Brain reorganization as a function of walking experience in 12-month-old infants: implications for the development of manual laterality

Infant motor development predicts the dynamics of movement during sleep

The characteristics of infant sleep change over the first year. Generally, infants wake and move less at night as they grow older. However, acquisition of new motor skills leads to temporary increases in night waking and movement at night. Indeed, sleep-dependent movement at night is important for sensorimotor development. Nevertheless, little is known about how movement during sleep changes as infants accrue locomotor experience. The current study investigated whether infant sleep and movement during sleep were predicted by infants' walking experience. Seventy-eight infants wore an actigraph to measure physical activity during sleep. Parents reported when their infants first walked across a room >10 feet without stopping or falling. Infants in the midst of walking skill acquisition had worse sleep than an age-group estimate. Infants with more walk experience had more temporally sporadic movement during sleep and a steeper hourly increase in physical activity over the course of the night. Ongoing motor skill consolidation changes the characteristics of movement during sleep and may alter sleep state-dependent memory consolidation. We propose a model whereby changes in gross motor activity during night sleep reflect movement-dependent consolidation.

Longitudinal study of infants receiving extra motor stimulation, full‐term control infants, and infants born preterm: High‐density EEG analyses of cortical activity in response to visual motion

Electroencephalography was used to investigate the effects of extrastimulation and preterm birth on the development of visual motion perception during early infancy. Infants receiving extra motor stimulation in the form of baby swimming, a traditionally raised control group, and preterm born infants were presented with an optic flow pattern simulating forward and reversed self‐motion and unstructured random visual motion before and after they achieved self‐produced locomotion. Extrastimulated infants started crawling earlier and displayed significantly shorter N2 latencies in response to visual motion than their full‐term and preterm peers. Preterm infants could not differentiate between visual motion conditions, nor did they significantly decrease their latencies with age and locomotor experience. Differences in induced activities were also observed with desynchronized theta‐band activity in all infants, but with more mature synchronized alpha–beta band activity only in extrastimulated infants after they had become mobile. Compared with the other infants, preterm infants showed more widespread desynchronized oscillatory activities at lower frequencies at the age of 1 year (corrected for prematurity). The overall advanced performance of extrastimulated infants was attributed to their enriched motor stimulation. The poorer responses in the preterm infants could be related to impairment of the dorsal visual stream that is specialized in the processing of visual motion.

Neural correlates of familiar and unfamiliar action in infancy

Behavioral evidence shows that experience with an action shapes action perception. Neural mirroring has been suggested as a mechanism underlying this behavioral phenomenon. Suppression of electroencephalogram (EEG) power in the mu frequency band, an index of motor activation, typically reflects neural mirroring. However, contradictory findings exist regarding the association between mu suppression and motor familiarity in infant EEG studies. In this study, we investigated the neural underpinnings reflecting the role of familiarity in action perception. We measured neural processing of familiar (grasp) and novel (tool-use) actions in 9- and 12-month-old infants. Specifically, we measured infants' distinct motor/visual activity and explored functional connectivity associated with these processes. Mu suppression was stronger for grasping than for tool use, whereas significant mu and occipital alpha (indexing visual activity) suppression were evident for both actions. Interestingly, selective motor-visual functional connectivity was found during observation of familiar action, a pattern not observed for novel action. Thus, the neural correlates of perception of familiar actions may be best understood in terms of a functional neural network rather than isolated regional activity. Our findings provide novel insights on analytic approaches for identifying motor-specific neural activity while also considering neural networks involved in observing motorically familiar versus unfamiliar actions.

Electroencephalography measures of relative power and coherence as reaching skill emerges in infants born preterm

Electroencephalography (EEG) measures of relative power and coherence are associated with motor experience in infants with typical development, but these relationships have not been assessed in infants born preterm. The goal of our study was to investigate the changing patterns of relative power and coherence in the alpha band during resting state EEG in infants born preterm as they developed the skill of reaching. We collected monthly longitudinal data from fourteen infants born preterm between the adjusted ages of 56 and 295 days for a total of 37 sessions of EEG data. Alpha band power at motor cortices and cross-regional connectivity do not present consistent changing trends at the group level in infants born preterm. Individual level analysis reveals that infants born preterm are a heterogeneous group with subtypes of neural function development, some presenting similar changing trends as observed in the typically developing group while others present atypical patterns. This may be linked to the variability in developmental outcomes in infants born preterm. This study was a critical first step to support EEG as a potential tool for identifying and quantifying the developmental trajectories of neuromotor control in infants born preterm.

Mu Rhythm during Standing and Walking Is Altered in Children with Unilateral Cerebral Palsy Compared to Children with Typical Development

Background: Rehabilitation in cerebral palsy (CP) seeks to harness neuroplasticity to improve movement, including walking, yet cortical activation underlying gait is not well understood. Methods: We used electroencephalography (EEG) to compare motor related cortical activity, measured by mu rhythm, during quiet standing and treadmill walking in 10 children with unilateral CP and 10 age- and sex-matched children with typical development (TD). Peak mu band frequency, mu rhythm desynchronization (MRD), and gait related intra- and inter-hemispheric coherence were examined. Results: MRD during walking was observed bilaterally over motor cortex in both cohorts but peak mu band frequency showing MRD was significantly lower in CP compared to TD. Coherence during quiet standing between motor and frontal regions was significantly higher in the non-dominant compared to dominant hemisphere in CP with no hemispheric differences in TD. Conclusions: EEG-based measures should be further investigated as clinical biomarkers for atypical motor development and to assess rehabilitation effectiveness.

The Development of Bimanual Coordination Across Toddlerhood

As one of the hallmarks of human activity and cultural achievement, bimanual coordination has been the focus of research efforts in multiple fields of inquiry. Since the seminal work of Cohen (1971) and Kelso and colleagues (Haken, Kelso, & Bunz, 1985; Kelso, Southard, & Goodman, 1979), bimanual action has served as a model system used to investigate the role of cortical, perceptual, cognitive, and situational underpinnings of coordinated movement sequences (e.g., Bingham, 2004; Oliveira & Ivry, 2008). This work has been guided primarily by dynamical systems theory in general, and by the formal Haken-Kelso-Bunz (HKB; 1985) model of bimanual coordination, in particular. The HKB model describes the self-organizing relationship between a coordinated movement pattern and the underlying parameters that support that pattern, and can also be used to conceptualize and test predictions of how changes in coordination occur. Much of the work investigating bimanual control under the HKB model has been conducted with adults who are acting over time periods of a few seconds to a few days. However, there are also changes in bimanual control that occur over far longer time spans, including those that emerge across childhood and into adolescence (e.g., Wolff, Kotwica, & Obregon, 1998). Using the formal HKB model as a starting point, we analyzed the ontogenetic emergence of a particular pattern of bimanual coordination, specifically, the anti-phase (or inverse oscillatory motion) coordination pattern between the upper limbs in toddlers who are performing a drumming task (see Brakke, Fragaszy, Simpson, Hoy, & Cummins-Sebree, 2007). This study represents a first attempt to document the emergence of the anti-phase pattern by examining both microgenetic and ontogenetic patterns of change in bimanual activity. We report the results of a longitudinal study in which seven toddlers engaged monthly in a bimanual drumming task from 15 to 27 months of age. On some trials, an adult modeled in-phase or anti-phase action; on other trials, no action was modeled. We documented the motion dynamics accompanying the emergence of the anti-phase bimanual coordination pattern by assessing bout-to-bout and month-to-month changes in several movement parameters-oscillation frequency, amplitude ratio of the drumsticks, initial position of the limbs to begin bouts, and primary arm-joint involvement. These parameters provided a good starting point to understand how toddlers explore movement space in order to achieve greater stability in performing the anti-phase coordination pattern. Trained research assistants used Motus software to isolate each bout of drumming and to digitize the movement of the two drumstick heads relative to the stationary drum surface. Because we were primarily interested in the vertical movement of the drumsticks that were held in the child's hands, we relied on two-dimensional analyses and analyzed data that were tracked by a single camera. We used linear mixed effects analyses as well as qualitative analyses for each participant to help elucidate the emergence and stability of the child's use of anti-phase coordination. This approach facilitated descriptions of individual pathways of behavior that are possible only with longitudinal designs such as the one used here. Our analyses indicated that toddlers who were learning to produce anti-phase motion in this context employed a variety of strategies to adjust the topography of their action. Specifically, as we hypothesized, toddlers differentially exploited oscillation frequency and movement amplitude to support change to anti-phase action, which briefly appeared as early as 15 months of age but did not become relatively stable until approximately 20 months of age. We found evidence that many toddlers reduced oscillation frequency before transitioning from in-phase to anti-phase drumming. Toddlers also used different means of momentarily modulating the amplitude ratio between limbs to allow a change in coordination from in-phase to anti-phase. Nevertheless, these oscillation-frequency and amplitude-ratio strategies were interspersed by periods of nonsystematic exploration both within and between bouts of practice. We also observed that toddlers sometimes changed their initial limb positions to start a bout or altered which primary arm joints they used when drumming. When they enacted these changes, the toddlers increased performance of the anti-phase coordination pattern in their drumming. However, we found no evidence of systematic exploration with these changes in limb position and joint employment, suggesting that the toddlers did not intentionally employ these strategies to improve their performance on the task. Although bimanual drumming represents a highly specific behavior, our examination of the mechanisms underlying emergence of the anti-phase coordination pattern in this context is one of the missing pieces needed to understand the development of motor coordination more broadly. Our results document that the anti-phase coordination pattern emerges and stabilizes through modulation of the dynamics of the movement and change of the attractor landscape (i.e., the motor repertoire). Consistent with literatures in motor control, motor learning, and skill development, our results suggest that the acquisition of movements in ontogenetic development can be thought of as exploration of the emergent dynamics of perception and action. This conclusion is commensurate with a systemic approach to motor development in which functional dynamics, rather than specific structures, provide the basis for understanding developmental changes in skill. Based on our results as well as the relevant previous empirical literature, we present a conceptual model that incorporates developmental dynamics into the HKB model. This conceptual model calls for new investigations using a dynamical systems approach that allows direct control of movement parameters, and that builds on the methods and phenomena that we have described in the current work.

Motor Development Research: II. The First Two Decades of the 21st Century Shaping Our Future

In Part I of this series I, we looked back at the 20th century and re-examined the history of Motor Development research described in Clark & Whitall’s 1989 paper “What is Motor Development? The Lessons of History”. We now move to the 21st century, where the trajectories of developmental research have evolved in focus, branched in scope, and diverged into three new areas. These have progressed to be independent research areas, co-existing in time. We posit that the research focus on Dynamical Systems at the end of the 20th century has evolved into a Developmental Systems approach in the 21st century. Additionally, the focus on brain imaging and the neural basis of movement have resulted in a new approach, which we entitled Developmental Motor Neuroscience. Finally, as the world-wide obesity epidemic identified in the 1990s threatened to become a public health crisis, researchers in the field responded by examining the role of motor development in physical activity and health-related outcomes; we refer to this research area as the Developmental Health approach. The glue that holds these research areas together is their focus on movement behavior as it changes across the lifespan.

Measuring infant handedness reliably from reaching: A systematic review

Researchers have utilized reaching paradigms to measure infant handedness for more than a century. However, methods vary widely. Recent research has identified that the number of trials used in assessment is critical with the recommendation that at least 15 trials are necessary to reliably classify infants into handedness categories via statistical cutoffs. As a first step towards establishing best practices for the field, we identified, categorized, and synthesized findings according to trial number from studies that utilized reaching to index handedness in infants across the first two years of life using PRISMA guidelines. Database searches were conducted in PsycINFO, PubMed, and Ovid MEDLINE®. All articles published through May 2018 were included. Additional records were identified through other sources. After removing duplicates, 1,116 records were screened using the online software program Abstrackr. Of these records, 125 full-text articles were further assessed for eligibility, and 87 articles were included in the qualitative synthesis. Results revealed that the majority of papers published since 1890 (70%) do not meet the 15-trial minimum criterion for statistically reliable measurement of infant handedness. Broad themes from articles meeting the measurement criterion and implications for future research are discussed.

Right-handed one day, right-handed the next day?

Although a population bias toward right-hand preference is observed at the early stage of grasping, hand preference fluctuates in infancy. Given these fluctuations, one can wonder whether testing a young infant on a single occasion gives reliable results of its handedness. Very few studies have evaluated short-term test-retest reliability. This was the goal of this study in which 21 infants aged 9-15 months were tested for handedness every day for a total of 5 sessions. The infants were given a classical handedness baby test. Their handedness index (HI) and their category of handedness were compared across sessions. The results show that at the group level the distribution of handedness does not differ significantly across the five sessions. At the individual level, only 19% of infants were categorized as right-handed at all five sessions while 52.4% were consistent in using more one hand than the other across the five sessions (right hand: 47.6%). Most of the fluctuations across sessions occurred between being lateralized and non-lateralized rather than between being right-handed and left-handed. These figures indicate that testing handedness at that age gives fairly reliable results in terms of direction of hand preference, but less so in terms of degree.

Motorische Entwicklung und Händigkeit in den ersten beiden Lebensjahren

Zusammenfassung. Der Zusammenhang von motorischer Entwicklung in den ersten beiden Lebensjahren und der Händigkeit von Kindern (N = 367) wurde untersucht. 18 motorische Meilensteine wurden erfasst, 14 betreffen die Grob- und vier die Handmotorik. Die Händigkeit wurde durch eine Befragung der Eltern zum Zeitpunkt des Erreichens des Meilensteins („Freies und sicheres Gehen“) ermittelt, den die Kinder im durchschnittlichen Alter von 14 Monaten bewältigten. 42.1 % der Kinder bevorzugten ihre rechte, 9.6 % ihre linke Hand, 32 % gebrauchten beide Hände gleich häufig. 16.4 % der Eltern konnten keine Angaben zur Händigkeit machen. Kinder, die bereits eine ausgeprägte Präferenz für die rechte Hand zeigten, bewältigten die meisten der Meilensteine früher als linkshändige und Kinder ohne Bevorzugung einer Hand. Kinder, deren Eltern keine Angabe zur Händigkeit machten, zeigten keine Nachteile gegenüber Rechtshändern. Unterschiede hinsichtlich der Entwicklung körperlicher Merkmale konnten zwischen den Gruppen nicht nachgewiesen werden. Der Anteil der Jungen unter den Linkshändern war deutlich höher als der der Mädchen. Mit Ausnahme des Meilensteins „Sitzen“ konnten keine Unterschiede im Erreichen der Meilensteine zwischen den Geschlechtern nachgewiesen werden.

Electroencephalography power and coherence changes with age and motor skill development across the first half year of life

Existing research in infants has correlated electroencephalography (EEG) measures of power and coherence to cognitive development and to locomotor experience, but only in infants older than 5 months of age. Our goal was to explore the relationship between EEG measures of power and coherence and motor skill development in younger infants who are developing reaching skill. Twenty-one infants with typical development between 38 and 203 days of age participated. Longitudinal EEG recording sessions were recorded in monthly increments, with 3-5 sessions acquired for 19 participants and 1 session for 2 participants, resulting in 71 sessions in total. EEG variables of interest were relative power in the 6-9 Hz range and coherence between selected electrode pairs. We describe the development of the peak in relative power in the 6-9 Hz frequency band of EEG; it is not present around 1 month of age and starts to appear across the following months. Coherence generally increased in the bilateral frontal-parietal networks, while the interhemispheric connectivity in motor cortices generally decreased. The results of this relatively small pilot study provide a foundational description of neural function changes observed as motor skills are changing across the first half year of life. This is a first step in understanding experience-dependent plasticity of the infant brain and has the potential to aid in the early detection of atypical brain development.

A study of reaching actions in walking infants

Acquiring motor skills transforms the perceptual and cognitive world of infants and expands their exploratory engagement with objects. This study investigated how reaching is integrated with walking among infant walkers (n=23, 14.5-15.5 months). In a walk-to-reach paradigm, diverse object retrieval strategies were observed. All infants were willing to use their upper and lower bodies in concert, and the timing of this coordination reflected features of their environment. Infants with an older walking age (months since walking onset) retrieved items more rapidly and exploited their non-reaching hand more effectively during object retrieval than did same-age infants with a younger walking age. This suggests that the actions of the upper- and lower-body are flexibly integrated and that this integration may change across development. Mechanisms that shape sophisticated upper-body use during upright object retrieval are discussed. Infants flexibly integrate emerging motor skills in the service of object retrieval in ways not previously documented.

fNIRS: An Emergent Method to Document Functional Cortical Activity during Infant Movements

The neural basis underlying the emergence of goal-directed actions in infants has been severely understudied, with minimal empirical evidence for hypotheses proposed. This was largely due to the technological constraints of traditional neuroimaging techniques. Recently, functional near-infrared spectroscopy (fNIRS) technology has emerged as a tool developmental scientists are finding useful to examine cortical activity, particularly in young children and infants due to its greater tolerance to movements than other neuroimaging techniques. fNIRS provides an opportunity to finally begin to examine the neural underpinnings as infants develop goal-directed actions. In this methodological paper, I will outline the utility, challenges, and outcomes of using fNIRS to measure the changes in cortical activity as infants reach for an object. I will describe the advantages and limitations of the technology, the setup I used to study primary motor cortex activity during infant reaching, and example steps in the analyses processes. I will present exemplar data to illustrate the feasibility of this technique to quantify changes in hemodynamic activity as infants move. The viability of this research method opens the door to expanding studies of the development of neural activity related to goal-directed actions in infants. I encourage others to share details of techniques used, as well, including analyticals, to help this neuroimaging technology grow as others, such as EEG and fMRI have.

Quantifying Motor Experience in the Infant Brain: EEG Power, Coherence, and Mu Desynchronization

The emergence of new motor skills, such as reaching and walking, dramatically changes how infants engage with the world socially and cognitively. Several examples of how motor experience can cascade into cognitive and social development have been documented, yet a significant knowledge gap remains in our understanding of whether these observed behavioral changes are accompanied by underlying neural changes. We propose that electroencephalography (EEG) measures such as power, coherence, and mu desynchronization are optimal tools to quantify motor experience in the infant brain. In this mini-review, we will summarize existing infant research that has separately assessed the relation between motor, cognitive, or social development with coherence, power, or mu desynchronization. We will discuss how the reviewed neural changes seen in seemingly separate developmental domains may be linked based on existing behavioral evidence. We will further propose that power, coherence, and mu desynchronization be used in research exploring the links between motor experience and cognitive and social development.