Patterns of change in ocular motor development

Neurobehavioral maturation of motor response inhibition in adolescence - A narrative review

Immature motor response inhibition in adolescence is considered contributory to adolescent risk-taking and externalizing behaviors. We review studies reporting age-related variations in motor response inhibition and MRI measurements from typically-developing adolescents. Reviewed studies measured response inhibition using one of three tasks-the Stop Signal Task, Go/No-Go, and Antisaccade Task. Task reliability appears to be particularly strong for the SST. Across tasks and study designs, results indicate that inhibitory control improves markedly through early adolescence. The trajectory of change in later adolescence and into young adulthood (i.e., linear or plateauing) varies depending on the task design. Neuroimaging studies identify adult-like response inhibition networks that are involved in behavioral development. The pros and cons of each task are discussed, including recommendations to guide future studies. Ongoing studies in large longitudinal datasets offer opportunities for further exploration of the shape of change in response inhibition, related neural regions, and associations with other affective and cognitive processes to identify potential impacts of motor response inhibition immaturities or individual differences on adolescent risk-taking behaviors.

Working memory improves developmentally as neural processes stabilize

Working memory performance is a key indicator of cognitive and developmental status. While recent evidence indicates that stabilizing neural gain supports the stabilization of working memory during adolescence, the computational mechanisms linking neural stabilization to behavior are poorly understood. We develop a mechanistic account of behavior during the memory-guided saccade task based on a stochastic accumulator framework. Results indicate that a specific balance of independent gain signals affecting working memory representations and oculomotor response thresholds can account for a peculiar U-shaped feature of the speed-accuracy relationship. Additionally, aspects of behavioral variability and mean behavioral performance, as well as subtle shifts in the shape of the speed-accuracy relationship across development, can be accounted for by the stabilization of these two sources of variability. Thus, the stabilization of neural variability can, in part, account for developmental improvements in behavioral variability as well as some improvement in mean behavioral performance.

Developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion position

Background

We investigated developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion.

Methods

Subjects comprised 135 children (3–14 years) and 29 young adults (19–23 years). Children were divided into six groups in 2-year age strata. Pro-saccade reaction tasks for 30 s were performed in neck rest and flexion positions. Reaction times under each position were averaged in every 10-s period.

Results

Under neck rest position, reaction time in the 0–10 s period was significantly longer in the 3- to 4-year-old group than in the 5- to 6-year-old group and above. No significant age effect was found for reaction time in the 0–10 s period in the 5- to 6-year-old group and above. Although a significant effect of neck flexion was not observed until the 9- to 10-year-old group, significant shortening of reaction time with neck flexion was found in the 11- to 12-year-old group and above. Furthermore, this shortening was maintained until the first 20–s period in the 11- to 12-year-old group and during the entire 30 s in the 13- to 14-year-old and above.

Conclusions

These results suggest that brain activation with the maintenance of neck flexion, related to shortening of the pro-saccade reaction time, was found from a later age of approximately 11 years and above, compared with the age at which information-processing function in the pro-saccade was enhanced. In addition, brain activation with the maintenance of neck flexion was sustained longer with age.

The expression of established cognitive brain states stabilizes with working memory development

We present results from a longitudinal study conducted over 10 years in a sample of 126 8–33 year olds demonstrating that adolescent development of working memory is supported by decreased variability in the amplitude of expression of whole brain states of task-related activity. fMRI analyses reveal that putative gain signals affecting maintenance and retrieval aspects of working memory processing stabilize during adolescence, while those affecting sensorimotor processes do not. We show that trial-to-trial variability in the reaction time and accuracy of eye-movements during a memory guided saccade task are related to fluctuations in the amplitude of expression of task-related brain states, or brain state variability, and also provide evidence that individual developmental trajectories of reaction time variability are related to individual trajectories of brain state variability. These observations demonstrate that the stabilization of widespread gain signals affecting already available cognitive processes underlies the maturation of cognition during adolescence.

Adolescence is a period of change: physically, socially and intellectually. During the teenage years, the brain undergoes changes in structure and connectivity that lead to improvements in areas such as self-control, social skills and cognition. Adolescence is also a time during which cognitive skills, such as problem solving and memory, become more stable. Whereas a child will perform a task markedly better on some days or trials than others, adolescents become increasingly consistent.

But why does cognitive performance fluctuate at all? Studies in monkeys suggest that momentary fluctuations in processes like attention and alertness are linked to changes in the level of activity within brain regions that are active during a task. Areas of the brain that are relatively active tend to become even more active, whereas those that are relatively inactive reduce their activity even further. These changes lead to variable accuracy and reaction times. Montez et al. hypothesized that as adolescents become better at controlling processes such as attention and alertness, they show fewer and/or smaller fluctuations in brain-wide activity during a task. This in turn leads to more stable performance.

To test this idea, Montez et al. asked healthy volunteers aged 8 years and above to perform a memory task while lying inside a brain scanner. Over the next 10 years, the volunteers returned about once a year to perform the task again, thereby revealing how their brain activity changed as they grew older. Over the course of adolescence, the volunteers performed the task increasingly accurately and consistently. As predicted, their overall level of brain activity during the task also became less variable over the same period.

These findings challenge the current view of adolescent development, which assumes that teenagers acquire new cognitive skills with age. The results of Montez et al. suggest instead that improvements in cognitive performance reflect teenagers’ increasing ability to stably engage skills that they have possessed since childhood. This difference has implications for education, healthcare, parenting, and even for the juvenile justice system.

Deficits in motor abilities and developmental fractionation of imitation performance in high-functioning autism spectrum disorders

The co-occurrence of motor and imitation disabilities often characterises the spectrum of deficits seen in patients with autism spectrum disorders (ASD). Whether these seemingly separate deficits are inter-related and whether, in particular, motor deficits contribute to the expression of imitation deficits is the topic of the present study and was investigated by comparing these deficits' cross-sectional developmental trajectories. To that end, different components of motor performance assessed in the Zurich Neuromotor Assessment and imitation abilities for facial movements and non-meaningful gestures were tested in 70 subjects (aged 6-29 years), including 36 patients with high-functioning ASD and 34 age-matched typically developed (TD) participants. The results show robust deficits in probands with ASD in timed motor performance and in the quality of movement, which are all independent of age, with one exception. Only diadochokinesis improves moderately with increasing age in ASD probands. Imitation of facial movements and of non-meaningful hand, finger, hand finger gestures not related to social context or tool use is also impaired in ASD subjects, but in contrast to motor performance this deficit overall improves with age. A general imitation factor, extracted from the highly inter-correlated imitation tests, is differentially correlated with components of neuromotor performance in ASD and TD participants. By developmentally fractionating developmentally stable motor deficits from developmentally dynamic imitation deficits, we infer that imitation deficits are primarily cognitive in nature.

Variability in the decision process leading to saccades: a specific marker for schizophrenia?

In a previous study, deviance in the reaction time (RT) distribution of saccades for patients with schizophrenia was explained using an oculomotor decision model. Here, RTs of visually guided saccades in young healthy men, healthy children, older adults, patients with schizophrenia, and patients with obsessive compulsive disorder (OCD) were modeled to study the specificity of this decision process deviance for schizophrenia. The mean decision rate to saccade decreased with age in children and increased in older adults while the decision rate intrasubject variability (ISV) was not modulated by age. A significant increase in ISV of the decision rate was confirmed for patients with schizophrenia but not OCD compared to healthy controls. There was no effect of medication on model parameters in the OCD patient group. These results confirm the specificity of the deviance in a simple oculomotor decision process in schizophrenia.

Vertical saccades in children: a developmental study

There are no studies exploring the development of vertical saccades in large populations of children. In this study, we examined the development of vertical saccades in sixty-nine children. Binocular eye movements were recorded using an infrared video oculography system [Mobile EBT(®), e(ye)BRAIN], and movements from both eyes had been analyzed. The gain and the peak velocity of vertical saccades show an up-down asymmetry. Latency value decreases with the age of children, and it does not depend on the direction of the saccades; in contrast, the gain and the peak velocity values of vertical saccades are stable during childhood. We suggest that the up-down asymmetry is developed early, or is innate, in humans. Latencies of vertical saccades develop with the age of children, in relationship with the development of the cortical network responsible for the saccade preparation. In contrast, the precision and the peak velocity are not age-dependent as they are controlled by the cerebellum and brainstem structures.

The saccadic system does not compensate for the immaturity of the smooth pursuit system during visual tracking in children

Motor skills improve with age from childhood into adulthood, and this improvement is reflected in the performance of smooth pursuit eye movements. In contrast, the saccadic system becomes mature earlier than the smooth pursuit system. Therefore, the present study investigates whether the early mature saccadic system compensates for the lower pursuit performance during childhood. To answer this question, horizontal eye movements were recorded in 58 children (ages 5-16 yr) and 16 adults (ages 23-36 yr) in a task that required the combination of smooth pursuit and saccadic eye movements. Smooth pursuit performance improved with age. However, children had larger average position error during target tracking compared with adults, but they did not execute more saccades to compensate for their low pursuit performance despite the early maturity of their saccadic system. This absence of error correction suggests that children have a lower sensitivity to visual errors compared with adults. This reduced sensitivity might stem from poor internal models and longer processing time in young children.

Predictive smooth eye pursuit in a population of young men: I. Effects of age, IQ, oculomotor and cognitive tasks

Smooth eye pursuit is believed to involve the integration of an extraretinal signal formed by an internal representation of the moving target and a retinal signal using the visual feedback to evaluate performance. A variation of the smooth eye pursuit paradigm (in which the moving target is occluded for a short period of time and subjects are asked to continue tracking) designed to isolate the predictive processes that drive the extraretinal signal was performed by 1,187 young men. The latency to the onset of change in pursuit speed, the time of decelerating eye-movement speed and the steady state residual gain were measured for each subject and correlated with measures of other oculomotor (closed-loop smooth eye pursuit, saccade, antisaccade, active fixation) and cognitive tasks (measuring sustained attention and working memory). Deceleration time increased with increasing age, while education, general IQ and cognitive variables had no effect on predictive pursuit performance. Predictive pursuit indices were correlated to those of closed-loop pursuit and antisaccade performance, but these correlations were very weak except for a positive correlation of residual gain to saccade frequency in the fixation task with distracters. This correlation suggested that the maintenance of active fixation is negatively correlated with the ability to maintain predictive pursuit speed. In conclusion, this study presents predictive pursuit performance in a large sample of apparently healthy individuals. Surprisingly, predictive pursuit was weakly if at all related to closed-loop pursuit or other oculomotor and cognitive tasks, supporting the usefulness of this phenotype in the study of frontal lobe integrity in normal and patient populations.