Spontaneous kicking behavior in infants: age-related effects of unilateral weighting

Body Weight Control Is a Key Element of Motor Control for Toddlers' Walking

New-borns can step when supported for about 70-80% of their own body weight. Gravity-related sensorimotor information might be an important factor in developing the ability to walk independently. We explored how body weight support alters motor control in toddlers during the first independent steps and in toddlers with about half a year of walking experience. Sixteen different typically developing children were assessed during (un)supported walking on a running treadmill. Electromyography of 18-24 bilateral leg and back muscles and vertical ground reaction forces were recorded. Strides were grouped into four levels of body weight support ranging from no (<10%), low (10-35%), medium (35-55%), and high (55-95%) support. We constructed muscle synergies and muscle networks and assessed differences between levels of support and between groups. In both groups, muscle activities could be described by four synergies. As expected, the mean activity decreased with body weight support around foot strikes. The younger first-steps group showed changes in the temporal pattern of the synergies when supported for more than 35% of their body weight. In this group, the muscle network was dense with several interlimb connections. Apparently, the ability to process gravity-related information is not fully developed at the onset of independent walking causing motor control to be fairly disperse. Synergy-specific sensitivity for unloading implies distinct neural mechanisms underlying (the emergence of) these synergies.

Integrated iterative musculoskeletal modeling predicts bone morphology following brachial plexus birth injury (BPBI)

Brachial plexus birth injury (BPBI) is the most common nerve injury among children. The glenohumeral joint of affected children can undergo severe osseous deformation and altered muscle properties, depending on location of the injury relative to the dorsal root ganglion (preganglionic or postganglionic). Preganglionic injury results in lower muscle mass and shorter optimal muscle length compared to postganglionic injury. We investigated whether these changes to muscle properties over time following BPBI provide a mechanically-driven explanation for observed differences in bone deformity between preganglionic and postganglionic BPBI. We developed a computational framework integrating musculoskeletal modeling to represent muscle changes over time and finite element modeling to simulate bone growth in response to mechanical and biological stimuli. The simulations predicted that the net glenohumeral joint loads in the postganglionic injury case were nearly 10.5% greater than in preganglionic. Predicted bone deformations were more severe in the postganglionic case, with the glenoid more declined (pre: -43.8°, post: -51.0°), flatter with higher radius of curvature (pre: 3.0 mm, post: 3.7 mm), and anteverted (pre: 2.53°, post: 4.93°) than in the preganglionic case. These simulated glenoid deformations were consistent with previous experimental studies. Thus, we concluded that the differences in muscle mass and length between the preganglionic and postganglionic injuries are critical mechanical drivers of the altered glenohumeral joint shape.

Computational analysis of glenohumeral joint growth and morphology following a brachial plexus birth injury

Children affected with brachial plexus birth injury (BPBI) undergo muscle paralysis. About 33% of affected children experience permanent osseous deformities of the glenohumeral joint. Recent evidence suggests that some cases experience restricted muscle longitudinal growth in addition to paralysis and reduced range of motion at the shoulder and elbow. It is unknown whether altered loading due to paralysis, muscle growth restriction and contracture, or static loading due to disuse is the primary driver of joint deformity after BPBI. This study uses a computational framework integrating finite element analysis and musculoskeletal modeling to examine the mechanical factors contributing to changes in bone growth and morphometry following BPBI. Simulations of 8 weeks of glenohumeral growth in a rat model of BPBI predicted that static loading of the joint is primarily responsible for joint deformation consistent with experimental measures of bone morphology, whereas dynamic loads resulted in normal bone growth. Under dynamic loading, glenoid version angle (GVA), glenoid inclination angle (GIA), and glenoid radius of curvature (GRC) (-1.3°, 38.2°, 2.5 mm respectively) were similar to the baseline values (-1.8°, -38°, 2.1 mm respectively). In the static case with unrestricted muscle growth, these measures increased in magnitude (5.2°, -48°, 3.5 mm respectively). More severe joint deformations were observed in GIA and GRC when muscle growth was restricted (GVA: 3.6°, GIA: -55°, GRC: 4.0 mm). Predicted morphology was consistent with literature reports of in vivo glenoid morphology following postganglionic BPBI. This growth model provides a framework for understanding the most influential mechanical factors driving glenohumeral deformity following BPBI.

Range of motion (ROM) restriction influences quipazine-induced stepping behavior in postnatal day one and day ten rats

Previous research has shown that neonatal rats can adapt their stepping behavior in response to sensory feedback in real-time. The current study examined real-time and persistent effects of ROM (range of motion) restriction on stepping in P1 and P10 rats. On the day of testing, rat pups were suspended in a sling. After a 5-min baseline, they were treated with the serotonergic receptor agonist quipazine (3.0mg/kg) or saline (vehicle control). Half of the pups had a Plexiglas plate placed beneath them at 50% of limb length to induce a period of ROM restriction during stepping. The entire test session included a 5-min baseline, 15-min ROM restriction, and 15-min post-ROM restriction periods. Following treatment with quipazine, there was an increase in both fore- and hindlimb total movement and alternated steps in P1 and P10 pups. P10 pups also showed more synchronized steps than P1 pups. During the ROM restriction period, there was a suppression of forelimb movement and synchronized steps. We did not find evidence of persistent effects of ROM restriction on the amount of stepping. However, real-time and persistent changes in intralimb coordination occurred. Developmental differences also were seen in the time course of stepping between P1 and P10 pups, with P10 subjects showing show less stepping than younger pups. These results suggest that sensory feedback modulates locomotor activity during the period of development in which the neural mechanisms of locomotion are undergoing rapid development.

Sensory feedback alters spontaneous limb movements in newborn rats: effects of unilateral forelimb weighting

Perinatal mammals show spontaneous movements that often appear random and uncoordinated. Here, we examined if spontaneous limb movements are responsive to a proprioceptive manipulation by applying a weight unilaterally to a forelimb of postnatal day 0 (P0; day of birth) and P1 rats. Weights were calibrated to approximate 0%, 25%, 50%, or 100% of the average mass of a forelimb, and were attached at the wrist. P0 and P1 pups showed different levels of activity during the period of limb weighting, in response to weight removal, and during the period after weighting. Pups exposed to 50% and 100% weights showed proportionately more activity in the nonweighted forelimb during the period of weighting, suggesting a threshold for evoking proprioceptive changes. Findings suggest that newborn rats use movement-related feedback to modulate spontaneous motor activity, and corroborate studies of human infants that have suggested a role for proprioception during early motor development.

Método para análise cinemática dos chutes de lactentes

Os objetivos deste estudo foram descrever o método utilizado para a análise cinemática dos movimentos de chutes em lactentes e testar sua viabilidade de uso, empregando o sistema Dvideow. Para adequação do método, quatro lactentes foram filmados, longitudinalmente, nas idades de um a seis meses na posição supina. O experimento teve a duração de dois minutos, subdivididos em duas condições: treinamento e observação. O sistema Dvideow 6.3 foi utilizado para análise das imagens. Foi verificado que o uso de quatro câmeras de vídeo é mais apropriado para garantir a visibilidade de dois marcadores, simultaneamente, permitindo a reconstrução tridimensional do movimento. Além disso, utilizamos 6 fios de prumo para calibrar o sistema e garantir uma precisão de 2 mm. Portanto, concluímos que a utilização do sistema Dvideow para realizar a análise cinemática dos chutes de lactentes mostrou-se adequada e viável, uma vez que esse sistema é acessível, de baixo custo e de fácil utilização para os pesquisadores em geral.

Preferência podal em lactentes com síndrome de Down: fatores extrínsecos e intrínsecos

Durante o processo de aquisição do chute em lactentes, a preferência podal pode ser influenciada de forma diferente pelos fatores extrínsecos e intrínsecos. O objetivo foi comparar a preferência podal e verificar a influência do peso adicional e do Reflexo Tônico Cervical Assimétrico (RTCA) na preferência podal entre lactentes com síndrome de Down e típicos. Participaram do estudo cinco lactentes com síndrome de Down e cinco típicos aos três e quatro meses de idade. O experimento foi subdividido em quatro condições experimentais: Treinamento, Linha de Base, Peso e Pós-Peso. Os lactentes com síndrome de Down apresentaram preferência à esquerda ou indefinida e os típicos, preferência à direita. O RTCA influenciou na preferência podal em ambos os grupos, indicando que o lado de rotação da cabeça orientou o chute do mesmo lado. Nos lactentes com síndrome de Down a correlação entre RTCA e chutes foi positiva, sendo forte aos três meses e moderada aos quatro meses. Para os lactentes típicos foi observada correlação positiva fraca aos três meses, e aos quatro meses a correlação não foi estatisticamente significativa. Lactentes com síndrome de Down apresentam preferência podal contrária aos lactentes típicos. O RTCA exerce influência na preferência podal por um período mais longo em lactentes com síndrome de Down em comparação aos lactentes típicos.

Exploring objects with feet advances movement in infants born preterm: a randomized controlled trial

BACKGROUND

Previous work has shown that full-term infants who were healthy contacted a toy with their feet several weeks before they did so with their hands and that movement training advanced feet reaching. Certain populations of preterm infants are delayed in hand reaching; however, feet reaching has not been investigated in any preterm population.

OBJECTIVE

The primary purpose of this study was to determine whether preterm infants born at less than 33 weeks of gestational age contacted a toy with their feet at 2 months of corrected age, before doing so with their hands, and whether movement training advanced feet reaching.

DESIGN

This study was a randomized controlled trial.

METHODS

Twenty-six infants born preterm were randomly assigned to receive daily movement training or daily social training. During the 8-week training period, the infants were videotaped in a testing session every other week from 2 to 4 months of age.

RESULTS

Both groups contacted the toy with their feet at 2 months of age during the first testing session prior to training, at an age when no infants consistently contacted the toy with their hands. After 8 weeks of training, the movement training group displayed a greater number and longer duration of foot-toy contacts compared with the social training group.

CONCLUSIONS

These results suggest that movement experiences advance feet reaching as they do for hand reaching. For clinicians, feet-oriented play may provide an early intervention strategy to encourage object interaction for movement impairments within the first months of postnatal life. Future studies can build on these results to test the long-term benefit of encouraging early purposeful leg movements.

Toy-oriented changes during early arm movements IV: shoulder-elbow coordination

Our recent work on the initial emergence of reaching identified a mosaic of developmental changes and consistencies within the hand and joint kinematics of arm movements across the pre-reaching period. The purpose of this study was to test hypotheses regarding the coordination of hand and joint kinematics over this same pre-reaching period. Principal component analysis (PCA) was conducted on hand, shoulder, and elbow kinematic data from 15 full-term infants observed biweekly from 8 weeks of age through the week of reach onset. Separate PCAs were calculated for spatial variables and for velocity variables in trials with a toy and without a toy. From the PCA results, we constructed 'variance profiles' to reflect the coordinative structure of the hand, shoulder, and elbow. By coordinative structure is meant here the relative contribution of each joint to the factors revealed by the PCA. Shifts in these profiles, which reflected coordination changes, were compared across the hand and joints within each pre-reaching phase (Early, Mid, Late) as well as across phases and trial conditions (no-toy and toy). Results identified both surprising consistencies and important developmental changes in coordination. First, over development, spatial coordination changed in different ways for the shoulder and elbow. Between the Early and Late phases, spatial coordination at the shoulder showed more adult-like coordination during both spontaneous movements and movements with a toy present. In contrast, elbow spatial coordination became more adult-like only during movements with a toy and less adult-like during spontaneous movements. Second, over development, velocity coordination became more adult-like at both joints in movements with and without a toy present. We propose that the features of coordination that changed over development suggest explanations for the differential roles and developmental trajectories of the control of arm movements between the shoulder and elbow. We propose that features that remained consistent over development suggest the presence of developmentally important constraints inherent in arm biomechanics, which may simplify arm control for reaching. Taken together, these findings highlight the critical role of spontaneous arm movements in the emergence of purposeful reaching.

Load perturbation does not influence spontaneous movements in 3-month-old infants

BACKGROUND

The assessment of the quality of general movements (GMs) in young infants is a reliable and valid diagnostic tool for detecting brain dysfunction early in life. Of special interest is a type of GMs called fidgety movements (FMs) characteristic for 3- to 5-month-old infants. GMs are part of an infant's spontaneous motor repertoire and as such endogenously generated by the nervous system. Visual, acoustic and social stimuli hardly had any influence on FMs.

AIM

Our main purpose was to find out whether FMs are sensitive to load perturbation.

STUDY DESIGN

Spontaneous motility in supine position, with and without weighting was recorded on video and the data were semiquantitatively analysed. Weights were attached to the ankles and wrists of all four limbs; on one side of the body only; or without visual feedback of the weighted arm.

SUBJECTS

We studied 29 healthy infants with normal FMs at the age of 12 weeks.

RESULTS

Spontaneous motility remained symmetrical during all the experimental trails. Weighting had no influence on the quality or temporal organisation of FMs.

CONCLUSION

This study demonstrated that the mechanisms responsible for FMs in 3-month-old infants are all but impervious to weight perturbation, at least not with the loads studied. FMs is the stable and predominant motor pattern of this age.

Mismatch negativity and late discriminative negativity in sleeping human newborns

Event-related potentials were recorded from sleeping newborns to compare amplitudes and latencies of mismatch negativity (MMN) and late discriminative negativity (LDN) in active and quiet sleep stages. MMN and LDN were obtained in response to changes in semi-synthesized vowels from 20 healthy newborn infants. MMN and LDN responses were significant for both active and quiet sleep. The amplitude and latency of MMN or LDN did not differ between the sleep stages. Thus, in contrast to adult studies that show a significant drop in the MMN amplitude and an increase in the MMN latency as the sleep gets deeper, arousal stages do not seem to effect either MMN or LDN characteristics in newborns. These results suggest functional differences between infant and adult sleep.

Kinematic Analysis of Kicking Movements in Preterm Infants With Very Low Birth Weight and Full-Term Infants

Background and Purpose. Study of kicking development provides important information to understand how early spontaneous movements change in infants as they acquire voluntary control. Researchers have investigated the kicking movements of preterm infants; however, the movement patterns that they have described were inconsistent. The purpose of this study, therefore, was to examine the development of kicking movements with kinematic analysis in preterm infants with very low birth weight (VLBW) and full-term infants. Subjects and Methods. Twenty-two infants with VLBW who were divided into low gestational age (gestational age of &lt;30 weeks, n=9) and high gestational age (gestational age of ≥30 weeks, n=13) classes and 22 full-term infants were evaluated during kicking movements using 4 synchronized cameras and 3-dimensional kinematic analysis when the infants were 2 and 4 months of corrected age. Results. The infants with VLBW and a high gestational age showed similar kicking movements compared with the full-term infants. In contrast, the infants with VLBW and a low gestational age exhibited a higher kick frequency and a shorter flexion phase at 4 months of corrected age. They also exhibited a higher hip-knee correlation and lower variability in the interlimb coordination pattern at 2 and 4 months of corrected age. Discussion and Conclusion. The findings indicate that infants with VLBW, particularly those with a low gestational age, have age-related differences in movement organization and coordination of kicking compared with full-term infants.

Spontaneous leg movements in infants with and without periventricular leukomalacia: effects of unilateral weighting

The present study was designed to investigate the contribution of the corticospinal tracts in the regulation and coordination of interlimb couplings and the spatio-temporal organization of kicking movements in young infants. Both healthy infants and those with differing degrees of periventricular leukomalacia (PVL) were subjected to a unilateral weight manipulation at the (corrected) age of 26 weeks. Infants with PVL were grouped according to the amount of damage in the area in which the corticospinal tracts are located as shown by neonatal MRI and confirmed with MRI recordings at 18 months. The main question asked was whether unilateral weighting would reveal different adjustment in infants with and without PVL and whether these differences were related to the severity of the lesions, if present. The major finding was that no differences were evident between groups in adjusting to the weight manipulation with regard to the tightness of interlimb couplings. This finding corroborates the suggestion that corticospinal influences are not directly involved in the regulation of these parameters. Although the same conclusion could be drawn concerning the kinematic details of kicks on the basis of group data, individual analyses revealed that kinematics in a few infants with PVL were markedly affected by the weighting. Thus, combining group with individual analyses may have additional value in the clinical interpretation of the effects of PVL on the neural functions of young infants.