Control Of Saccadic Eye Movements Research Articles

Modeling kinematic variability reveals displacement and velocity based dual control of saccadic eye movements.

Noise is a ubiquitous component of motor systems that leads to behavioral variability of all types of movements. Nonetheless, systems-based models investigating human movements are generally deterministic and explain only the central tendencies like mean trajectories. In this paper, a novel approach to modeling kinematic variability of movements is presented and tested on the oculomotor system. This approach reconciles the two prominent philosophies of saccade control: displacement-based control versus velocity-based control. This was achieved by quantifying the variability in saccadic eye movements and developing a stochastic model of its control. The proposed stochastic dual model generated significantly better fits of inter-trial variances of the saccade trajectories compared to existing models. These results suggest that the saccadic system can flexibly use the information of both desired displacement and velocity for its control. This study presents a potential framework for investigating computational principles of motor control in the presence of noise utilizing stochastic modeling of kinematic variability.

Neuronal activity in posterior parietal cortex area LIP is not sufficient for saccadic eye movement production

It is widely recognized that the posterior parietal cortex (PPC) plays a role in active exploration with eye movements, arm reaching, and hand grasping. Whether this role is causal in nature is largely unresolved. One region of the PPC appears dedicated to the control of saccadic eye movement—lateral intraparietal (LIP) area. This area LIP possesses direct projections to well-established oculomotor centers and contains neurons with movement-related activity. In this study, we tested whether these neurons are implicated in saccade initiation and production. The movement-related activity of LIP neurons was tested by recording these neurons while monkeys performed a countermanding task. We found that LIP neuronal activity is not different before the execution or the cancelation of commanded saccades and thereby is not sufficient for the initiation and production of saccades. Consistent with the evolutionarily late emergence of the PPC, this finding relegates the role of this PPC area to processes that can regulate but not trigger eye movements.

Eye Movement Latency Coefficient of Variation as a Predictor of Cognitive Impairment: An Eye Tracking Study of Cognitive Impairment.

Studies demonstrated impairment in the control of saccadic eye movements in Alzheimer's disease (AD) and people with mild cognitive impairment (MCI) when conducting the pro-saccade and antisaccade tasks. Research showed that changes in the pro and antisaccade latencies may be particularly sensitive to dementia and general executive functioning. These tasks show potential for diagnostic use, as they provide a rich set of potential eye tracking markers. One such marker, the coefficient of variation (CV), is so far overlooked. For biological markers to be reliable, they must be able to detect abnormalities in preclinical stages. MCI is often viewed as a predecessor to AD, with certain classifications of MCI more likely than others to progress to AD. The current study examined the potential of CV scores on pro and antisaccade tasks to distinguish participants with AD, amnestic MCI (aMCI), non-amnesiac MCI (naMCI), and older controls. The analyses revealed no significant differences in CV scores across the groups using the pro or antisaccade task. Antisaccade mean latencies were able to distinguish participants with AD and the MCI subgroups. Future research is needed on CV measures and attentional fluctuations in AD and MCI individuals to fully assess this measure's potential to robustly distinguish clinical groups with high sensitivity and specificity.

Inhibitory Control of Saccadic Eye Movements and Cognitive Impairment in Mild Cognitive Impairment

AbstractBackgroundMild cognitive impairment (MCI) may occur due to several forms of neurodegenerative diseases and non‐degenerative conditions and is associated with cognitive impairment that does not affect everyday activities. For a timely diagnosis of MCI to prevent progression to dementia, a screening tool of fast, low‐cost and easy access is needed. Recent research on eye movement hints it a potential application for the MCI screening. However, the precise extent of cognitive function decline and eye‐movement control alterations in patients with MCI is still unclear.MethodPatients with MCI (n = 79) and age‐matched cognitively healthy controls (HC) (n = 170) completed four saccadic eye‐movement paradigms: prosaccade (PS)/antisaccade (AS), Go/No‐go, and a battery of neuropsychological tests.ResultThe findings revealed significantly longer latency in patients with MCI than in HC during the PS task. Additionally, patients with MCI had a lower proportion of correct responses and a marked increase in inhibition errors for both PS/AS and Go/No‐go tasks. Furthermore, when patients with MCI made errors, they failed to self‐correct many of these inhibition errors. In addition to the increase in inhibition errors and uncorrected inhibition errors, patients with MCI demonstrated a trend toward increased correction latencies. We also showed a relationship between neuropsychological scores and correct and error saccade responses.ConclusionOur results demonstrate that, similar to patients with Alzheimer’s dementia (AD), patients with MCI generate a high proportion of erroneous saccades toward the prepotent target and fail to self‐correct many of these errors, which is consistent with an impairment of inhibitory control and error monitoring.

HOW EVENT-DRIVEN INTERMITTENT CONTROL WITH UNSTABLE OPEN & CLOSED-LOOP DYNAMICS LEAD TO BOUNDED RESPONSE IN HUMAN POSTURAL CONTROL

Event-driven intermittent feedback control is a form of feedback control in which the variables of interest are observed continuously, but corrective control action is only initiated intermittently based on certain threshold criteria. According to the literature, the human central nervous system (CNS) adopts event-driven intermittent control strategy while performing various tasks such as stabilize upright posture, control of saccadic eye movement or while driving. In this paper, we examine whether event-driven intermittent control when applied to a system wherein both open-loop dynamics and continuous closed-loop dynamics are unstable can yield bounded overall response (as has been observed in some situations of human postural control). With the help of both illustrative example simulations and experimental results from a table-top experiment inspired from human postural control, we show that this is indeed possible. We further provide insights using passivity theory and phase space analysis. Our analysis shows that bounded response is possible even if the phase trajectories of unstable open-loop and unstable closed-loop systems do not diverge in opposite directions or when Hurwitz convex combinations are not feasible. This study does not necessitate any assumption regarding the stabilizability or passivity of any of the constituent subsystems.

Inhibitory Control of Saccadic Eye Movements and Cognitive Impairment in Mild Cognitive Impairment.

BackgroundMild cognitive impairment (MCI) may occur due to several forms of neurodegenerative diseases and non-degenerative conditions and is associated with cognitive impairment that does not affect everyday activities. For a timely diagnosis of MCI to prevent progression to dementia, a screening tool of fast, low-cost and easy access is needed. Recent research on eye movement hints it a potential application for the MCI screening. However, the precise extent of cognitive function decline and eye-movement control alterations in patients with MCI is still unclear.ObjectiveThis study examined executive control deficits and saccade behavioral changes in patients with MCI using comprehensive neuropsychological assessment and interleaved saccade paradigms.MethodsPatients with MCI (n = 79) and age-matched cognitively healthy controls (HC) (n = 170) completed four saccadic eye-movement paradigms: prosaccade (PS)/antisaccade (AS), Go/No-go, and a battery of neuropsychological tests.ResultsThe findings revealed significantly longer latency in patients with MCI than in HC during the PS task. Additionally, patients with MCI had a lower proportion of correct responses and a marked increase in inhibition errors for both PS/AS and Go/No-go tasks. Furthermore, when patients with MCI made errors, they failed to self-correct many of these inhibition errors. In addition to the increase in inhibition errors and uncorrected inhibition errors, patients with MCI demonstrated a trend toward increased correction latencies. We also showed a relationship between neuropsychological scores and correct and error saccade responses.ConclusionOur results demonstrate that, similar to patients with Alzheimer’s dementia (AD), patients with MCI generate a high proportion of erroneous saccades toward the prepotent target and fail to self-correct many of these errors, which is consistent with an impairment of inhibitory control and error monitoring.SignificanceThe interleaved PS/AS and Go/No-go paradigms are sensitive and objective at detecting subtle cognitive deficits and saccade changes in MCI, indicating that these saccadic eye movement paradigms have clinical potential as a screening tool for MCI.

Enhanced reading abilities is modulated by faster visual spatial attention

Research has shown improved reading following visual magnocellular training in individuals with dyslexia. Many studies have demonstrated how the magnocellular pathway controls visual spatial attention. Therefore, we have investigated the relationship between magnocellular pathway and visual spatial attention deficits in dyslexia in order to better understand how magnocellular-based interventions may help children to learn to read. Magnocellular function, visual spatial attention, and reading abilities of thirty elementary school students with dyslexia, aged between 8 and 10, were measured. The experimental group received magnocellular-based visual motion training for 12 sessions, while the control group received neutral sessions. All tests were repeated at the end of the training and after 1month. The magnocellular functioning, visual spatial attention, and reading abilities of the experimental group improved significantly compared to the controls. Additionally, improvement in reaction time of invalid conditions predicted improvements in saccadic eye movements. We conclude that visual magnocellular training improved saccadic eye movement control, visual spatial orientation, and reading ability.

A Stochastic Optimal Control Model with Internal Feedback and Velocity Tracking for Saccadic Eye Movements

A new stochastic optimal control model with internal feedback and velocity tracking is presented in this paper to study saccadic eye movement control. Recent evidence from neurophysiological studies of superior colliculus suggests the presence of a dynamic input to the saccade generation system that encodes saccade velocity, rather than just the static information of the desired saccade amplitude and direction. The new evidence makes it imperative to test if the saccadic control system can use a desired velocity input to achieve accurate behavioral outcomes. To test such a velocity-based architecture of saccade control, a new optimal control tracking model that incorporated two unique characteristics of internal feedback and stochasticity has been developed. The proposed model was validated using behavioral data of saccades generated by healthy human subjects in an experimental setup. The model was able to generate displacement and velocity trajectories of horizontal saccades made to different amplitudes and predict saccades made to vertical and oblique directions. It captured the main sequence relationship between saccade amplitude and peak velocities that were observed in the behavioral data. This paper presents a novel optimal control framework with tracking and internal feedback and proposes the first-ever model of the saccadic system that uses an alternate interpretation of velocity-based control, contrary to the dominant end-point based models available in the literature.

Inhibition of saccade initiation improves saccade accuracy: The role of local and remote visual distractors in the control of saccadic eye movements.

When a distractor appears close to the target location, saccades are less accurate. However, the presence of a further distractor, remote from those stimuli, increases the saccade response latency and improves accuracy. Explanations for this are either that the second, remote distractor impacts directly on target selection processes or that the remote distractor merely impairs the ability to initiate a saccade and changes the time at which unaffected target selection processes are accessed. In order to tease these two explanations apart, here we examine the relationship between latency and accuracy of saccades to a target and close distractor pair while a remote distractor appears at variable distance. Accuracy improvements are found to follow a similar pattern, regardless of the presence of the remote distractor, which suggests that the effect of the remote distractor is not the result of a direct impact on the target selection process. Our findings support the proposal that a remote distractor impairs the ability to initiate a saccade, meaning the competition between target and close distractor is accessed at a later time, thus resulting in more accurate saccades.

Cerebellar adaptive mechanisms explain the optimal control of saccadic eye movements

Cerebellar synaptic plasticity is vital for adaptability and fine tuning of goal-directed movements. The perceived sensory errors between desired and actual movement outcomes are commonly considered to induce plasticity in the cerebellar synapses, with an objective to improve desirability of the executed movements. In rapid goal-directed eye movements called saccades, the only available sensory feedback is the direction of reaching error information received only at end of the movement. Moreover, this sensory error dependent plasticity can only improve the accuracy of the movements, while ignoring other essential characteristics such as reaching in minimum-time. In this work we propose a rate based, cerebellum inspired adaptive filter model to address refinement of both accuracy and movement-time of saccades. We use optimal control approach in conjunction with information constraints posed by the cerebellum to derive bio-plausible supervised plasticity rules. We implement and validate this bio-inspired scheme on a humanoid robot. We found out that, separate plasticity mechanisms in the model cerebellum separately control accuracy and movement-time. These plasticity mechanisms ensure that optimal saccades are produced by just receiving the direction of end reaching error as an evaluative signal. Furthermore, the model emulates encoding in the cerebellum of movement kinematics as observed in biological experiments.

Primate Amygdalo-Nigral Pathway for Boosting Oculomotor Action in Motivating Situations.

SummaryA primary function of the primate amygdala is to modulate behavior based on emotional cues. To study the underlying neural mechanism, we first inactivated the amygdala locally and temporarily by injecting a GABA agonist. Then, saccadic eye movements and gaze were suppressed only on the contralateral side. Next, we performed optogenetic activation after injecting a viral vector into the amygdala. Optical stimulation in the amygdala excited amygdala neurons, whereas optical stimulation of axon terminals in the substantia nigra pars reticulata inhibited nigra neurons. Optical stimulation in either structure facilitated saccades to the contralateral side. These data suggest that the amygdala controls saccades and gaze through the basal ganglia output to the superior colliculus. Importantly, this amygdala-derived circuit mediates emotional context information, whereas the internal basal ganglia circuit mediates object value information. This finding demonstrates a basic mechanism whereby basal ganglia output can be modulated by other areas conveying distinct information.

Влияние мозжечковой дисфункции, приобретенной в результате лечения опухоли, на функционирование саккадической системы у детей

Cerebellum plays a crucial role in control of saccadic eye movements and gaze fixation. The cerebellar impairment leads to various disorders of oculomotor behavior and related psychophysiological processes, which, in turn, may affect the efficiency of rehabilitation process of patients who underwent tumor resection surgery on cerebellum. The purpose of this work was to determine the ways and the extent of influence of surgery-related cerebellar dysfunction on visuomotor system of children. We also intended to develop criteria based on these findings to assess the patient’s rehabilitation progress quantitatively as well as qualitatively. 66 children between 9 and 17 years old with surgery-related cerebellar dysfunction were enrolled in this study. The control group consisted of 54 healthy children of the same age. The subjects were to perform 3 oculomotor tasks while their eye movements were recorded using eye tracking technique. We found that children with cerebellar dysfunction had impaired gaze fixation ability, executed more hypermetric saccades and experienced difficulties with visual scanning. These oculomotor system deficiencies inevitably lead to disturbances of various cognitive processes such as visual perception, attention focusing, memory and reading. Also, hypermetric saccades can be treated as a special case of ataxia usually found in patients with cerebellar dysfunction. We conclude that assessment of oculomotor deficiencies should be used to increase the effectiveness of rehabilitation procedures for patients with cerebellar dysfunction.

Saccadic Eye Movements in Young-Onset Parkinson’s Disease - A BOLD fMRI Study

ABSTRACTThe objective of the present study was to understand control of saccadic eye movements in patients with young onset Parkinson’s disease (YOPD) where onset of disease symptoms appears early in life (<40 years of age). Functional magnetic resonance imaging (fMRI) was performed in patients with YOPD and control subjects while they performed saccadic tasks, which consisted of a reflexive task and another task that required inhibitory control of eye movements (Go-NoGo task). Functional imaging related to saccadic eye movements in this group of patients has not been widely reported. A 1.5T MR scanner was used for structural and functional imaging. Analysis of blood-oxygen-level-dependent (BOLD) fMRI was performed using Statistical Parametric Mapping (SPM) software and compared in patients and controls. In patients with YOPD greater activation was seen significantly in the middle frontal gyrus, medial frontal gyrus, angular gyrus, cingulate gyrus, precuneus and cerebellum, when compared with the control group, during the saccadic tasks. Gap and overlap protocols revealed differential activation patterns. The abnormal activation during reflexive saccades was observed in the overlap condition, while during Go-NoGo saccades in the gap condition. The results suggest that impaired circuitry in patients with YOPD results in recruitment of more cortical areas. This increased frontal and parietal cortical activity possibly reflects compensatory mechanisms for impaired cognitive and saccadic circuitry.

Gain control of saccadic eye movements is probabilistic

Saccades are rapid eye movements that orient the visual axis toward objects of interest to allow their processing by the central, high-acuity retina. Our ability to collect visual information efficiently relies on saccadic accuracy, which is limited by a combination of uncertainty in the location of the target and motor noise. It has been observed that saccades have a systematic tendency to fall short of their intended targets, and it has been suggested that this bias originates from a cost function that overly penalizes hypermetric errors. Here, we tested this hypothesis by systematically manipulating the positional uncertainty of saccadic targets. We found that increasing uncertainty produced not only a larger spread of the saccadic endpoints but also more hypometric errors and a systematic bias toward the average of target locations in a given block, revealing that prior knowledge was integrated into saccadic planning. Moreover, by examining how variability and bias covaried across conditions, we estimated the asymmetry of the cost function and found that it was related to individual differences in the additional time needed to program secondary saccades for correcting hypermetric errors, relative to hypometric ones. Taken together, these findings reveal that the saccadic system uses a probabilistic-Bayesian control strategy to compensate for uncertainty in a statistically principled way and to minimize the expected cost of saccadic errors.

Evidence Transcranial Direct Current Stimulation Can Improve Saccadic Eye Movement Control in Older Adults.

Objectives: Ageing is associated with declines in voluntary eye movement control, which negatively impact the performance of daily activities. Therapies treating saccadic eye movement control deficits are currently lacking. To address the need for an effective therapy to treat age-related deficits in saccadic eye movement control, the current study investigated whether saccadic behaviour in older adults can be improved by anodal transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex using a montage that has been proven to be effective at improving nonoculomotor control functions. Method: The tDCS protocol entailed a 5 cm × 7 cm anodal electrode and an encephalic cathodal reference electrode positioned over the contralateral supraorbital area. In two experiments, healthy older men completed one active (1.5 mA current for 10 min) and one sham stimulation session, with the session order counterbalanced across participants, and eye movement testing following stimulation. In the first experiment, participants rested during the tDCS (offline), whereas in the follow-up experiment, participants engaged in antisaccades during the tDCS (online). Results: Analyses revealed improvements in saccadic performance following active anodal tDCS relative to sham stimulation in the online experiment, but not in the offline experiment, which was presumably due to the activation of the relevant networks during tDCS promoting more targeted effects. Discussion: These outcomes converge with findings pertaining to nonoculomotor cognitive functions, and provide evidence that tDCS can improve saccadic eye movement control in older adults.

Instantaneous Midbrain Control of Saccade Velocity.

The ability to interact with our environment requires the brain to transform spatially represented sensory signals into temporally encoded motor commands for appropriate control of the relevant effectors. For visually guided eye movements, or saccades, the superior colliculus (SC) is assumed to be the final stage of spatial representation, and instantaneous control of the movement is achieved through a rate code representation in the lower brain stem. We investigated whether SC activity in nonhuman primates (Macaca mulatta, 2 male and 1 female) also uses a dynamic rate code, in addition to the spatial representation. Noting that the kinematics of amplitude-matched movements exhibit trial-to-trial variability, we regressed instantaneous SC activity with instantaneous eye velocity and found a robust correlation throughout saccade duration. Peak correlation was tightly linked to time of peak velocity, the optimal efferent delay between SC activity and eye velocity was constant at ∼12 ms both at onset and during the saccade, and SC neurons with higher firing rates exhibited stronger correlations. Moreover, the strong correlative relationship and constant efferent delay observation were preserved when eye movement profiles were substantially altered by a blink-induced perturbation. These results indicate that the rate code of individual SC neurons can control instantaneous eye velocity and argue against a serial process of spatial-to-temporal transformation. They also motivated us to consider a new framework of saccade control that does not incorporate traditionally accepted elements, such as the comparator and resettable integrator, whose neural correlates have remained elusive.SIGNIFICANCE STATEMENT All movements exhibit time-varying features that are under instantaneous control of the innervating neural command. At what stage in the brain is dynamical control present? It is well known that, in the skeletomotor system, neurons in the motor cortex use dynamical control. In the oculomotor system, in contrast, instantaneous velocity control of saccadic eye movements is not thought to be enforced until the lower brainstem. Using correlations between residual signals across trials, we show that instantaneous control of saccade velocity is present earlier in the visuo-oculomotor neuraxis, at the level of superior colliculus. The results require us to consider alternate frameworks of the neural control of saccades.

Signatures of a probabilistic strategy in the control of saccadic eye movements

Signatures of a probabilistic strategy in the control of saccadic eye movements

Eye movement control during visual pursuit in Parkinson's disease.

BackgroundPrior studies of oculomotor function in Parkinson’s disease (PD) have either focused on saccades without considering smooth pursuit, or tested smooth pursuit while excluding saccades. The present study investigated the control of saccadic eye movements during pursuit tasksand assessed the quality of binocular coordinationas potential sensitive markers of PD.MethodsObservers fixated on a central cross while a target moved toward it. Once the target reached the fixation cross, observers began to pursue the moving target. To further investigate binocular coordination, the moving target was presented on both eyes (binocular condition), or on one eye only (dichoptic condition).ResultsThe PD group made more saccades than age-matched normal control adults (NC) both during fixation and pursuit. The difference between left and right gaze positions increased over time during the pursuit period for PD but not for NC. The findings were not related to age, as NC and young-adult control group (YC) performed similarly on most of the eye movement measures, and were not correlated with classical measures of PD severity (e.g., Unified Parkinson’s Disease Rating Scale (UPDRS) score).DiscussionOur results suggest that PD may be associated with impairment not only in saccade inhibition, but also in binocular coordination during pursuit, and these aspects of dysfunction may be useful in PD diagnosis or tracking of disease course.

Saccadic oscillations in 4 dogs and 1 cat

Disorders affecting the control of saccadic eye movements result in involuntary saccadic oscillations and are widely reported in human medicine. Information regarding the occurrence and potential importance of saccadic oscillations in veterinary medicine is currently limited. The clinical histories of three dogs and one cat displaying involuntary eye movements consistent with opsoclonus are presented, with final diagnoses including idiopathic generalized tremor syndrome and neuronal ceroid lipofuscinosis (NCL). A dog with eye movements closely resembling macrosaccadic oscillations is also presented, for which a final diagnosis of NCL was made. All animals had clinical signs of cerebellar disease. As in human medicine, recognition of these forms of involuntary eye movement might suggest a cerebellar neuroanatomic localization. Opsoclonus and macrosaccadic oscillations are forms of involuntary saccadic eye movement that are both unrecognized and under‐reported in veterinary medicine.

AB073. Correlations between control of saccadic eye movements and performance in other cognitive tasks in younger adults, older adults and patients with Parkinson’s disease

Background: Cognitive control is defined as the ability to act flexibly in the environment by either behaving automatically or inhibiting said automatic behaviour and it can be measured using an interleaved pro/anti-saccade task. Decline in cognitive control has been attributed to normal aging and neurological illnesses such as Parkinson’s disease (PD) as well as decline in other cognitive abilities. This parallel might highlight the role played by cognitive control in information processing and working memory. However, little is known about the relationship between cognitive control and other cognitive processes such as visual memory, decision making, and visual search. We thus propose to correlate the incidence of impaired cognitive control with deficits in visual memory, decision making and visual search in three groups: younger adults, older adults and patients with idiopathic PD.