Variability in infant motor behavior: A hallmark of the healthy nervous system

Towards novel classification of infants' movement patterns supported by computerized video analysis

BACKGROUND

Positional preferences, asymmetry of body position and movements potentially indicate abnormal clinical conditions in infants. However, a lack of standardized nomenclature hinders accurate assessment and documentation of these preferences over time. Video tools offer a safe and reproducible method to analyze and describe infant movement patterns, aiding in physiotherapy management and goal planning. The study aimed to develop an objective classification system for infant movement patterns with particular emphasis on the specific distribution of muscle tension, using methods of computer analysis of video recordings to enhance accuracy and reproducibility in assessments.

METHODS

The study involved the recording of videos of 51 infants between 6 and 15 weeks of age, born at term, with an Apgar score of at least 8 points. Based on observations of a recording of infant spontaneous movements in the supine position, experts identified postural-motor patterns: symmetry and typical asymmetry linked to the asymmetrical tonic neck reflex. Deviations from the typical postural-motor system were indicated, and subcategories of atypical patterns were distinguished. A computer-based inference system was developed to automatically classify individual patterns.

RESULTS

The following division of motor patterns was used: (1) normal patterns, including (a) typical (symmetrical, asymmetrical: variants 1 and 2); and (b) atypical (variants: 1 to 4), (2) positional preference, and (3) abnormal patterns. The proposed automatic classification method achieved an expert decision mapping accuracy of 84%. For atypical patterns, the high reproducibility of the system's results was confirmed. Lower reproducibility, not exceeding 70%, was achieved with typical patterns.

CONCLUSIONS

Based on the observation of infant spontaneous movements, it is possible to identify movement patterns divided into typical and atypical patterns. Computer-based analysis of infant movement patterns makes it possible to objectify and satisfactorily reproduce diagnostic decisions.

A model for using developmental science to create effective early intervention programs and technologies to improve children's developmental outcomes

Children born with a variety of environmental or medical risk factors may exhibit delays in global development. Very often, such delays are identified at preschool or school age, when children are severely overdue for effective early interventions that can alleviate the delays. This chapter proposes a conceptual model of child development to inform the creation of interventions and rehabilitative technologies that can be provided very early in development, throughout the first year of life, to optimize children's future developmental outcomes. The model suggests that early sensorimotor skills are antecedent and foundational for future motor, cognitive, language, and social development. As an example, this chapter describes how children's early postural control and exploratory movements facilitate the development of future object exploration behaviors that provide enhanced opportunities for learning and advance children's motor, cognitive, language, and social development. An understanding of the developmental pathways in the model can enable the design of effective intervention programs and rehabilitative technologies that target sensorimotor skills in the first year of life with the goal of minimizing or ameliorating the delays that are typically identified at preschool or school age. Specific examples of early interventions and rehabilitative technologies that have effectively advanced children's motor and cognitive development by targeting early sensorimotor skills and behaviors are provided.

Adaptive capacity of 2- to 5-month-old infants to the flow, shape, and flexibility of different teats during bottle feeding: a cross-sectional study

Background

Nutritive sucking is a complex activity, the biomechanical components of which may vary in relation to respiratory phase, swallow-rate per minute, suck-swallow ratio, and swallow non-inspiratory flow (SNIF). Quantitative measurement of these components during nutritive sucking in healthy infants could help us to understand the complex development of sucking, swallowing, and breathing. This is important because the coordination between these components is often disturbed in infants with feeding difficulties. The aims of this study were to describe the biomechanical components of sucking and swallowing in healthy 2- to 5-month-old infants during bottle feeding, to assess whether infants adapt to the characteristics of two different teats, and to determine which independent variables influence the occurrence of SNIF.

Methods

Submental muscle activity, nasal airflow, and cervical auscultation were evaluated during bottle-feeding with two different teats.

Results

Sixteen term-born infants (6 boys) aged 2–5 months were included. All infants showed variable inhalation and exhalation after swallowing. The swallow rate per minute was significantly higher when infants fed with a higher flow teat (Philips Avent Natural 2.0™). Infants had suck:swallow ratios ranging from 1:1 to 4:1. A suck:swallow ratio of 1:1 occurred significantly more often when infants fed with a higher flow teat, whereas a suck:swallow ratio of 2:1 occurred significantly more often when infants fed with a low-flow teat (Philips Avent Classic+™). A suck:swallow ratio of 1:1 was negatively correlated with SNIF, whereas a suck:swallow ratio of 2:1 was positively correlated with SNIF.

Conclusion

Healthy infants aged 2–5 months can adapt to the flow, shape, and flexibility of different teats, showing a wide range of biomechanical and motor adaptations.

Motor trajectories of preterm and full-term infants in the first year of life

BACKGROUND

Motor development occurs throughout periods of motor skill acquisition, adjustment and variability. The objectives of this study were to analyze and compare biological and health characteristics and motor skill acquisition trajectories in preterm and full-term infants during the first year of life.

METHODS

Two thousand, five hundred and seventy-nine infants (1,361 preterm) from 22 states were assessed using the Alberta Infant Motor Scale. Multivariate General Linear Model, t-tests, ANOVA, and Tukey tests were used.

RESULTS

An age × group significant interaction was found for motor scores. On follow-up tests full-term infants had higher scores in prone, supine, sitting and standing postures that require trunk control from 9 to 10 months of age; although this advantage was observed for sitting from the second month of life.

CONCLUSION

During the first trimester of life, preterm infants have higher scores in the supine and standing postures. Regarding motor trajectories, from newborn to 12 months, the period of higher motor acquisition was similar between full-term and preterm infants for prone (3-10 months), supine (1-6 months), and standing (6-12 months). For the sitting posture, however, full-term infants had a period of intensive motor learning of acquisition from the first to 7 months of life, whereas for preterm infants a shorter period was observed (3-7 months).

CONCLUSION

Although the periods of higher motor acquisition were similar, full-term infants had higher scores in more control-demanding postures. Intervention for preterm infants needs to extend beyond the first months of life, and include guidance to parents to promote motor development strategies to achieve control in the higher postures.

Use it or lose it? Effects of age, experience, and disuse on crawling

What happens to early acquired but later abandoned motor skills? To investigate effects of disuse on early-developing motor skills, we examined crawling in two groups of habitual crawlers (34 6-12-month-old infants and five adults with Uner Tan Syndrome) and two groups of rusty crawlers (27 11-12-year-old children and 13 college-aged adults). Habitual crawlers showed striking similarities in gait patterns, limbs supporting the body, and crawling speed, despite dramatic differences in crawling practice, posture, and body size. Habitual crawlers trotted predominantly, whereas rusty crawlers showed a variety of gait patterns. Within sequences, habitual crawlers and children showed more switches in gait patterns than young adults. Children crawled faster and kept fewer limbs on the grounds than the other groups. Old crawling patterns were retained despite disuse, but new ones were also added. Surprisingly, results indicate that nothing was lost with disuse, but some features of crawling were gained or altered.

Are postural adjustments during reaching related to walking development in typically developing infants and infants at risk of cerebral palsy?

BACKGROUND

In typical development, postural adjustments during reaching change in the second half of infancy, including increasing rates of direction-specific adjustments. These changes are absent or different in infants at risk of cerebral palsy (CP). To discover whether these changes are related to acquisition of independent walking, we studied postural adjustments during reaching in infants before and after they learned to walk.

METHODS

Ten typically developing (TD) infants and 11 infants at very high risk (VHR) of CP were assessed before and after they learned to walk. Reaching movements were elicited during supported sitting, while surface electromyography was recorded of arm, neck, and trunk muscles. Percentages of direction-specific adjustments (first level of control), and recruitment patterns and anticipatory activation (second level of control) were calculated.

RESULTS

In both groups, postural adjustments during reaching were similar before and after acquisition of independent walking. Direction-specificity increased with age in typically developing infants but not in VHR-infants.

CONCLUSION

Increasing age rather than the transition to independent walking is associated with increasing direction-specificity of TD-infants during reaching while sitting, while infants at very high risk of CP show no increase in direction-specificity, suggesting that they gradually grow into a postural deficit.

Infants Born Preterm Demonstrate Impaired Exploration of Their Bodies and Surfaces Throughout the First 2 Years of Life

BACKGROUND

Non-object-oriented exploratory behaviors infants perform with their bodies and surfaces have been proposed to be key precursors of infants' object exploration, early learning, and future cognitive development. Little is known about the developmental trajectories of these behaviors, especially for infants born preterm.

OBJECTIVE

The purpose of the study was to longitudinally compare non-object-oriented exploratory behaviors performed by full-term and preterm infants.

DESIGN

The study followed 24 full-term and 30 preterm infants (6 with significant brain injury) performing non-object-oriented exploratory behaviors in prone, supine, and sitting from birth through 24 months.

METHODS

Infants were observed without objects or direct social interaction for 3 minutes in prone and supine (0 through 9 months) and in sitting (3 through 24 months). Behavioral coding produced data that were analyzed using hierarchical linear modeling. Developmental trajectories of behaviors were compared among full-term infants, preterm infants without significant brain injury, and preterm infants with significant brain injury.

RESULTS

Compared to full-term peers, preterm infants showed poorer postural control (less head lifting in prone), midline behavior (holding the head in midline, holding both hands in midline), hand-to-mouth and visual-motor behaviors against gravity, and more asymmetrical one-handed fisting. Preterm infants performed fewer bouts of non-object-oriented exploratory behaviors, and their behaviors were less variable with fewer combinations.

LIMITATIONS

There was a limited sample of infants born preterm with significant brain injury.

CONCLUSIONS

Non-object-oriented exploratory behaviors are important for early perceptual-motor development. Key differences were noted in these behaviors for infants born preterm. These differences may lead to impaired reaching, object exploration, and cognition. Early intervention programs should utilize assessments and interventions that target these very early non-object-oriented exploratory behaviors.

Postural variability and sensorimotor development in infancy

Infants develop skills through a coupling between their sensory and motor systems. Newborn infants must interpret sensory information and use it to modify movements and organize the postural control system based on the task demands. This paper starts with a brief review of evidence on the use of sensory information in the first months of life, and describes the importance of movement variability and postural control in infancy. This introduction is followed by a review of the evidence for the interactions between the sensory, motor, and postural control systems in typically development infants. The paper highlights the ability of young infants to use sensory information to modify motor behaviors and learn from their experiences. Last, the paper highlights evidence of atypical use of sensory, motor, and postural control in the first months of life in infants who were born preterm, with neonatal brain injury or later diagnosed with cerebral palsy (CP).

How else can we study sex differences in early infancy?

This paper revisits group difference and individual variability in birth weight, head size, Apgar score, and motor performance in neonatal and 8-month-old males and females using a large existing data set. The goal is primarily theoretical--to reframe existing analyses with an eye toward designing and executing more predictive analyses in the future. 3D graphing to visualize both the areas of overlap and regions of disparity between boys and girls has been used. A two-step cluster analysis of boys and girls together revealed three clusters. One was almost equally divided between boys and girls, but a second was highly enriched for boys and the third highly skewed toward girls. The relationship between cluster membership and Bayley motor scores at 8 months tested the hypothesis that initial differences that have no sex-related behavioral content might start processes that produce later sex-related differences. Initially, parental belief systems may be less important than infant care patterns evoked by basic size and health characteristics, even though later parental behaviors assume a decidedly gendered pattern.

Characterization and intervention for upper extremity exploration & reaching behaviors in infancy

This article aims to: 1) highlight general exploration, reaching, and object exploration behaviors as key activities of daily living in infancy, 2) describe how knowledge of early warning signs for these behaviors may improve early assessment, and 3) discuss interventions that may advance performance of these behaviors. Early intervention should focus on improving performance of these behaviors because: a) these early, interrelated upper extremity behaviors serve an integral role in global learning and development in infancy, b) among at-risk populations, differences have been observed in the quantity and quality of performance of these behaviors and, in many cases, these differences are associated with related perceptual-motor and cognitive delays. This article highlights how early assessment and intervention can target these key early behaviors in populations at risk for upper extremity disabilities, such as those born preterm, with Down syndrome, brachial plexus palsy, or arthrogryposis multiplex congentia.

A model to investigate the mechanisms underlying the emergence and development of independent sitting

When infants first begin to sit independently, they are highly unstable and unable to maintain upright sitting posture for more than a few seconds. Over the course of 3 months, the sitting ability of infants drastically improves. To investigate the mechanisms controlling the development of sitting posture, a single-degree-of-freedom inverted pendulum model was developed. Passive muscle properties were modeled with a stiffness and damping term, while active neurological control was modeled with a time-delayed proportional-integral-derivative (PID) controller. The findings of the simulations suggest that infants primarily utilize passive muscle stiffness to remain upright when they first begin to sit. This passive control mechanism allows the infant to remain upright so that active feedback control mechanisms can develop. The emergence of active control mechanisms allows infants to integrate sensory information into their movements so that they can exhibit more adaptive sitting.

Emerging therapy approaches: an emphasis on function

Children and youth with cerebral palsy receive ongoing physical and occupational therapy services to improve their functional performance and participation in activities at home, school, and in the community. Over the past 2 decades, rehabilitation interventions have become more functional and goal oriented. In this article, we discuss factors that have influenced emerging intervention approaches. These factors include greater involvement of families in decision making, changing conceptual frameworks and theories underlying skill development and improved outcome measures. New research findings indicate that rehabilitation interventions embracing family-centered services and focusing on functional improvement can be more effective in promoting participation. This knowledge can serve as the platform for further examination of the most effective rehabilitation interventions for children and youth with cerebral palsy.

Postural complexity differs between infant born full term and preterm during the development of early behaviors

BACKGROUND AND AIMS

Postural control differs between infants born preterm and full term at 1-3weeks of age. It is unclear if differences persist or alter the development of early behaviors. The aim of this longitudinal study was to compare changes in postural control variability during development of head control and reaching in infants born preterm and full term.

METHODS

Eighteen infants born preterm (mean gestational age 28.3±3.1weeks) were included in this study and compared to existing data from 22 infants born full term. Postural variability was assessed longitudinally using root mean squared displacement and approximate entropy of the center of pressure displacement from birth to 6months as measures of the magnitude of the variability and complexity of postural control. Behavioral coding was used to quantify development of head control and reaching.

RESULTS

Group differences were identified in postural complexity during the development of head control and reaching. Infants born preterm used more repetitive and less adaptive postural control strategies than infants born full term. Both groups changed their postural complexity utilized during the development of head control and reaching.

DISCUSSION

Early postural complexity was decreased in infants born preterm, compared to infants born full term. Commonly used clinical assessments did not identify these early differences in postural control. Altered postural control in infants born preterm influenced ongoing skill development in the first six months of life.

Normal psychomotor development

"Psychomotor" development refers to changes in a child's cognitive, emotional, motor, and social capacities from the beginning of life throughout fetal and neonatal periods, infancy, childhood, and adolescence. It occurs in a variety of domains and a wide range of theories makes understanding children's development a challenging undertaking. Different models have tried to interpret the origins of human behavior, the pattern of developmental changes over time, and the individual and contextual factors that could direct child development. No single theory has been able to account for all aspects of child development, but each of them may contribute an important piece to the child development puzzle. Although theories sometimes disagree, much of their information is complementary rather than contradictory. The knowledge of child typical development and related theories and models is greatly useful for clinical practice, leading to recognition of developmental disorders and the ways in which they can be approached and treated. In this chapter, traditional and more modern concepts around functional development of psychomotor abilities are reported, firstly more in general and then specifically in the motor domain.

From children to adults: motor performance across the life-span

The life-span approach to development provides a theoretical framework to examine the general principles of life-long development. This study aims to investigate motor performance across the life span. It also aims to investigate if the correlations between motor tasks increase with aging. A cross-sectional design was used to describe the effects of aging on motor performance across age groups representing individuals from childhood to young adult to old age. Five different motor tasks were used to study changes in motor performance within 338 participants (7–79 yrs). Results showed that motor performance increases from childhood (7–9) to young adulthood (19–25) and decreases from young adulthood (19–25) to old age (66–80). These results are mirroring results from cognitive research. Correlation increased with increasing age between two fine motor tasks and two gross motor tasks. We suggest that the findings might be explained, in part, by the structural changes that have been reported to occur in the developing and aging brain and that the theory of Neural Darwinism can be used as a framework to explain why these changes occur.

Early complexity supports development of motor behaviors in the first months of life

Complexity in motor behavior is a hallmark of healthy systems. The purpose of this study was to investigate postural complexity during development of early motor behaviors and under two conditions. Twenty-two infants participated from 1 to 6 months of age. Linear and nonlinear measures of displacement of the center of pressure at the base of support were used to quantify magnitude and temporal structure of postural control. Behavioral coding was used to quantify the emergence of midline head control and early reaching. Results suggest that infants have complexity in postural control strategies early in development. This complexity decreases as infants learn motor behaviors, even when magnitude of the postural variability does not change. Infants were able to adapt the magnitude of postural control variability under different conditions. We propose that infants proceed through three stages which support the infant's ability to adapt motor behaviors.

Height gain during early childhood is an important predictor of schooling and mathematics ability outcomes

AIM

To examine the association between height gain at different stages of early childhood and schooling and cognitive outcomes in 12-year-old Malawian children.

METHODS

A prospective cohort study looking at the growth and development of 325 rural Malawian children. Main outcome measures were highest school grade completed, number of times repeating grades and percentage of correctly answered mathematical questions at 12 years of age. Height-for-age at 1 month and conditional height gain for 6, 18 and 60 months were used as predictors. Ordinal logistic and linear regression analyses were used to estimate the association and adjust for confounder.

RESULTS

The conditional height gain during 18-60 months was positively associated with mathematics test results (p=0.003) and negatively associated with number of times repeating grades (p=0.011). It was not significantly associated with highest grade completed (p=0.194) if those who never attended school were included as having completed zero grade, but was positively (p=0.049) associated with this outcome among those who ever attended school.

CONCLUSION

Height gain during the 18-60 months period of age was related to schooling and mathematics ability at age 12 years. The importance of promoting catch-up growth after the period when stunting is common should receive attention.

Initial-state dependency of learning in young infants

With the aim of investigating the effect of the initial state of pre-learning on subsequent infant learning (i.e., the initial-state dependency), we observed the limb movements in 3-month-old infants in the course of a motor learning task. The session comprised 2-min pre-learning and 4-min learning periods, and the infants learned to move a toy using a string attached to either an arm (arm-based learning, Experiment 1) or a leg (leg-based learning, Experiment 2). Infants were assigned to low- and high-state groups in the initial-state condition according to the average velocity of the arm (Experiment 1) or leg (Experiment 2) movements during the pre-learning period. The results revealed that, during the learning period, infants in the low-state group increased the movement of their limbs, whereas those in the high-state group showed no significant changes in the movement of most of their limbs. These results suggest that infants demonstrating a low average velocity of movement in the initial state easily observed and learned the circular causality between self-produced movements and environmental changes. On the other hand, it seemed that infants demonstrating a high average velocity of movement in the initial state could not or did not need to increase their limb movements (the toy would already be shaking enough to form striking movements).

Variability in postural control during infancy: implications for development, assessment, and intervention

Variability is commonly considered a key to typical motor development. However, multiple definitions and quantification systems have limited the clinical interpretation of variability and the translation of developmental research to assessment and intervention. The purposes of this perspective article are to highlight the importance of statistical variability and complexity in postural control during development and to describe implications for assessment and intervention during infancy and early childhood. Five tenets are proposed describing the role of variability in postural control to support movement experiences, exploration, and global development. Evidence for assessment and intervention focused on variability in postural control are introduced.

Growth trajectories and intellectual abilities in young adulthood: The Helsinki Birth Cohort study

Slow childhood growth is associated with poorer intellectual ability. The critical periods of growth remain uncertain. Among 2,786 Finnish male military conscripts (1952-1972) born in 1934-1944, the authors tested how specific growth periods from birth to age 20 years predicted verbal, visuospatial, and arithmetic abilities at age 20. Small head circumference at birth predicted poorer verbal, visuospatial, and arithmetic abilities. The latter 2 measures were also associated with lower weight and body mass index (weight (kg)/height (m)(2)) at birth (for a 1-standard-deviation (SD) decrease in test score per SD decrease in body size > or = 0.05, P's < 0.04). Slow linear growth and weight gain between birth and age 6 months, between ages 6 months and 2 years, or both predicted poorer performance on all 3 tests (for a 1-SD decrease in test score per SD decrease in growth > or = 0.05, P's < 0.03). Reduced linear growth between ages 2 and 7 years predicted worse verbal ability, and between age 11 years and conscription it predicted worse performance on all 3 tests. Prenatal brain growth and linear growth up to 2 years after birth form a first critical period for intellectual development. There is a second critical period, specific for verbal development, between ages 2 and 7 years and a third critical period for all 3 tested outcomes during adolescence.

Emergence of neuromuscular patterns during walking in toddlers with typical development and with Down syndrome

During the development of walking, toddlers with Down syndrome (DS) and typical development (TD) face challenges controlling muscles, joints, and body segments. Toddlers with DS have additional challenges including increased joint laxity and decreased muscle tone and show delayed walking onset; the underlying activity of the neuromotor system remains unclear. Here we investigated the emergence of muscle activity from walking onset through 6 months of practice in eight toddlers with DS and eight with TD. We monitored the activity of core gait muscles and motion of leg segments as toddlers walked at their self-selected speeds. At walking onset muscle bursts were frequent with inconsistent burst durations. Over time, both groups of toddlers began to activate their leg muscles by using energy-efficient strategies: decreased muscle burst frequency (Wilks' Lambda=0.364, F(12, 103.476)=4.009, p< .001) and increased muscle burst duration (Wilks' Lambda=0.346, F(12, 71.727)=2.946, p= .002). Toddlers with TD increased normalized inter-burst intervals over time but toddlers with DS decreased these interval durations. By 6 months of experience toddlers with TD showed an efficient synergy among muscles, allowing increased relaxation time between bursts. Toddlers with DS improved the rhythmicity of their muscle burst, sustaining longer bursts but timing remained inconsistent. We propose increased muscle burst duration in toddlers with DS may add control by stabilizing their lax joints. Thus, their similar yet different emergent strategy may reflect their unique biomechanical and neurophysiological constraints and represent an efficient control strategy.

Early changes in muscle activation patterns of toddlers during walking

Early locomotor behavior has been the focus of considerable attention by developmentalists over several decades. Few studies have addressed explicitly patterns of muscle activity that underlie this coordination pattern. Our purposes were to illustrate a method to determine objectively the onset and offset of muscle firings during early walking and to investigate the emergence of patterns of activation of the core locomotor muscles. We tested eight toddlers as they walked overground at walking onset (max. of 3-6 independent steps) and after three months of walking experience. Surface electrodes monitored activity of the gastrocnemius, tibialis anterior, quadriceps, and hamstrings. We reduced EMG signals to a frame-by-frame designation of "on-off," followed by muscle state and co-contraction analyses, and probability distributions for each muscle's activity across multiple cycles. Our results clearly show that at walking onset muscle activity was highly variable with few, if any, muscles showing recurring patterns of behavior, within or among toddlers. Variability and co-activation decreased with walking experience but remained inconsistent, in contrast to the significant increase in stability shown for joint coordination and endpoint (foot placement) parameters. We propose this trend emerges because of the high number of options (muscle combinations) available. Toddlers learn first to marshal sufficient force to balance and make forward progress but slowly discover how to optimize these resources.