispositional, mindfulness is associated with improved attention and sensorimotor control as indexed by SPEM and AS tasks.

[On the Relationship between EMDR and Eye Movements - An Analysis of the Current State of Neurobiological Research]. / Zur Beziehung von EMDR und Augenbewegungen - Eine Analyse der aktuellen neurobiologischen Studienlage.

EMDR is an effective treatment for people diagnosed with posttraumatic stress disorder. The traditional technique of EMDR combines the activation of distressing reminders with guided rhythmic eye movements. The present article reviews the current state of research on the neurobiological correlates of the eye movements occurring during EMDR. The distinction between saccades and smooth pursuit eye movements allows for detailed analyses of ocular motor connections with cerebral networks of attention, memory and emotion. Possible consequences for research and clinical practice with EMDR are discussed.

Ophthalmology issues in schizophrenia.

Schizophrenia is a complex mental disorder associated with not only cognitive dysfunctions, such as memory and attention deficits, but also changes in basic sensory processing. Although most studies on schizophrenia have focused on disturbances in higher-order brain functions associated with the prefrontal cortex or frontal cortex, recent investigations have also reported abnormalities in low-level sensory processes, such as the visual system. At very early stages of the disease, schizophrenia patients frequently describe in detail symptoms of a disturbance in various aspects of visual perception that may lead to worse clinical symptoms and decrease in quality of life. Therefore, the aim of this review is to describe the various studies that have explored the visual issues in schizophrenia.

Bedside evaluation of smooth pursuit eye movements in acute sensory stroke patients.

BACKGROUND AND PURPOSE: Unilateral saccadic pursuit is reported to be suggestive of a pontine lesion in sensory stroke patients. We attempted to verify this eye sign in just-hospitalized pontine sensory stroke patients. METHODS: Horizontal smooth pursuit eye movements were evaluated upon hospital arrival in 4 pontine sensory stroke patients and were compared with those in 6 thalamic sensory stroke patients. Eye movements were evaluated with the patient lying down on the emergency room or stroke care unit bed by means of a newly developed video-oculography-based eye movement recording system equipped to project a moving laser pointer onto the ceiling. RESULTS: Laterality of horizontal smooth pursuit gain in pontine sensory stroke patients was evident upon arrival; in thalamic sensory stroke patients, horizontal smooth pursuit gain was equal in both directions. These characteristics were easily detected at bedside. CONCLUSION: Unilateral saccadic pursuit in pontine sensory stroke patients may be a practical diagnostic sign that can be detected even in the emergency room. The video-oculography-based recording system equipped to project a moving laser pointer onto the ceiling may be useful for detecting this eye sign.

Effects of hyperbaric oxygen on eye tracking abnormalities in males after mild traumatic brain injury.

The effects of hyperbaric oxygen (HBO2) on eye movement abnormalities in 60 military servicemembers with at least one mild traumatic brain injury (TBI) from combat were examined in a single-center, randomized, double-blind, sham-controlled, prospective study at the Naval Medicine Operational Training Center. During the 10 wk of the study, each subject was delivered a series of 40, once a day, hyperbaric chamber compressions at a pressure of 2.0 atmospheres absolute (ATA). At each session, subjects breathed one of three preassigned oxygen fractions (10.5%, 75%, or 100%) for 1 h, resulting in an oxygen exposure equivalent to breathing either surface air, 100% oxygen at 1.5 ATA, or 100% oxygen at 2.0 ATA, respectively. Using a standardized, validated, computerized eye tracking protocol, fixation, saccades, and smooth pursuit eye movements were measured just prior to intervention and immediately postintervention. Between and within groups testing of pre- and postintervention means revealed no significant differences on eye movement abnormalities and no significant main effect for HBO2 at either 1.5 ATA or 2.0 ATA equivalent compared with the sham-control. This study demonstrated that neither 1.5 nor 2.0 ATA equivalent HBO2 had an effect on postconcussive eye movement abnormalities after mild TBI when compared with a sham-control.

Coupling between spontaneous (resting state) fMRI fluctuations and human oculo-motor activity.

The recent discovery of incessant spontaneous fluctuations in human brain activity (also termed resting state fMRI) has been a focus of intense research in brain imaging. The spontaneous BOLD activity shows organized anatomical specialization as well as disruption in a number of brain pathologies. The link between the spontaneous fMRI fluctuations and human behavior is therefore of acute interest and importance. Here we report that a highly significant correlation exists between spontaneous BOLD fluctuations and eye movements which occur subliminally and spontaneously in the absence of any visual stimulation. Of the various eye movement parameters tested, we found robust and anatomically consistent correlations with both the amplitude and velocity of spontaneous eye movements. Control experiments ruled out a contribution of spatial and visual attention as well as smooth pursuit eye movements to the effect. The consistent anatomical specificity of the correlation patterns and their tight temporal link at the proper hemodynamic delay argues against a non-neuronal explanation of the effect, such as cardiac or respiratory cycles. Our results thus demonstrate a link between resting state and spontaneously emerging subconscious oculo-motor behavior.

Inhibition of steady-state smooth pursuit and catch-up saccades by abrupt visual and auditory onsets.

It is known that visual transients prolong saccadic latency and reduce saccadic frequency. The latter effect was attributed to subcortical structures because it occurred only 60-70 ms after stimulus onset. We examined the effects of large task-irrelevant transients on steady-state pursuit and the generation of catch-up saccades. Two screen-wide stripes of equal contrast (4, 20, or 100%) were briefly flashed at equal eccentricities (3, 6, or 12°) from the pursuit target. About 100 ms after flash onset, we observed that pursuit gain dropped by 6-12% and catch-up saccades were entirely suppressed. The relatively long latency of the inhibition suggests that it results from cortical mechanisms that may act by promoting fixation or the deployment of attention over the visual field. In addition, we show that a loud irrelevant sound is able to generate the same inhibition of saccades as visual transients, whereas it only induces a weak modulation of pursuit gain, indicating a privileged access of acoustic information to the saccadic system. Finally, irrelevant changes in motion direction orthogonal to pursuit had a smaller and later inhibitory effect.

EMDR effects on pursuit eye movements.

This study aimed to objectivize the quality of smooth pursuit eye movements in a standard laboratory task before and after an Eye Movement Desensitization and Reprocessing (EMDR) session run on seven healthy volunteers. EMDR was applied on autobiographic worries causing moderate distress. The EMDR session was complete in 5 out of the 7 cases; distress measured by SUDS (Subjective Units of Discomfort Scale) decreased to a near zero value. Smooth pursuit eye movements were recorded by an Eyelink II video system before and after EMDR. For the five complete sessions, pursuit eye movement improved after their EMDR session. Notably, the number of saccade intrusions-catch-up saccades (CUS)-decreased and, reciprocally, there was an increase in the smooth components of the pursuit. Such an increase in the smoothness of the pursuit presumably reflects an improvement in the use of visual attention needed to follow the target accurately. Perhaps EMDR reduces distress thereby activating a cholinergic effect known to improve ocular pursuit.

A model-based theory on the origin of downbeat nystagmus.

The pathomechanism of downbeat nystagmus (DBN), an ocular motor sign typical for vestibulo-cerebellar lesions, remains unclear. Previous hypotheses conjectured various deficits such as an imbalance of central vertical vestibular or smooth pursuit pathways to be causative for the generation of spontaneous upward drift. However, none of the previous theories explains the full range of ocular motor deficits associated with DBN, i.e., impaired vertical smooth pursuit (SP), gaze evoked nystagmus, and gravity dependence of the upward drift. We propose a new hypothesis, which explains the ocular motor signs of DBN by damage of the inhibitory vertical gaze-velocity sensitive Purkinje cells (PCs) in the cerebellar flocculus (FL). These PCs show spontaneous activity and a physiological asymmetry in that most of them exhibit downward on-directions. Accordingly, a loss of vertical floccular PCs will lead to disinhibition of their brainstem target neurons and, consequently, to spontaneous upward drift, i.e., DBN. Since the FL is involved in generation and control of SP and gaze holding, a single lesion, e.g., damage to vertical floccular PCs, may also explain the associated ocular motor deficits. To test our hypothesis, we developed a computational model of vertical eye movements based on known ocular motor anatomy and physiology, which illustrates how cortical, cerebellar, and brainstem regions interact to generate the range of vertical eye movements seen in healthy subjects. Model simulation of the effect of extensive loss of floccular PCs resulted in ocular motor features typically associated with cerebellar DBN: (1) spontaneous upward drift due to decreased spontaneous PC activity, (2) gaze evoked nystagmus corresponding to failure of the cerebellar loop supporting neural integrator function, (3) asymmetric vertical SP deficit due to low gain and asymmetric attenuation of PC firing, and (4) gravity-dependence of DBN caused by an interaction of otolith-ocular pathways with impaired neural integrator function.

Physiology of schizophrenia, bipolar disorder, and schizoaffective disorder.

OBJECTIVE: Endophenotypes have been proposed to identify the genetic and biological substrates of complex disorders. Three physiological inhibitory endophenotypes of large effect size in schizophrenia include suppression of P50 auditory evoked responses, inhibition of leading (small anticipatory) saccades during smooth pursuit eye movements, and cancellation of reflexive saccades in the antisaccade eye movement task. The aim of this study was to determine if the pattern of endophenotype abnormalities within individuals with schizophrenia differed from that within individuals with bipolar disorder. A second aim was to determine whether subjects with schizoaffective disorder, bipolar type, were neurophysiologically more similar to subjects with schizophrenia or subjects with bipolar disorder. METHOD: Endophenotypes were recorded for subjects diagnosed with schizophrenia (N=29), bipolar disorder (DSM-IV-TR) (N=40), and schizoaffective disorder, bipolar type (N=18). Data from normal comparison subjects were used to establish normal performance. RESULTS: Logistic regression determined that P50 ratio and frequency of leading saccades identified subjects with schizophrenia and bipolar disorder with a sensitivity of 95% and a specificity of 83%. The schizoaffective disorder group was split, with six subjects physiologically classified as schizophrenia-like and 12 subjects as bipolar-like. Those classified as schizophrenia-like were significantly younger at illness onset and had higher symptom ratings. CONCLUSION: A composite endophenotype of P50 ratio and frequency of leading saccades is consistent with the current clinical nosology of schizophrenia and bipolar disorder and parses patients with schizoaffective disorder, bipolar type, into two subgroups.

Atypical involvement of frontostriatal systems during sensorimotor control in autism.

Autism is a neurodevelopmental disorder involving dysmaturation of widely distributed brain systems. Accordingly, behaviors that depend on distributed systems, such as higher level cognition and sensorimotor control, are compromised in the disorder. The current study investigated alterations in neural systems underlying sensorimotor disturbances in autism. An fMRI investigation was conducted using saccadic and pursuit eye movement paradigms with 13 high functioning individuals with autism and 14 age- and IQ-matched typically developing individuals. Individuals with autism had reduced activation in cortical eye fields and cerebellar hemispheres during both eye movement tasks. When executing visually guided saccades, individuals with autism had greater activation bilaterally in a frontostriatal circuit including dorsolateral prefrontal cortex, caudate nucleus, medial thalamus, anterior and posterior cingulate cortex, and right dentate nucleus. The increased activation in prefrontal-striatal-thalamocortical circuitry during visually guided saccades indicates that systems typically dedicated to cognitive control may need to compensate for disturbances in lower-level sensorimotor systems. Reduced activation throughout visual sensorimotor systems may contribute to saccadic and pursuit disturbances that have been reported in autism. These findings document that neurodevelopmental disturbances in autism affect widely distributed brain systems beyond those mediating language and social cognition.

Present concepts of oculomotor organization.

This chapter gives an introduction to the oculomotor system, thus providing a framework for the subsequent chapters. This chapter describes the characteristics, and outlines the structures involved, of the five basic types of eye movements, for gaze holding ("neural integrator") and eye movements in three dimensions (Listing's law, pulleys).

Smooth pursuit-like eye movements during mental extrapolation of motion: the facilitatory effect of drowsiness.

We studied eye movements during mental extrapolation of motion. Subjects tracked with the eyes a target oscillating sinusoidally by +/- 5 degrees on the horizontal plane at frequencies between 0.15 and 0.5 Hz. After 4 cycles the target disappeared and subjects had to mentally extrapolate its motion in imagery for 5 further cycles. Subjects were invited to relax. We recorded eye movements with infrared oculography and the lid aperture with a webcam. Typically, in the imagery phase, sequences of saccades "reproduced" the macroscopic characteristics of the to-be-imagined motion. However, slow eye movements substituting the sequence of saccades emerged repeatedly in the course of the experiment, to the extent that sometimes it was almost impossible to distinguish the pattern of eye movements during tracking from that during imagery. These smooth pursuit-like eye movements lasted up to 17 s, although they were more commonly intermingled with saccades. It turned out that this phenomenon occurred mostly, although not exclusively, when the lids were partially lowered suggesting an association with drowsiness. The average gain of smooth pursuit-like eye movements in imagery passed from 0.09 when the lids were open, to 0.27 when they were partially lowered. A control experiment excluded that the lowering of the lids per se had played any important role. This finding has implications for both the physiology of the oculomotor system and for the debate on the relation between imagery and perception.

Involvement of the central thalamus in the control of smooth pursuit eye movements.

During maintenance of smooth pursuit eye movements, the brain must keep track of pursuit velocity to reconstruct target velocity from motion of retinal images. Although a recent study showed that corollary discharge signals through the thalamus to the cortex are used for internal monitoring of saccades, it remains unknown whether signals in the thalamus also contribute to monitoring and on-line regulation of smooth pursuit. The present study sought possible roles of the thalamocortical pathways in pursuit by recording activities of single thalamic neurons and by analyzing the effects of local inactivation. Data showed that many neurons in the ventrolateral thalamus exhibited directional modulation during pursuit. Most neurons discharged before or during initiation of pursuit, and the firing rate was proportional to the speed of target motion in a preferred direction. When the tracking target was extinguished briefly during maintenance of pursuit, these neurons continued firing, indicating that they carried extra-retinal, eye movement signals. The majority of neurons showed no change in activity around the time of small catch-up saccades during pursuit but responded transiently to large (16 degrees) memory-guided saccades in the preferred pursuit direction. Local inactivation of the recording sites did not alter pursuit latency but reduced eye velocity modestly during initiation and maintenance of ipsiversive pursuit. The results suggest that the central thalamus lies within pathways that regulate and monitor smooth pursuit eye movements.

Symptomatic Arnold-Chiari malformation and cranial nerve dysfunction: a case study of applied kinesiology cranial evaluation and treatment.

OBJECTIVE: To present an overview of possible effects of Arnold-Chiari malformation (ACM) and to offer chiropractic approaches and theories for treatment of a patient with severe visual dysfunction complicated by ACM. CLINICAL FEATURES: A young woman had complex optic nerve neuritis exacerbated by an ACM type I of the brain. INTERVENTION AND OUTCOME: Applied kinesiology chiropractic treatment was used for treatment of loss of vision and nystagmus. After treatment, the patient's ability to see, read, and perform smooth eye tracking showed improvement. CONCLUSION: Further studies into applied kinesiology and cranial treatments for visual dysfunctions associated with ACM may be helpful to evaluate whether this single case study can be representative of a group of patients who might benefit from this care.

Effects of vestibular and support afferentation upon visual pursuit in microgravity.

Evaluation of the accuracy of eye turns (saccades) to fix a jerky pointed stimulus, and smooth pursuit of slow linear and sinusoidal movements of both pointed and optokinetic stimuli was performed in 31 cosmonauts on flight days 2-3, 5-8, 30, and once in one or two months of mission. An additional investigation of the eye pursuit function involved 10 cosmonauts, who, after testing during free floating, fulfilled stimulus tracking following a cycle of active head rotation, and 14 cosmonauts who received support afferentation. It was found that at the beginning of adaptation and periodically in the course of long mission, the systems of slow pursuit tracking adopted the strategy of saccadic approximation whereby gaze fixation was achieved through a sequence of macro- or microsaccadic movements. It was demonstrated that these disturbances, practically in all investigated cosmonauts, were consequent to the vestibular deprivation developing in microgravity. Vestibular afferentation produced by active head rotation improved characteristics of visual pursuit. Support deprivation also affects pursuit tracking by cosmonauts who form the concept of space orientation based on perception of their head and leg position. With support afferentation, these cosmonauts demonstrated improved visual pursuit characteristics.

Visual-ocular motor activity in the macaque pregeniculate complex.

The anatomical connections of the pregeniculate complex (PrGC) with components of the visual-ocular motor system suggested its contribution to ocular motor behavior. Subsequent studies reported saccade-related activity in the primate PrGC. To determine its contribution, we characterized pregeniculate units (n = 128) in alert macaques during ocular motor tasks and visual stimulation. We found that 36/109 saccade-related units exhibited postsaccadic bursts or pauses in tonic discharge for saccades of any amplitude or direction. In contrast to previous results, 46/109 responses preceded or coincided with the saccade, while 47/109 responses were directionally tuned. Pregeniculate units were modulated not only in association with saccades (109/128) but also with smooth eye movements and visual motion (20/128) or eye position (23/128). Multiple ocular motor signals were recorded from 19% of the units, indicating signal convergence on individual neurons. Visual responses were demonstrated in 51% of PrGC units: visual field illumination modulated the resting discharge of 33 units; the responses of 37 saccade-related units and all 23 position-dependent units were modulated by visual stimulation. Early saccadic activity in the PrGC suggests that it contributes more to gaze than postsaccadic modulation of visual or ocular motor activity. The patterns of saccadic responses and the modulation of PrGC activity in association with a variety of visual-ocular motor behaviors suggest its potential role as a relay between the parietal cortex and elements of the brain stem ocular motor pathways, such as the superior colliculus and pretectal nucleus of the optic tract.

The effects of hyperventilation on postural control mechanisms.

The effect of hyperventilation on postural balance was investigated. Voluntary hyperventilation increased body sway in normal subjects, particularly in the sagittal plane. The possibility that this hyperventilation-induced unsteadiness is due to interference with lower limb somatosensory input, vestibular reflexes or cerebellar function was assessed. (i) The effect of hyperventilation on peripheral compound sensory action potentials (SAPs) and somatosensory evoked potentials (SEPs) (recorded centrally, from the scalp) elicited by electrical stimulation of the sural nerve was measured in six normal adults. A reduction in the scalp SEP amplitude and an increase in the peripheral SAP amplitude were observed during hyperventilation, which reversed during the recovery period. These changes indicate increased peripheral neural excitability which could lead to a higher level of ectopic activity; the latter would interfere with central reception of peripheral input. (ii) The click-evoked vestibulo-collic reflex was recorded to study the effect of hyperventilation on vestibulo-spinal activity. EMG recordings from both sternocleidomastoid muscles of six healthy subjects were made in response to loud clicks presented to either ear. Neither the amplitude nor the latency of the response were altered significantly by hyperventilation. (iii) Eye-movement recordings were obtained in the six normal subjects to assess the effect of hyperventilation on the vestibulo-ocular reflex and its visual suppression, the latter being a function largely mediated by the cerebellum; no changes were detected. (iv) Three-dimensional eye-movement recordings and body-sway measurements were obtained in six patients with longstanding unilateral vestibular loss in order to evaluate if hyperventilation disrupts vestibular compensation. In all patients, a horizontal nystagmus either appeared or was significantly enhanced for > or = 60 s after voluntary hyperventilation. Sway was also enhanced by hyperventilation in these patients, particularly in the frontal plane. This study suggests that hyperventilation disrupts mechanisms mediating vestibular compensation. The increase in sway may be, at least partly, mediated by deranged peripheral and central somatosensory signals from the lower limbs. Hyperventilation seems to spare vestibular reflex activity and cerebellar-mediated eye movements.