Human oculomotor function: reliability and diurnal variation

Normative tDCS over V5 and FEF reveals practice-induced modulation of extraretinal smooth pursuit mechanisms, but no specific stimulation effect

The neural networks subserving smooth pursuit eye movements (SPEM) provide an ideal model for investigating the interaction of sensory processing and motor control during ongoing movements. To better understand core plasticity aspects of sensorimotor processing for SPEM, normative sham, anodal or cathodal transcranial direct current stimulation (tDCS) was applied over visual area V5 and frontal eye fields (FEF) in sixty healthy participants. The identical within-subject paradigm was used to assess SPEM modulations by practice. While no specific tDCS effects were revealed, within- and between-session practice effects indicate plasticity of top-down extraretinal mechanisms that mainly affect SPEM in the absence of visual input and during SPEM initiation. To explore the potential of tDCS effects, individual electric field simulations were computed based on calibrated finite element head models and individual functional localization of V5 and FEF location (using functional MRI) and orientation (using combined EEG/MEG) was conducted. Simulations revealed only limited electric field target intensities induced by the applied normative tDCS montages but indicate the potential efficacy of personalized tDCS for the modulation of SPEM. In sum, results indicate the potential susceptibility of extraretinal SPEM control to targeted external neuromodulation (e.g., personalized tDCS) and intrinsic learning protocols.

Visuomotor Synchronization: Military Normative Performance

INTRODUCTION

Cognitive processes such as perception and reasoning are preceded and dependent on attention. Because of the close overlap between neural circuits of attention and eye movement, attention may be objectively quantified with recording of eye movements during an attention-dependent task. Our previous work demonstrated that performance scores on a circular visual tracking task that requires dynamic synchronization of the gaze with the target motion can be impacted by concussion, sleep deprivation, and attention deficit/hyperactivity disorder. The current study examined the characteristics of performance on a standardized predictive visual tracking task in a large sample from a U.S. Military population to provide military normative data.

MATERIALS AND METHODS

The sample consisted of 1,594 active duty military service members of either sex aged 18-29 years old who were stationed at Fort Hood Army Base. The protocol was reviewed and approved by the U.S. Army Medical Research and Materiel Command Institutional Review Board. Demographic, medical, and military history data were collected using questionnaires, and performance-based data were collected using a circular visual tracking test and Trail Making Test. Differences in visual tracking performance by demographic characteristics were examined with a multivariate analysis of variance, as well as a Kolmogorov-Smirnov test and a rank-sum test. Associations with other measures were examined with a rank-sum test or Spearman correlations.

RESULTS

Robust sex differences in visual tracking performance were found across the various statistical models, as well as age differences in several isolated comparisons. Accordingly, norms of performance scores, described in terms of percentile standings, were developed adjusting for age and sex. The effects of other measures on visual tracking performance were small or statistically non-significant. An examination of the score distributions of various metrics suggested that strategies preferred by men and women may optimize different aspects of visual tracking performance.

CONCLUSION

This large-scale quantification of attention, using dynamic visuomotor synchronization performance, provides rigorously characterized age- and sex-based military population norms. This study establishes analytics for assessing normal and impaired attention and detecting changes within individuals over time. Practical applications for combat readiness and surveillance of attention impairment from sleep insufficiency, concussion, medication, or attention disorders will be enhanced with portable, easily accessible, fast, and reliable dynamic eye-tracking technologies.

One-year-later spontaneous EEG features predict visual exploratory human phenotypes

During visual exploration, eye movements are controlled by multiple stimulus- and goal-driven factors. We recently showed that the dynamics of eye movements -how/when the eye move- during natural scenes' free viewing were similar across individuals and identified two viewing styles: static and dynamic, characterized respectively by longer or shorter fixations. Interestingly, these styles could be revealed at rest, in the absence of any visual stimulus. This result supports a role of intrinsic activity in eye movement dynamics. Here we hypothesize that these two viewing styles correspond to different spontaneous patterns of brain activity. One year after the behavioural experiments, static and dynamic viewers were called back to the lab to record high density EEG activity during eyes open and eyes closed. Static viewers show higher cortical inhibition, slower individual alpha frequency peak, and longer memory of alpha oscillations. The opposite holds for dynamic viewers. We conclude that some properties of spontaneous activity predict exploratory eye movement dynamics during free viewing.

Eye tracking to assess concussions: an intra-rater reliability study with healthy youth and adult athletes of selected contact and collision team sports

Eye movements that are dependent on cognition hold promise in assessing sports-related concussions but research on reliability of eye tracking measurements in athletic cohorts is very limited. This observational test-retest study aimed to establish whether eye tracking technology is a reliable tool for assessing sports-related concussions in youth and adult athletes partaking in contact and collision team sports. Forty-three youth (15.4 ± 2.2 years) and 27 adult (22.2 ± 2.9 years) Rugby Union and soccer players completed the study. Eye movements were recorded using SMIRED250mobile while participants completed a test battery twice, with a 1-week interval that included self-paced saccade (SPS), fixation stability, memory-guided sequence (MGS), smooth pursuit (SP), and antisaccades (AS) tasks. Intra-class correlation coefficient (ICC), measurement error (SEM) and smallest real difference (SRD) were calculated for 47 variables. Seventeen variables achieved an ICC > 0.50. In the adults, saccade count in SPS had good reliability (ICC = 0.86, SRD = 146.6 saccades). In the youth, the average blink duration in MGS had excellent reliability (ICC = 0.99, SRD = 59.4 ms); directional errors in AS tasks and gain of diagonal SP had good reliability (ICC = 0.78 and 0.77, SRD = 25.3 and 395.1%, respectively). Four metrics were found in this study to be reliable candidates for further biomarker validity research in contact and collision sport cohorts. Many variables failed to present a sufficient level of robustness for a practical diagnostic tool; possibly, because athletic cohorts have higher homogeneity, along with latent adverse effects of undetected concussions and repetitive head impacts. Since reliability of a measure can influence type II error, effect sizes, and confidence intervals, it is strongly advocated to conduct dedicated reliability evaluations prior to any validity studies.

Replicability and reliability of the background and target velocity effects in smooth pursuit eye movements

When we follow a slowly moving target with our eyes, we perform smooth pursuit eye movements (SPEM). Previous investigations point to significantly and robustly reduced SPEM performance in the presence of a stationary background and at higher compared to lower target velocities. However, the reliability of these background and target velocity effects has not yet been investigated systematically. To address this issue, 45 healthy participants (17 m, 28 f) took part in two experimental sessions 7 days apart. In each session, participants were instructed to follow a horizontal SPEM target moving sinusoidally between ±7.89° at three different target velocities, corresponding to frequencies of 0.2, 0.4 and 0.6 Hz. Each target velocity was presented once with and once without a stationary background, resulting in six blocks. The blocks were presented twice per session in order to additionally explore potential task length effects. To assess SPEM performance, velocity gain was calculated as the ratio of eye to target velocity. In line with previous research, detrimental background and target velocity effects were replicated robustly in both sessions with large effect sizes. Good to excellent test-retest reliabilities were obtained at higher target velocities and in the presence of a stationary background, whereas lower reliabilities occurred with slower targets and in the absence of background stimuli. Target velocity and background effects resulted in largely good to excellent reliabilities. These findings not only replicated robust experimental effects of background and target velocity at group level, but also revealed that these effects can be translated into reliable individual difference measures.

Measuring Saccade Latency Using Smartphone Cameras

OBJECTIVE

Accurate quantification of neurodegenerative disease progression is an ongoing challenge that complicates efforts to understand and treat these conditions. Clinical studies have shown that eye movement features may serve as objective biomarkers to support diagnosis and tracking of disease progression. Here, we demonstrate that saccade latency-an eye movement measure of reaction time-can be measured robustly outside of the clinical environment with a smartphone camera.

METHODS

To enable tracking of saccade latency in large cohorts of patients and control subjects, we combined a deep convolutional neural network for gaze estimation with a model-based approach for saccade onset determination that provides automated signal-quality quantification and artifact rejection.

RESULTS

Simultaneous recordings with a smartphone and a high-speed camera resulted in negligible differences in saccade latency distributions. Furthermore, we demonstrated that the constraint of chinrest support can be removed when recording healthy subjects. Repeat smartphone-based measurements of saccade latency in 11 self-reported healthy subjects resulted in an intraclass correlation coefficient of 0.76, showing our approach has good to excellent test-retest reliability. Additionally, we conducted more than 19 000 saccade latency measurements in 29 self-reported healthy subjects and observed significant intra- and inter-subject variability, which highlights the importance of individualized tracking. Lastly, we showed that with around 65 measurements we can estimate mean saccade latency to within less-than-10-ms precision, which takes within 4 min with our setup.

CONCLUSION AND SIGNIFICANCE

By enabling repeat measurements of saccade latency and its distribution in individual subjects, our framework opens the possibility of quantifying patient state on a finer timescale in a broader population than previously possible.

Parametric Covariability in the Standard Model of the Saccadic Main Sequence

SIGNIFICANCE

Saccades present a direct relationship between the size of the movement (SACSIZE) and its peak velocity (SACPEAK), the main sequence, which is traditionally quantified using the model SACPEAK = Vmax × (1 - e). This study shows that Vmax and SAT are not veridical indicators of saccadic dynamics.

PURPOSE

Alterations in saccadic dynamics are used as a diagnostic tool. Are the 95% reference ranges (RRs) of Vmax and SAT correctly quantifying the variability in saccadic dynamics of a population?

METHODS

Visually driven horizontal and vertical saccades were acquired from 116 normal subjects using the Neuro Kinetics Inc. Concussion Protocol with a 100-Hz I-Portal NOTC Vestibular System, and the main sequence models were computed.

RESULTS

The 95% RRs of Vmax, the asymptotic peak velocity, and SAT, the speed of the exponential rise toward Vmax, were quite large. The finding of a strong correlation between Vmax and SAT suggests that their variability might be, in part, a computational interaction. In fact, the interplay between the two parameters greatly reduced the actual peak velocity variability for saccades less than 15°. This correlation was not strong enough to support the adoption of a one-parameter model, where Vmax is estimated from SAT using the regression parameters. We also evaluated the effects of interpolating the position data to a simulated acquisition rate of 1 kHz. Interpolation had no effect on the population average of Vmax and brought a decrease of the average SAT by roughly 8%.

CONCLUSIONS

The 95% RRs of Vmax and SAT, treated as independent entities, are not a veridical representation of the variability in saccadic dynamics inside a population, especially for small saccades. We introduce a novel three-step method to determine if a data set is inside or outside a reference population that takes into account the correlation between Vmax and SAT.

The Area under the Main Sequence as an Alternative Method to Measure Saccadic Dynamics

SIGNIFICANCE

This study shows that the area under the main sequence (MSAREA) is a valid alternative to the standard peak-velocity main sequence in measuring saccadic dynamics. A one-parameter area model, MSAREA = GPW = 1.55 × SACSIZE, with SACSIZE as the size of the saccade, 1.55 as a power factor, and GPW = 1.55 as a gain parameter, is presented.

PURPOSE

SACPEAK = Vmax × (1 - e) is the traditional model used to describe the saccadic main sequence, the relationship between the size of the movement and its peak velocity (SACPEAK). In the previous article, we have shown that there is a strong linear correlation between the two parameters Vmax and SAT, which severely affects the model's clinical applicability. The purpose of this study is to see if, by using the MSAREA as an alternative approach, we can overcome the limitations of the traditional model.

METHODS

Participants and main sequence data are the same as the previous study. A trapezoidal integration was used to estimate the MSAREAs as a function of SACSIZE.

RESULTS

A two-parameter area model was computed to determine the range of variability of its parameters and R values. These were then used as reference values in the search for one-parameter alternatives. The one-parameter model MSAREA = GPW = 1.55 × SACSIZE performed well for all data sets. We tested its validity by performing a comparison with other one-parameter area models.

CONCLUSIONS

Area models are superior to peak-velocity models in terms of R and stability and can be reduced to robust one-parameter expressions with only limited degradation in R. This not only greatly simplifies the determination if a set is inside or outside a reference population but also allows for direct comparisons between sets, with the saccadic dynamics expressed by a simple linear gain factor (GPW = 1.55).

A post-exercise facilitation of executive function is independent of aerobically supported metabolic costs

A single-bout of aerobic or resistance training facilitates executive function and is a benefit thought to be specific to exercise durations greater than 20 min. We sought to determine whether an executive benefit is observed for a session as brief as 10-min, and whether distinct and participant-specific exercise intensities - and associated metabolic costs - influence the magnitude of the benefit. Participants completed exercise sessions - via cycle ergometer - at moderate (80% of lactate threshold [LT]), heavy (15% of the difference between LT and VO_{2 peak}) and very-heavy (50% of the difference between LT and VO_{2 peak}) intensities determined via an incremental ramp test to volitional exhaustion. Pre- and post-exercise executive function was examined via antisaccades - an executive task requiring a saccade mirror-symmetrical to a visual stimulus. Antisaccades are an ideal tool for examining post-exercise executive changes due to the resolution of eye-tracking and because the task is mediated via the same frontoparietal networks as modified following single-bout and chronic exercise. A non-executive prosaccade task (i.e., saccade to veridical target location) was also completed to determine if the putative post-exercise benefit was specific to executive function. Results showed a 20 ms reduction in pre- to post-exercise antisaccade RTs (p < .02) and was independent of exercise intensity, whereas no such change was observed for prosaccades (p = .14). Furthermore, the antisaccade benefit occurred without concomitant changes in directional errors or endpoint accuracy; that is, participants did not decrease their post-exercise RTs at the cost of increased planning and execution errors (ps > 0.34). Accordingly, we propose that an exercise duration as brief as 10-min provides a reliable benefit to executive function and is an effect observed across the continuum of moderate to very-heavy intensities.

Association of Visual Tracking Metrics With Post-concussion Symptomatology

Attention impairment may provide a cohesive neurobiological explanation for clusters of clinical symptoms that occur after a concussion; therefore, objective quantification of attention is needed. Visually tracking a moving target is an attention-dependent sensorimotor function, and eye movement can be recorded easily and objectively to quantify performance. Our previous work suggested the utility of gaze-target synchronization metrics of a predictive visual tracking task in concussion screening and recovery monitoring. Another objectively quantifiable performance measure frequently suggested for concussion screening is simple visuo-manual reaction time (simple reaction time, SRT). Here, we used visual tracking and SRT tasks to assess changes between pre- and within-2-week post-concussion performances and explore their relationships to post-concussion symptomatology. Athletes participating in organized competitive sports were recruited. Visual tracking and SRT records were collected from the recruited athlete pool as baseline measures over a 4-year period. When athletes experienced a concussion, they were re-assessed within 2 weeks of their injury. We present the data from a total of 29 concussed athletes. Post-concussion symptom burden was assessed with the Rivermead Post-Concussion Symptoms Questionnaire and subscales of the Brain Injury Screening Questionnaire. Post-concussion changes in visual tracking and SRT performance were examined using a paired t-test. Correlations of changes in visual tracking and SRT performance to symptom burden were examined using Pearson's coefficients. Post-concussion changes in visual tracking performance were not consistent among the athletes. However, changes in several visual tracking metrics had moderate to strong correlations to symptom scales (r up to 0.68). On the other hand, while post-concussion SRT performance was reduced (p < 0.01), the changes in the performance metrics were not meaningfully correlated to symptomatology (r ≤ 0.33). Results suggest that visual tracking performance metrics reflect clinical symptoms when assessed within 2 weeks of concussion. Evaluation of concussion requires assessments in multiple domains because the clinical profiles are heterogeneous. While most individuals show recovery within a week of injury, others experience prolonged recovery periods. Visual tracking performance metrics may serve as a biomarker of debilitating symptoms of concussion implicating attention as a root cause of such pathologies.

A standardized protocol for quantification of saccadic eye movements: DEMoNS

OBJECTIVE

Quantitative saccadic testing is a non-invasive method of evaluating the neural networks involved in the control of eye movements. The aim of this study is to provide a standardized and reproducible protocol for infrared oculography measurements of eye movements and analysis, which can be applied for various diseases in a multicenter setting.

METHODS

Development of a protocol to Demonstrate Eye Movement Networks with Saccades (DEMoNS) using infrared oculography. Automated analysis methods were used to calculate parameters describing the characteristics of the saccadic eye movements. The two measurements of the subjects were compared with descriptive and reproducibility statistics.

RESULTS

Infrared oculography measurements of all subjects were performed using the DEMoNS protocol and various saccadic parameters were calculated automatically from 28 subjects. Saccadic parameters such as: peak velocity, latency and saccade pair ratios showed excellent reproducibility (intra-class correlation coefficients > 0.9). Parameters describing performance of more complex tasks showed moderate to good reproducibility (intra-class correlation coefficients 0.63-0.78).

CONCLUSIONS

This study provides a standardized and transparent protocol for measuring and analyzing saccadic eye movements in a multicenter setting. The DEMoNS protocol details outcome measures for treatment trial which are of excellent reproducibility. The DEMoNS protocol can be applied to the study of saccadic eye movements in various neurodegenerative and motor diseases.

Long-Term Maintenance of Executive-Related Oculomotor Improvements in Older Adults with Self-Reported Cognitive Complaints Following a 24-Week Multiple Modality Exercise Program

Adults (≥55 years) with self-reported cognitive complaints (sCC) were randomized to: multiple-modality exercise (M2), or multiple-modality plus mind-motor exercise (M4), for 24-weeks. Participants (n = 58) were assessed on antisaccade reaction time (RT) to examine executive-related oculomotor control and self-reported physical activity (PA) at pre-intervention (V0), post-intervention (V1), and 52-weeks follow-up (V2). We previously reported significant improvements in antisaccade RT of 23 ms at V1, in both groups. We now report maintenance of antisaccade RT improvement from V1 to V2, t(57) = 0.8, p = 0.45, and improved PA from V1 to V2, t(56) = -2.4, p = 0.02. Improvements in executive-related oculomotor control attained at V1 were maintained at V2.

A 24-Week Multi-Modality Exercise Program Improves Executive Control in Older Adults with a Self-Reported Cognitive Complaint: Evidence from the Antisaccade Task

Exercise programs involving aerobic and resistance training (i.e., multiple-modality) have shown promise in improving cognition and executive control in older adults at risk, or experiencing, cognitive decline. It is, however, unclear whether cognitive training within a multiple-modality program elicits an additive benefit to executive/cognitive processes. This is an important question to resolve in order to identify optimal training programs that delay, or ameliorate, executive deficits in persons at risk for further cognitive decline. In the present study, individuals with a self-reported cognitive complaint (SCC) participated in a 24-week multiple-modality (i.e., the M2 group) exercise intervention program. In addition, a separate group of individuals with a SCC completed the same aerobic and resistance training as the M2 group but also completed a cognitive-based stepping task (i.e., multiple-modality, mind-motor intervention: M4 group). Notably, pre- and post-intervention executive control was examined via the antisaccade task (i.e., eye movement mirror-symmetrical to a target). Antisaccades are an ideal tool for the study of individuals with subtle executive deficits because of its hands- and language-free nature and because the task's neural mechanisms are linked to neuropathology in cognitive decline (i.e., prefrontal cortex). Results showed that M2 and M4 group antisaccade reaction times reliably decreased from pre- to post-intervention and the magnitude of the decrease was consistent across groups. Thus, multi-modality exercise training improved executive performance in persons with a SCC independent of mind-motor training. Accordingly, we propose that multiple-modality training provides a sufficient intervention to improve executive control in persons with a SCC.

A Six-Month Cognitive-Motor and Aerobic Exercise Program Improves Executive Function in Persons with an Objective Cognitive Impairment: A Pilot Investigation Using the Antisaccade Task

Persons with an objective cognitive impairment (OCI) are at increased risk for progression to Alzheimer's disease and related dementias. The present pilot project sought to examine whether participation in a long-term exercise program involving cognitive-motor (CM) dual-task gait training and aerobic exercise training improves executive function in persons with an OCI. To accomplish our objective, individuals with an OCI (n = 12) as determined by a Montreal Cognitive Assessment (MoCA) score of less than 26 and older adults (n = 11) deemed to be cognitively healthy (i.e., control group: MoCA score ≥26) completed a six-month moderate-to-high intensity (65-85% maximum heart rate) treadmill-based CM and aerobic exercise training program wherein pre- and post-intervention executive control was examined via the antisaccade task. Notably, antisaccades require a goal-directed eye-movement mirror-symmetrical to a target and represent an ideal tool for the study of executive deficits because of its hands- and language-free nature. As well, the cortical networks mediating antisaccades represent regions associated with neuropathology in cognitive decline and dementia (e.g., dorsolateral prefrontal cortex). Results showed that antisaccade reaction times for the OCI group reliably decreased by 30 ms from pre- to post-intervention, whereas the control group did not produce a reliable pre- to post-intervention change in reaction time (i.e., 6 ms). Thus, we propose that in persons with OCI long-term CM and aerobic training improves the efficiency and effectiveness of the executive mechanisms mediating high-level oculomotor control.

Effects of Dopamine and Norepinephrine on Exercise-induced Oculomotor Fatigue

INTRODUCTION

Fatigue-induced impairments in the control of eye movements are detectable via reduced eye movement velocity after a bout of prolonged, strenuous exercise. Slower eye movements caused by neural fatigue within the oculomotor system can be prevented by caffeine, and the upregulation of central catecholamines may be responsible for this effect. This study explored the individual contribution of dopamine and norepinephrine to fatigue-related impairments in oculomotor control.

METHODS

The influence of a dopamine reuptake inhibitor (methylphenidate) and a norepinephrine reuptake inhibitor (reboxetine) was assessed in 12 cyclists performing 180 min of stationary cycling within a placebo-controlled crossover design. Eye movement kinematics (saccades, smooth pursuit, and optokinetic nystagmus) were measured using infrared oculography. Visual attention was assessed with overt and covert spatial attention tasks.

RESULTS

Exercise-induced fatigue was associated with a 6% ± 8% reduction in the peak velocity of visually guided, reflexive prosaccades. Importantly, both dopamine reuptake inhibition and norepinephrine reuptake inhibition prevented fatigue-related decrements in the peak velocity of prosaccades. Pursuit eye movements, optokinetic nystagmus, and visual attention tasks were unaffected by exercise or drug treatments.

CONCLUSION

Overall, our findings suggest that alterations in norepinephrinergic and dopaminergic neurotransmission are linked with the development of fatigue within circuits that control eye movements. Psychiatric medications that target central catecholamines can exert a protective effect on eye movements after prolonged exercise.

Executive-related oculomotor control is improved following a 10-min single-bout of aerobic exercise: Evidence from the antisaccade task

Previous work has shown that a single-bout of moderate-to-vigorous intensity exercise improves task-specific activity within frontoparietal networks and produces a short-term 'boost' to executive-related cognitive control - an effect in healthy young adults that is reported to be selective to exercise durations of 20min or greater. The present study sought to determine whether such a 'boost' extends to an exercise duration as brief as 10min. Healthy young adults performed a 10-min single-bout of moderate-to-vigorous intensity aerobic exercise (i.e., via a cycle ergometer) and pre- and post-exercise executive control was examined via the antisaccade task. Antisaccades are an executive task requiring a goal-directed eye movement (i.e., a saccade) mirror-symmetrical to a visual stimulus. The hands- and language-free nature of antisaccades coupled with the temporal precision of eye-tracking technology make it an ideal tool for identifying executive performance changes. Moreover, an extensive literature has shown that antisaccades are mediated via frontoparietal networks that are modulated following single-bout and chronic exercise training. Results showed that antisaccade reaction time (RT) reliably decreased by 27ms from pre- to post-exercise assessments. Further, the percentage of antisaccade directional errors did not reliably vary from the pre- (13%) to post-exercise (9%) assessments - a result indicating that the RT improvement was unrelated to a speed-accuracy trade-off. A follow-up experiment involving antisaccade sessions separated by a non-exercise interval did not show a similar RT modulation. Thus, a 10-min bout of moderate-to-vigorous intensity aerobic exercise benefits executive-related oculomotor control, and is a finding we attribute to an exercise-based increase in attention/arousal and/or improved task-specific activity within the frontoparietal networks supporting antisaccades.

Caffeine increases the velocity of rapid eye movements in unfatigued humans

BACKGROUND

Caffeine is a widely used dietary stimulant that can reverse the effects of fatigue on cognitive, motor and oculomotor function. However, few studies have examined the effect of caffeine on the oculomotor system when homeostasis has not been disrupted by physical fatigue. This study examined the influence of a moderate dose of caffeine on oculomotor control and visual perception in participants who were not fatigued.

METHODS

Within a placebo-controlled crossover design, 13 healthy adults ingested caffeine (5 mg·kg^-1 body mass) and were tested over 3 h. Eye movements, including saccades, smooth pursuit and optokinetic nystagmus, were measured using infrared oculography.

RESULTS

Caffeine was associated with higher peak saccade velocities (472 ± 60° s^-1) compared to placebo (455 ± 62° s^-1). Quick phases of optokinetic nystagmus were also significantly faster with caffeine, whereas pursuit eye movements were unchanged. Non-oculomotor perceptual tasks (global motion and global orientation processing) were unaffected by caffeine.

CONCLUSIONS

These results show that oculomotor control is modulated by a moderate dose of caffeine in unfatigued humans. These effects are detectable in the kinematics of rapid eye movements, whereas pursuit eye movements and visual perception are unaffected. Oculomotor functions may be sensitive to changes in central catecholamines mediated via caffeine's action as an adenosine antagonist, even when participants are not fatigued.

Fatigue-related impairments in oculomotor control are prevented by norepinephrine-dopamine reuptake inhibition

Fatigue-induced reductions in saccade velocity have been reported following acute, prolonged exercise. Interestingly, the detrimental impact of fatigue on oculomotor control can be prevented by a moderate dose of caffeine. This effect may be related to central catecholamine upregulation via caffeine's action as an adenosine antagonist. To test this hypothesis, we compared the protective effect of caffeine on oculomotor control post-exercise to that of a norepinephrine-dopamine reuptake inhibitor. Within a placebo-controlled crossover design, 12 cyclists consumed placebo, caffeine or a norepinephrine-dopamine reuptake inhibitor (bupropion) during 180 minutes of stationary cycling. Saccades, smooth pursuit and optokinetic nystagmus were measured using infrared oculography. Exercise fatigue was associated with an 8 ± 11% reduction in the peak velocity of prosaccades, and a 10 ± 11% decrement in antisaccade peak velocity. Optokinetic nystagmus quick phases decreased in velocity by 15 ± 17%. These differences were statistically significant (p < 0.05). Norepinephrine-dopamine reuptake inhibition and caffeine prevented fatigue-related decrements in eye movement velocity. Pursuit eye movements and visual attention were unaffected. These findings show that norepinephrine-dopamine reuptake inhibition protects oculomotor function during exercise fatigue. Caffeine's fatigue-reversing effects on eye movements appear to be mediated, at least in part, via modulation of central catecholamines.

Exercise-Induced Fatigue and Caffeine Supplementation Affect Psychomotor Performance but Not Covert Visuo-Spatial Attention

Fatigue resulting from strenuous exercise can impair cognition and oculomotor control. These impairments can be prevented by administering psychostimulants such as caffeine. This study used two experiments to explore the influence of caffeine administered at rest and during fatiguing physical exercise on spatial attention—a cognitive function that is crucial for task-based visually guided behavior. In independent placebo-controlled studies, cohorts of 12 healthy participants consumed caffeine and rested or completed 180 min of stationary cycling. Covert attentional orienting was measured in both experiments using a spatial cueing paradigm. We observed no alterations in attentional facilitation toward spatial cues suggesting that covert attentional orienting is not influenced by exercise fatigue or caffeine supplementation. Response times were increased (impaired) after exercise and this deterioration was prevented by caffeine supplementation. In the resting experiment, response times across all conditions and cues were decreased (improved) with caffeine. Covert spatial attention was not influenced by caffeine. Together, the results of these experiments suggest that covert attentional orienting is robust to the effects of fatiguing exercise and not influenced by caffeine. However, exercise fatigue impairs response times, which can be prevented by caffeine, suggesting that pre-motor planning and execution of the motor responses required for performance of the cueing task are sensitive to central nervous system fatigue. Caffeine improves response time in both fatigued and fresh conditions, most likely through action on networks controlling motor function.

Behavioral and Neural Plasticity of Ocular Motor Control: Changes in Performance and fMRI Activity Following Antisaccade Training

The antisaccade task provides a model paradigm that sets the inhibition of a reflexively driven behavior against the volitional control of a goal-directed behavior. The stability and adaptability of antisaccade performance was investigated in 23 neurologically healthy individuals. Behavior and brain function were measured using functional magnetic resonance imaging (fMRI) prior to and immediately following 2 weeks of daily antisaccade training. Participants performed antisaccade trials faster with no change in directional error rate following 2 weeks of training; however this increased speed came at the cost of the spatial accuracy of the saccade (gain) which became more hypometric following training. Training on the antisaccade task resulted in increases in fMRI activity in the fronto-basal ganglia-parietal-cerebellar ocular motor network. Following training, antisaccade latency was positively associated with fMRI activity in the frontal and supplementary eye fields, anterior cingulate and intraparietal sulcus; antisaccade gain was negatively associated with fMRI activity in supplementary eye fields, anterior cingulate, intraparietal sulcus, and cerebellar vermis. In sum, the results suggest that following training, larger antisaccade latency is associated with larger activity in fronto-parietal-cerebellar ocular motor regions, and smaller antisaccade gain is associated with larger activity in fronto-parietal ocular motor regions.

Meta-analysis of the association of the SLC6A3 3'-UTR VNTR with cognition

The gene coding for the dopamine transporter (DAT), SLC6A3, contains a 40-base pair variable number of tandem repeats (VNTR) polymorphism (rs28363170) in its 3' untranslated region. This VNTR has been associated with attention deficit hyperactivity disorder (ADHD) and has been investigated in relation to cognition and brain function. Here, we report the results of a comprehensive meta-analysis with meta-regression examining the association of the VNTR with different domains of cognition in healthy adults. We extracted data from 28 independent studies and carried out meta-analyses for associations with working memory (k=10 samples, N=1193 subjects), inhibition (k=8 samples, N=829 subjects), executive functions including inhibition (k=10 samples, N=984 subjects), attention (k=6 samples, N=742 subjects) and declarative long-term memory (k=5 samples, N=251 subjects). None of the investigated dimensions showed significant associations with the VNTR (all p>0.26). Meta-regression including year of publication, gender, age, ethnicity and percentage of 10R-homozygotes similarly did not attain significance. We conclude that there is no evidence that rs28363170 may be a significant predictor of cognitive function in healthy adults.

Predictive smooth eye pursuit in a population of young men: II. Effects of schizotypy, anxiety and depression

Smooth pursuit eye movement dysfunction is considered to be a valid schizophrenia endophenotype. Recent studies have tried to refine the phenotype in order to identify the specific neurophysiological deficits associated with schizophrenia. We used a variation of the smooth eye pursuit paradigm, during which the moving target is occluded for a short period of time and subjects are asked to continue tracking. This is designed to isolate the predictive processes that drive the extraretinal signal, a process previously reported to be defective in schizophrenia patients as well as their healthy relatives. In the current study, we investigated the relationship between predictive pursuit performance indices and age, education, non-verbal IQ, schizotypy and state anxiety, depression in 795 young Greek military conscripts. State anxiety was related to better predictive pursuit performance (increase in residual pursuit gain), while disorganized schizotypy was related to deficient predictive pursuit performance (decreased residual gain). This effect was independent of the effect of disorganized schizotypy on other oculomotor functions supporting the hypothesis that predictive pursuit might be specifically affected in schizophrenia spectrum disorders and could be considered as a distinct oculomotor endophenotype.

Saccadic latency in Parkinson's disease correlates with executive function and brain atrophy, but not motor severity

Brain regions related to saccadic control are affected by Parkinson's disease (PD) pathology and a relationship between abnormal saccades and cognitive features of PD has been suggested. We measured the latency of visually-evoked saccades, and correlated best-fit parameters in a LATER neuronal decision model μ and σ (mean and SD of the distribution of reciprocal latency, i.e. speed of response), and σ(E) (SD of the early component) with motor function, cognition and grey matter volume in 18 patients with PD and 17 controls. There was a negative correlation between verbal fluency and σ; no correlation was found between motor function and any of the latency parameters. Higher μ (shorter latency) positively correlated with grey matter volume in the prefrontal cortex, the cerebellar vermis, and the fusiform gyrus. There was a negative correlation between σ and grey matter volume in the frontal and parietal eye fields, the premotor cortex, and the lateral prefrontal cortex. σ(E) negatively correlated with grey matter volume in the frontal eye fields and the middle frontal gyrus. Our behavioural and imaging findings point to an association between saccade latency, executive function and the structural integrity within a well-defined oculomotor network.

Horizontal gaze nystagmus: a review of vision science and application issues

The Horizontal Gaze Nystagmus (HGN) test is one component of the Standardized Field Sobriety Test battery. This article reviews the literature on smooth pursuit eye movement and gaze nystagmus with a focus on normative responses, the influence of alcohol on these behaviors, and stimulus conditions similar to those used in the HGN sobriety test. Factors such as age, stimulus and background conditions, medical conditions, prescription medications, and psychiatric disorder were found to affect the smooth pursuit phase of HGN. Much less literature is available for gaze nystagmus, but onset of nystagmus may occur in some sober subjects at 45 degrees or less. We conclude that HGN is limited by large variability in the underlying normative behavior, from methods and testing environments that are often poorly controlled, and from a lack of rigorous validation in laboratory settings.

The effect of change in clinical state on eye movement dysfunction in schizophrenia

Measures of eye movement dysfunction have been considered as candidate endophenotypes for the study of genetic liability in schizophrenia. In this respect it is crucial to confirm a clinical state independentce of these measures. Twenty people with DSM-IV schizophrenia were assessed using a battery of oculomotor tasks in the acute phase of their disorder without being treated with antipsychotic medication and then again in the remission phase under treatment with antipsychotic medication. The saccade latency in the saccade task, the error rate and antisaccade latency in the antisaccade task, and the frequency of unwanted saccades in the active fixation task were stable in time both at the group level and within each individual, showing no relation to the significant improvement in different psychopathological dimensions of these patients. The root mean square error, gain and saccade frequency in the pursuit task were not stable over time, although again this instability was not related to the changes in psychopathological status of these patients. Finally, the saccade frequency in the active fixation task with distracters was not stable in time and was correlated with changes in specific dimensions of psychopathology. These results provide further evidence that saccade and smooth eye pursuit dysfunction measures are not affected by the substantial change in the clinical state of schizophrenia from the acute phase to remission, and strengthen the current view that they can be used as endophenotypes. On the other hand, active fixation might be state-dependent adding to the evidence against its use as a candidate endophenotype in schizophrenia.

Fixation and attention control in lateralised target detection and free recall with words

The purpose of the present study was to test the hypothesis that lateralised target detection in the visual modality would produce results similar in magnitude, reliability, and validity to those obtained in the auditory modality with an analogue task. Thus, it was expected that it would produce laterality effects that are larger, more reliable, and more valid than those obtained in a free recall task. The claim that target detection provides its own attention control also led to the hypothesis that the magnitude of laterality effects should be affected by fixation control in free recall but not target detection. A total of 349 right-handed participants completed a word recognition task with either free recall or target detection with or without fixation control. Only the finding that free recall was generally more reliable than target detection went contrary to the hypotheses. This finding is interpreted as reflecting a consistent attentional bias that stems from task requirements. In general, the results suggest that target detection without fixation control has much potential as a measure of perceptual asymmetries in the visual modality.

Test-retest reliability of fMRI activation during prosaccades and antisaccades

Various studies have investigated reproducibility of fMRI results. Whereas group results can be highly reproducible, individual activity maps tend to vary across sessions. Individual reliability is of importance for the application of fMRI in endophenotype research, where brain activity is linked to genetic polymorphisms. In this study, the test-retest reliability of activation maps during the antisaccade paradigm was assessed for individual and group results. Functional MRI images were acquired during two sessions of prosaccades and antisaccades in twelve healthy subjects using an event-related fMRI design. Reliability was assessed for both individual and group-wise results. In addition, the reliability of differences between subjects was established in predefined regions of interest. The reliability of group activation maps was high for prosaccades and antisaccades, but only moderate for antisaccades vs. prosaccades, probably as a result of low statistical power of individual results. Reproducibility of individual subject maps was highly variable, indicating that reliable results can be obtained in some but not all subjects. Reliability of individual activity maps was largely explained by individual differences in the global temporal signal to noise ratio (SNR). As the global SNR was stable over sessions, it explained a large portion of the differences between subjects in regional brain activation. A low SNR in some subjects may be dealt with either by improving the statistical sensitivity of the fMRI procedure or by subject exclusion. Differences in the global SNR between subjects should be addressed before using regional brain activation as phenotype in genetic studies.

Saccadic latency distributions in Parkinson's disease and the effects of L-dopa

Parkinson's disease (PD) is associated with a loss of central dopaminergic pathways in the brain leading to an abnormality of movement, including saccades. In PD, analysis of saccadic latency distributions, rather than mean latencies, can provide much more information about how the neural decision process that precedes movement is affected by disease or medication. Subject to the constraints of intersubject variation and reproducibility, latency distribution may represent an attractive potential biomarker of PD. Here we report two studies that provide information about these parameters, and demonstrate a novel effect of dopamine on saccadic latency, implying that it influences the neural decision process itself. We performed a detailed cross-sectional study of saccadic latency distributions during a simple step task in 22 medicated patients and 27 age-matched controls. This revealed high intersubject variability and an overlap of PD and control distributions. A second study was undertaken on a different population specifically to investigate the effects of dopamine on saccadic latency distributions in 15 PD patients. L-dopa was found to prolong latency, although the magnitude of the effect varied between subjects. The implications of these observations for the use of saccadic latency distributions as a potential biomarker of PD are discussed, as are the effects of L-dopa on neural decision making, where it is postulated to increase the criterion level of evidence required before the decision to move is made.

Impaired oculomotor response inhibition in children of alcoholics: The role of attention deficit hyperactivity disorder

OBJECTIVE

The aim of the project was to determine whether children at high risk for alcohol use disorder (AUD) are impaired at performing oculomotor response inhibition tasks sensitive to detecting prefrontal cortex dysfunction.

METHODS

Three antisaccade tasks were administered to 67 10-12-year-old children having fathers with AUD and 12 children whose fathers had no psychiatric disorder.

RESULTS

Children of AUD+ fathers performed similar to children of AUD- fathers on measures of response latency and gain to target. Peak velocity discriminated the two groups on only one task. Children of AUD+ fathers exhibited a higher rate of prosaccade errors on the most difficult antisaccade task. Within the AUD+ group of men, offspring who qualified for attention deficit hyperactivity disorder (ADHD; N = 13) exhibited more response suppression errors than children without ADHD on two of three tasks. No differences were observed between children without ADHD whose fathers either qualified for AUD+ or had no psychiatric disorder.

CONCLUSION

Inhibiting a response to a prepotent stimulus in children of AUD+ fathers is circumscribed to ADHD youths. These findings suggest that frontal-striatal mechanisms may underlie the risk for AUD among ADHD children.

Instrumental and test–retest reliability of saccadic measures

Little is known about the reliabilities of the various measures of saccade control that can be derived from pro- and anti-saccade tasks. This paper presents correlational results of 2 different studies comprising altogether 446 psychiatrically and neurologically healthy participants in the range of 6-88 years. Saccades were elicited under different stimulation conditions and during task blocks of 100 or 200 trials. Odd-even and split-half correlations determined for study 1 (N = 327, age 9-88 years) were found to be good to excellent (.60 < or = r < or = .97) for most measures and generalisable over the entire life-span. The 19-month test-retest correlations obtained in study 2 (N = 117, age 6-18 years) ranged between .43 and .66 after controlling for age, and suggest moderate stability of individual differences over time during childhood and adolescence. Hence, these parameters are very useful for concurrent validity studies at every age, but less so for predictive validity studies with children and adolescents.

Saccadic performance in questionnaire-identified schizotypes over time

In the present study, 121 young adults (mean age=19 years), hypothesized to be at varying levels of risk for psychosis on the basis of their psychometric profiles, were administered saccadic (antisaccade and refixation) tasks at two separate assessments. At Time 1, individuals posited to be at heightened risk for the later development of schizophrenia-spectrum disorders (i.e., those individuals with elevated Social Anhedonia Scale [SAS] scores) produced significantly more antisaccade task errors than the controls. Despite apparent improvement in antisaccade task performance from initial testing to the follow-up (mean test-retest interval=59 months) across all groups, the Social Anhedonia (SocAnh) group continued to produce significantly more errors than the control group. The antisaccade task performance of the control group showed good temporal stability (Pearson's r=0.70, ICC=0.52), and the SocAnh group's performance showed excellent temporal stability (Pearson's r=0.85, ICC=0.83). The results of this investigation are twofold: First, antisaccade task performance is temporally stable, even in psychometrically identified schizotypes over long test-retest intervals; and secondly, Social Anhedonia Scale scores as well as Time 1 antisaccade task accuracy accounted for much of the variability in Time 2 antisaccade task performance. These findings add to the growing body of literature suggesting that antisaccade task deficits may serve as an endophenotypic marker of a schizophrenia diathesis.

Behavioral plasticity of antisaccade performance following daily practice

The ability to change behavior to adapt to the environment, known as behavioral plasticity, is an important part of daily life. In the present study subjects' performances on antisaccade tasks were manipulated by training them on one of three different eye movement tasks (antisaccade, prosaccade, and fixation). Thirty subjects were tested at three time points over a 2-week period and practiced their assigned task every day between test sessions. Subjects who trained on antisaccades significantly decreased their error rates, while maintaining their reaction time, suggesting that accuracy did not improve at the expense of speed. Subjects who practiced the prosaccade task made more errors on the antisaccade task on subsequent test sessions, while those who practiced the fixation task showed no change across test sessions. These results suggest that deliberate practice of eye movement tasks can alter antisaccade performance, and that the direction of the effect is dependent upon the type of practice in which the subject engages.

Effect of Sleep Deprivation on Saccades and Eyelid Blinking

In this study the effect of sleep deprivation on specific components of eye and eyelid movement was investigated in a group of young and healthy subjects. The duration of sleep deprivation was 20 h. Each subject had to execute different saccade tasks: reflexive saccades, voluntary prosaccades and antisaccades. Saccade latency, number of saccade errors and blink rate during the saccade tasks were evaluated as predictors of performance decrements resulting from sleep deprivation. The present study showed no significant deterioration of latency and number of errors in the different saccade tasks. However, the blink rate was significantly higher after a night without sleep than before. It is concluded that the blink rate appears to be a promising psychophysical measurement and a more sensitive parameter than saccade performance to evaluate the effects of 20 h of sleep deprivation. These results encourage further research on this topic.

Smooth pursuit and antisaccade performance evidence trait stability in schizophrenia patients and their relatives

Several forms of eye movement dysfunction (EMD) have been widely regarded as candidate endophenotypes of schizophrenia, ultimately capable of identifying individuals carrying schizophrenia susceptibility genes and elucidating the pathophysiology of schizophrenia. As an indication of their trait-like status, candidate endophenotypes optimally evidence stability over time. However, there have been few published reports of test-retest reliability of several forms of EMD in schizophrenia patients and their relatives. In the current investigation, schizophrenia patients and the first-degree biological relatives of schizophrenia patients (n=15) were administered by an eye movement battery including smooth pursuit, antisaccade and prosaccade tasks, and re-tested after an average of 1.82 years (range=14-24 months). Adequate test-retest reliabilities of smooth pursuit closed-loop gain (Pearson r=0.72), antisaccade error rate (r=0.73), saccade reaction time to correct antisaccade responses (r=0.73), and prosaccade hypometria (r=0.72) were observed. Lower reliabilities were obtained for smooth pursuit open-loop gain (r=0.52) and prosaccade reaction time (r=0.43). The results are supportive of the trait-like characteristics of particular forms of EMD in schizophrenia families and of the candidacy of EMD as an endophenotypic marker of schizophrenia.

Reliability of smooth pursuit, fixation, and saccadic eye movements

The present study investigated the reliability and susceptibility to practice effects of oculomotor tasks. Smooth pursuit, fixation, antisaccade, and prosaccade tasks were administered to 31 healthy participants to assess internal consistency (Cronbach's alpha) and within-session practice effects. Twenty-one of these participants were retested after an average interval of 57.86 days to assess temporal stability and between-session practice effects. Internal consistencies were high for most measures, with few within-session performance changes. Test-retest reliabilities of most measures were good. Between-session practice effects were most consistently observed on the antisaccade task, indicated by reduced error rate and improved spatial accuracy at retest. Magnitude of improvement on these measures was related to performance, indicating that poor performers benefited most from repeated assessment. These findings support the trait nature of oculomotor function and point to the need to take into consideration between-session practice effects on the antisaccade task in longitudinal studies.

Early expression of a pathophysiological feature of schizophrenia: saccadic intrusions into smooth-pursuit eye movements in school-age children vulnerable to schizophrenia

OBJECTIVE

Neurodevelopmental hypotheses of schizophrenia propose that the responsible pathology occurs much earlier than the usual onset of illness in late adolescence. Nonspecific neurocognitive and behavioral deficits found in children vulnerable to schizophrenia support this hypothesis. This report describes early deficits in a putative genetic endophenotype, saccadic intrusions into smooth-pursuit eye movements (SPEM).

METHOD

SPEM were recorded in 189 children aged 6-15 years: 49 children with schizophrenia, 60 nonpsychotic first-degree relatives, and 80 typically developing children.

RESULTS

Children with schizophrenia demonstrated poorer gain and a significantly increased frequency of leading saccades and large anticipatory saccades; however, only leading saccades differentiated first-degree relatives from typical children. Admixture analysis indicates that 94% of children with schizophrenia, 50% of first-degree relatives, and 19% of typically developing children have abnormally increased frequencies of leading saccades.

CONCLUSIONS

Typically developing young school-age children have a leading saccade phenotype similar to that of adults, suggesting this brain function is fully developed by early school-age years. The abnormal leading saccade phenotype, a schizophrenia-associated familial brain dysfunction, is present by 6 years of age, more than a decade before the highest risk for onset of psychosis. Treatment and prevention strategies will need to consider the early neurodevelopmental nature of schizophrenia.

Brain activation during smooth-pursuit eye movements

A potential application of studying eye movements with functional MRI (fMRI) is to examine patient populations with known eye movement dysfunction, but the reliability with which normal subjects demonstrate activity in specific brain regions has not been established. To date, fMRI studies of smooth-pursuit eye movements have used relatively small numbers of subjects and have been restricted to fixed-effects analyses. We extend these studies to whole brain imaging at 1.5 T, properly accounting for intersubject variation using random effects analysis. Smooth-pursuit eye movements elicited activation consistently in dorsal cortical eye fields and cerebellum. Subcortical activation was greatly attenuated, but not eliminated, with the random-effects second-level analysis. In addition, session-dependent changes in activation were greater in some regions than others and may indicate areas of brain, such as the supplementary eye fields, that are sensitive to attentional modulation of eye movements.

Smooth pursuit eye movements in schizophrenia and attentional dysfunction: adults with schizophrenia, ADHD, and a normal comparison group

BACKGROUND

Smooth pursuit eye movement (SPEM) abnormalities are found in schizophrenia. These deficits often are explained in the context of the attentional and inhibitory deficits central to schizophrenia psychopathology. It remains unclear, however, whether these attention-associated eye movement abnormalities are specific to schizophrenia or are a nonspecific expression of attentional deficits found in many psychiatric disorders. Adult attention-deficit/hyperactivity disorder (ADHD) is an alternative disorder with chronic attentional and inhibitory dysfunction. Thus, a comparison of SPEM in adult schizophrenia and adult ADHD will help assess the specificity question.

METHODS

SPEM is recorded during a 16.7 degrees per second constant velocity task in 17 adults with ADHD, 49 adults with schizophrenia, and 37 normal adults; all groups included individuals between ages 25-50 years.

RESULTS

Smooth pursuit gain and the frequency of anticipatory and leading saccades are worse in schizophrenic subjects, with normal and ADHD subjects showing no differences on these variables.

CONCLUSIONS

Many attention-associated SPEM abnormalities are not present in most subjects with ADHD, supporting the specificity of these findings to the attentional deficits seen in schizophrenia.

Executive function oculomotor tasks in girls with ADHD

OBJECTIVE

To assess executive function in girls with attention-deficit/hyperactivity disorder (ADHD) using oculomotor tasks as possible trait markers for neurobiological studies.

METHOD

Thirty-two girls aged 6 to 13 years with DSM-IV ADHD and 20 age-matched, normal control girls were tested on a variety of oculomotor tasks requiring attention, working memory, and response inhibition, which included smooth pursuit, delayed response, and go-no go tasks.

RESULTS

Girls with ADHD performed the delayed response task correctly on 32% of trials as measured by number of memory-guided saccades, in contrast to 62% of trials for control subjects (p = .0009). Patients made twice as many commission errors to no go stimuli (p = .0001) and 3 times as many intrusion errors (saccades in the absence of go or no go stimuli; p = .004) during the go-no go task compared with controls. Smooth pursuit performance was statistically equivalent across subject groups. Repeated testing in a subgroup of 15 patients revealed substantial practice effects on go-no go performance.

CONCLUSIONS

The data confirm that girls with ADHD exhibit impairments in executive function, as has been reported in boys, implying a similar pathophysiology of ADHD in both sexes. However, practice effects may limit the utility of the oculomotor go-no go task for some neurobiological studies.

Subthreshold symptoms and vulnerability indicators (e.g., eye tracking dysfunction) in schizophrenia

Subthreshold symptoms in schizophrenia can be prodromal signs of a psychotic relapse. In people without schizophrenia, similar symptoms may indicate the presence of disorders termed schizophrenia spectrum disorders. Subthreshold schizophrenia-like symptoms may indicate a genetically transmitted higher proneness to schizophrenia. Such a higher liability to develop schizophrenia is ascertained on a symptom level. In genetic studies, asymptomatic members of a pedigree are therefore classified as unaffected although they may possess the genes in question. On a biological level, eye tracking dysfunction has been shown to fulfill certain criteria for a vulnerability indicator and therefore promises to offer more information on genetically transmitted proneness to schizophrenia even in people without psychopathological symptoms. Subthreshold symptoms may warrant treatment. The database for prophylactic treatment in populations at high risk, especially those without symptoms, is currently very small.

The effects of age on a smooth pursuit tracking task in adults with schizophrenia and normal subjects

BACKGROUND

Performance during a smooth pursuit eye movement (SPEM) task has been proposed as a marker of genetic risk for schizophrenia, although the precise component of SPEM tracking most associated with genetic risk remains undetermined. Normal adult aging is associated with deterioration on SPEM tasks; it remains unclear whether investigations of SPEM abnormalities will allow inclusion of older subjects in genetic studies. This study examines 1) the effect of normal aging on several components of SPEM performance; and 2) whether schizophrenic-normal differences found in young adults continue over a broad adult age span.

METHODS

SPEM was recorded during a 16.7 degrees per sec constant velocity task in 64 normal adults, ages 18 to 79 years, and 58 schizophrenic subjects, ages 18 to 70 years.

RESULTS

Smooth pursuit gain, the percent of total eye movements due to catch-up saccades, the frequency of large anticipatory saccades, and the frequency of leading saccades all deteriorate with increasing age. After correction for age, schizophrenic to control differences persist on most eye movement variables with the largest effect sizes for leading saccades (1.56) and smooth pursuit gain (1.17).

CONCLUSIONS

The tendency to use saccades to anticipate target motion, even in small steps (leading saccades), deserves further attention as a potential marker useful in genetic analyses.

Eye tracking in normals: spem asymmetries and association with schizotypy

SPEM was recorded electro-oculographically during visual tracking of sinusoidal targets oscillating at .4 and .8 cycles per second in one hundred nineteen undergraduates. The logarithms of median root mean square values were used to assess tracking accuracy for leftward and rightward halfcycles of tracking. Over the entire sample, there was a significant superiority of rightward over leftward tracking, which, given evidence for the ipsilateral mediation of SPEM at the cortical level, suggests a right hemisphere predominance in the control of SPEM in normal subjects. Individual tracking asymmetry was associated with overall tracking accuracy such that subjects with relatively deficient leftward tracking and those with a larger absolute magnitude of asymmetry had poorer overall tracking. High scores on an MMPI schizotypy measure (Sum 2-7-8-0) were significantly related to poorer overall SPEM accuracy, individual tracking asymmetry, the absolute magnitude of tracking asymmetry, and phase lag, though the subjects' sex, handedness, and crossed hand-foot dominance were found to affect the relationships between schizotypy and tracking accuracy. These findings suggest that although control of SPEM may be predominantly right hemispheric, in some persons with a vulnerability to schizophrenia spectrum disorders, expressed as poorer overall SPEM accuracy and high schizotypy scores, left hemisphere-mediated (leftward) SPEM may be particularly impaired.

Differences in cerebral activation during smooth pursuit and saccadic eye movements using positron-emission tomography

BACKGROUND

Abnormalities of smooth pursuit eye movements occur commonly in schizophrenia, but the pathophysiological significance of these abnormalities is unknown. To address this, the authors conducted a pilot study in which we examined differences in regional cerebral activation using positron-emission tomography (PET) in normal volunteers as they performed two types of eye movements.

METHODS

Cerebral activation in 10 normal volunteers was studied using C15O2 PET while subjects tracked a visual target using smooth pursuit and saccadic eye movements. A left-hand movement comparison task provided a physiologic landmark for verification of the location of the frontal eye fields (FEFs).

RESULTS

Subjects exhibited FEF activation during both smooth pursuit and saccadic eye movements, which was greater in the latter. During smooth pursuit, subjects also exhibited increased cerebral activation in the left temporal-occipital border and left superior frontal cortex and decreased activation in medial superior parietal and insular regions relative to saccades. Other cortical visual and eye-movement brain regions also demonstrated differences in activation between the two visual tasks.

CONCLUSIONS

Significant fEF activation appears to underlie both smooth pursuit and saccadic eye movements but may be more critical in the former. Dysfunction of the frontal lobe, and possibly of other areas in the pursuit pathway such as the temporo-occipital motion area, may contribute to observed eye-movement abnormalities in patients with schizophrenia.

Eye tracking abnormalities in schizophrenia: evidence for dysfunction in the frontal eye fields

BACKGROUND

Eye tracking deficits are robust abnormalities in schizophrenia, but the neurobiological disturbance underlying these deficits is not known.

METHODS

To clarify the pathophysiology of eye tracking disturbances in schizophrenia, we tested 12 first-episode treatment-naive schizophrenic patients and 10 matched healthy individuals on foveofugal and foveopetal step-ramp pursuit tasks.

RESULTS

On foveopetal tasks, the initiation of pursuit eye movements was delayed in schizophrenic patients, and their steady-state pursuit gain was reduced particularly at slower target speeds (8 and 16 deg/sec). In foveofugal step-ramp tasks, their primary catch-up saccades were normal in latency and accuracy, but their postsaccadic pursuit in the first 100 msec after the primary catch-up saccade was significantly reduced even relative to their slow steady-state pursuit, especially during and immediately after an acute episode of illness.

CONCLUSIONS

These observations indicate that motion-sensitive areas in posterior temporal cortex provide sufficiently intact information about moving targets to guide accurate catch-up saccades, but that the sensory processing of motion information is not being used effectively for pursuit eye movements. Low-gain pursuit after the early stage of pursuit initiation suggests that the use of extraretinal signals about target motion (e.g., anticipatory prediction) only partially compensates for this deficit. The pattern of low-gain pursuit, impaired pursuit initiation, and intact processing of motion information for catch-up saccades but not pursuit eye movements, was consistent in the schizophrenic patients tested at five time points over a 2-year follow-up period, and implicates the frontal eye fields or their efferent or afferent pathways in the pathophysiology of eye tracking abnormalities in schizophrenia.

Relationships between neuropsychological and oculomotor measures in schizophrenia patients and normal controls

Establishing the relationship between oculomotor and neuropsychological impairments might facilitate a more coherent description of schizophrenia-associated neurocognitive deficits. Therefore, we assessed several aspects of neuropsychological and oculomotor function in 25 medicated schizophrenia patients and 24 age-matched controls. Neuropsychological tasks included the Wisconsin Cart Sort Test (WCST), the Trail Making Test (TMT), the Rey Auditory Verbal Learning Test, and finger tapping speed. Oculomotor functions assessed included smooth pursuit, initiation of smooth pursuit, predictive pursuit, fixation, visually guided saccades, remembered saccades, and antisaccades. Among the schizophrenia patients, predictive pursuit performance correlated significantly with finger tapping (dominant hand), TMT (both parts), and one WCST measure (categories completed). The only other significant correlation among the schizophrenia patients was between antisaccade performance and part A of the TMT. Perseverative errors during the WCST and antisaccade performance were the only measures significantly correlated among the normals. Closely related neurocognitive deficits may be responsible for impairments in TMT, WCST, predictive pursuit, and antisaccade performance in schizophrenia.