Development of human locomotion

Neural control of locomotion in human adults involves the generation of a small set of basic patterned commands directed to the leg muscles. The commands are generated sequentially in time during each step by neural networks located in the spinal cord, called Central Pattern Generators. This review outlines recent advances in understanding how motor commands are expressed at different stages of human development. Similar commands are found in several other vertebrates, indicating that locomotion development follows common principles of organization of the control networks. Movements show a high degree of flexibility at all stages of development, which is instrumental for learning and exploration of variable interactions with the environment

Development of Locomotor-Related Movements in Early Infancy

This mini-review focuses on the emergence of locomotor-related movements in early infancy. In particular, we consider multiples precursor behaviors of locomotion as a manifestation of the development of the neuronal networks and their link in the establishment of precocious locomotor skills. Despite the large variability of motor behavior observed in human babies, as in animals, afferent information is already processed to shape the behavior to specific situations and environments. Specifically, we argue that the closed-loop interaction between the neural output and the physical dynamics of the mechanical system should be considered to explore the complexity and flexibility of pattern generation in human and animal neonates

Immature Spinal Locomotor Output in Children with Cerebral Palsy

Cappellini G, P. Ivanenko Y, Martino G, et al. Immature Spinal Locomotor Output in Children with Cerebral Palsy. Frontiers in Physiology. 2016;7:478

Early human motor development:From variation to the ability to vary and adapt

This review summarizes early human motor development. From early fetal age motor behavior is based on spontaneous neural activity: activity of networks in the brainstem and spinal cord that is modulated by supraspinal activity. The supraspinal activity, first primarily brought about by the cortical subplate, later by the cortical plate, induces movement variation. Initially, movement variation especially serves exploration; its associated afferent information is primarily used to sculpt the developing nervous system, and less to adapt motor behavior. In the next phase, beginning at function-specific ages, movement variation starts to serve adaptation. In sucking and swallowing, this phase emerges shortly before term age. In speech, gross and fine motor development, it emerges from 3-4 months post-term onwards, i.e., when developmental focus in the primary sensory and motor cortices has shifted to the permanent cortical circuitries. With increasing age and increasing trial-and-error exploration, the infant improves its ability to use adaptive and efficicient forms of upright gross motor behavior, manual activities and vocalizations belonging to the native language

The Effect of Locomotor Assisted Therapy on Lower Extremity Motor Performance in Typically Developing Children and Children with Cerebral Palsy

Indiana University-Purdue University Indianapolis (IUPUI)Background: Ambulation is critical to a child’s participation, development of selfconcept, and quality of life. Children with cerebral palsy (CP) frequently exhibit limitation in walking proficiency which has been identified as the primary physical disability. Traditional rehabilitative treatment techniques to improve ambulation for children with CP reveal inconsistent results. Driven gait orthosis (DGO) training is a novel approach focusing on motor learning principles that foster cortical neural plasticity. Objective: The objectives are to determine if: (i) the lower extremity muscle activation patterns of children with CP are similar to age-matched TD children in overground (OG) walking, (ii) DGO training replicates muscle activation patterns in OG ambulation in TD children, (iii) the lower extremity muscle activation patterns in OG walking of children with CP are similar to their muscle activation patterns with DGO assistance, and (iv) DGO training promotes unimpaired muscle activation patterns in children with CP. Methods: Muscle activity patterns of the rectus femoris, semitendinosus, gluteus maximus and gluteus medius were recorded in the OG and DGO walking conditions of children with CP and age-matched TD. The gait cycles were identified and the data was averaged to produce final average gait cycle time normalized values. Results: In comparing the variability of the muscle activation patterns within the subject groups, CP DGO walking was considerably lower than CP OG. In comparing the muscle activation patterns in each condition, consistent differences (p < .05) were noted in terminal stance, pre-swing and initial swing phases of gait with the DGO condition consistently revealing greater muscle unit recruitment. Conclusion: The results indicate that training in the DGO provided the ability to practice with measurably repetitive movement as evidenced by decreased variability. Consistent differences were noted in muscle activation patterns in the terminal stance, pre-swing and initial swing phases of gait when most of these muscles are primarily inactive. The alteration in ground reaction force within the DGO environment may play a role in this variance. With the goal of normalizing gait, it is important that the effect of these parameters on ground reaction forces be considered in the use of DGO rehabilitation

Emergence of Cortical Activity Patterns as Infants Develop Functional Motor Skills.

Despite the careful examination of the developmental changes in overt behavior and the underlying muscle activity and joint movement patterns, there is very little empirical evidence on how the brain and its link to behavior evolves during the first year of life. The dynamic systems approach and theory of neuronal group selection provides a framework that hypothesizes the development of the CNS early in life. However, the direct examination of the changes in brain activation that underlie the development of functional motor control in infants have yet to be determined or tested. The goal of my dissertation was to use functional near-infrared spectroscopy (fNIRS) to document the changes in brain activation patterns as infants acquired functional motor skills. My studies show that fNIRS is a viable and useful tool to examine brain activity in the context of infant movements. My findings demonstrate that as the behavioral and motor outcomes improve, the underlying neural activation patterns emerge. When functional motor skills are unstable and not fully functional, larger areas of the broad brain regions are recruited. As the skills become more reliable and functional, the brain activation patterns become refined and show an increase in strength of activity. The results from the studies in my dissertation take an important first step of describing the typical neural patterns that emerge with functional motor skills early in life. This work will help future studies build the body of empirical evidence that will improve our knowledge regarding the developing link between brain development and behavior. Finally, these studies provide foundational knowledge to better understand the atypical development of the CNS in those with disabilities.PhDKinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133452/1/ryonish_1.pd

Modeling Relationships Between Brain/Muscle Activity and Locomotive Behavior

The dynamics of locomotion involve a fine-tuned, continuous feedback loop between processes in the brain, functioning of the muscles, and interactions with the environment. Neurological or motor disability can often disrupt this loop and alter muscle activation patterns and corresponding behavior. In order to maintain some level of function, the brain and body adopt atypical locomotive strategies that are often sub-optimal, which can have negative impacts on overall health and inhibit continued motor learning. Therefore, it is crucial to accurately and holistically characterize and diagnose motor behavior when providing interventions. In this dissertation, I propose an approach for comprehensively describing the variations in motor behavior within and across individuals, in addition to an approach for relating brain activity to motor behavior. Many traditional locomotive analyses utilize subjective metrics derived from manually observed measures of the behavior, making it infeasible for high volumes of data with large numbers of trials or individuals. Additionally, broad summary statistics from a subset of the behavioral measures are typically used but fall short of capturing the full context or the inter-dependencies of the most important locomotive variables. In this work, I develop an approach to uncover the underlying characteristics defining distinct locomotive behaviors across multiple limbs and individuals, simultaneously. I apply higher-order statistics, not utilized in standard gait analyses, to identify time-varying, multi-modal activation patterns for comprehensive descriptions and visualizations. With these methods, I describe muscle recruitment strategies during gait of individuals with and without osteomyoplastic transfemoral amputation (OTFA) using pressure and electromyography (EMG) data and provide a robust approach for extracting, characterizing, and grouping the motor behavior across strides. I demonstrate the presence of muscle activity within the distal-residuum of multiple individuals with OTFA, which has not been shown before. I provide a novel perspective on co-contraction and compare the distributions of co-contraction timing between individuals with and without OTFA. Additionally, I provide quantitative descriptions of the distribution of pressures to objectively determine the quality of prosthetic fit. These results have potential implications for improving rehabilitation outcomes, prosthetic design, and reducing the risk of injury. I also propose an approach for relating limb movements (from kinematic data) with brain activity (from electroencephalography, EEG) in infants during the acquisition of crawling. In this approach, I decompose the EEG signals into constituent frequency components and measure their relevance using machine learning models that predict movement from three developmental periods. This approach enables the examination of longitudinal changes in brain activity as infants are learning to crawl. I demonstrate that multiple frequency components of the EEG signals at distinct locations are relevant for predicting limb movements and I provide evidence for increasing functional connectivity at higher brain activation frequencies

Role of Activity in the Optimization of Neural and Non-Neural Systems in Infants.

From basic neuroscience evidence and theoretical explanation of the development of neuromotor skill, we know that the emergence of behavior is a self-organized process that results from the cooperative tendencies of multiple, heterogeneous subsystems within contextual demands. Via sufficient repeated cycles of perceiving and acting, many intrinsic and extrinsic resources are intertwined to produce new behavior patterns eventually becoming stable, functional skills. This means that through exploration and experience, underlying factors can be strengthened to foster the functional foundation for neuromotor and non-neural areas. This foundation leads to a proactive view on neuromotor rehabilitation for the development of functional motor skills in infants with neurologic problems: suggesting ways to optimize residual recourses, to increase functionality, to maximize neuromotor control, and to minimize the cascading effects on other systems. Therefore, multilayered reciprocal interactions among underlying factors should be studied during the emergence and control of behavior longitudinally for populations with neuromotor difficulties. The overall goal of this dissertation was to design empirical studies to identify changes in underlying subsystems in response to motor activity and to address how rigorous practice affects the development and recovery of neuromotor function in infants. With this series of studies, we examined changes in subsystems at multiple levels: At the neural level, we tested the integrity of spinal-level reflexes and concurrent functional skills. At the non-neural level, we determined behavioral adaptations to upright activity practice and the impact of practice on bone mineral content. Our results showed improvements in neuromotor and non-neural areas via massive repetitions of specific activities in infants with Myelomeningocele as well as with typical development. But, each subsystem showed its own unique rate of change in response to the massive activity. Gradual changes emerged first at the behavioral level such as walking skill changes with toddler or stepping pattern changes with Myelomeningocele infants, followed by non-neural levels, such as bone mineral content, and then slowly at the neural level such as integrity of sensorimotor loops. The study results will help researchers to design better, assertive early intervention protocols for infants who have neuromotor disabilities.PhDKinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99861/1/doklee_1.pd