Key role of Rho GTPases in motor disorders associated with neurodevelopmental pathologies.

Growing evidence suggests that Rho GTPases and molecules involved in their signaling pathways play a major role in the development of the central nervous system (CNS). Whole exome sequencing (WES) and de novo examination of mutations, including SNP (Single Nucleotide Polymorphism) in genes coding for the molecules of their signaling cascade, has allowed the recent discovery of dominant autosomic mutations and duplication or deletion of candidates in the field of neurodevelopmental diseases (NDD). Epidemiological studies show that the co-occurrence of several of these neurological pathologies may indeed be the rule. The regulators of Rho GTPases have often been considered for cognitive diseases such as intellectual disability (ID) and autism. But, in a remarkable way, mild to severe motor symptoms are now reported in autism and other cognitive NDD. Although a more abundant litterature reports the involvement of Rho GTPases and signaling partners in cognitive development, molecular investigations on their roles in central nervous system (CNS) development or degenerative CNS pathologies also reveal their role in embryonic and perinatal motor wiring through axon guidance and later in synaptic plasticity. Thus, Rho family small GTPases have been revealed to play a key role in brain functions including learning and memory but their precise role in motor development and associated symptoms in NDD has been poorly scoped so far, despite increasing clinical data highlighting the links between cognition and motor development. Indeed, early impairements in fine or gross motor performance is often an associated feature of NDDs, which then impact social communication, cognition, emotion, and behavior. We review here recent insights derived from clinical developmental neurobiology in the field of Rho GTPases and NDD (autism spectrum related disorder (ASD), ID, schizophrenia, hypotonia, spastic paraplegia, bipolar disorder and dyslexia), with a specific focus on genetic alterations affecting Rho GTPases that are involved in motor circuit development.

Newborns modulate their crawling in response to their native language but not another language.

Human newborns can propel themselves to their mother's breast when positioned skin to skin on her abdomen just after birth. For decades, researchers have considered this primitive crawling behavior a spinal reflex, immune to supra spinal control. However, recent research suggests that neonatal crawling is already responsive to visual and olfactory stimuli processed at a supra spinal level. Here we report that a few hours post birth, French newborns can also modulate their crawling in response to their native language - a source of information that is processed supra-spinally. The crawling patterns of 23 French-born newborns were recorded on video and via an infrared motion capture system during two randomly ordered 2-min trials. The newborns were secured on a mini skateboard to facilitate arm and leg movements during their crawling propulsion. They heard a repetitive sequence of the same sentences either in French, their native language, or in English, a rhythmically different and hence discriminable unfamiliar language, on each trial. In French, compared to English, crawling was enhanced, with significantly more arm and leg steps and significantly more and larger trunk rotations in the cephalo-caudal axis. Moreover, newborns rotated their heads and trunk toward the appropriate loud speaker when hearing French but not English. These preliminary findings suggest that newborn crawling is not a simple stereotyped reflex under spinal control, but a complex pattern that can be modulated in response to higher-order, supra-spinally processed stimuli. The findings open fascinating questions about the range of stimuli to which newborn crawling is responsive.

Effect of baby swimming lessons on infants' avoidance of bodies of water.

Despite the popularity of infant swimming programs, no evidence exists to determine whether they influence infants' judgments and behavior when confronted with bodies of water. We conducted two separate studies examining if the total number of swimming sessions an infant participated in predicted whether they avoided a body of water they could enter via an edge (Study 1-Water Cliff: n = 101 infants) or a slope (Study 2-Water Slope: n = 77 infants). The results revealed a significant interaction between number of sessions and type of entry into the water. Infants who participated in 10 or more sessions were more likely to avoid falling on the edge leading into the water but entered the water significantly more if they could access it via a slope. These findings suggest that while experience in baby swimming programs can promoted more adaptive behaviors on drop-offs leading into bodies of water, sloped entries may heighten drowning risks for young children with greater familiarity with water. Because we tested the two groups of infants in different countries, further research is warranted to determine if cultural differences in child rearing practices or variations in the content and/or teaching of the swimming programs might explain these intriguing findings.

Evidence of tactile arm stepping in newborns and its responsiveness to optic flows specifying self-translation.

Although the arms participate in many forms of human locomotion, we know very little about when arm movements emerge during locomotor development. Here we investigated whether newborns would make tactile arm stepping movements when we supported them almost horizontally so their hands touched a surface and blocked their leg movements. Building off prior work showing that newborns make more crawling and air stepping leg movements when exposed to optic flows specifying forward and backward self-translation, we also examined whether newborns would make more tactile arm steps when exposed to forward and backward optic flows compared to a random optic flow that did not specify translation. We found that newborns can perform arm stepping and produce a significantly higher number of tactile arm steps in the optic flow condition specifying backward translation than in the random optic flow condition. Both translating optic flow conditions had significantly higher numbers of alternating arm steps than the random optic flow condition. These findings show that tactile arm stepping exists at birth and that optic flows can facilitate their production, similar to leg stepping. We argue that these results further support the idea that a quadrupedal organization underlies early upright stepping.

The Effect of Physical Activity Intervention on Motor Proficiency in Children and Adolescents with ADHD: A Systematic Review and Meta-analysis.

Attention deficit hyperactivity disorder (ADHD) is a frequently diagnosed neurodevelopmental disorder in children and adolescents. The objective of this review was to synthesize empirical studies that investigated the effects of physical activity (PA) on motor proficiency in this population. A systematic review and meta-analysis were conducted following the cochrane guidelines for systematic reviews. In May 2022, a systematic search of eight electronic databases retrieved 476 results, which were screened independently by two reviewers. Based on the inclusion and exclusion criteria, 12 studies were selected for systematic review, and 10 were included in the meta-analysis. A beneficial effect of PA on overall motor proficiency (SMD = 1.12; 95% CI [0.63 to 1.61]; p < 0.05) was observed. Similar positive effects were found for motor proficiency composites, including object control, fine manual control, and body coordination. These results indicate that PA improves the motor proficiency of children and adolescents with ADHD.

The effect of specific locomotor experiences on infants' avoidance behaviour on real and water cliffs.

Infants' avoidance of drop-offs has been described as an affordance learning that is not transferable between different locomotor postures. In addition, there is evidence that infants perceive and act similarly around real and water cliffs. This cross-sectional study investigated the effects of specific locomotor experiences on infants' avoidance behaviour using the Real Cliff/Water Cliff paradigm. The experiments included 102 infants, 58 crawling, but pre-walking, infants (Mage  = 11.57 months, SD = 1.65) with crawling experience ranging between 0.03 and 7.4 months (M = 2.16, SD = 1.71) and 44 walking infants (Mage  = 14.82 months, SD = 1.99), with walking experience ranging between 0.13 and 5.2 months (M = 1.86, SD = 1.28). The association between crawling experience and crawlers' avoidance of the real and water cliffs was confirmed. Importantly, crawling and total self-produced locomotor experience, and not walking experience, were associated with walkers' avoidance behaviour on both cliffs. These results suggest that some degree of perceptual learning acquired through crawling experience was developmentally transferred to the walking posture. A longer duration of crawling experience facilitates a more rapid recalibration to the new walking capability. In addition, there was no difference in infants' avoidance of falling on the real and the water cliff. However, infants explored the water cliff more than the real cliff, revealing more enticement to examine bodies of water than for drop-offs. A video abstract of this article can be viewed at https://youtu.be/23LXIGiLhHI.

Newborn crawling and rooting in response to maternal breast odor.

A growing literature shows that perception and action are already tightly coupled in the newborn. The current study aimed to examine the nature of the coupling between olfactory stimuli from the mother and the newborn's crawling and rooting (exploratory movements of the head). To examine the coupling, the crawling and rooting behavior of 28 2-day-old newborns were studied while they were supported prone on a mobility device shaped like a mini skateboard, the Crawliskate®, their head positioned directly on top of a pad infused with either their mother's breast odor (Maternal) or the odor of water (Control). Video and 3D kinematic analyses of the number and types of limb movements and quantification of displacement across the surface revealed that newborns are significantly more efficient crawlers when they smell the maternal odor, moving greater distances although performing fewer locomotor movements. In addition, the newborns made significantly more head rooting movements in the presence of the maternal odor. These findings suggest that the circuitry underlying quadrupedal locomotion and exploratory movements of the head is already adaptable to olfactory information via higher brain processing. Moreover, the coupling between olfaction and the two action systems, locomotion and rooting, is already differentiated. As crawling enables the newborn to move toward the mother's breast immediately after birth and facilitates mother-infant interaction, the results of this study highlight the potential value of using maternal odors to stimulate mobility in infants at risk of motor delay and/or deprived of this odor when born prematurely.

Do infants avoid a traversable slope leading into deep water?

Ramps used to access swimming pools are designed with a shallow slope that affords easy access for all including infants. Locomotor experience has been linked to infants' avoidance of falling into the water from drop-offs; however, the effect of such experience on infants' behavior when a slope is offered to access the water has not been addressed. Forty-three crawling infants (Mage  = 10.63 ± 1.91 months; Mcrawling  = 2.38 ± 1.77 months) and 34 walking infants (Mage  = 14.90 ± 2.18 months; Mwalking  = 2.59 ± 1.56 months) were tested on a new Water Slope paradigm, a sloped surface (10°) leading to deep water. No association between infants' avoidance of submersion and locomotor experience was found. Comparison with the results of infants' behavior on the water cliff revealed that a greater proportion of infants reached the submersion point on the water slope than fell into the water cliff. Collectively, these results indicate a high degree of specificity in which locomotor experience teaches infants about risky situations. Importantly, sloped access to deep water appears to increase the risk of infants moving into the water thereby making them more vulnerable to drowning.

Experienced crawlers avoid real and water drop-offs, even when they are walking.

Crawling experience was recently linked to crawling and walking infants' avoidance of falling on real and water cliffs, whereas walking experience had no effect on walkers' avoidance behavior (Burnay et al., 2021). In the current study, the behavior of 25 infants was analyzed on the Real Cliff/Water Cliff apparatus using a longitudinal study design. Infants were tested as experienced crawlers (Mcrawling = 2.93 months, SD = 1.07), novice walkers (Mwalking = 0.68 months, SD = 0.29), and experienced walkers (Mwalking = 4.90 months, SD = 0.92). Infants avoided falling on both cliffs when tested as experienced crawlers and their behavior was not different when tested as novice or experienced walkers. These findings confirmed the effect of crawling experience on crawling and walking infants' avoidance of falls from heights and into water and the transfer of perceptual learning from crawling to walking postures.

What Does Prone Skateboarding in the Newborn Tell Us About the Ontogeny of Human Locomotion?

The crawling behavior of sixty 2-day-old newborns was studied while they were supported prone on a mini skateboard and on a pediatric mattress without additional support. Analyses of the number and types of limb movements and their characteristics, the coactivation of limb pairs, and the displacement across the surface, revealed that newborns can crawl with locomotor patterns similar to those documented during quadrupedal locomotion in animals and human adults. This was particularly apparent on the skateboard. This discovery suggests that locomotor circuitry underlying quadrupedal locomotion develops during fetal life. Drawing upon other evidence for a quadrupedal organization underlying bipedal gait, we argue that early quadrupedal training may enhance interventions designed to hasten the onset of independent walking.

Effect of optic flows on newborn crawling.

This study examined the crawling characteristics of newborns placed prone on a water-filled, transparent pediatric mattress and whether exposure to terrestrial optic flows that specify forward and backward displacement would influence leg and arm crawling movements. Twenty-six 3-day-old newborns were exposed to a static checkerboard pattern that was back-projected onto the surface underneath the mattress or a checkerboard pattern that moved toward or away from them at 0.12 m/s. Significantly more flexion and extension crawling movements of the legs were observed in the optic flow conditions, although infants did not displace their bodies significantly further on the mattress in these conditions. Unique aspects of newborn crawling were also identified.

Why does infant stepping disappear and can it be stimulated by optic flow?

Two independent experiments (n = 22 and n = 22) showed that 2-month-old infants displayed significantly more stepping movements when supported upright in the air than when supported with their feet contacting a surface. Air- and surface-stepping kinematics were quite similar (Experiment 2). In addition, when data were collapsed across both experiments, more air steps and more donkey kicks were seen when infants were exposed to optic flows that specified backward compared to forward translation. The findings challenge the currently accepted heavy legs explanation for the disappearance of stepping at 2 months of age and raise new questions about the visual control of stepping.

Treadmill stimulation improves newborn stepping.

To shed further light on infant stepping, we investigated whether newborns could step on a treadmill and adapt their steps to graded velocities. Twenty-one newborns (mean = 3 days) were supported for 60 s trials on a treadmill that was static or moved at 13.4, 17.2, or 23.4 cm/s. Video analysis revealed that newborns made more real steps than in-place "pumps" on the moving treadmill than on the static treadmill and made more real steps at 17.2 than 23.4 cm/s. While the treadmill had no effect on arousal, stepping increased and showed higher quality and coordination across conditions when infants were crying. These findings suggest that treadmill interventions currently used to promote the development of independent locomotion in infants at risk of delay could begin at birth. Further investigation is needed to establish the optimal conditions for newborn treadmill stepping and to specify how arousal affects step rate, quality, and coordination.

Air stepping in response to optic flows that move Toward and Away from the neonate.

To shed further light on the perceptual regulation of newborn stepping, we compared neonatal air stepping in response to optic flows simulating forward or backward displacement with stepping forward on a surface. Twenty-two 3-day-olds performed four 60 s trials in which they stepped forward on a table (Tactile) or in the air in response to a pattern that moved toward (Toward) or away (Away) from them or was static (Static). Significantly more steps were taken in the Tactile and Toward conditions than the Static condition. The Away condition was intermediate to the other conditions. The knee joint activity across the entire trial was significantly greater in the Toward than the Away condition. Within-limb kinematics and between-limb coordination were very similar for steps taken in the air and on the table, particularly in the Toward and Tactile conditions. These findings highlight that visual and tactile stimulation can equally elicit neonatal stepping.

The relationships among executive functions, self-regulation, and physical exercise in children with autism spectrum disorder.

LAY ABSTRACT: This study examined the impacts of two types of physical exercises (two-wheel cycling vs stationary cycling) on cognition and self-regulation among 64 children with autism spectrum disorder. It also explored the role of social, emotional, and physical needs of an individual in the relationship between exercise, cognition, and self-regulation. Results showed that participants in the two-wheel cycling group showed significant improvements in their cognition and that the two exercise groups also enhanced their self-regulation. Moreover, this study also revealed that the social need is crucial in mediating the relationship between exercise and self-regulation. This study strengthens the notion that cognitively engaging exercise is more beneficial than the non-cognitively engaging exercise in enhancing cognition in children with autism spectrum disorder.

Are There Sensitive Periods for Skill Development in Male Adolescent Basketball Players?

PURPOSE: Although spurts in physical capacities during adolescence are well known, little is known about the existence of such spurts in sport-specific skill development, especially during the period of rapid growth in stature. Our aims were to examine the timing, intensity, and sequence of basketball-specific skill spurts aligned with biological (years from peak height velocity (PHV)) rather than chronological age. We then defined putative sensitive periods (windows of optimal development) for each skill aligned to the adolescent growth spurt. METHODS: Altogether, 160 adolescent male basketballers aged 11-15 yr were tested biannually over 3 consecutive years. The years from attainment of PHV was estimated, and six skill tests were aligned to each year from PHV in 3-month intervals. Skill velocities were estimated using a nonsmooth polynomial model. RESULTS: Maximal gains in slalom dribble occurred 12 months before PHV attainment (intensity, 0.18 m·s -1 ·yr -1 ), whereas in speed shot shooting (intensity, 9.91 pts·yr -1 ), passing (intensity, 19.13 pts·yr -1 ), and slalom sprint (intensity, 0.19 m·s -1 ·yr -1 ), these skill spurts were attained 6 months before PHV attainment. The mean gains in control dribble (intensity, 0.10 m·s -1 ·yr -1 ) and defensive movement (intensity, 0.12 m·s -1 ·yr -1 ) peaks coincided with attainment of PHV. We identified different sized windows for optimal development for each skill. CONCLUSIONS: Peak spurts in skill development, for most basketball skills, were attained at the same time as PHV. The multiple peaks observed within the defined windows of optimal development suggest that there is room for skill improvement even if gains might be greater earlier rather than later in practice. Our findings highlight the need to make coaches aware of where their players are relative to the attainment of PHV because different skills appear to develop differently relative to PHV. Such knowledge may help in designing more relevant training regimes that incorporate the athlete's current growth status so that skill development can be maximized.

The epigenesis of wariness of heights.

Human infants with little or no crawling experience surprisingly show no wariness of heights, but such wariness becomes exceptionally strong over the life span. Neither depth perception nor falling experiences explain this extraordinary developmental shift; however, something about locomotor experience does. The crucial component of locomotor experience in this emotional change is developments in visual proprioception-the optically based perception of self-movement. Precrawling infants randomly assigned to drive a powered mobility device showed significantly greater visual proprioception, and significantly greater wariness of heights, than did controls. More important, visual proprioception mediated the relation between wariness of heights and locomotor experience. In a separate study, crawling infants' visual proprioception predicted whether they would descend onto the deep side of a visual cliff, a finding that confirms the importance of visual proprioception in the development of wariness of heights.

Does self-efficacy mediate transfer effects in the learning of easy and difficult motor skills?

The effect of task difficulty on inter-task transfer is a classic issue in motor learning. We examined the relation between self-efficacy and transfer of learning after practicing different versions of a stick balancing task. Practicing the same task or an easier version led to significant pre- to post-test transfer of learning, whereas practicing a more difficult version did not. Self-efficacy increased modestly from pre- to post-test with easy practice, but decreased significantly with difficult practice. In addition, self-efficacy immediately prior to the post-test was significantly lower after difficult practice than easy or intermediate practice. Self-efficacy immediately prior to the post-test, performance at the end of practice, and pre-test performance explained 75% of the variance in post-test performance. The mediating role of self-efficacy on transfer of learning offers an alternative explanation for recent findings on the superiority of easy-to-difficult transfer and may help clarify inconsistencies in earlier research.