On the development of voluntary and reflexive components in human saccade generation

Development of eye-movement control

Cognitive control of behavior continues to improve through adolescence in parallel with important brain maturational processes including synaptic pruning and myelination, which allow for efficient neuronal computations and the functional integration of widely distributed circuitries supporting top-down control of behavior. This is also a time when psychiatric disorders, such as schizophrenia and mood disorders, emerge reflecting a particularly vulnerability to impairments in development during adolescence. Oculomotor studies provide a unique neuroscientific approach to make precise associations between cognitive control and brain circuitry during development that can inform us of impaired systems in psychopathology. In this review, we first describe the development of pursuit, fixation, and visually-guided saccadic eye movements, which collectively indicate early maturation of basic sensorimotor processes supporting reflexive, exogenously-driven eye movements. We then describe the literature on the development of the cognitive control of eye movements as reflected in the ability to inhibit a prepotent eye movement in the antisaccade task, as well as making an eye movement guided by on-line spatial information in working memory in the oculomotor delayed response task. Results indicate that the ability to make eye movements in a voluntary fashion driven by endogenous plans shows a protracted development into adolescence. Characterizing the transition through adolescence to adult-level cognitive control of behavior can inform models aimed at understanding the neurodevelopmental basis of psychiatric disorders.

Neurodevelopment and executive function in autism

Autism is a neurodevelopmental disorder characterized by social and communication deficits, and repetitive behavior. Studies investigating the integrity of brain systems in autism suggest a wide range of gray and white matter abnormalities that are present early in life and change with development. These abnormalities predominantly affect association areas and undermine functional integration. Executive function, which has a protracted development into adolescence and reflects the integration of complex widely distributed brain function, is also affected in autism. Evidence from studies probing response inhibition and working memory indicate impairments in these core components of executive function, as well as compensatory mechanisms that permit normative function in autism. Studies also demonstrate age-related improvements in executive function from childhood to adolescence in autism, indicating the presence of plasticity and suggesting a prolonged window for effective treatment. Despite developmental gains, mature executive functioning is limited in autism, reflecting abnormalities in wide-spread brain networks that may lead to impaired processing of complex information across all domains.

Brain activation, response inhibition, and increased risk for substance use disorder

BACKGROUND

Youth at high risk for developing substance use disorders (SUDs) often exhibit differences which suggest inhibitory impairments when compared to average risk youth.

METHODS

To examine the underlying neural activity related to these impairments, functional MRI (fMRI) was employed in adolescents during an antisaccade task requiring inhibition of an eye movement response. Each subject's level of neurobehavioral disinhibition (ND) was assessed using a multi-informant, multi-method approach, which has been shown to be highly predictive of SUD onset. The fMRI data was categorized into neural regions of interest according to total frontal, parietal, occipital, and temporal lobe activation.

RESULTS

Results demonstrated that ND score was negatively correlated with total amount of frontal activation, but was not significantly correlated with total activation in any other neural region.

CONCLUSIONS

These results indicate deficits in frontal activation in youth with high amounts of ND, suggesting a possible developmental delay of executive processes in high-risk youth.

Maturational changes in anterior cingulate and frontoparietal recruitment support the development of error processing and inhibitory control

Documenting the development of the functional anatomy underlying error processing is critically important for understanding age-related improvements in cognitive performance. Here we used functional magnetic resonance imaging to examine time courses of brain activity in 77 individuals aged 8-27 years during correct and incorrect performance of an oculomotor task requiring inhibitory control. Canonical eye-movement regions showed increased activity for correct versus error trials but no differences between children, adolescents and young adults, suggesting that core task processes are in place early in development. Anterior cingulate cortex (ACC) was a central focus. In rostral ACC all age groups showed significant deactivation during correct but not error trials, consistent with the proposal that such deactivation reflects suspension of a "default mode" necessary for effective controlled performance. In contrast, dorsal ACC showed increased and extended modulation for error versus correct trials in adults, which, in children and adolescents, was significantly attenuated. Further, younger age groups showed reduced activity in posterior attentional regions, relying instead on increased recruitment of regions within prefrontal cortex. This work suggests that functional changes in dorsal ACC associated with error regulation and error-feedback utilization, coupled with changes in the recruitment of "long-range" attentional networks, underlie age-related improvements in performance.

Adolescent neurological development and its implications for adolescent substance use prevention

Recent technological advancements have facilitated the study of adolescent neurological development and its implications for adolescent decision-making and behavior. This article reviews findings from the adolescent neurodevelopment and substance use prevention literatures. It also discusses how findings from these two distinct areas of adolescent development can complement each other and be used to build more developmentally appropriate interventions for preventing adolescent substance use. Specifically, a combination of child-centered and family-based strategies is advocated based on extant neurological and prevention literature. EDITORS' STRATEGIC IMPLICATIONS: Researchers are encouraged to take up the authors' challenge and study the links between adolescent neurological development/decision making ability and the long term efficacy of comprehensive interventions for preventing adolescent substance use.

Inhibition errors in borderline personality disorder with psychotic-like symptoms

BACKGROUND

The aim of this study was to examine whether patients with borderline personality disorder (BPD) have deficits in cognitive inhibition as measured with an anti-saccade eye task similar to patients with schizophrenia (Sz). Furthermore, we investigated whether these inhibition errors were more prominent among BPD patients with psychotic-like symptoms than among BPD patients without these symptoms.

METHODS

An anti-saccade task was administered in 32 BPD patients (among them, 20 had with psychotic-like symptoms), 21 patients with recent onset schizophrenia (Sz), and 25 healthy controls (HC). The percentage inhibition errors in the anti-saccade task were the primary outcome variable, in addition, the percentage of anticipatory errors was measured.

RESULTS

Sz patients showed more inhibition errors than HC and BPD (p<.001 and p<.05 resp.), whereas BPD patients scored in between Sz and HC. The difference with HC was significant as well (p<.05). BPD patients with psychotic-like symptoms showed more inhibition errors than BPD patients without these symptoms (p<.05). BPD patients showed more anticipatory errors than HC (p<.001), whereas Sz patients did not (p<.26).

CONCLUSION

The data demonstrate that inhibition deficits, as measured with anti-saccadic eye movement task, may be characteristic among BPD patients and in a larger extent in patients with psychotic-like symptoms. This inhibition deficit was distinct from a general predisposition to response impulsively as measured by anticipatory errors, which was found in the whole group of BPD patients. Psychotic-like symptoms may be an important target dimension for future BPD research and treatment.

Effects of age on latency and error generation in internally mediated saccades

Most studies on the effects of ageing on saccades have examined reflexive saccades; the only commonly studied volitional task has been the antisaccade task, with contradictory results. We examined in both young and elderly normal subjects the latency of anti-, memory-guided, and predictable saccades and the timing of self-paced saccades; we also evaluated errors made on the first two tasks. We expected errors to be correlated between tasks; we also expected antisaccade latencies and errors to be inversely correlated. We also expected antisaccade and memory-guided saccade latencies to be longer in individuals with a high self-paced rate. Except for predictable saccades, mean latencies were significantly higher in the elderly. However, their performance was more variable. Errors were also significantly more frequent on anti- and memory-guided saccade tasks. Most of the hypothesised correlations were not observed. Analysis of error latencies showed that whilst most antisaccade errors were reflexive, for memory-guided saccades both express errors and errors with latencies between 0.4 and 2.5 s were observed. The latter appeared to be a premature release of what would otherwise have been a properly planned response. Age thus impaired all but the predictable saccade task; nevertheless, there were few relationships between measures across tasks. This suggests that a range of processes mediate peoples' performance on these saccade paradigms.

fMRI studies of eye movement control: investigating the interaction of cognitive and sensorimotor brain systems

Functional neuroimaging studies of eye movement control have been a useful approach for investigating the interaction of cognitive and sensorimotor brain systems. Building on unit recording studies of behaving nonhuman primates and clinical studies of patients with a focal brain lesion, functional neuroimaging studies have elucidated a pattern of hierarchical organization through which prefrontal and premotor systems interact with sensorimotor systems to support context-dependent adaptive behavior. Studies of antisaccades, memory-guided saccades, and predictive saccades have helped clarify how cognitive brain systems support contextually guided and internally generated action. The use of cognitive and sensorimotor eye movement paradigms is being used to develop a better understanding of life span changes in neurocognitive systems from childhood to late life, and about behavioral and systems-level brain abnormalities in neuropsychiatric disorders.

Deficits in Eye Movement Control in Children With Fetal Alcohol Spectrum Disorders

BACKGROUND

Prenatal exposure to alcohol can result in a spectrum of adverse developmental outcomes in offspring, collectively termed fetal alcohol spectrum disorders (FASD). Deficits in executive function--the psychological processes involved in controlling voluntary goal-oriented behavior--are prevalent in FASD. Oculomotor tasks have been designed as highly sensitive tools to evaluate components of executive function. Because of the extensive overlap in the brain areas controlling eye movements and those affected in FASD, we hypothesized that individuals with FASD display specific neurobehavioral abnormalities that can be quantified with eye movement testing.

METHODS

Subjects (8-12 years old) were instructed to look either toward (prosaccade) or away from (antisaccade) a stimulus that appeared in the peripheral visual field. Two fixation conditions were used. In the gap condition, the central fixation point (FP) was removed before the appearance of the peripheral stimulus; in the overlap condition, the FP remained illuminated. Saccadic reaction times (SRTs, time from stimulus appearance to saccade initiation), direction errors (saccades made in the incorrect direction relative to instruction), and express saccades (short-latency: SRT=90-140 ms) were measured to assess automatic and volitional saccade control.

RESULTS

Compared with controls, FASD children had elongated reaction times, excessive direction errors, and no express saccades. Metric analysis of correct prosaccades revealed a trend toward increased saccadic duration and decreased saccadic velocity in FASD subjects.

CONCLUSION

These results reflect deficits in executive function and motor control, and are consistent with dysfunction of the frontal lobes, possibly due to disrupted inhibitory mechanisms. Therefore, eye movement tasks may be powerful and easy tools for assessing executive function deficits in FASD.

Regression-based developmental models exemplified for Wisconsin Card Sorting Test parameters: Statistics and software for individual predictions

The prediction of an individual's score is relevant in clinical research and requires normative data and a statistical rationale. In the case of developmental research the latter is typically a set of descriptive statistics (e.g., standard scores) for a set of age groups. Here we illustrate a multiple regression approach with a set of 345 Wisconsin Card Sorting Test (WCST) data obtained from subjects aged 6 to 26 years. We modeled linear and curvilinear age effects for each of the 11 WCST variables and, based on this, determined confidence limits for the expected value (mean) and the prediction of individual scores. In these multiple regression models, which accounted for 2% to 26% of the variance, curvilinear age effects clearly dominated linear ones, suggesting the features under scrutiny to be negatively accelerated functions of age. Finally, we developed a statistics program that can be used to apply multiple regression models for individual predictions that are based on normative data with up to 7 predictor variables. We discuss the conditions of applicability of the approach, compare it with the conventional standard score approach, discuss its cognitive-developmental implications, and outline the applicability in applied research and practising.

Inhibitory control in children with phenylketonuria

Past studies have reported impairments in children with early-treated phenylketonuria (PKU) in executive abilities such as strategic processing and working memory. Findings have been inconsistent in terms of the integrity of inhibitory control, another executive ability. This study administered 4 inhibitory tasks (flanker, Stroop, go/no-go, antisaccade) to 26 children with PKU and 25 typically developing control children. Children with PKU performed more poorly than typically developing children on the 2 inhibitory tasks with the strongest experimental manipulations (go/no-go and antisaccade) between control and inhibitory conditions. Findings suggest that the inhibitory deficit associated with PKU is subtle and that inconsistent findings in past studies may be largely due to the insensitivity of experimental manipulations in some tasks.

Age deficits in the control of prepotent responses: evidence for an inhibitory decline

Older adults have more difficulty than younger adults appropriately directing their behavior when the required response is in competition with a prepotent response. The authors varied the difficulty of inhibiting a prepotent eye movement response by varying the response cue (peripheral onset or central arrow). The response cue manipulation did not affect prosaccade accuracy and latency for either age group and did not affect younger adults' antisaccades. Older adults' antisaccades were slower in the peripheral cue condition than in the central arrow condition. These findings are taken as support for the inhibitory deficit hypothesis of aging (L. Hasher, R. T. Zacks, & C. P. May, 1999).

The effect of age on inhibition of return is independent of non-ocular response inhibition

Inhibition of return (IOR) refers to the slowing of a response to a target stimulus presented in the same location as a previous stimulus. Increased IOR has been observed in older adults, despite a reduction in other 'inhibitory' processes. However, cue-target tasks have been used in all previous studies and because of this, IOR may have been overestimated due to non-ocular response inhibition associated with withholding a response from the cue. Could increased levels of response inhibition account for the observations of increased IOR in older adults? This confound can be circumvented by using a target-target paradigm, in which a response is made to all stimuli. We tested three groups of 24 subjects: young (mean 22.5 years), young-old (mean 61.9 years) and old-old (mean 74.8 years). Subjects completed both visual cue-target and target-target tasks with identical inter-stimulus intervals of 1400 and 1800ms. IOR magnitude increased with age in both the cue-target task and the target-target task. Furthermore, the magnitude of visual IOR was found to increase with age even when individual differences in baseline response speed were taken into account. Thus, there appears to be a genuine increase in IOR magnitude with age.

Developmental changes in oculomotor control and working-memory efficiency

In the present study, we examined the developmental changes in the efficiency of saccadic inhibitory control. More specifically, the contribution of age-related changes in working-memory engagement was investigated. We manipulated the efficiency of inhibitory oculomotor control in antisaccade tasks by using fixation-offset conditions, which are supposed to affect inhibitory demands, and by adding increasing working-memory loads to the antisaccade task. In general, in comparison to antisaccade performance of adults, the antisaccade performance of 8-year-old and 12-year-old children was characterized by an increase in direction errors, and/or longer saccadic onset latencies on correct antisaccades. However, this pattern was not altered by the fixation-offset manipulations. In contrast, increased working-memory demands deteriorated 8-year-olds' antisaccade performance unequally as compared to older children and young adults. These findings suggest that - at least in young children - the available functional working-memory capacity is engaged in oculomotor inhibition.

Application of video-based technology for the simultaneous measurement of accommodation and vergence

Accommodation and vergence are two ocular motor systems that interact during binocular vision. Independent measurement of the response dynamics of each system has been achieved by the application of optometers and eye trackers. However, relatively few devices, typically earlier model optometers, allow the simultaneous assessment of accommodation and vergence. In this study we describe the development and application of a custom designed high-speed digital photorefractor that allows for rapid measures of accommodation (up to 75Hz). In addition the photorefractor was also synchronized with a video-based stereo eye tracker to allow a simultaneous measurement of accommodation and vergence. Analysis of accommodation and vergence could then be conducted offline. The new instrumentation is suitable for investigation of young children and could be potentially used for clinical populations.

The influence of stimulus direction and eccentricity on pro- and anti-saccades in humans

We examined the sensory and motor influences of stimulus eccentricity and direction on saccadic reaction times (SRTs), direction-of-movement errors, and saccade amplitude for stimulus-driven (prosaccade) and volitional (antisaccade) oculomotor responses in humans. Stimuli were presented at five eccentricities, ranging from 0.5 degrees to 8 degrees , and in eight radial directions around a central fixation point. At 0.5 degrees eccentricity, participants showed delayed SRT and increased direction-of-movement errors consistent with misidentification of the target and fixation points. For the remaining eccentricities, horizontal saccades had shorter mean SRT than vertical saccades. Stimuli in the upper visual field trigger overt shifts in gaze more easily and faster than in the lower visual field: prosaccades to the upper hemifield had shorter SRT than to the lower hemifield, and more anti-saccade direction-of-movement errors were made into the upper hemifield. With the exception of the 0.5 degrees stimuli, SRT was independent of eccentricity. Saccade amplitude was dependent on target eccentricity for prosaccades, but not for antisaccades within the range we tested. Performance matched behavioral measures described previously for monkeys performing the same tasks, confirming that the monkey is a good model for the human oculomotor function. We conclude that an upper hemifield bias lead to a decrease in SRT and an increase in direction errors.

The antisaccade task as a research tool in psychopathology: a critical review

The antisaccade task is a measure of volitional control of behavior sensitive to fronto-striatal dysfunction. Here we outline important issues concerning antisaccade methodology, consider recent evidence of the cognitive processes and neural mechanisms involved in task performance, and review how the task has been applied to study psychopathology. We conclude that the task yields reliable and sensitive measures of the processes involved in resolving the conflict between volitional and reflexive behavioral responses, a key cognitive deficit relevant to a number of neuropsychiatric conditions. Additionally, antisaccade deficits may reflect genetic liability for schizophrenia. Finally, the ease and accuracy with which the task can be administered, combined with its sensitivity to fronto-striatal dysfunction and the availability of suitable control conditions, may make it a useful benchmark tool for studies of potential cognitive enhancers.

Effects of aging on BOLD fMRI during prosaccades and antisaccades

Age affects the ability to inhibit saccadic eye movements. According to current theories, this may be associated with age-induced neurophysiological changes in the brain and with compensatory activation in frontal brain areas. In the present study, the effects of aging are assessed on brain systems that subserve generation and inhibition of saccadic eye movements. For this purpose, an event-related functional magnetic resonance imaging design was used in adults covering three age ranges (18-30, 30-55, and 55-72 years). Group differences were controlled for task performance. Activity associated with saccadic inhibition was represented by the contrast between prosaccade and antisaccade activation. The tasks activated well-documented networks of regions known to be involved in generation and inhibition of saccadic eye movements. There was an age-related shift in activity from posterior to frontal brain regions after young adulthood. In addition, old adults demonstrated an overall reduction in the blood oxygenation level dependent (BOLD) signal in the visual and oculomotor system. Age, however, did not affect saccade inhibition activity. Mid and old adults appear to increase frontal activation to maintain performance even during simple prosaccades. The global reduction of the BOLD response in old adults could reflect a reduction in neural activity, as well as changes in the neuronal-vascular coupling. Future research should address the impact of altered vascular dynamics on neural activation and the BOLD signal.

Frontal lobe involvement in the processing of meaningful auditory stimuli develops during childhood and adolescence

Auditory event-related N1b reflects attention-related processing in bilateral temporal auditory cortex. Frontal contributions indicating an orienting reaction have been suggested. We analyzed the maturation of frontal contributions to the auditory event-related potential following the warning stimulus in a contingent negative variation (CNV) task by high-resolution current source density mapping and spatio-temporal source analysis in 80 healthy subjects and 121 primary headache patients (migraine with/without aura, tension type headache) from 6 to 18 years; as increased orienting responses and disturbed maturation have been described in migraineurs. A selective local increase of N1b with age occurred at mid-frontocentral leads. This increase could not be explained sufficiently by overlapping bilateral temporal sources but pointed towards additional frontal activation over the supplementary motor area (SMA) in adolescents which was absent in children. A second frontal N1 component peaked about 50 ms later, showed an earlier maturation and has been suggested to reflect early response selection processes in the anterior cingulate. Primary headache patients showed the same component structure and developmental trajectory as healthy subjects without significant influences of differential diagnosis. We conclude that: (1) Brain maturation crucially influences N1b. (2) Two frontal lobe N1 components can be dissociated in their maturational trajectory. (3) Early SMA activation could be elicited by rare auditory stimuli from about 12 years on, allowing fast sensory-motor coupling without previous categorical stimulus classification. (4) Primary headache patients did not differ in their maturation of frontal or temporal contributions to N1b when elicited by moderately loud short tone bursts.

Cognitive processes in the development of TOL performance

Components of executive function continue to develop through adolescence. There is limited knowledge of how these cognitive components impact complex cognitive function requiring their integration. This study examines the development of response planning, a complex cognitive function, and the contributions of selected cognitive processes, including speed of processing, response inhibition, and working memory to its development. We tested 100 healthy 8-30 year old individuals with a computerized version to the Tower of London (TOL) task and cognitive oculomotor tests including the visually guided saccade, oculomotor delayed response, and antisaccade tasks. Speed of processing, response inhibition, working memory, and TOL performance all demonstrated maturation in adolescence. While all processes were correlated with the development of TOL performance, antisaccade performance showed the strongest association indicating an important role for response inhibition in planning. These results indicate that the development of converging cognitive processes in adolescence, including response inhibition and working memory, support response planning and may serve as a model for the development of performance in other complex problem solving tasks.

Age-related influence of contingencies on a saccade task

Adolescence is characterized by increased risk-taking and sensation-seeking, presumably brought about by developmental changes within reward-mediating brain circuits. A better understanding of the neural mechanisms underlying reward-seeking during adolescence can have critical implications for the development of strategies to enhance adolescent performance in potentially dangerous situations. Yet little research has investigated the influence of age on the modulation of behavior by incentives with neuroscience-based methods. A monetary reward antisaccade task (the RST) was used with 23 healthy adolescents and 30 healthy adults. Performance accuracy, latency and peak velocity of saccade responses (prosaccades and antisaccades) were analyzed. Performance accuracy across all groups was improved by incentives (obtain reward, avoid punishment) for both, prosaccades and antisaccades. However, modulation of antisaccade errors (direction errors) by incentives differed between groups: adolescents modulated saccade latency and peak velocity depending on contingencies, with incentives aligning their performance to that of adults; adults did not show a modulation by incentives. These findings suggest that incentives modulate a global measure of performance (percent direction errors) in adults and adolescents, and exert a more powerful influence on the control of incorrect motor responses in adolescents than in adults. These findings suggest that this task can be used in neuroimaging studies as a probe of the influence of incentives on cognitive control from a developmental perspective as well as in health and disease.

Improving antisaccade performance in adolescents with attention-deficit/hyperactivity disorder (ADHD)

The goal of the study was to examine the effects of task manipulations on antisaccade accuracy and response times (RTs) of adolescents with attention-deficit/hyperactivity disorder (ADHD), age-matched controls, 10-year-olds and young adults. Order effects were tested by administering the task at the beginning and end of the session. Other manipulations involved a visual landmark to reduce demands on working memory and internal generation of saccades; spatially specific and non-specific cues at three intervals; and central engagement of attention through perceptual and cognitive means at three intervals. As expected, adolescents with ADHD were impaired relative to age-matched controls in terms of accuracy and saccadic RT on the first administration of the task. Although their accuracy improved with most of the manipulations, it did not improve disproportionately compared to age-matched controls. Nevertheless, with most of the manipulations, they could achieve the same level of accuracy as unaided controls on the first administration of the task. In contrast, the saccadic RTs of the ADHD group came close to normal under several conditions, indicating that elevated antisaccade RTs in this disorder may be related to attentional factors. The ADHD group made more premature saccades and fewer corrective saccades than both the age-matched and younger groups, suggesting difficulties with impulsivity and goal neglect. The findings suggest that cognitive scaffolds can ameliorate at least some of the inhibition deficits in adolescents with ADHD.

Development of cognitive control and executive functions from 4 to 13 years: evidence from manipulations of memory, inhibition, and task switching

Predictions concerning development, interrelations, and possible independence of working memory, inhibition, and cognitive flexibility were tested in 325 participants (roughly 30 per age from 4 to 13 years and young adults; 50% female). All were tested on the same computerized battery, designed to manipulate memory and inhibition independently and together, in steady state (single-task blocks) and during task-switching, and to be appropriate over the lifespan and for neuroimaging (fMRI). This is one of the first studies, in children or adults, to explore: (a) how memory requirements interact with spatial compatibility and (b) spatial incompatibility effects both with stimulus-specific rules (Simon task) and with higher-level, conceptual rules. Even the youngest children could hold information in mind, inhibit a dominant response, and combine those as long as the inhibition required was steady-state and the rules remained constant. Cognitive flexibility (switching between rules), even with memory demands minimized, showed a longer developmental progression, with 13-year-olds still not at adult levels. Effects elicited only in Mixed blocks with adults were found in young children even in single-task blocks; while young children could exercise inhibition in steady state it exacted a cost not seen in adults, who (unlike young children) seemed to re-set their default response when inhibition of the same tendency was required throughout a block. The costs associated with manipulations of inhibition were greater in young children while the costs associated with increasing memory demands were greater in adults. Effects seen only in RT in adults were seen primarily in accuracy in young children. Adults slowed down on difficult trials to preserve accuracy; but the youngest children were impulsive; their RT remained more constant but at an accuracy cost on difficult trials. Contrary to our predictions of independence between memory and inhibition, when matched for difficulty RT correlations between these were as high as 0.8, although accuracy correlations were less than half that. Spatial incompatibility effects and global and local switch costs were evident in children and adults, differing only in size. Other effects (e.g., asymmetric switch costs and the interaction of switching rules and switching response-sites) differed fundamentally over age.

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.

Development of saccadic suppression in children

We measured saccadic suppression in adolescent children and young adults using spatially curtailed low spatial frequency stimuli. For both groups, sensitivity for color-modulated stimuli was unchanged during saccades. Sensitivity for luminance-modulated stimuli was greatly reduced during saccades in both groups but far more for adolescents than for young adults. Adults' suppression was on average a factor of about 3, whereas that for the adolescent group was closer to a factor of 10. The specificity of the suppression to luminance-modulated stimuli excludes generic explanations such as task difficulty and attention. We suggest that the enhanced suppression in adolescents results from the immaturity of the ocular-motor system at that age.

Development of attentional and oculomotor control

The present study was conducted to examine the development of attentional and oculomotor control. More specifically, the authors were interested in the development of the ability to inhibit an incorrect but prepotent response to a salient distractor. Participants, who ranged in age from 8 to 25 years, performed 3 different eye movement tasks: a prosaccade, an antisaccade, and an oculomotor capture task. The time required to initiate a saccade decreased with age across all 3 tasks. Consistent with previous reports, accuracy was relatively age invariant in the prosaccade task. Performance improved with age, asymptoting at 16 years in the antisaccade task. It is interesting to note that despite the superficial similarity of the antisaccade and oculomotor capture tasks, performance was relatively age invariant in the latter. These results are discussed in terms of developmental differences in the interaction of goal-directed and stimulus-driven processes in the control of attention and action.

Lifespan development of pro- and anti-saccades: multiple regression models for point estimates

The comparative study of anti- and pro-saccade task performance contributes to our functional understanding of the frontal lobes, their alterations in psychiatric or neurological populations, and their changes during the life span. In the present study, we apply regression analysis to model life span developmental effects on various pro- and anti-saccade task parameters, using data of a non-representative sample of 327 participants aged 9 to 88 years. Development up to the age of about 27 years was dominated by curvilinear rather than linear effects of age. Furthermore, the largest developmental differences were found for intra-subject variability measures and the anti-saccade task parameters. Ageing, by contrast, had the shape of a global linear decline of the investigated saccade functions, lacking the differential effects of age observed during development. While these results do support the assumption that frontal lobe functions can be distinguished from other functions by their strong and protracted development, they do not confirm the assumption of disproportionate deterioration of frontal lobe functions with ageing. We finally show that the regression models applied here to quantify life span developmental effects can also be used for individual predictions in applied research contexts or clinical practice.

The control of vertical saccades in aged subjects

In real life we produce vertical saccades at different distances and eccentricities, and while our fixation is more or less actively engaged. The goal of this study is to examine vertical saccades in aged and young subjects, taking into consideration all these parameters. Eleven adults (20-28 years) and 11 aged subjects (63-83 years) were recruited. We used LED targets at 7.5 degrees or 15 degrees, up or down in four conditions: gap and overlap tasks, each done at two distances-at near (40 cm) and at far (150 cm). In the gap task fixation target extinguishes prior to target onset, while in the overlap condition it stays on after target onset; consequently, visual attention and fixation are employed differently in the two tasks. Eye movements were recorded with the Chronos video eye tracker. Results showed that vertical saccades were longer for aged subjects than for young adults under almost all conditions. For both aged and young subjects, latencies were shorter under the gap than under the overlap task. Latencies for eccentric targets at 15 degrees were significantly longer than those at 7.5 degrees but for aged subjects only; this effect was more pronounced for upward saccades under the overlap condition. Express type of latencies (80-120 ms) occurred frequently in the gap task and at similar rates for young adults (16%) and aged subjects (12%); in the overlap task express latencies were scarce in young adults (0.4%) and aged subjects (1.8%). Age deteriorates the ability to trigger regular volitional saccades but not the ability to produce express type of saccades. Latency increase with aging is attributed to the degeneration of central areas, e.g. oculomotor cortical areas involved in the initiation of vertical saccades.

How do children prepare to react? Imaging maturation of motor preparation and stimulus anticipation by late contingent negative variation

Both the motor system and the frontal executive control system show a late maturation in humans which continues into school-age and even adolescence. We investigated the maturation of preparation processes towards a fast motor reaction in 74 healthy right-handed children aged 6 to 18 years and analyzed the topography of the late component of contingent negative variation (lCNV) in a 64-electrode high density sensor array. While adolescents from about 12 years on showed a bilaterally distributed centro-parietal maximum like adults do, younger children almost completely missed the negativity over the left central area contralaterally to the side of the anticipated movement. The reason, as revealed by current source density, was that only adolescents showed significant evoked activity of the left pre-/primary motor and supplementary/cingulate motor areas, while in contrast both age groups displayed significant current sinks over the right (ipsilateral) centro-temporal area and right posterior parietal cortex. Spatio-temporal source analysis confirmed that negativity over the right posterior parietal area could not be explained by a projection via volume conduction from frontal areas involved in motor preparation but represented an independent component with a different maturational course most likely related to sensory attention. Significant event-related desynchronization of alpha-power over the contralateral sensorimotor cortex was found in the younger age group, indicating that also 6- to 11-year-old children were engaged in motor preparation. Thus, the missing current sink over the contalateral sensorimotor cortex during late CNV in 6- to 11-year-old children might reflect the immaturity of a specific subcomponent of the motor preparation system which is related to evoked (late CNV) but not induced activity (alpha-ERD).

An independent components analysis (ICA) approach to the study of developmental differences in the saccadic contingent negative variation

This study investigated the development of the saccadic CNV in 74 subjects aged 7-18 years, using pro- and anti-saccade tasks, and independent components analysis (ICA) for data analysis. Within the 2-stimulus paradigm, a central fixation point (S1) was followed 2.5s later by a peripheral cue (S2) presented at 4 degrees to the left or right of S1 in random order. The EEG was recorded from 40 electrodes applied over both hemispheres using a DC amplifier. With increasing age, pro- and anti-saccadic reaction times became faster, this effect being slightly more pronounced during childhood for the anti-saccade task. ICA revealed a lateral-posterior sCNV in younger children, and the known anterior-central sCNV in late adolescents. By contrast, the gaze maintenance negativity (GMNb), an anterior-central negativity accompanying the excursion of the eye, was present in all age groups. Our results underline the importance of topographical approaches in developmental ERP research and the usefulness of ICA. They suggest major task-dependent developmental differences in the spatial modulation of frontal-lobe sensitive ERP components.

Latency of saccades, vergence, and combined movements in children with early onset convergent or divergent strabismus

The goal of this study was to examine latency of horizontal eye movements in the natural space (saccades, vergence, and combined saccade-vergence movements) in children with early onset convergent or divergent strabismus. Ten children were tested (8-11 years old): three with divergent strabismus, seven with convergent strabismus. A paradigm was used to elicit pure lateral saccades at far and near distance, pure vergence (convergence and divergence) and saccades combined with vergence movements. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). The latency of saccades (at far and near distance), of vergence (convergence and divergence), and of combined movements greatly varies among subjects and has tendency to be longer than that observed in normal children of matched age, however, these differences reach significance in only a few cases. Children with divergent strabismus and residual gross binocular vision show abnormally longer vergence latencies than children with convergent strabismus without binocular vision. The initiation of combined movements does not show a dominant pattern, such as preceding vergence, as is found in normal children. Finally, strabismus surgery has no major effect on latencies. We conclude that there is no overall deficiency in latencies of eye movements in 3D space in children with early onset strabismus. Most likely, monocular visual input can be efficient as normal binocular vision for vergence movements. In a few subjects with divergent strabismus and fragile, intermittent binocular vision, latencies can be abnormally long, just because of the fragile binocular input and/or attention effort needs to use it. The absence of a pattern of initiation similar to normal children could be due to attention and fixation capabilities.

Age-related changes in smooth pursuit initiation

Quantitative analysis of eye movements is a useful tool for examining the behavioural effects of ageing. Although the effect of ageing on saccadic eye movement has been examined in some detail, the effect of ageing on a second class of eye movement, smooth pursuit (SP), has received less attention. We examined the initiation of SP in a group of fifteen healthy older people (mean age 72 years) and compared their performance with that of ten young controls (mean age 21 years). Although their performance was qualitatively similar, pursuit latency was increased in the older group. Investigation of the gap effect on pursuit revealed that, while the gap effect was present in the older group, it seemed to be directionally asymmetrical. When the longer absolute latencies were taken into account, although the gap effect in the two groups was identical for leftward tasks, for rightward tasks it was reduced in the older group, although this did not reach statistical significance. The difference between the old and young groups was driven by some of the older subjects. At the longest gap duration employed (400 ms), while there was a clear gap effect for leftward tasks in these subjects, there was no reduction in latency, or increases in latency, for rightward tasks. This asymmetry was not related to chronological age within the older group. These results suggest an age-related alteration in SP initiation that is more complex than general slowing of information processing in ageing. They may be indicative of additional ageing effects specific to the oculomotor or closely related systems.

Mapping brain maturation and cognitive development during adolescence

Non-invasive mapping of brain structure and function with magnetic resonance imaging (MRI) has opened up unprecedented opportunities for studying the neural substrates underlying cognitive development. There is an emerging consensus of a continuous increase throughout adolescence in the volume of white matter, both global and local. There is less agreement on the meaning of asynchronous age-related decreases in the volume of grey matter in different cortical regions; these might equally represent loss ("pruning") or gain (intra-cortical myelination) of tissue. Functional MRI studies have so far focused mostly on executive functions, such as working memory and behavioural inhibition, with very few addressing questions regarding the maturation of social cognition. Future directions for research in this area are discussed in the context of processing biological motion and matching perceptions and actions.

Developmental fractionation and differential discrimination of the anti-saccadic direction error

This partial re-analysis of the data of a total of 433 experimental sessions transfers the distinction of "express" and "regular" latency ranges from the pro-saccade task to the latencies of the anti-saccadic direction errors. Express errors and express saccades (ES) loaded on one and the same PCA factor, and both variables were subject to only minor developmental changes from childhood to young adulthood. Regular direction errors loaded, with opposite signs, on the same factor as pro-saccadic reaction times and were unrelated to express errors; these direction errors showed substantial developmental changes. Our data contribute with new evidence from the anti-saccade task to the long standing debate on whether ES should be considered as a separate type of saccade. Anti-saccadic direction errors with express latencies can be distinguished from those with regular latencies. Future anti-saccade task research should therefore analyse these error types separately in order to look for further evidence in favour of their conceptual and statistical distinction.

Dorsolateral prefrontal cortex prevents short-latency saccade and vergence: a TMS study

This study explores whether vergence eye movements along the median plane can be triggered with short latencies, and the role of the dorsolateral prefrontal cortex (DLPFC) in controlling such movements. We used a gap paradigm and applied transcranial magnetic stimulation (TMS) in 10 humans making saccades or vergence. TMS over the motor cortex had no effect on any eye movement parameter. TMS over DLPFC influenced eye movement initiation but not their metrics. TMS over the right DLPFC accelerated the triggering of saccades bilaterally but did not influence divergence. TMS over the left DLPFC speeded up the triggering of ipsilateral saccades and exacerbated the anticipatory mode of triggering of divergence. For convergence, TMS effects were mild: rightward TMS increased the proportion of short latencies but failed to shorten the group mean latency; leftward TMS influenced triggering in some individuals only. For saccades and convergence under TMS, some subjects showed an emerging population of short latencies in their latency distribution. Horizontal saccadic intrusions (80% of trials) and vertical saccades (recorded in one subject) intruding on vergence were unlikely to assist vergence triggering. We conclude that the prefrontal mechanisms underlying voluntary eye movement control are similar for saccades and vergence although some specificities exist.

Executive functions and methylphenidate response in subtypes of attention-deficit/hyperactivity disorder

BACKGROUND

Oculomotor tasks are a well-established means of studying executive functions and frontal-striatal functioning in both nonhuman primates and humans. Attention-deficit/hyperactivity disorder (ADHD) is thought to implicate frontal-striatal circuitry. We used oculomotor tests to investigate executive functions and methylphenidate response in two subtypes of ADHD.

METHODS

Subjects were boys, aged 11.5-14 years, with ADHD-combined (n = 10), ADHD-inattentive (n = 12), and control subjects (n = 10). Executive functions assessed were motor planning (tapped with predictive saccades), response inhibition (antisaccades), and task switching (saccades-antisaccades mixed).

RESULTS

The ADHD-combined boys were impaired relative to control subjects in motor planning (p < .003) and response inhibition (p < .007) but not in task switching (p > .92). They were also significantly impaired relative to ADHD-inattentive boys, making fewer predictive saccades (p < .03) and having more subjects with antisaccade performance in the impaired range (p < .04). Methylphenidate significantly improved motor planning and response inhibition in both subtypes.

CONCLUSIONS

ADHD-combined but not ADHD-inattentive boys showed impairments on motor planning and response inhibition. These deficits might be mediated by brain structures implicated specifically in the hyperactive/impulsive symptoms. Methylphenidate improved oculomotor performance in both subtypes; thus, it was effective even when initial performance was not impaired.

Gap effect in reflexive and intentional prosaccades

The analysis of saccadic eye movements has assumed an important role as a pathophysiological approach in neuropsychiatric diseases. However, before abnormal cognitive saccade behavior can be fully understood, some basic psychophysiological aspects have to be further investigated. Previous studies have demonstrated a shortening of saccade latency when the fixation stimulus was removed prior to the appearance of a peripheral visual target. This gap effect is smaller for antisaccades (AS; away from the target) than for reflexive saccades (RS; towards the target). Apart from the generation of an intentional eye movement, AS rely on different processes including reflex inhibition and spatial reversal of the saccade direction. We wondered whether intentional prosaccades (IpS) that do not rely on these additional processes also show a reduced gap effect. Therefore, we compared the gap effect in a saccade paradigm for RS and IpS in healthy subjects. We found a smaller gap effect in IpS than in RS and suggest that this reduction reflects endogenous strategic processes. Our findings further imply that reflex inhibition is not the unique cause for the smaller gap effect in AS than in RS and suggest that an endogenous component may be involved. We hypothesize that frontal control on the superior colliculus fixation cell activity may continue even after the fixation stimulus has disappeared, thus inhibiting a fixation offset and reducing the gap effect.

To Look or Not to Look? Typical and Atypical Development of Oculomotor Control

The ability to inhibit saccades toward suddenly appearing peripheral stimuli (prosaccades) and direct them to contralateral locations instead (antisaccades) is a crucial marker of eye movement control. Typically developing infants as young as 4-month-olds can learn to inhibit reflexive saccades to peripheral stimuli, but they do not produce antisaccades, whose development later in infancy and its underlying neural computations remain unexplored. Here we tested oculomotor control in typically developing toddlers and toddlers with fragile X syndrome (FXS), a disorder of known genetic origin that allows the investigation of the neuro-computational properties contributing to the development of saccadic control. Typically developing toddlers decreased looking toward peripheral cues that predicted contralateral rewards, whose appearance they anticipated. Furthermore, this correlated with age, indicating a gradual development of saccadic control. In contrast with the typical case, toddlers with FXS did not decrease their looks to peripheral onsets that predicted contralateral events. Importantly, the atypical pattern of performance was also evident in the elimination of the correlation with mental or chronological age found in controls. Taken together, the findings suggest that control of saccades and its developmental trajectory is atypical in toddlers with FXS, consistent with inhibitory deficits previously shown at later ages in this condition. Potential implications for the neural mechanisms underlying the typical and atypical development of oculomotor control are discussed.

Saccadic instabilities and voluntary saccadic behaviour

Primary gaze fixation is never perfectly stable but can be interrupted by involuntary, conjugate saccadic intrusions (SI). SI have a high prevalence in the normal population and are characterised by a horizontal fast eye movement away from the desired eye position, followed, after a variable duration, by a return saccade or drift. Amplitudes are usually below 1 degrees and they often exhibit a directional bias. The aim of the present study was to investigate the aetiology of SI in relation to saccadic behaviour. It was hypothesised that if SI resulted from deficits in the saccadic system (i.e. reduced inhibitory mechanisms), changes in voluntary saccade behaviour may be apparent and related to SI frequency. To examine this, synchrony (no gap), gap, overlap and antisaccade tasks were conducted on ten normal subjects. No significant correlations were found between SI frequency and voluntary saccade latencies, the percentage of express saccades, or the percentage of antisaccade errors. In addition, no significant correlations were found between SI directional biases and saccade latency directional biases, express saccade biases or antisaccade error biases. These results suggest that an underlying alteration to saccadic behaviour is unlikely to be involved in SI production, and that the SI command signal may arise from the influence of attention on an intact saccadic system. Specifically, descending corticofugal signals relating to attention level and orientation may alter the balance between fixation and saccade generation, so determining SI characteristics.

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.

Influence of gap and overlap paradigms on saccade latencies and vergence eye movements in seven-year-old children

The latency of eye movements is influenced by the fixation task; when the fixation stimulus is switched off before the target presentation (gap paradigm) the latency becomes short and express movements occur. In contrast, when the fixation stimulus remains on when the target appears (overlap paradigm), eye movement latency is longer. Several previous studies have shown increased rates of express saccades in children; however the presence of an express type of latency for vergence and combined movements in children has never been explored. The present study examines the effects of the gap and the overlap paradigms on horizontal saccades at far (150 cm) and at close (20 cm) viewing distances, on vergence along the median plane, and on saccades combined with convergence or divergence in 15 normal seven-year-old children. The results show that the gap paradigm produced shorter latency for all eye movements than the overlap paradigm, but the difference was only significant for saccades at close viewing distances, for divergence (pure and combined), and for saccades combined with vergence. The gap paradigm produced significantly higher rates of express latencies for saccades at close viewing distances, for divergence, and for saccades combined with divergence; in contrast, the frequencies of express latencies for saccades at far viewing distances and for convergence (pure or combined) were similar in the gap and the overlap paradigms. Interestingly, the rate of anticipatory latencies (<80 ms) was particularly high for divergence in the gap paradigm. Our collective findings suggest that the initiation of saccades at close viewing distances and of divergence is more reflexive, particularly in the gap paradigm. The finding of frequent anticipatory divergence that occurs at similar rates for seven-year-old children (this study) and for adults (Coubard et al., 2004, Exp Brain Res 154:368-381) indicates that predictive initiation of divergence is dominant.

Prefrontal activation due to Stroop interference increases during development—an event-related fNIRS study

Although it is well known that executive processes supported by the frontal lobe develop during childhood and adolescence, only one functional imaging study has used the Stroop task to investigate the relationship between frontal lobe function and cognition from a developmental point of view. Hence, we measured brain activation in the lateral prefrontal cortex of children with functional near-infrared imaging during an event-related, color-word matching Stroop task and compared results with a previous study, conducted with the same paradigm in adults. In children, the Stroop task elicited significant brain activation in the left lateral prefrontal cortex comparable to adults. However, the hemodynamic response occurred later in children than adults. Individual brain activation due to Stroop interference varied much more in children than adults, which was paralleled by a higher behavioral variance in children. Data suggest that children differed in their individual cognitive development independent of their chronological age more than adults. Brain activation due to Stroop interference increased with age in the dorsolateral prefrontal cortex in correlation with an improvement of behavioral performance. In conclusion, our results indicate that neuromaturational processes regarding resolution of Stroop interference may depend on increased ability to recruit frontal neural resources.

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.

A goal activation approach to the study of executive function: An application to antisaccade tasks

We argue that a general control process, responsible for the activation and maintenance of task goals, is central to the concept of executive function. Failures of this process can become manifest as goal neglect: disregard of a task requirement even though it has been understood (Duncan, 1995). We discuss the results of several published and new experiments using various versions of the antisaccade task in order to investigate the circumstances under which goal neglect is likely to occur. Potentially conflicting results in the literature on adaptive control of saccadic eye movements are argued to be attributable to the extent to which different task versions elicit goal neglect. The results suggest an increased susceptibility to goal neglect of high-functioning older adults (Experiment 1) and of first-episode schizophrenia patients (Experiment 2), but not of patients with obsessive-compulsive disorder (Experiment 3). However, the degree to which such differences in susceptibility become manifest in task performance, is shown to be strongly influenced by manipulations of the relative saliency of task requirements. Theoretical and methodological implications for the study of executive function are discussed.