The control of vertical saccades in aged subjects

Exploring age-related changes in saccades during cognitive tasks in healthy adults

Introduction

Although eye movements such as saccades are related to internal cognitive processes and are independent of visual processing, few studies have investigated whether non-visual cognitive tasks simultaneously affect horizontal and vertical saccades in younger and older adults.

Methods

We recruited 28 younger adults aged 20-29 years and 26 older adults aged >60 years through advertisements in community settings. All participants were free of major psychiatric, neurological, or ocular diseases. All participants performed the mental arithmetic task (MAT) and verbal fluency task (VFT). The primary measures were saccade parameters, including frequency, mean amplitude, and mean velocity.

Results

During MAT and VFT, the frequencies of horizontal and vertical saccades increased (p = 0.0005 for horizontal saccade in MAT; p < 0.0001 for horizontal saccade in VFT; p = 0.012 for vertical saccade in MAT; p = 0.001 for vertical saccade in VFT), but were comparable between MAT and VFT. The old group showed a slower vertical saccade than the young group during the tasks (p = 0.011 in the MAT phase; p = 0.006 in the VFT phase). The amplitude of the horizontal saccade decreased in both groups during MAT compared to the resting period (p = 0.013), but did not change significantly during VFT.

Discussion

Saccade parameters can change during non-visual cognitive tasks with differences between age groups and saccade directions. This study significantly contributes to our understanding of the distinct dynamics of horizontal and vertical saccades across various age group in cognitive aging, despite its restricted focus on specific saccade parameters and cognitive tasks, and inclusion solely of cognitively normal individuals. This study highlights the importance of saccade analysis in elucidating age-related cognitive changes. In conclusion, saccades should be examined in future studies as a potential non-invasive biomarker for early detection of cognitive decline and neurodegenerative diseases.

Saccadic Eye Movements in Patients with Mild Cognitive Impairment: A Longitudinal Study

Saccadic eye movements are one of the sensitive and noninvasive methods to help monitor the cognitive course of mild cognitive impairment (MCI). The study aimed to evaluate both pro and anti-saccade longitudinally and the relationship between cognitive functions and eye movements in MCI subgroups and healthy controls (HCs) at a two-year follow-up. This study revealed that the anti-saccade anticipatory responses decreased in amnestic MCI (aMCI). Correct vertical pro-saccades increased in non-amnestic MCI (naMCI), while the express saccades decreased. Our study demonstrated that longer than two years of follow-up is necessary to monitor the course of MCI. Findings of the relationships between longitudinal changes of saccades and cognitive measurements demonstrated the usability of eye movements in evaluating the process of MCI.

The effects of age and sex on the incidence of multiple step saccades and corrective saccades

Objective

Although multiple step saccades (MSS) is occasionally observed in healthy subjects, it is more pronounced in patients with aging-related neurodegenerative diseases, particularly Parkinson’s disease (PD). Thus, MSS has been treated as a complementary biomarker for diagnosing PD. Despite the aforementioned knowledge, several questions remain unexplored: (1) How does aging affect MSS? (2) Is there a sex difference in MSS? (3) Are there differences in MSS between vertical and horizontal saccades? (4) Are MSS and corrective saccade (CS) the same behavior? (5) How do age and sex affect CS? The objectives of the present study are to address these questions.

Method

Four hundred eighty healthy participants were recruited to perform a visually guided reactive saccade task. Participants were divided into six groups according to their ages. Each group consisted of 40 male and 40 female participants. Eye movements were recorded with infrared eye trackers.

Results

The incidence of MSS increased as a function of age, whereas the incidence of CS first increased with age 20–49 and then decreased with age 50–79. The incidences of both MSS and CS did not show sex differences. The incidence of MSS in vertical saccades was significantly higher than that in horizontal saccades, and their difference increased with increasing age, whereas the incidence of CS showed a reversed pattern.

Conclusion

Age and saccadic direction affect the occurrences of MSS and CS differently, indicating that MSS and CS are different saccadic behaviors. In addition, measuring saccades could reliably reflect the function of human’s brain which is affected by aging.

Saccadic eye movement performance reduces visual manipulation influence and center of pressure displacements in older fallers

This study examined changes in postural control and gaze performance of faller and non-faller older adults under conditions of visual tasks and optical flow manipulations. Fifteen older non-fallers (69.8 years, ± 3.2) and fifteen older fallers (71.1 years, ± 6.4) stood on a force platform inside a moving room wearing an eye tracker. Four tasks were performed: gaze fixation; predictable saccades; unpredictable saccades; and free-viewing. The stimuli appeared at a frequency of 1.1 Hz during conditions of predictable and unpredictable saccades. Sixteen trials were divided into two blocks. In the first block, the room remained stationary. In the second block, the room oscillated, without the participant's awareness, with a 0.6 cm amplitude and 0.2 Hz frequency. Results showed postural sway attenuation in older fallers during the saccadic tasks compared to gaze fixation and free-viewing tasks, in both stationary and moving room conditions. Both groups showed increased center of pressure (CoP) magnitude during the moving room condition and CoP displacements strongly coupled to the room's movement. The influence of the moving room on the postural sway was reduced during the saccadic tasks for both older groups. Older fallers exhibited higher variability compared to older non-fallers. Gaze behavior differences between groups were dependent on the goals of the visual tasks. Therefore, CoP displacements of older adults are reduced during saccadic tasks regardless of their falling history. However, postural and gaze performance of older fallers suggests increased deterioration of postural and oculomotor control which may be used as a predictor of fall risk.

Deficits in saccadic eye movements differ between subtypes of patients with mild cognitive impairment

Introduction: Mild cognitive impairment (MCI) is known to be heterogeneous in its cognitive features and course of progression. Whilst memory impairment is characteristic of amnestic MCI (aMCI), cognitive deficits other than memory can occur in both aMCI and non-amnestic MCI (naMCI) and accurate assessment of the subtypes of MCI is difficult for clinicians without the application of extensive neuropsychological testing. In this study, we examine metrics derived from recording of reflexive and voluntary saccadic eye movements as a potential alternative method for discriminating between subtypes and assessing cognitive functions in MCI.Method: A total of 29 MCI patients and 29 age- and education-matched healthy controls (HCs) participated in the cross-sectional study. We recorded horizontal and vertical pro-saccades and anti-saccade responses. All the participants also completed a comprehensive neuropsychological tests battery.Results: Significant differences in saccadic eye movement were found between the subtypes of MCI and HCs. Patients with aMCI had a higher percentage of short latency "express" saccades than HCs. We found strong associations between saccadic reaction times and cognitive domains, including executive functions and attention. The mini-mental state examination (MMSE) was also found to correlate with uncorrected errors in the anti-saccade task.Conclusions: The increased proportion of saccades in the express latency range in aMCI may be indicative of problems with cognitive inhibitory control in these patients. A focus on this and other saccade metrics in the preclinical and prodromal stages of dementia may help to predict the clinical progression of the disease and direct interventions for the management of MCI. The clinical significance of saccadic eye movement impairments in MCI is not yet fully understood and should be investigated in further studies using larger samples.

Premature saccades: A detailed physiological analysis

OBJECTIVE

Premature saccades (PSs) are those made with latencies too short for the direction and amplitude to be specifically programmed. We sought to determine the minimum latency needed to establish accurate direction and amplitude, and observed what occurs when saccades are launched before this minimum latency.

METHODS

In Experiment 1, 249 normal subjects performed the gap saccade task with horizontal targets. In Experiment 2, 28 normal subjects performed the gap saccade task with the targets placed in eight directions. In Experiment 3, 38 normal subjects, 49 patients with Parkinson's disease (PD), and 10 patients with spinocerebellar degeneration (SCD) performed the gap saccade task with horizontal targets.

RESULTS

In Experiment 1, it took 100 ms to accurately establish saccade amplitudes and directions. In Experiment 2, however, the latencies needed for accurate amplitude and direction establishment were both approximately 150 ms. In Experiment 3, the frequencies of PSs in patients with PD and SCD were lower than those of normal subjects.

CONCLUSIONS

The saccade amplitudes and directions are determined simultaneously, 100-150 ms after target presentation. PSs may result from prediction of the oncoming target direction or latent saccade activities in the superior colliculus.

SIGNIFICANCE

Saccade direction and amplitude are determined simultaneously.

Semi tandem base of support degrades both saccadic gaze control and postural stability particularly in older adults

Differences in the postural stabilization of older and young adults have been shown to be task-dependent on both visual and postural challenges; however, the gaze behavior during such tasks has rarely been examined. This study investigated the effects of horizontal and vertical saccades on gaze control, center of pressure (CoP) and head displacement of young and older adults on different bases of support. Ten young adults (20.7 ± 3.4 years) and ten older adults (71.6 ± 3.1 years) remained in an upright stance on a force platform wearing an eye-head tracker device. The participants performed 30-second trials according to two bases of support (feet apart and semi-tandem) and three gaze behavior (fixation, horizontal and vertical saccades) conditions. Older adults presented greater CoP amplitude (p < 0.002) and velocity (p < 0.001) (ML axis), and higher head amplitude (ML) (p < 0.002) than young adults during the semi tandem base. Head displacement of both groups presented higher velocity (ML axis) during horizontal (p < 0.001) and vertical saccades (p < 0.01) than the fixation task only on the semi tandem base. There was higher number of fixations (p < 0.001) and lower mean fixation duration (p < 0.001) on the semi-tandem base (p < 0.05). The results showed higher gaze latency variability in vertical saccades for older adults (p < 0.01). Challenging postural tasks may alter postural adjustments and gaze control during saccadic tasks. Particularly, the greater postural instability of older adults increased the gaze latency variability during saccadic tasks, suggesting some deterioration in the posture-gaze relation with aging.

Age related prefrontal compensatory mechanisms for inhibitory control in the antisaccade task

Cognitive decline during aging includes impairments in frontal executive functions like reduced inhibitory control. However, decline is not uniform across the population, suggesting individual brain response variability to the aging process. Here we tested the hypothesis, within the oculomotor system, that older adults compensate for age-related neural alterations by changing neural activation levels of the oculomotor areas, or even by recruiting additional areas to assist with cognitive performance. We established that the observed changes had to be related to better cognitive performance to be considered as compensatory. To probe this hypothesis we used the antisaccade paradigm and analyzed the effect of aging on brain activations during the inhibition of prepotent responses to visual stimuli. While undergoing a fMRI scan with concurrent eye tracking, 25 young adults (21.7 y/o ± 1.9 SDM) and 25 cognitively normal older adults (66.2 y/o ± 9.8 SDM) performed an interleaved pro/antisaccade task consisting of a preparatory stage and an execution stage. Compared to young adults, older participants showed a larger increase in antisaccade reaction times, while also generating more antisaccade direction errors. BOLD signal analyses during the preparatory stage, when response inhibition processes are established to prevent an automatic response, showed decreased activations in the anterior cingulate and the supplementary eye fields in the older group. Moreover, older adults also showed additional recruitment of the frontal pole not seen in the younger group, and larger activations in the dorsolateral prefrontal cortex during antisaccade preparation. Additional analyses to address the performance variability in the older group showed distinct behavioral-BOLD signal correlations. Larger activations in the saccade network, including the frontal pole, positively correlated with faster antisaccade reaction times, suggesting a functional recruitment of this area. However, only the activation in the dorsolateral prefrontal cortex during the antisaccade events showed a negative correlation with the number of errors across older adults. These findings support the presence of two dissociable age-related plastic mechanisms that result in different behavioral outcomes. One related to the additional recruitment of neural resources within anterior pole to facilitate modulation of cognitive responses like faster antisaccade reaction times, and another related to increased activation of the dorsolateral prefrontal cortex resulting in a better inhibitory control in aging.

Differential age-related changes in localizing a target among distractors across an extended visual field

Age differences in the spatial distribution of attention over a wide field of view have only been described in terms of the spatial extent, leaving the topographical aspect unexplored. This study examined age differences between younger and older adults in good general health in an important topographical characteristic, the asymmetry between the upper and lower visual fields. In Experiment 1, we found age differences across the entire attentional visual field. In addition, age differences were greater in the upper compared to the lower field. In Experiment 2, we examined whether the finding of a greater age difference in the ability to localize a target among distractors in the upper visual field in Experiment 1 was a result of possible differential age differences between the upper and lower visual fields in the ability to localize a target even when there was no distractor competing for attention. Our results suggested that the age differences we observed were linked to age differences in the ability to filter out distractors that compete with the target for attention rather than the ability to process only the target over a wide field of view. While younger adults demonstrated an upper visual field advantage in the ability to localize a target among distractors, there was no such field advantage in older adults. We discuss this finding of diminished upper visual field advantage in older adults in light of an account of pervasive loss of neural specialization with age. We postulate that one possible explanation of age differences in the asymmetry between the upper and lower visual fields may be an adaptation to age-related physical decline. We also discuss important implications of our findings in risks of falls and vehicle crashes.

When do you look where you look? A visual field asymmetry

Pre-saccadic fixation durations associated with saccades directed in different directions were compared in three endogenous-attention oriented saccadic scanning tasks (i.e. visual search and scene viewing). Pre-saccadic fixation durations were consistently briefer before the execution of upward saccades, than downward saccades. Saccades also had a higher probability of being directed upwards than downwards. Pre-saccadic fixation durations were symmetric and longer for horizontally-directed saccades. The vertical visual field asymmetry in pre-saccadic fixation durations reflects an influence of factors not directly related to currently fixated elements. The ability to predict pre-saccadic fixation durations is important for computational modelling of real-time saccadic scanning, and the findings make a case for including directional constraints in computational modelling of when the eyes move.

Both age and physical activity level impact on eye-hand coordination

Aging impacts on our ability to perform goal-directed aiming movements. Older adults generally make slower and shorter initial impulses towards the end target, and therefore require more time for corrections in the final movement stage. Recent studies however suggest that a physically active lifestyle may attenuate these age-related changes. Also, it remains unclear whether eye-movement control exhibits a similar pattern of adaptation in older adults. Therefore, the first aim of this study was to describe how age and physical activity level impact eye-hand coordination during discrete manual aiming. Young and older participants were divided into physically active and sedentary subgroups, and performed discrete aiming movements while hand and eye movements were recorded. Secondly, to determine whether older adults depend more on vision during aiming, the task was repeated without visual feedback. The results revealed that the typical age-related hand movement adaptations were not only observed in older, but also in sedentary young participants. Older and sedentary young participants also spent more hand movement time after the eyes fixated the end target. This finding does not necessarily reflect an augmented reliance on vision, as all groups showed similar aiming errors when visual feedback was removed. In conclusion, both age and physical activity level clearly impacted eye-hand coordination during discrete manual aiming. This adapted coordination pattern seems to be caused by other factors than an increased reliance on vision.

Horizontal and vertical eye movement metrics: what is important?

OBJECTIVE

To assist other eye movement investigators in the design and analysis of their studies.

METHODS

We examined basic saccadic eye movements and smooth pursuit in the horizontal and vertical directions with video-oculography in a group of 145 healthy subjects between 19 and 82 years of age.

RESULTS

Gender and education level did not influence eye movement metrics. With age, the latency of leftward and vertical pro- and antisaccades increased (p<0.001), velocity of upward prosaccades decreased (p<0.001), gain of rightward and upward prosaccades diminished (p<0.001), and the error rate of antisaccades increased (p<0.001). Prosaccades and antisaccades were influenced by the direction of the target, resulting in a right/left and up/down asymmetry. The skewness of the saccade velocity profile was stable throughout the lifespan, and within the range of saccades analyzed in the present study, correlated with amplitude and duration only for antisaccades (p<0.001).

CONCLUSIONS

Some eye movement metrics must be separated by the direction of movement, others according to subject age, while others may be pooled.

SIGNIFICANCE

This study provides important information for new oculomotor laboratories concerning the constitution of subject groups and the analysis of eye movement metrics.

Deterioration of horizontal saccades in progressive supranuclear palsy

OBJECTIVE

To investigate horizontal saccade changes according to disease stage in patients with progressive supranuclear palsy (PSP).

METHODS

We studied visually and memory guided saccades (VGS and MGS) in 36 PSP patients at various disease stages, and compared results with those in 66 Parkinson's disease (PD) patients and 58 age-matched normal controls.

RESULTS

Both vertical and horizontal saccades were affected in PSP patients, usually manifesting as "slow saccades" but sometimes as a sequence of small amplitude saccades with relatively well preserved velocities. Disease progression caused saccade amplitude reduction in PSP but not PD patients. In contrast, VGS and MGS latencies were comparable between PSP and PD patients, as were the frequencies of saccades to cue, suggesting that voluntary initiation and inhibitory control of saccades are similar in both disorders. Hypermetria was rarely observed in PSP patients with cerebellar ataxia (PSPc patients).

CONCLUSIONS

The progressively reduced accuracy of horizontal saccades in PSP suggests a brainstem oculomotor pathology that includes the superior colliculus and/or paramedian pontine reticular formation. In contrast, the functioning of the oculomotor system above the brainstem was similar between PSP and PD patients.

SIGNIFICANCE

These findings may reflect a brainstem oculomotor pathology.

Different effects of double-pulse TMS of the posterior parietal cortex on reflexive and voluntary saccades

Gap and overlap tasks are widely used to promote automatic versus controlled saccades. This study examines the hypothesis that the right posterior parietal cortex (PPC) is differently involved in the two tasks. Twelve healthy students participated in the experiment. We used double-pulse transcranial magnetic stimulation (dTMS) on the right PPC, the first pulse delivered at the target onset and the second 65 or 80 ms later. Each subject performed several blocks of gap or overlap task with or without dTMS. Eye movements were recorded with an Eyelink device. The results show an increase of latency of saccades after dTMS of the right PPC for both tasks but for different time windows (0–80 ms for the gap task, 0–65 ms for the overlap task). Moreover, for rightward saccades the coefficient of variation of latency increased in the gap task but decreased in the overlap task. Finally, in the gap task and for leftward saccades only, dTMS at 0–80 ms decreased the amplitude and the speed of saccades. Although the study is preliminary and needs further investigation in detail, the results support the hypothesis that the right PPC is involved differently in the initiation of the saccades for the two tasks: in the gap task the PPC controls saccade triggering while in the overlap task it could be a relay to the Frontal Eye Fields which is known to control voluntary saccades, e.g., memory-guided and perhaps the controlled saccades in the overlap task The results have theoretical and clinical significance as gap-overlap tasks are easy to perform even in advanced age and in patients with neurodegenerative diseases.

Long latency and high variability in accuracy-speed of prosaccades in Alzheimer's disease at mild to moderate stage

BACKGROUND

Studying saccades is a useful tool to investigate brain function. There is still controversy regarding deficits in prosaccades in Alzheimer's disease (AD), and a study of saccades in subjects with mild cognitive impairment (MCI) has not been published to date.

METHODS

We examined horizontal saccades in 10 healthy elderly, and 9 MCI and 9 AD patients. Two tasks were used: gap (fixation target extinguishes prior to target onset) and overlap (fixation stays on after target onset). Eye movements were recorded with the Skalar IRIS system.

RESULTS

(1) Latencies were shorter in the gap than in the overlap task (a gap effect) in all three groups of subjects: healthy elderly, MCI and AD; (2) for both tasks, latency of saccades was longer for AD patients than for healthy and MCI subjects, and (3) accuracy and mean velocity were normal in MCI and AD subjects, however, variability in accuracy-speed was higher for AD patients than for healthy and MCI subjects in the overlap task.

CONCLUSIONS

Abnormalities in reaction time and accuracy-speed variability reflect deficits in cerebral areas involved in the triggering and execution of saccades; a saccade test can be useful to follow up the evolution of MCI subjects as some of them may develop AD disease.

Spread deficits in initiation, speed and accuracy of horizontal and vertical automatic saccades in dementia with lewy bodies

Background: Mosimann et al. (2005) reported prolongation of saccade latency of prosaccades in dementia with Lewy body (DLB). The goal of this study is to go further examining all parameters, such as rates of express latency, but also accuracy and velocity of saccades, and their variability. Methods: We examined horizontal and vertical saccades in 10 healthy elderly subjects and 10 patients with DLB. Two tasks were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset). Eye movements were recorded with the Eyelink II eye tracker. Results: The main findings were: (1) as for healthy, latencies were shorter in the gap than in the overlap task (a gap effect); (2) for both tasks latency of saccades was longer for DLB patients and for all directions; (3) express latency in the gap task was absent for large majority of DLB patients while such saccades occurred frequency for controls; (4) accuracy and peak velocity were lower in DLB patients; (5) variability of all parameters was abnormally high in DLB patients. Conclusions: Abnormalities of all parameters, latency, accuracy and peak velocity reflect spread deficits in cortical-subcortical circuits involved in the triggering and execution of saccades.

Rare express saccades in elderly fallers

OBJECTIVE

To examine horizontal saccades in elderly subjects with falling history; prior extensive screening was done to recruit subjects with falling history in the absence of pathology.

METHODS

Twelve elderly with falling history were tested. Two testing conditions were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset) paradigms. Each condition was run at three viewing distances--20 cm, 40 cm, and 150 cm, corresponding to convergence angle at 17.1 degrees, 8.6 degrees, and 2.3 degrees, respectively. Eye movements were recorded with the photoelectric IRIS (Skalar medical).

RESULTS

(i) like in healthy elderly subjects, elderly with falling history produce shorter latencies in the gap paradigm than in the overlap paradigm; (ii) their latencies are shorter at near distances (20 and 40 cm) relative to 150 cm for both paradigms; (iii) the novel result is that they fail to produce express latencies even in the conditions (near viewing distance and the gap task) known to promote high rates of express in adults (25%) or in healthy elderly (20%). Seven from the 10 healthy elderly produced express saccades at rates >12%, while 9 of the 12 older subjects with falling history showed no express saccades at all; the remaining 3 subjects showed low rates <12%.

CONCLUSION

The quasi paucity of express saccades could be due to the disequilibrium of complex cortical/subcortical networks needed for making express saccades. The results support models suggesting specific network for express saccades; missing of such optomotor reflex may go along with missing other reflexes as well increasing the chances of falling.

Divergence influences triggering of both vertical and horizontal saccades

PURPOSE

In real life, divergence is frequently combined with vertical saccades. The purpose of this study was to examine the initiation of vertical and horizontal saccades, pure or combined with divergence.

METHODS

We used a gap paradigm to elicit vertical or horizontal saccades (10 degrees), pure or combined with a predictable divergence (10 degrees). Eye movements from 12 subjects were recorded with EyeLink II.

RESULTS

The major results were (i) when combined with divergence, the latency of horizontal saccades increased but not the latency of vertical saccades; (ii) for both vertical and horizontal saccades, a tight correlation between the latency of saccade and divergence was found; (iii) when the divergence was anticipated, the saccade was delayed.

CONCLUSION

We conclude that the initiation of both components of combined movements is interdependent.

Aging does not affect the accuracy of vertical saccades nor the quality of their binocular coordination: a study of a special elderly group

Fine binocular coordination of vertical saccades is a complex process requiring appropriate distribution of innervations to all six extraocular muscles. Loss of such coordination causes vertical binocular disparities that are particularly bothersome. We studied the quality of binocular control of vertical saccades in healthy subjects, 11 young adults (20-28 years) and 11 elderly adults (63-75 years). We used LED targets at 7.5 degrees or 15 degrees from the center (fixation), up or down in four conditions: gap and overlap tasks, each done at two distances--near (40 cm) and far (150 cm). Vertical eye movements were recorded with video-oculography (CHRONOS). The results showed: aged subjects performed vertical saccades as accurately as young subjects. Importantly, the binocular coordination of vertical saccades was well preserved in the elderly; the mean difference of vertical saccades between the two eyes was 0.10 degrees and 0.09 degrees in young and elderly subjects, respectively. Upward saccades were associated with divergence, downward ones with convergence. This secondary phenomenon was also the same and of the similar amplitude for young (1.30 degrees ) and elderly (1.25 degrees) subjects. Thus, despite its complexity, the quality of binocular coordination of vertical saccades remains intact with age. The other observations are mostly dependent of several aspects on the direction (up/down), viewing distances and eccentricities; the horizontal vergence during or after vertical saccades was found to be larger for downward saccades than for upward saccades, for saccades at far distance than at close, and for the more eccentric targets (15 degrees versus 7.5 degrees). All these phenomena are the same for both young and elderly subjects. We conclude that the accuracy and the binocular coordination of vertical saccades, at least for target steps less than 15 degrees , are preserved in elderly subjects <75 years who maintain good physical and intellectual form. The data are consistent with the idea of the existence of non-aging system function in the human CNS.